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micrometre to sub-micrometre-scale alloys of platinum group elements (pges) known as refractory metal nuggets (rmns) have been observed in primitive meteorites. the australian synchrotron x-ray fluorescence (xrf) beamline, in tandem with the maia detector, allows rapid detection of pges in concentrations as low as 50-100 ppm at 2 μm resolution. corroborating these analyses with traditional electron microscopy techniques, rmns can be rapidly identified in situ within carbonaceous chondrites. these results dispute the assumption of most previous studies: that rmns are unique to ca-al-rich inclusions (cais). we find that rmns are, in fact, observed within all components of carbonaceous chondrites, such as the matrix, chondrules (consistent with observations from schwander et al. (2015b) and wang et al. (2007)), and sulphides; though the majority of rmns are still found in cais. the chemistry of rmns reveals a complex diversity of compositions, which nevertheless averages to ci chondrite abundance ratios. this implies that rmns are the dominant, if not sole host phase for pges. one hundred and thirteen rmns from this study are combined with reported compositions in the literature, and compared to condensation model compositions similar to berg et al. (2009), rmns derived experimentally by precipitation (schwander et al., 2015a), host phase and host meteorite. comparisons reveal only weak correlations between parent body processes (sulphidation) and nebular processes (condensation and precipitation) with rmn compositions. it appears that none of these processes acting in isolation or in tandem can explain the diversity observed in the rmn population. our interpretation is that the solar nebula inherited an initially compositionally diverse population of rmns from the giant molecular cloud; that a variety of solar system processes have acted on that population; but none have completely homogenised it. most rmns have experienced disk and asteroidal processing, but some may have retained a primordial composition. rmns have been identified in pre-solar graphite grains (croat et al., 2013). we anticipate that pre-solar rmns will be present elsewhere in primitive meteorites. | in situ analysis of refractory metal nuggets in carbonaceous chondrites |
we used three different sets of arecibo delay-doppler radar images and five well-covered occultations to generate a revised three-dimensional shape model of asteroid (216) kleopatra with a spatial resolution of ∼10 km. we find kleopatra to be a bi-lobate contact binary of overall dimensions 276 × 94 × 78 km ± 15% and equivalent diameter deq = 122 ± 30 km; our uncertainties are upper and lower bounds. separated binary models are ruled out by multi-chord occultations. our model is 27% longer than the "dog-bone" model originally published by ostro et al. (2000) but is similar to their model in the minor and intermediate axes extents. our model's dimensions are also consistent with more recent ones based on lightcurves, adaptive-optics, and interferometric imaging. we confirm a rotational period of p = 5.385280 h ± 0.000001 h and a rotation pole at ecliptic longitude and latitude (λ, β) = (74°, + 20°) ± 5°. over its southern hemisphere (the one most frequently observed on earth), kleopatra's radar albedo is 0.43 ± 0.10, consistent with a high near-surface bulk density and, by inference, the high metal content expected for m-class asteroids. however, the radar albedo for equatorial observations is considerably lower and more typical of a dominantly silicate composition. this observation could readily be explained by a relatively thin (1-2 m) silicate mantle over equatorial latitudes. kleopatra's surface is relatively smooth with a mean slope of 12° at the ∼10 km baseline scale. analysis of its geopotential surface suggests loose material will preferentially migrate to the neck, and this is supported by our radar observations. | a revised shape model of asteroid (216) kleopatra |
we examine how the history of phanerozoic marine biodiversity relates to environmental change. our focus is on north america, which has a relatively densely sampled history. by transforming time series into the time-frequency domain using wavelets, histories of biodiversity are shown to be similar to sea level, temperature and oceanic chemistry at multiple timescales. fluctuations in sea level play an important role in driving phanerozoic biodiversity at timescales >50 myr, and during finite intervals at shorter periods. subsampled and transformed marine genera time series reinforce the idea that permian-triassic, triassic-jurassic, and cretaceous-paleogene mass extinctions were geologically rapid, whereas the ordovician-silurian and late devonian `events' were longer lived. high cross wavelet power indicates that biodiversity is most similar to environmental variables (sea level, plate fragmentation, δ18o, δ13c, δ34s and 87sr/86sr) at periods >200 myr, when they are broadly in phase (i.e. no time lag). they are also similar at shorter periods for finite durations of time (e.g. during some mass extinctions). these results suggest that long timescale processes (e.g. plate kinematics) are the primary drivers of biodiversity, whilst processes with significant variability at shorter periods (e.g. glacio-eustasy, continental uplift and erosion, volcanism, asteroid impact) play a moderating role. wavelet transforms are a useful approach for isolating information about times and frequencies of biological activity and commonalities with environmental variables. | timing and periodicity of phanerozoic marine biodiversity and environmental change |
purposeprecise delineation of organs at risk is a crucial task in radiotherapy treatment planning for delivering high doses to the tumor while sparing healthy tissues. in recent years, automated segmentation methods have shown an increasingly high performance for the delineation of various anatomical structures. however, this task remains challenging for organs like the esophagus, which have a versatile shape and poor contrast to neighboring tissues. for human experts, segmenting the esophagus from ct images is a time‑consuming and error‑prone process. to tackle these issues, we propose a random walker approach driven by a 3d fully convolutional neural network (cnn) to automatically segment the esophagus from ct images.methodsfirst, a soft probability map is generated by the cnn. then, an active contour model (acm) is fitted to the cnn soft probability map to get a first estimation of the esophagus location. the outputs of the cnn and acm are then used in conjunction with a probability model based on ct hounsfield (hu) values to drive the random walker. training and evaluation were done on 50 cts from two different datasets, with clinically used peer‑reviewed esophagus contours. results were assessed regarding spatial overlap and shape similarity.resultsthe esophagus contours generated by the proposed algorithm showed a mean dice coefficient of 0.76 ± 0.11, an average symmetric square distance of 1.36 ± 0.90 mm, and an average hausdorff distance of 11.68 ± 6.80, compared to the reference contours. these results translate to a very good agreement with reference contours and an increase in accuracy compared to existing methods. furthermore, when considering the results reported in the literature for the publicly available synapse dataset, our method outperformed all existing approaches, which suggests that the proposed method represents the current state‑of‑the‑art for automatic esophagus segmentation.conclusionwe show that a cnn can yield accurate estimations of esophagus location, and that the results of this model can be refined by a random walk step taking pixel intensities and neighborhood relationships into account. one of the main advantages of our network over previous methods is that it performs 3d convolutions, thus fully exploiting the 3d spatial context and performing an efficient volume‑wise prediction. the whole segmentation process is fully automatic and yields esophagus delineations in very good agreement with the gold standard, showing that it can compete with previously published methods. | esophagus segmentation in ct via 3d fully convolutional neural network and random walk |
we have obtained polarimetric measurements of asteroid (101955) bennu, a presumably primitive near-earth object (neo) that is the target of nasa's sample return mission osiris-rex. during our observing campaign, bennu was visible from earth under a wide range of illumination conditions, with phase angle in the range 16°-57°. together with (3200) phaethon and (152679) 1998 ku2, observed very recently, bennu is the only existing example of a primitive neo observed in polarimetric mode over a wide interval of phase angles. based on our polarimetric data, we propose that bennu belongs to the unusual f taxonomic class defined in the 80s. according to previous works, the f-class includes objects with cometary features. this fact can be of great importance for the interpretation of the results of the exploration of this object by osiris-rex. from polarimetry we also derive an estimate of the geometric albedo of bennu: pr = 0.059 ± 0.003. | unusual polarimetric properties of (101955) bennu: similarities with f-class asteroids and cometary bodies |
learning an unknown $n$-qubit quantum state $\rho$ is a fundamental challenge in quantum computing. information-theoretically, it is known that tomography requires exponential in $n$ many copies of $\rho$ to estimate it up to trace distance. motivated by computational learning theory, aaronson et al. introduced many (weaker) learning models: the pac model of learning states (proceedings of royal society a'07), shadow tomography (stoc'18) for learning "shadows" of a state, a model that also requires learners to be differentially private (stoc'19) and the online model of learning states (neurips'18). in these models it was shown that an unknown state can be learned "approximately" using linear-in-$n$ many copies of rho. but is there any relationship between these models? in this paper we prove a sequence of (information-theoretic) implications from differentially-private pac learning, to communication complexity, to online learning and then to quantum stability. our main result generalizes the recent work of bun, livni and moran (journal of the acm'21) who showed that finite littlestone dimension (of boolean-valued concept classes) implies pac learnability in the (approximate) differentially private (dp) setting. we first consider their work in the real-valued setting and further extend their techniques to the setting of learning quantum states. key to our results is our generic quantum online learner, robust standard optimal algorithm (rsoa), which is robust to adversarial imprecision. we then show information-theoretic implications between dp learning quantum states in the pac model, learnability of quantum states in the one-way communication model, online learning of quantum states, quantum stability (which is our conceptual contribution), various combinatorial parameters and give further applications to gentle shadow tomography and noisy quantum state learning. | private learning implies quantum stability |
pollution of white dwarf atmospheres may be caused by asteroids that originate from the locations of secular and mean-motion resonances in planetary systems. asteroids in these locations experience increased eccentricity, leading to tidal disruption by the white dwarf. we examine how the ν6 secular resonance shifts outwards into a previously stable region of the asteroid belt, as the star evolves to a white dwarf. analytic secular models require a planet to be engulfed in order to shift the resonance. we show with numerical simulations that as a planet gets engulfed by the evolving star, the secular resonance shifts and the rate of tidal disruption events increases with the engulfed planet's mass and its orbital separation. we also investigate the behaviour of mean-motion resonances. the width of a mean-motion resonance increases as the star loses mass and becomes a white dwarf. the ν6 secular resonance is more efficient at driving tidal disruptions than mean-motion resonances with jupiter. by examining 230 observed exoplanetary systems whose central star will evolve into a white dwarf, we find that along with an earth mass planet at $1\, \rm au$, hot jupiters at a semimajor axis $a\gtrsim 0.05\, \rm au$ and super-earths of mass $10\, \rm m_\oplus$ at $a\gtrsim 0.3\, \rm au$ represent planet types whose engulfment shifts resonances enough to cause pollution of the white dwarfs to a degree in agreement with observations. | on the role of resonances in polluting white dwarfs by asteroids |
context. stellar radial velocities play a fundamental role in the discovery of extrasolar planets and the measurement of their physical parameters as well as in the study of stellar physical properties.aims: we investigate the impact of the solar activity on the radial velocity of the sun using the harps spectrograph to obtain measurements that can be directly compared with those acquired in the extrasolar planet search programmes.methods: we used the moon, the galilean satellites, and several asteroids as reflectors to measure the radial velocity of the sun as a star and correlated this velocity with disc-integrated chromospheric and magnetic indexes of solar activity that are similar to stellar activity indexes. we discuss in detail the systematic effects that affect our measurements and the methods to account for them.results: we find that the radial velocity of the sun as a star is positively correlated with the level of its chromospheric activity at ~95 percent significance level. the amplitude of the long-term variation measured in the 2006-2014 period is 4.98 ± 1.44 m/s, which is in good agreement with model predictions. the standard deviation of the residuals obtained by subtracting a linear best fit is 2.82 m/s and is due to the rotation of the reflecting bodies and the intrinsic variability of the sun on timescales shorter than the activity cycle. a correlation with a lower significance is detected between the radial velocity and the mean absolute value of the line-of-sight photospheric magnetic field flux density.conclusions: our results confirm similar correlations found in other late-type main-sequence stars and provide support to the predictions of radial velocity variations induced by stellar activity based on current models. | long-term radial-velocity variations of the sun as a star: the harps view |
here we report on the significant role of a so far overlooked dynamical aspect, namely, a secular resonance between the dwarf planet ceres and other asteroids. we demonstrate that this type of secular resonance can be the dominant dynamical factor in certain regions of the main asteroid belt. specifically, we performed a dynamical analysis of the asteroids belonging to the (1726) hoffmeister family. to identify which dynamical mechanisms are actually at work in this part of the main asteroid belt, i.e., to isolate the main perturber(s), we study the evolution of this family in time. the study is accomplished using numerical integrations of test particles performed within different dynamical models. the obtained results reveal that the post-impact evolution of the hoffmeister asteroid family is a direct consequence of the nodal secular resonance with ceres. this leads us to the conclusion that similar effects must exist in other parts of the asteroid belt. in this respect, the obtained results shed light on an important and entirely new aspect of the long-term dynamics of small bodies. ceres’ fingerprint in asteroid dynamics, expressed through the discovered secular resonance effect, completely changes our understanding of the way in which perturbations by ceres-like objects affect the orbits of nearby bodies. | asteroid secular dynamics: ceres’ fingerprint identified |
we perform high-fidelity simulations of a wide-field telescopic survey searching for near-earth objects (neos) larger than 140 m, focusing on the observation and detection model, as well as detection efficiency and accuracy. as a test survey, we select the large synoptic survey telescope (lsst). we use its proposed pointings for a 10-year mission, and model the detection of neos in the fields. we discuss individual model parameters for magnitude losses, vignetting, fading, asteroid rotation and colors, fill factor, limiting magnitude, rate of motion, field shape and rotation, and survey patterns. we assess results in terms of the cumulative completeness of the detected population as a function of size and time. additionally, we examine the sources of modeling uncertainty, and derive the overall neo population completeness for the baseline lsst survey to be 55 ± 5% for neos with absolute magnitude brighter than 22. including already discovered objects and ongoing surveys, the neo completeness at the end of the lsst baseline survey should reach ∼77%. | high-fidelity simulations of the near-earth object search performance of the large synoptic survey telescope |
we present the first results of our survey of asteroid polarization phase curves in the near-infrared j and h bands using the wirc+pol instrument on the palomar 200-inch telescope. we confirm through observations of standard stars that wirc+pol can reach the 0.1% precision needed for asteroid phase curve characterization, and we show that c-complex asteroids could act as an alternate calibration source, as they show less wavelength variation than stellar polarized standards. initial polarization phase curve results for s-complex asteroids show a shift in behavior as a function of wavelength from visible to near-infrared bands, extending previously observed trends. full near-infrared polarization phase curve characterization of individual asteroids will provide a unique constraint on surface composition of these objects by probing the wavelength dependence of albedo and index of refraction of the surface material. | asteroid polarimetric phase behavior in the near-infrared: s- and c-complex objects |
fragments of small solar system bodies entering earth's atmosphere have possibly been important contributors of organic compounds to the early earth. the cyano radical (cn) emission from meteors is considered as potentially one of the most suitable markers of organic compounds in meteoroids, however, its detection in meteor spectra has been thus far unsuccessful. with the aim to improve our abilities to identify cn emission in meteor observations and use its spectral features to characterize the composition of incoming asteroidal meteoroids, we present a detailed analysis of cn emission from high-resolution spectra of 22 laboratory simulated meteors including ordinary, carbonaceous, and enstatite chondrites, as well as a large diversity of achondrites (i.e., ureilite, aubrite, lunar, martian, howardite, eucrite, and diogenite), mesosiderite, and iron meteorites. we describe the variations of cn emission from different classes of asteroidal meteor analogues, its correlation and time evolution relative to other major meteoroid components. we demonstrate that cn can be used as a diagnostic spectral feature of carbonaceous and carbon-rich meteoroids, while most ordinary chondrites show no signs of cn. our results point out strong correlation between cn and h emission and suggest both volatile features are suitable to trace contents of organic matter and water molecules present within meteoroids. for the application in lower resolution meteor observations, we demonstrate that cn can be best recognized in the early stages of ablation and for carbon-rich materials by measuring relative intensity ratio of cn band peak to the nearby fe i-4 lines. | analysis of cn emission as a marker of organic compounds in meteoroids using laboratory simulated meteors |
the timing of formation of the first planetesimals determines the mode of planetary accretion and their geophysical and compositional evolution. astronomical observations of circumstellar disks and solar system geochronology provide evidence for planetesimal formation during molecular cloud collapse, much earlier than previously estimated. here we present distinct observational evidence from white dwarf planetary systems for planetesimal formation occurring during the first few hundred thousand years after cloud collapse in exoplanetary systems. a substantial fraction of white dwarfs have accreted planetary material rich in iron core or mantle material. for the exo-asteroids accreted by white dwarfs to form iron cores, substantial heating is required. by simulating planetesimal evolution and collisional evolution, we show that the most likely heat source is short-lived radioactive nuclides such as 26al (which has a half-life of ~0.7 myr). core-rich materials in the atmospheres of white dwarfs, therefore, provide independent evidence for rapid planetesimal formation, concurrent with star formation. | rapid formation of exoplanetesimals revealed by white dwarfs |
a series of high pressure and temperature experiments were conducted to better constrain the fe isotope fractionation during core-mantle differentiation in planetesimal and planetary bodies. synthetic mixtures of oxides and metal having varying amounts of sulfur, approximating terrestrial and martian compositions, were melted at 1-2 gpa and 1650 °c. iron isotopic equilibrium between the resulting metal and glass run products was verified for all experiments using the three-isotope technique. purified fe from metal and glass was analyzed by multiple-collector icp-ms in high resolution mode. iron alloy and silicate glass show a well-resolved δ57femetal-silicate of +0.12 ± 0.04‰ in a sulfur-free system. isotope fractionation increases with sulfur content to +0.43 ± 0.03‰ at 18 wt.% sulfur in the metal. these results cannot be easily interpreted within the context of known fe isotope ratios in most natural samples of planetary and asteroidal mantles and therefore suggest more complex processes affected the fe isotope fractionation therein. however, to reconcile martian meteorite iron isotopic signatures with geophysical models using this new experimental data requires a smaller amount of sulfur in the martian core than previous estimates, with an upper limit of ∼8 wt.%. | sulfur-controlled iron isotope fractionation experiments of core formation in planetary bodies |
oxygen is the dominant element in our planetary system. it is therefore remarkable that it shows substantial isotopic diversity both in mass-dependent fractionation, because it is a light element, and in mass-independent fractionation, primarily associated with variation in abundance of 16o. on earth, the primary variation in isotopic composition is related to temperature-dependent kinetic mass fractionation between hydrosphere and atmosphere. meteorites provide samples of primitive bodies, that have not experienced melting, and planetesimals that have melted early in their history. samples of mars, vesta, and the moon are present in the meteorite collections. in meteorites, the cosmochemical fractionation related to the abundance of 16o provides a useful classification scheme. inclusions in chondrites show a large range in 16o abundances from highly enriched (solar) through to compositions closer to terrestrial (planetary). the variability in 16o appears originally to be related to predissociation and self-shielding of carbon monoxide likely in the primordial molecular cloud. within the chondrite parent bodies, exchange between 16o-poor fluids and relatively 16o-rich solids created isotopic mixing lines. this model makes specific predictions for isotopic compositions of silicates and water ice throughout the solar system. one prediction, that the earth should be isotopically heavier than the sun, appears to be verified. but other tests based on oxygen isotopes within the solar system require either remote analysis or sample return missions. remote analysis will require new instrumentation and analytical techniques to achieve the precision and accuracy required for three oxygen isotope analysis. methodologies associated with cavity ring-down spectroscopy appear promising. sample return appears viable only for the inner solar system including mars and asteroids. while sample return missions to either venus or mercury appear highly challenging, the scientific benefits are immense both in oxygen isotope characterisation, and in a variety of other geochemical analyses. measurement of three oxygen isotopes throughout the solar system would further our concepts for formation of other solar systems, and give us insight into the general mechanisms of planetary system formation and the role of water in the formation and evolution of the chondrite parent bodies and planets. | oxygen isotopes and sampling of the solar system |
the origin of life on earth would benefit from a prebiotic atmosphere that produced nitriles, like hcn, which enable ribonucleotide synthesis. however, geochemical evidence suggests that hadean air was relatively oxidizing with negligible photochemical production of prebiotic molecules. these paradoxes are resolved by iron-rich asteroid impacts that transiently reduced the entire atmosphere, allowing nitriles to form in subsequent photochemistry. here we investigate impact-generated reducing atmospheres using new time-dependent, coupled atmospheric chemistry and climate models that account for gas-phase reactions and surface catalysis. the resulting h2-, ch4-, and nh3-rich atmospheres persist for millions of years, until the hydrogen escapes to space. the hcn and hcccn production and rainout to the surface can reach 109 molecules cm-2 s-1 in hazy atmospheres with a mole ratio of ch4/co2 > 0.1. smaller ch4/co2 ratios produce hcn rainout rates of <105 molecules cm-2 s-1 and negligible hcccn. the minimum impactor mass that creates atmospheric ch4/co2 > 0.1 is 4 × 1020-5 × 1021 kg (570-1330 km diameter), depending on how efficiently iron reacts with a steam atmosphere, the extent of atmospheric equilibration with an impact-induced melt pond, and the surface area of nickel that catalyzes ch4 production. alternatively, if steam permeates and deeply oxidizes the crust, impactors of ~1020 kg could be effective. atmospheres with copious nitriles have >360 k surface temperatures, perhaps posing a challenge for rna longevity, although cloud albedo can produce cooler climates. regardless, postimpact cyanide can be stockpiled and used in prebiotic schemes after hydrogen has escaped to space. | origin-of-life molecules in the atmosphere after big impacts on the early earth |
rimmed grooves, lineations and elongate craters around mare imbrium shape much of the nearside moon. this pattern was coined the imbrium sculpture, and it was originally argued that it must have been formed by a giant oblique (~30°) impact, a conclusion echoed by later studies. some investigators, however, noticed that many elements of the imbrium sculpture are not radial to imbrium, thereby implicating an endogenic or structural origin. here we use these non-radial trends to conclude that the imbrium impactor was a proto-planet (half the diameter of vesta), once part of a population of large proto-planets in the asteroid belt. such independent constraints on the sizes of the imbrium and other basin-forming impactors markedly increase estimates for the mass in the asteroid belt before depletion caused by the orbital migration of jupiter and saturn. moreover, laboratory impact experiments, shock physics codes and the groove widths indicate that multiple fragments (up to 2% of the initial diameter) from each oblique basin-forming impactor, such as the one that formed imbrium, should have survived planetary collisions and contributed to the heavy impact bombardment between 4.3 and 3.8 billion years ago. | origin and implications of non-radial imbrium sculpture on the moon |
wd 1145+017 is currently the only white dwarf known to exhibit periodic transits of planetary debris as well as absorption lines from circumstellar gas. we present the first simultaneous fast optical spectrophotometry and broad-band photometry of the system, obtained with the gran telescopio canarias (gtc) and the liverpool telescope, respectively. the observations spanned 5.5 h, somewhat longer than the 4.5-h orbital period of the debris. dividing the gtc spectrophotometry into five wavelength bands reveals no significant colour differences, confirming grey transits in the optical. we argue that absorption by an optically thick structure is a plausible alternative explanation for the achromatic nature of the transits that can allow the presence of small-sized (∼µm) particles. the longest (87 min) and deepest (50 per cent attenuation) transit recorded in our data exhibits a complex structure around minimum light that can be well modelled by multiple overlapping dust clouds. the strongest circumstellar absorption line, fe ii λ5169, significantly weakens during this transit, with its equivalent width reducing from a mean out-of-transit value of 2 to 1 å in-transit, supporting spatial correlation between the circumstellar gas and dust. finally, we made use of the gaia data release 2 and archival photometry to determine the white dwarf parameters. adopting a helium-dominated atmosphere containing traces of hydrogen and metals, and a reddening e(b - v) = 0.01 we find t_eff=15 020 ± 520 k, log g = 8.07 ± 0.07, corresponding to m_wd=0.63± 0.05 m_{⊙} and a cooling age of 224 ± 30 myr. | fast spectrophotometry of wd 1145+017 |
context. near-earth objects (neos), thanks to their proximity, provide a unique opportunity to investigate asteroids with diameters down to dozens of meters. the study of neos is also important because of their potential hazard to the earth. the investigation of small neos is challenging from earth as they are observable only for a short time following their discovery and can sometimes only be reached again years or decades later.aims: we aim to derive the visible colors of neos and perform an initial taxonomic classification with a main focus on smaller objects and recent discoveries.methods: photometric observations were performed using the 1.2 m telescope at the haute-provence observatory and the 1.0 m telescope at the pic du midi observatory in broadband johnson-cousins and sloan photometric systems.results: we present new photometric observations for 55 neos. our taxonomic classification shows that almost half (43%) of the objects in our sample are classified as s+q-complex members, 19% as x-complex, 16% as c-complex, 12% as d-types, and finally 6% and 4% as a- and v-types, respectively. the distribution of the observed objects with h > 19 and h ≤ 19 remains almost the same. however, the majority of the objects in our dataset with d < 500 m belong to the "silicate" group, which is probably a result of an observational bias towards brighter and more accessible objects. "carbonaceous" objects are predominant among those with a jovian tisserand parameter of tj < 3. these bodies could be dormant or extinct comets. the median values of the absolute magnitude for "carbonaceous" and "silicate" groups are h = 18.10 ± 0.95 and h = 19.50 ± 1.20, whereas the estimated median diameters are d = 1219 ± 729 m and d = 344 ± 226 m, respectively. "silicate" objects have a much lower median earth's minimum orbit intersection distance (moid) and a somewhat lower orbital inclination in comparison to "carbonaceous" objects. about half of the observed objects are potentially hazardous asteroids and are mostly (almost 65%) represented by "silicate" objects. array(0x2b5f030) | photometric survey of 55 near-earth asteroids |
the double asteroid redirection test (dart) is a nasa-sponsored mission that will be the first direct test of the kinetic impactor technique for planetary defense. the dart spacecraft will impact into didymos-b, the moon of the binary system 65803 didymos, and the resulting period change will be measured from earth. impact simulations will be used to predict the crater size and momentum enhancement expected from the dart impact. because the specific material properties (strength, porosity, internal structure) of the didymos-b target are unknown, a wide variety of numerical simulations must be performed to better understand possible impact outcomes. this simulation campaign will involve a large parameter space being simulated using multiple different shock physics hydrocodes. in order to understand better the behaviors and properties of numerical simulation codes applicable to the dart impact, a benchmarking and validation program using different numerical codes to solve a set of standard problems was designed and implemented. the problems were designed to test the effects of material strength, porosity, damage models, and target geometry on the ejecta following an impact and thus the momentum transfer efficiency. several important results were identified from comparing simulations across codes, including the effects of model resolution and porosity and strength model choice: 1) momentum transfer predictions almost uniformly exhibit a larger variation than predictions of crater size; 2) the choice of strength model, and the values used for material strength, are significantly more important in the prediction of crater size and momentum enhancement than variation between codes; 3) predictions for crater size and momentum enhancement tend to be similar (within 15-20%) when similar strength models are used in different codes. these results will be used to better design a modeling plan for the dart mission as well as to better understand the potential results that may be expected due to unknown target properties. the dart impact simulation team will determine a specific desired material parameter set appropriate for the didymos system that will be standardized (to the extent possible) across the different codes when making predictions for the dart mission. some variation in predictions will still be expected, but that variation can be bracketed by the results shown in this study. | benchmarking impact hydrocodes in the strength regime: implications for modeling deflection by a kinetic impactor |
we present the identification and preliminary analysis of a dust trail following the orbit of (3200) phaethon as seen in white-light images recorded by the wide-field imager for parker solar probe (wispr) instrument on the nasa parker solar probe (psp) mission. during psp's first solar encounter in 2018 november, a dust trail following phaethon's orbit was visible for several days and crossing two fields of view. preliminary analyses indicate this trail to have a visual magnitude of 15.8 ± 0.3 per pixel and a surface brightness of 25.0 mag arcsec-2 as seen by psp/wispr from a distance of ∼0.2 au from the trail. we estimate the total mass of the stream to be ∼(0.4-1.3) × 1012 kg, which is consistent with, though slightly underestimates, the assumed mass of the geminid stream, but is far larger than the current dust production that phaethon could support. our results imply that we are observing a natural clustering of at least some portion of the geminid meteor stream through its perihelion, as opposed to dust produced more recently from perihelion activity of phaethon. | parker solar probe observations of a dust trail in the orbit of (3200) phaethon |
the influence of fe concentration on heat transport properties of olivine was investigated to understand the cooling history of rocky planets such as mercury, mars and asteroids. thermal conductivity (λ) and thermal diffusivity (κ) were measured simultaneously for olivine polycrystal with different fe contents (fo, fo90, fo70, fo50, fo31 and fo0) up to 10 gpa and 1100 k by a pulse heating method. with increasing fe in olivine, thermal conductivity of olivine first decreases and then slightly increases. the minimum λ was found to be at composition near fo31; the absolute λ value of fo31 is about 65% lower than that of fo. small amounts of fe in olivine can strongly reduce the thermal conductivity at low temperature; λ value of fo90 is about 50% of fo at room temperature. thermal conductivities of polycrystalline olivine have smaller absolute values and weaker pressure and temperature dependences, compared with those of natural single crystal olivine determined by previous studies. heat capacity of fo70 and fo50 calculated from λ and κ is independent of pressure and is controlled by nearly constant thermal expansion coefficient with increasing temperature. smaller λ of olivine aggregate with high fe content would produce a warmer mantle and, in turn, possibly a thicker crust in the fe-rich mars, while heat in the fe-poor mercury can escape faster than the other terrestrial planets. olivine-dominant asteroids with high fe concentration could have longer cooling history and lower thermal inertia on the surface. | effect of iron content on thermal conductivity of olivine with implications for cooling history of rocky planets |
gaseous circumbinary disks (cbds) that are highly inclined to the binary orbit are commonly observed in nature. these disks harbor particles that can reach large mutual inclinations as a result of nodal precession once the gas disk has dissipated. with n-body simulations that include fragmentation we demonstrate that misaligned disks of particles can be efficient progenitors of interstellar asteroids (isas). collisions that take place between particles with large mutual inclinations have large impact velocities, which can result in mass ejection, with a wide range of fragment sizes and ejection velocities. we explore the binary parameters for which the majority of the terrestrial planet-forming material is ejected rather than accreted into planets. the misalignment required to eject significant material decreases with binary eccentricity. if the distribution of binary eccentricity is uniform and the initial particle cbd orientation relative to the binary orbit is isotropic, about 59% of binaries are more likely to eject the majority of their cbd terrestrial planet disk mass through high-velocity body-body collisions than to retain this material and build terrestrial planets. however, binary-disk interactions during the gas disk phase with nonzero disk viscosity will reduce this fraction. the composition, small size, highly elongated shape, and tumbling motion of 'oumuamua are consistent with isas generated by misaligned cbds. | misaligned circumbinary disks as efficient progenitors of interstellar asteroids |
context. we assess statistical inversion of asteroid rotation periods, pole orientations, shapes, and phase curve parameters from photometric lightcurve observations, here sparse data from the esa gaia space mission (data release 2) or dense and sparse data from ground-based observing programs.aims: assuming general convex shapes, we develop inverse methods for characterizing the bayesian a posteriori probability density of the parameters (unknowns). we consider both random and systematic uncertainties (errors) in the observations, and assign weights to the observations with the help of bayesian a priori probability densities.methods: for general convex shapes comprising large numbers of parameters, we developed a markov-chain monte carlo sampler (mcmc) with a novel proposal probability density function based on the simulation of virtual observations giving rise to virtual least-squares solutions. we utilized these least-squares solutions to construct a proposal probability density for mcmc sampling. for inverse methods involving triaxial ellipsoids, we update the uncertainty model for the observations.results: we demonstrate the utilization of the inverse methods for three asteroids with gaia photometry from data release 2: (21) lutetia, (26) proserpina, and (585) bilkis. first, we validated the convex inverse methods using the combined ground-based and gaia data for lutetia, arriving at rotation and shape models in agreement with those derived with the help of rosetta space mission data. second, we applied the convex inverse methods to proserpina and bilkis, illustrating the potential of the gaia photometry for setting constraints on asteroid light scattering as a function of the phase angle (the sun-object-observer angle). third, with the help of triaxial ellipsoid inversion as applied to gaia photometry only, we provide additional proof that the absolute gaia photometry alone can yield meaningful photometric slope parameters. fourth, for (585) bilkis, we report, with 1-σ uncertainties, a refined rotation period of (8.5750559 ± 0.0000026) h, pole longitude of 320.6° ± 1.2°, pole latitude of - 25.6° ± 1.7°, and the first shape model and its uncertainties from convex inversion.conclusions: we conclude that the inverse methods provide realistic uncertainty estimators for the lightcurve inversion problem and that the gaia photometry can provide an asteroid taxonomy based on the phase curves. | asteroid lightcurve inversion with bayesian inference |
we designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the khatyrka meteorite. at the boundaries among cual5, (mg0.75fe2+0.25)2sio4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline phase displaying face-centered icosahedral symmetry and low phason strain. the compositional range of the icosahedral phase is al68-73fe11-16cu10-12cr1-4ni1-2 and extends toward higher al/(cu+fe) and fe/cu ratios than those reported for natural icosahedrite or for any previously known synthetic quasicrystal in the al-cu-fe system. the shock-induced synthesis demonstrated in this experiment reinforces the evidence that natural quasicrystals formed during a shock event but leaves open the question of whether this synthesis pathway is attributable to the expanded thermodynamic stability range of the quasicrystalline phase at high pressure, to a favorable kinetic pathway that exists under shock conditions, or to both thermodynamic and kinetic factors. | shock synthesis of quasicrystals with implications for their origin in asteroid collisions |
from mid-ordovician ~470 myr-old limestone >100 fossil l-chondritic meteorites have been recovered, representing the markedly enhanced flux of meteorites to earth following the breakup of the l-chondrite parent body. recently one anomalous meteorite, österplana 065 (öst 65), was found in the same beds that yield l chondrites. the cosmic-ray exposure age of öst 65 shows that it may be a fragment of the impactor that broke up the l-chondrite parent body. here we show that in a chromium versus oxygen-isotope plot öst 65 falls outside all fields encompassing the known meteorite types. this may be the first documented example of an `extinct' meteorite, that is, a meteorite type that does not fall on earth today because its parent body has been consumed by collisions. the meteorites found on earth today apparently do not give a full representation of the kind of bodies in the asteroid belt ~500 myr ago. | a new type of solar-system material recovered from ordovician marine limestone |
medical time series are sequential data collected over time that measures health-related signals, such as electroencephalography (eeg), electrocardiography (ecg), and intensive care unit (icu) readings. analyzing medical time series and identifying the latent patterns and trends that lead to uncovering highly valuable insights for enhancing diagnosis, treatment, risk assessment, and disease progression. however, data mining in medical time series is heavily limited by the sample annotation which is time-consuming and labor-intensive, and expert-depending. to mitigate this challenge, the emerging self-supervised contrastive learning, which has shown great success since 2020, is a promising solution. contrastive learning aims to learn representative embeddings by contrasting positive and negative samples without the requirement for explicit labels. here, we conducted a systematic review of how contrastive learning alleviates the label scarcity in medical time series based on prisma standards. we searched the studies in five scientific databases (ieee, acm, scopus, google scholar, and pubmed) and retrieved 1908 papers based on the inclusion criteria. after applying excluding criteria, and screening at title, abstract, and full text levels, we carefully reviewed 43 papers in this area. specifically, this paper outlines the pipeline of contrastive learning, including pre-training, fine-tuning, and testing. we provide a comprehensive summary of the various augmentations applied to medical time series data, the architectures of pre-training encoders, the types of fine-tuning classifiers and clusters, and the popular contrastive loss functions. moreover, we present an overview of the different data types used in medical time series, highlight the medical applications of interest, and provide a comprehensive table of 51 public datasets that have been utilized in this field. in addition, this paper will provide a discussion on the promising future scopes such as providing guidance for effective augmentation design, developing a unified framework for analyzing hierarchical time series, and investigating methods for processing multimodal data. despite being in its early stages, self-supervised contrastive learning has shown great potential in overcoming the need for expert-created annotations in the research of medical time series. | self-supervised contrastive learning for medical time series: a systematic review |
the helicopter vibrations generated by the main rotor/gearbox assembly are the principal cause of damage to cockpit instruments and discomfort of the crew in terms of cabin noise. the principal path of vibration transmission to the fuselage is through the gearbox rigid support struts. with the aim of reducing these vibrations, this paper presents the design of a low-weight high-performance active damper for vibration control developed by elettronica aster s.p.a. the system is intended to replace the conventional struts and is composed of an electro-hydraulic actuator hosted within a compliant structure. this parallel nested structure allows the system to reach a high-power density. a physics-based mathematical model was used as a design digital twin to optimize the performance to meet the strict requirements. the active damper was designed for a reference application of a 15-seat medium-sized twin-engine helicopter. the model was used to perform the tests specified in the acceptance and testing procedure document, showing the compliance with the requirements of the current design. the damper physical realization, test bench design, experimental campaign, and model validation will be presented in part 2. | development of a high-performance low-weight hydraulic damper for active vibration control of the main rotor on helicopters—part 1: design and mathematical model |
as technology continues to evolve, our society is becoming enriched with more intelligent devices that help us perform our daily activities more efficiently and effectively. one of the most significant technological advancements of our time is the internet of things (iot), which interconnects various smart devices (such as smart mobiles, intelligent refrigerators, smartwatches, smart fire alarms, smart door locks, and many more) allowing them to communicate with each other and exchange data seamlessly. we now use iot technology to carry out our daily activities, for example, transportation. in particular, the field of smart transportation has intrigued researchers due to its potential to revolutionize the way we move people and goods. iot provides drivers in a smart city with many benefits, including traffic management, improved logistics, efficient parking systems, and enhanced safety measures. smart transportation is the integration of all these benefits into applications for transportation systems. however, as a way of further improving the benefits provided by smart transportation, other technologies have been explored, such as machine learning, big data, and distributed ledgers. some examples of their application are the optimization of routes, parking, street lighting, accident prevention, detection of abnormal traffic conditions, and maintenance of roads. in this paper, we aim to provide a detailed understanding of the developments in the applications mentioned earlier and examine current researches that base their applications on these sectors. we aim to conduct a self-contained review of the different technologies used in smart transportation today and their respective challenges. our methodology encompassed identifying and screening articles on smart transportation technologies and its applications. to identify articles addressing our topic of review, we searched for articles in the four significant databases: ieee xplore, acm digital library, science direct, and springer. consequently, we examined the communication mechanisms, architectures, and frameworks that enable these smart transportation applications and systems. we also explored the communication protocols enabling smart transportation, including wi-fi, bluetooth, and cellular networks, and how they contribute to seamless data exchange. we delved into the different architectures and frameworks used in smart transportation, including cloud computing, edge computing, and fog computing. lastly, we outlined current challenges in the smart transportation field and suggested potential future research directions. we will examine data privacy and security issues, network scalability, and interoperability between different iot devices. | smart transportation: an overview of technologies and applications |
field-free magnetization switching by in-plane current injection via spin-orbit interactions in heavy-metal/ferromagnet bilayer systems is of great interest for applications of spin-orbit torque (sot). here, we demonstrate theoretically how to deterministically switch the magnetization of cofeb with a tilted perpendicular magnetic anisotropy (pma) by using the sot effect from the viewpoint of energy landscape. it is found that magnetization switching is dependent both on the polar angle θ and the azimuthal angle φ of the tilted pma. a tiny remnant magnetization component that deviates away from the film plane during the spin current pulse impulsion period is a key point for the subsequent switching. the underlying mechanism is attributed to the shift of pma energy barrier with the magnetization angle, which dominates the state of the tiny magnetization component and thereafter the bipolar deterministic switching. based on the simulation results, a phase diagram of deterministic switching regarding θ and φ is established. moreover, the positive and negative critical switching current densities are demonstrated to exhibit an astroid-like characteristic as a function of θ. this study provides a fundamental insight into the nature of sot-induced deterministic switching with the tilted pma method. | deterministic magnetization switching by spin-orbit torque in a ferromagnet with tilted magnetic anisotropy: a macrospin modeling |
this study has introduced a predictive framework including a heuristic guidance law named predictive path planning and multiple-horizon multiple-model predictive control as the control scheme for soft landing on an irregular-shaped asteroid. the dynamical model of spacecraft trajectory around an asteroid is introduced. the reference-landing trajectory is generated using predictive path planning. not only does the presented guidance law satisfy the collision avoidance constraint, but also guarantees the landing accuracy and vertical landing condition. multiple-horizon multiple-model predictive control is employed to make the spacecraft track the designed reference trajectory. the proposed control approach, which is a model predictive control scheme, utilizes several prediction models instead of one. in this manner, it heritages the advantages of optimality and tackling external disturbances and model uncertainties from classical model predictive control and at the same time has the advantage of lower computational burden than model predictive control. finally, numerical simulations are carried out to demonstrate the feasibility and effectiveness of the proposed control approach in achieving the desired conditions in presence of uncertainties and disturbances. | soft landing on an irregular shape asteroid using multiple-horizon multiple-model predictive control |
02.18.1930 a new body was discovered beyond the orbit of neptune. pluto is quite a large body rotates around the sun and is not a single on its orbit. that is why international astronomical union (iau) by its resolution of 24.08.2006 gave this "large" planet lower status. it was one of several new objects which are called dwarf planets. in the same decision, mac, ceres was transferred from the status of "asteroid" in the status of "dwarf" planet. 04.06.2002 was discovered kuiper belt objects (50000) kuaoar with a diameter of 1 110 km; 21.10.2003 was discovered eris (ub313), which classified as dwarf planet when determined its large size and weight. (136108) haumea with size of 1 960 × 1 518 × 996 km, and makemake (2005 fy9) with a diameter of 1 502 km were discovered in 2005. 03.05.2004 was announced the discovery of the farthest object in the solar system - sedna, on distant from the sun a nearly 100 a.u. thus the decade that had passed since the introduction of the new class of these large objects in the solar system as dwarf planets - has indicated on the correctness of this step of astronomical community. after all, most of the main methods of researches is quite specific and different from the methods for the study of great classical planets. they also differ significantly and in their physical parameters. | dwarf planets (to the 10th anniversary of the introduction of the new class of planets) |
determining the shapes of a rotating liquid droplet bound by surface tension is an archetypal problem in the study of the equilibrium shapes of a spinning and charged droplet, a problem that unites models of the stability of the atomic nucleus with the shapes of astronomical-scale, gravitationally-bound masses. the shapes of highly deformed droplets and their stability must be calculated numerically. although the accuracy of such models has increased with the use of progressively more sophisticated computational techniques and increases in computing power, direct experimental verification is still lacking. here we present an experimental technique for making wax models of these shapes using diamagnetic levitation. the wax models resemble splash-form tektites, glassy stones formed from molten rock ejected from asteroid impacts. many tektites have elongated or `dumb-bell' shapes due to their rotation mid-flight before solidification, just as we observe here. measurements of the dimensions of our wax `artificial tektites' show good agreement with equilibrium shapes calculated by our numerical model, and with previous models. these wax models provide the first direct experimental validation for numerical models of the equilibrium shapes of spinning droplets, of importance to fundamental physics and also to studies of tektite formation. | artificial tektites: an experimental technique for capturing the shapes of spinning drops |
we describe the mineralogy, petrology and oxygen isotopic compositions of high-temperature rims around mineralogically pristine calcium-aluminum-rich inclusions (cais) from the cr, cb and ch carbonaceous chondrites. in cr chondrites, nearly all cais are surrounded by single- or multi-layered rims composed of cai-like minerals; relict cais inside chondrules in which the rims were resorbed by the host chondrule melt (aléon et al., 2002; makide et al., 2009) are the only exception. a complete multi-layered rim sequence (from inside outward: spinel + hibonite + perovskite → melilite → anorthite replacing melilite → al-diopside → forsterite) is rarely observed; al-diopside ± forsterite rims are more common. the cr cais and all rim layers are uniformly 16o-rich (δ17o ∼-24‰), indicating formation in a 16o-rich gaseous reservoir. the mineralogy, petrology and 16o-rich compositions of these rims suggest formation by evaporation/condensation, melting (?), and thermal annealing in the formation region of the host cais. we define such rims as the primordial wark-lovering (wl) rims. in ch chondrites, most cais are uniformly 16o-rich and surrounded by the primordial wl rims. one of the 16o-rich cais is surrounded by an anorthite-al-diopside wl rim showing a range of δ17o values, from ∼-24‰ to ∼-6‰; δ17o decreases towards the cai core. we infer that this rim experienced incomplete melting and o-isotope exchange in an 16o-poor nebular gas, most likely during chondrule formation. most cais in cb chondrites and about 10% of cais in ch chondrites are uniformly 16o-depleted igneous inclusions; δ17o values between individual cais vary from ∼-12‰ to ∼-5‰. these cais have diverse mineralogies (grossite-rich, hibonite-rich, melilite-rich, spinel-rich, and al,ti-diopside ± forsterite-rich), but are surrounded by the mineralogically similar igneous rims composed of ±melilite, al-diopside and ca-rich forsterite (0.5-1.4 wt% cao). the igneous rims and the host igneous cais have identical (within uncertainties of our sims measurements) o-isotope compositions, suggesting that they crystallized from isotopically similar, but chemically distinct melts. we suggest that the uniformly 16o-depleted igneous rims around the uniformly 16o-depleted igneous cais in cb and ch chondrites formed during melting of pre-existing cais in an impact-generated plume invoked for the origin of cb chondrites (krot et al., 2005), followed by o-isotope exchange with an 16o-poor plume gas (δ17o ∼-2‰), condensation of gaseous sio and mg into cai melt, and its subsequent crystallization. we conclude that high-temperature rims around cais from cr, ch and cb chondrites recorded thermal processing in gaseous reservoirs with different oxygen isotopic compositions. in contrast to the isotopically heterogeneous wl rims around cv cais, our data provide no evidence that cais were transported between 16o-rich and 16o-poor gaseous reservoirs multiple times. we suggest instead that oxygen-isotope heterogeneity in the cv wl rims resulted from a fluid-rock interaction on the cv parent asteroid. | high-temperature rims around calcium-aluminum-rich inclusions from the cr, cb and ch carbonaceous chondrites |
the lunar cratering record is used to constrain the bombardment history of both the earth and the moon. however, it is suggested from different perspectives, including impact crater dating, asteroid dynamics, lunar samples, impact basin-forming simulations, and lunar evolution modelling, that the moon could be missing evidence of its earliest cratering record. here we report that impact basins formed during the lunar magma ocean solidification should have produced different crater morphologies in comparison to later epochs. a low viscosity layer, mimicking a melt layer, between the crust and mantle could cause the entire impact basin size range to be susceptible to immediate and extreme crustal relaxation forming almost unidentifiable topographic and crustal thickness signatures. lunar basins formed while the lunar magma ocean was still solidifying may escape detection, which is agreeing with studies that suggest a higher impact flux than previously thought in the earliest epoch of earth-moon evolution. | large impact cratering during lunar magma ocean solidification |
treatment protocols combining tamsulosin and solifenacin proved better management of the complicated urinary tract symptoms. the pharmaceutical preparations of tamsulosin and solifenacin suffered from the high difference in their ratio, 0.4 mg tamsulosin and 6 mg solifenacin, and strong spectral overlap. here, we developed four simple, accurate and selective spectrophotometric methods based on simple mathematical manipulations. these methods require the simplest mathematical filtration using short steps performed using built-in functions of the spectrophotometer operating software utilizing zero-order or derivative spectra. these methods are namely absorption correction method (acm), induced dual-wavelength (idw), absorptivity factor method (afm) and first derivative method (d1). the linear ranges were 15-70 μg/ml and 100-1200 μg/ml for tam and sfn, respectively. the limits of quantitation were in the range of 3.8-4.05 μg/ml and 23.34-59.05 μg/ml, while the limits of detection were in the range of 1.25-1.34 μg/ml and 7.7-24.6 μg/ml for tam and sfn, respectively. all validation parameters investigated as per ich guidelines. a statistical comparison executed for the proposed methods with each other and with the reported methods showed no significant difference between the proposed and the reported methods. | smart uv spectrophotometric methods based on simple mathematical filtration and classical methods for the simultaneous determination of tamsulosin and solifenacin: a comparative study of efficacy and spectral resolution |
so far, only two interstellar objects have been observed within our solar system. while the first one, 1i/`oumuamua, had asteroidal characteristics, the second one, 2i/borisov, showed clear evidence of cometary activity. we performed polarimetric observations of comet 2i/borisov using the european southern observatory very large telescope to derive the physical characteristics of its coma dust particles. here we show that the polarization of 2i/borisov is higher than what is typically measured for solar system comets. this feature distinguishes 2i/borisov from dynamically evolved objects such as jupiter-family and all short- and long-period comets in our solar system. the only object with similar polarimetric properties as 2i/borisov is comet c/1995 o1 (hale-bopp), an object that is believed to have approached the sun only once before its apparition in 1997. unlike hale-bopp and many other comets, though, comet 2i/borisov shows a polarimetrically homogeneous coma, suggesting that it is an even more pristine object. | unusual polarimetric properties for interstellar comet 2i/borisov |
we simulate the passage through the sun-jupiter system of interstellar objects (isos) similar to 1i/`oumuamua or 2i/borisov. capture of such objects is rare and overwhelmingly from low incoming speeds on to orbits akin to those of known long-period comets. this suggests that some of these comets could be of extrasolar origin, in particular inactive ones. assuming isos follow the local stellar velocity distribution, we infer a volume capture rate of 0.051 au^3 yr^{-1}. current estimates for orbital lifetimes and space densities then imply steady-state captured populations of ∼102 comets and ∼105 `oumuamua-like rocks, of which 0.033 per cent are within 6 au at any time. | capture of interstellar objects: a source of long-period comets |
in this study, we measured bidirectional reflectance spectra (0.5-4.0 μm) of 24 cms, five crs, one ci, one cv, and one c2 carbonaceous chondrites. these meteorites are known to have experienced an important variability in their relative degrees of aqueous alteration degree (rubin et al. [2007]. geochim. cosmochim. acta 71, 2361-2382; howard et al. [2009]. geochim. cosmochim. acta 73, 4576-4589; howard et al. [2011]. geochim. cosmochim. acta 75, 2735-2751; alexander et al. [2013]. geochim. cosmochim. acta 123, 244-260). these measurements were performed on meteorite powders inside an environmental cell under a primary vacuum and heated at 60 °c in order to minimize adsorbed terrestrial water. this protocol allows controlling of atmospheric conditions (i.e. humidity) in order to avoid contamination by terrestrial water. we discuss various spectral metrics (e.g. reflectance, band depth, single-scattering albedo, …) in the light of recent bulk composition characterization (howard et al. [2009]. geochim. cosmochim. acta 73, 4576-4589; howard et al. [2015]. geochim. cosmochim. acta 149, 206-222; alexander et al. [2012]. science 337, 721; beck et al. [2014]. icarus 229, 263-277; garenne et al. [2014]. geochim. cosmochim. acta 137, 93-112). this study reveals variability of reflectance among meteorite groups. the reflectance is not correlated with carbon or hydrogen abundance neither with measured grain size distribution. we suggest that it is rather controlled by the nature of accreted components, in particular the initial matrix/chondrule proportion. band depth, integrated band depth, mean optical path length, normalized optical path length, effective single-particle absorption thickness were calculated on the so called 3-μm band for reflectance spectra and for single scattering albedo spectra. they were compared with hydrated phase proportions from previous study on the same meteorites by thermogravimetric analyses and infrared spectroscopy in transmission. we find that normalized optical path length (nopl) is the most appropriate to quantify water abundance, with an absolute error of about 5 wt.%. these datasets also reveal a variability of the band shape between 2.8 and 2.9 μm, which is interpreted as reflecting variation in the chemical composition and structure of phyllosilicates. this chemical variation could also be used to quantify the aqueous alteration degree between meteorite groups. the combination of reflectance at 2 μm and the depth of 3-μm band can be combined, to classify carbonaceous chondrites in reflectance in term of primary composition (e.g. matrix/chondrule ratio, carbon content) and secondary processes (e.g. aqueous alteration, thermal metamorphism). this could be used to decipher the nature of aqueous alteration in c-complex asteroids. | bidirectional reflectance spectroscopy of carbonaceous chondrites: implications for water quantification and primary composition |
many if not most small asteroids are rubble piles covered by regolith, and small perturbations may be enough to disturb their surfaces in complex ways due to microgravity. experiments to study low-gravity regolith dynamics are challenging, and properly validated numerical simulations can provide valuable insights. in this paper, we investigate numerically size segregation among regolith grains, which is likely to occur after repeated shaking events. in particular, we are interested in the so-called brazil-nut effect (bne), i.e. the migration of a large intruder towards the top of a vertically shaken granular system. we go a step forward in simulating this effect by implementing horizontal periodic boundary conditions (pbc) in the n-body code pkdgrav, with the aim of making the simulations more representative of the expected asteroid environment. we study the influence of pbc on the bne in earth gravity and compare them with a walled case. we also investigate the influence of static and rolling friction on the bne. with walls, we observe the well-known convection mechanism driving the bne. however, we find that a different mechanism, consisting of void filling, is responsible for the bne with pbc, and we discuss its relevance in light of previous studies. by running simulations in 10-4g, we show that this void-filling mechanism remains relevant in a low-gravity environment. however, we find that depending on the gravity level, the void-filling mechanism is differently influenced by the friction properties of particles. we speculate that this is likely due to a change in the granular flow time-scales. | numerical simulations of oscillation-driven regolith motion: brazil-nut effect |
trajectory design in highly-perturbed environments like binary asteroids is challenging. it typically requires using realistic, non-autonomous dynamical models in which periodic solutions derived in autonomous systems vanish. in this work, lagrangian descriptors are employed in the perturbed planar bi-elliptic restricted four-body problem to find regions of bounded motion over a finite horizon about dimorphos, the secondary body of the (65803) didymos binary system. results show that lagrangian descriptors successfully reveal phase space organizing structures both in the unperturbed and perturbed planar bi-elliptic restricted four-body problem. with no solar radiation pressure, regions of bounded motion are visually identified, so granting access to a vast selection of bounded orbits about dimorphos. conversely, the presence of solar radiation pressure breaks down the majority of structures, leading to a large region of unstable motion with rare exceptions. lagrangian descriptors are computationally inexpensive dynamical indicators that could be conveniently applied to astrodynamics. | finding regions of bounded motion in binary asteroid environment using lagrangian descriptors |
in recent years, noncontact measurements of vital signs using cameras received a great amount of interest. however, some questions are unanswered: (i) which vital sign is monitored using what type of camera? (ii) what is the performance and which factors affect it? (iii) which health issues are addressed by camera-based techniques? following the preferred reporting items for systematic reviews and meta-analyses (prisma) statement, we conduct a systematic review of continuous camera-based vital sign monitoring using scopus, pubmed, and the association for computing machinery (acm) databases. we consider articles that were published between january 2018 and april 2021 in the english language. we include five vital signs: heart rate (hr), respiratory rate (rr), blood pressure (bp), body skin temperature (bst), and oxygen saturation (spo2). in total, we retrieve 905 articles and screened them regarding title, abstract, and full text. one hundred and four articles remained: 60, 20, 6, 2, and 1 of the articles focus on hr, rr, bp, bst, and spo2, respectively, and 15 on multiple vital signs. hr and rr can be measured using red, green, and blue (rgb) and near-infrared (nir) as well as far-infrared (fir) cameras. so far, bp and spo2 are monitored with rgb cameras only, whereas bst is derived from fir cameras only. under ideal conditions, the root mean squared error is around 2.60 bpm, 2.22 cpm, 6.91 mm hg, 4.88 mm hg, and 0.86 °c for hr, rr, systolic bp, diastolic bp, and bst, respectively. the estimated error for spo2 is less than 1%, but it increases with movements of the subject and the camera-subject distance. camera-based remote monitoring mainly explores intensive care, post-anaesthesia care, and sleep monitoring, but also explores special diseases such as heart failure. the monitored targets are newborn and pediatric patients, geriatric patients, athletes (e.g., exercising, cycling), and vehicle drivers. camera-based techniques monitor hr, rr, and bst in static conditions within acceptable ranges for certain applications. the research gaps are large and heterogeneous populations, real-time scenarios, moving subjects, and accuracy of bp and spo2 monitoring. | continuous monitoring of vital signs using cameras: a systematic review |
in this study we generate optimal runge-kutta (rk) schemes for converging the artificial compressibility method (acm) using dual time-stepping with high-order unstructured spatial discretizations. we present optimal rk schemes with between s = 2 and s = 7 stages for spectral difference (sd) and discontinuous galerkin (dg) discretizations obtained using the flux reconstruction (fr) approach with solution polynomial degrees of k = 1 to k = 8. these schemes are optimal in the context of linear advection with predicted speedup factors in excess of 1.80× relative to a classical rk4,4 scheme. speedup factors of between 1.89× and 2.11× are then observed for incompressible implicit large eddy simulation (iles) of turbulent flow over an sd7003 airfoil. finally, we demonstrate the utility of the schemes for incompressible iles of a turbulent jet, achieving good agreement with experimental data. the results demonstrate that the optimized rk schemes are suitable for simulating turbulent flows and can achieve significant speedup factors when converging the acm using dual time-stepping with high-order unstructured spatial discretizations. | optimal runge-kutta schemes for pseudo time-stepping with high-order unstructured methods |
chondrites are rocky fragments of asteroids that formed at different times and heliocentric distances in the early solar system. most chondrite groups contain water-bearing minerals, attesting that both water-ice and dust were accreted on their parent asteroids. nonetheless, the hydrogen isotopic composition (d/h) of water in the different chondrite groups remains poorly constrained, due to the intimate mixture of hydrated minerals and organic compounds, the other main h-bearing phase in chondrites. building on our recent works using in situ secondary ion mass spectrometry analyses, we determined the h isotopic composition of water in a large set of chondritic samples (ci, cm, co, cr, and c-ungrouped carbonaceous chondrites) and report that water in each group shows a distinct and unique d/h signature. based on a comparison with literature data on bulk chondrites and their water and organics, our data do not support a preponderant role of parent-body processes in controlling the d/h variations among chondrites. instead, we propose that the water and organic d/h signatures were mostly shaped by interactions between the protoplanetary disk and the molecular cloud that episodically fed the disk over several million years. because the preservation of d-rich interstellar water and/or organics in chondritic materials is only possible below their respective sublimation temperatures (160 and 350-450 k), the h isotopic signatures of chondritic materials depend on both the timing and location at which their parent body formed. | origin of hydrogen isotopic variations in chondritic water and organics |
superbolides, i.e. extremely bright meteors produced by entries of meter-sized bodies into terrestrial atmosphere, are rare events. we present here detailed analysis of a superbolide, which occurred over romania on january 7, 2015. the trajectory, velocity, and orbit were determined using two all-sky photographs from a station of the european fireball network (en) in slovakia and five casual video records from romania, which were carefully calibrated. bolide light curve was measured by en radiometers. we found that the entry speed was 27.76±0.19 km s-1, significantly lower than reported by us government sensors. the orbit was asteroidal with low inclination and aphelion inside jupiter's orbit. the atmospheric behavior was, however, not typical for an asteroidal body. the peak brightness of absolute magnitude of -21 was reached at a quite large height of 42.8 km and the brightness then decreased quickly. the bolide almost disappeared at a height of 38.7 km, leaving just a stationary luminous trail visible for several seconds. only one small fragment continued until the height of 36 km. brief meteorite searches were unsuccessful. the modeling of the light curve revealed that the body of initial mass of about 4500 kg remained almost intact until the dynamic pressure reached 0.9 mpa but it was then quickly disintegrated into many tiny fragments and dust under 1-3 mpa. a comparison was made with three other superbolides for which we have radiometric light curves: ordinary chondrite fall košice, carbonaceous chondrite fall maribo, and cometary taurid bolide of october 31, 2015. the romanian superbolide was not similar to any of these and represents probably a new type of material with intrinsic strength of about 1 mpa. | the january 7, 2015, superbolide over romania and structural diversity of meter-sized asteroids |
the osiris-rex asteroid sample return mission is the third mission in national aeronautics and space administration (nasa)'s new frontiers program and is the first u.s. mission to return samples from an asteroid to earth. the most important decision ahead of the osiris-rex team is the selection of a prime sample-site on the surface of asteroid (101955) bennu. mission success hinges on identifying a site that is safe and has regolith that can readily be ingested by the spacecraft's sampling mechanism. to inform this mission-critical decision, the surface of bennu is mapped using the osiris-rex camera suite and the images are used to develop several foundational data products. acquiring the necessary inputs to these data products requires observational strategies that are defined specifically to overcome the challenges associated with mapping a small irregular body. we present these strategies in the context of assessing candidate sample sites at bennu according to a framework of decisions regarding the relative safety, sampleability, and scientific value across the asteroid's surface. to create data products that aid these assessments, we describe the best practices developed by the osiris-rex team for image-based mapping of irregular small bodies. we emphasize the importance of using 3-d shape models and the ability to work in body-fixed rectangular coordinates when dealing with planetary surfaces that cannot be uniquely addressed by body-fixed latitude and longitude. | overcoming the challenges associated with image-based mapping of small bodies in preparation for the osiris-rex mission to (101955) bennu |
there has been speculation about a class of relativistic explosions with an initial lorentz factor γinit smaller than that of classical gamma-ray bursts (grbs). these “dirty fireballs” would lack prompt grb emission but could be pursued via their optical afterglow, appearing as transients that fade overnight. here we report a search for such transients (that fade by 5-σ in magnitude overnight) in four years of archival photometric data from the intermediate palomar transient factory (iptf). our search criteria yielded 50 candidates. of these, two were afterglows to grbs that had been found in dedicated follow-up observations to triggers from the fermi grb monitor. another (iptf14yb) was a grb afterglow discovered serendipitously. eight were spurious artifacts of reference image subtraction, and one was an asteroid. the remaining 38 candidates have red stellar counterparts in external catalogs. the photometric and spectroscopic properties of the counterparts identify these transients as strong flares from m dwarfs of spectral type m3-m7 at distances of d ≈ 0.15-2.1 kpc; three counterparts were already spectroscopically classified as late-type m stars. with iptf14yb as the only confirmed relativistic outflow discovered independently of a high-energy trigger, we constrain the all-sky rate of transients that peak at m = 18 and fade by δm = 2 mag in δt = 3 hr to be 680 {{yr}}-1, with a 68% confidence interval of 119{--}2236 {{yr}}-1. this implies that the rate of visible dirty fireballs is at most comparable to that of the known population of long-duration grbs. | iptf archival search for fast optical transients |
(3200) phaethon is a compelling object as it has an asteroidal appearance and spectrum, produces a weak dust tail during perihelion at just 0.14 au, and is the parent body of the geminid meteor shower. a better understanding of the physical properties of phaethon is needed to understand the nature of its current and previous activity, relationship to potential source populations, and to plan for the upcoming flyby of the destiny+ spacecraft of phaethon in the 2020s. we performed rotationally resolved spectroscopy of phaethon at visible and near-infrared wavelengths (0.4-2.5 μm) in 2007 and 2017, respectively, to better understand its surface properties. the visible and near-infrared observations both spanned nearly a full rotation or more and were under similar observing geometries, covering the entire surface with the exception of the north pole. the visible wavelengths show blue slopes with only minor slope variations and no absorption features. the nir data is minimally varying and concave upwards, from very blue to blue-neutral with increasing wavelength. we fit the short-wavelength tail of phaethon’s thermal emission and retrieve an average visible albedo of pv= 0.08 ± 0.01, which is lower than previous measurements but plausible in light of the recent larger radar-measured diameter of phaethon. we retrieve an average infrared beaming parameter of phaethon of η = 1.70 ± 0.05, which is similar to previous results. we discuss the implications of phaethon’s visible and near-infrared spectrum as well as the lower albedo on its origin, source population, and evolutionary history. | rotationally resolved spectroscopic characterization of near-earth object (3200) phaethon |
1i/’oumuamua was discovered by the panoramic survey telescope and rapid response system (pan-starrs 1) on 2017 october 19. unlike all previously discovered minor planets, this object was determined to have eccentricity e > 1.0, suggesting an interstellar origin. since this discovery and within the limited window of opportunity, several photometric and spectroscopic studies of the object have been made. using the measured light curve amplitudes and rotation periods we find that, under the assumption of a triaxial ellipsoid, a density range 1500 < ρ < 2800 kg m-3 matches the observations and no significant cohesive strength is required. we also determine that an aspect ratio of 6 ± 1:1 is most likely after accounting for phase-angle effects and considering the potential effect of surface properties. this elongation is still remarkable, but less than some other estimates. | constraints on the density and internal strength of 1i/’oumuamua |
secondary organic aerosols (soas) play a key role in climate change and air quality. determining the fundamental parameters that distribute organic compounds between the phases is essential, as atmospheric lifetime and impacts change drastically between the gas and particle phase. in this work, gas-to-particle partitioning of major biogenic oxidation products was investigated using three different aerosol chemical characterization techniques. the aerosol collection module, the collection thermal desorption unit, and the chemical analysis of aerosols online are different aerosol sampling inlets connected to a proton-transfer reaction time-of-flight mass spectrometer (acm-ptr-tof-ms, td-ptr-tof-ms, and charon-ptr-tof-ms, respectively, referred to hereafter as acm, td, and charon). these techniques were deployed at the atmosphere simulation chamber saphir to perform experiments on the soa formation and aging from different monoterpenes (β-pinene, limonene) and real plant emissions (pinus sylvestris l.). the saturation mass concentration c* and thus the volatility of the individual ions was determined based on the simultaneous measurement of their signal in the gas and particle phase. a method to identify and exclude ions affected by thermal dissociation during desorption and ionic dissociation in the ionization chamber of the proton-transfer reaction mass spectrometer (ptr-ms) was developed and tested for each technique. narrow volatility distributions with organic compounds in the semi-volatile (svocs - semi-volatile organic compounds) to intermediate-volatility (ivocs - intermediate-volatility organic compounds) regime were found for all systems studied. despite significant differences in the aerosol collection and desorption methods of the proton-transfer-reaction (ptr)-based techniques, a comparison of the c* values obtained with different techniques was found to be in good agreement (within 1 order of magnitude) with deviations explained by the different operating conditions of the ptr-ms. the c* of the identified organic compounds were mapped onto the two-dimensional volatility basis set (2d-vbs), and results showed a decrease in c* with increasing oxidation state. for all experiments conducted in this study, identified partitioning organic compounds accounted for 20-30 % of the total organic mass measured from an aerosol mass spectrometer (ams). further comparison between observations and theoretical calculations was performed for species found in our experiments that were also identified in previous publications. theoretical calculations based on the molecular structure of the compounds showed, within the uncertainties ranges, good agreement with the experimental c* for most svocs, while ivocs deviated by up to a factor of 300. these latter differences are discussed in relation to two main processes affecting these systems: (i) possible interferences by thermal and ionic fragmentation of higher molecular-weight compounds, produced by accretion and oligomerization reactions, that fragment in the m/z range detected by the ptr-ms and (ii) kinetic influences in the distribution between the gas and particle phase with gas-phase condensation, diffusion in the particle phase, and irreversible uptake. | gas-to-particle partitioning of major biogenic oxidation products: a study on freshly formed and aged biogenic soa |
the decay of radioactive 26al to 26mg (half-life of 730,000 years) is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system. high-resolution chronological information provided by the 26al-26mg decay system is, therefore, intrinsically linked to the thermal evolution of early-formed planetesimals. in this paper, we explore the timing and style of asteroidal differentiation by combining high-precision mg isotope measurements of meteorites with thermal evolution models for planetesimals. in detail, we report mg isotope data for a suite of olivine-rich [al/mg ∼ 0] achondritic meteorites, as well as a few chondrites. main group, pyroxene and the zinder pallasites as well as the lodranite all record deficits in the mass-independent component of μ26mg (μ26mg∗) relative to chondrites and earth. this isotope signal is expected for the retarded ingrowth of radiogenic 26mg∗ in olivine-rich residues produced through partial silicate melting during 26al decay and consistent with their marginally heavy mg isotope composition relative to ordinary chondrites, which may reflect the early extraction of isotopically light partial melts from the source rock. we propose that their parent planetesimals started forming within ∼250,000 years of solar system formation from a hot (>∼500 k) inner protoplanetary disk region characterized by a reduced initial (26al/27al)0 abundance (∼1-2 × 10-5) relative to the (26al/27al)0 value in cais of 5.25 × 10-5. this effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals. these 'non-carbonaceous' planetesimals acquired their mass throughout an extended period (>3 myr) of continuous accretion, thereby generating onion-shell structures of incompletely differentiated zones, consisting of olivine-rich residues, overlaid by metachondrites and undifferentiated chondritic crusts. in contrast, individual olivine crystals from eagle station pallasites record variable μ26mg∗ excesses, suggesting that these crystals captured the 26mg∗ evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26al. similar to previous suggestions based on isotopic evidence, we suggest that eagle station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by (26al/27al)0 ⩾ 2.7 × 10-5. protracted planetesimal accretion timescales at large orbital distances, with onset of accretion 0.3-1 myr post-cais, may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting 'carbonaceous' planetesimals. | accretion timescales and style of asteroidal differentiation in an 26al-poor protoplanetary disk |
any effort which intends to physically interact with specific asteroids requires understanding at least of the composition and multi-scale structure of the surface layers, sometimes also of the interior. therefore, it is necessary first to characterize each target object sufficiently by a precursor mission to design the mission which then interacts with the object. in small solar system body (sssb) science missions, this trend towards landing and sample-return missions is most apparent. it also has led to much interest in mascot-like landing modules and instrument carriers. they integrate at the instrument level to their mothership and by their size are compatible even with small interplanetary missions. the dlr-estec gossamer roadmap nea science working groups' studies identified multiple nea rendezvous (mnr) as one of the space science missions only feasible with solar sail propulsion. parallel studies of solar polar orbiter (spo) and displaced l1 (dl1) space weather early warning missions studies outlined very lightweight sailcraft and the use of separable payload modules for operations close to earth as well as the ability to access any inclination and a wide range of heliocentric distances. these and many other studies outline the unique capability of solar sails to provide access to all sssb, at least within the orbit of jupiter. since the original mnr study, significant progress has been made to explore the performance envelope of near-term solar sails for multiple nea rendezvous. however, although it is comparatively easy for solar sails to reach and rendezvous with objects in any inclination and in the complete range of semi-major axis and eccentricity relevant to neos and phos, it remains notoriously difficult for sailcraft to interact physically with a sssb target object as e.g. the hayabusa missions do. the german aerospace center, dlr, recently brought the gossamer solar sail deployment technology to qualification status in the gossamer-1 project. development of closely related technologies is continued for very large deployable membrane-based photovoltaic arrays in the gosolar project. we expand the philosophy of the gossamer solar sail concept of efficient multiple sub-spacecraft integration to also include landers for one-way in-situ investigations and sample-return missions. these are equally useful for planetary defence scenarios, sssb science and neo utilization. we outline the technological concept used to complete such missions and the synergetic integration and operation of sail and lander. we similarly extend the philosophy of mascot and use its characteristic features as well as the concept of constraints-driven engineering for a wider range of operations. | capabilities of gossamer-1 derived small spacecraft solar sails carrying mascot-derived nanolanders for in-situ surveying of neas |
the active contour model (acm) is a standard image analysis technique whose numerous variants have attracted an enormous amount of research attention across multiple fields. incorrectly, however, the acm's differential-equation-based formulation and prototypical dependence on user initialization have been regarded as being largely incompatible with the recently popular deep learning approaches to image segmentation. this paper introduces the first tight unification of these two paradigms. in particular, we devise deep convolutional active contours (dcac), a truly end-to-end trainable image segmentation framework comprising a convolutional neural network (cnn) and an acm with learnable parameters. the acm's eulerian energy functional includes per-pixel parameter maps predicted by the backbone cnn, which also initializes the acm. importantly, both the cnn and acm components are fully implemented in tensorflow, and the entire dcac architecture is end-to-end automatically differentiable and backpropagation trainable without user intervention. as a challenging test case, we tackle the problem of building instance segmentation in aerial images and evaluate dcac on two publicly available datasets, vaihingen and bing huts. our reseults demonstrate that, for building segmentation, the dcac establishes a new state-of-the-art performance by a wide margin. | end-to-end deep convolutional active contours for image segmentation |
the migration of cohesive regolith on the surface of an otherwise monolithic or strong asteroid is studied using theoretical and simulation models. the theory and simulations show that under an increasing spin rate (such as due to the yorp effect), the regolith covering is preferentially lost across certain regions of the body. for regolith with little or no cohesive strength, failure occurs by landsliding from the mid latitudes of the body at high enough spin rates. as the cohesive strength of the regolith increases, failure occurs by fission of grains (or coherent chunks of grains) across a greater extent of latitudes and eventually will first occur at the equator. as the spin rate is further increased, failure regions migrate from the first failure point to higher and lower latitudes. eventually failure will encompass the equatorial region, however there always remains a region of high latitudes (around the poles) that will not undergo failure for arbitrarily high spin rates (unless disturbed by some other phenomenon). with these results a scaling law is derived that can be used to determine whether observed asteroids could retain surface regolith grains of a given size. the implications of this for the interpretation of spectral observations of small asteroids and boulder migration on large asteroids are discussed. | cohesive regolith on fast rotating asteroids |
resonance capture is studied numerically in the three-body problem for arbitrary inclinations. massless particles are set to drift from outside the 1:5 resonance with a jupiter-mass planet thereby encountering the web of the planet's diverse mean motion resonances. randomly constructed samples explore parameter space for inclinations from 0 to 180° with 5° increments totalling nearly 6 × 105 numerical simulations. 30 resonances internal and external to the planet's location are monitored. we find that retrograde resonances are unexpectedly more efficient at capture than prograde resonances and that resonance order is not necessarily a good indicator of capture efficiency at arbitrary inclination. capture probability drops significantly at moderate sample eccentricity for initial inclinations in the range [10°,110°]. orbit inversion is possible for initially circular orbits with inclinations in the range [60°,130°]. capture in the 1:1 co-orbital resonance occurs with great likelihood at large retrograde inclinations. the planet's orbital eccentricity, if larger than 0.1, reduces the capture probabilities through the action of the eccentric kozai-lidov mechanism. a capture asymmetry appears between inner and outer resonances as prograde orbits are preferentially trapped in inner resonances. the relative capture efficiency of retrograde resonance suggests that the dynamical lifetimes of damocloids and centaurs on retrograde orbits must be significantly larger than those on prograde orbits implying that the recently identified asteroids in retrograde resonance, 2006 bz8, 2008 so218, 2009 qy6 and 1999 le31 may be among the oldest small bodies that wander between the outer giant planets. | resonance capture at arbitrary inclination |
the potentially hazardous asteroid (185851) 2000 dp107 was the first binary near-earth asteroid to be imaged. radar observations in 2000 provided images at 75 m resolution that revealed the shape, orbit, and spin-up formation mechanism of the binary. the asteroid made a more favorable flyby of the earth in 2008, yielding images at 30 m resolution. we used these data to obtain shape models for the two components and to improve the estimates of the mutual orbit, component masses, and spin periods. the primary has a sidereal spin period of 2.7745 ± 0.0007 hr and is roughly spheroidal with an equivalent diameter of 863 m +/- 5%. it has a mass of 4.656+/- 0.43× {10}11 kg and a density of 1381 ± 244 kg m-3. it exhibits an equatorial ridge similar to the (66391) 1999 kw4 primary; however, the equatorial ridge in this case is not as regular and has a ∼300 m diameter concavity on one side. the secondary has a sidereal spin period of 1.77 ± 0.02 days commensurate with the orbital period. the secondary is slightly elongated and has overall dimensions of 377× 314× 268 m (6% uncertainties). its mass is 0.178+/- 0.021× {10}11 kg and its density is 1047 ± 230 kg m-3. the mutual orbit has a semimajor axis of 2.659 ± 0.08 km, an eccentricity of 0.019 ± 0.01, and a period of 1.7556 ± 0.0015 days. the normalized total angular momentum of this system exceeds the amount required for the expected spin-up formation mechanism. an increase of angular momentum from non-gravitational forces after binary formation is a possible explanation. the two components have similar radar reflectivity, suggesting a similar composition consistent with formation by spin-up. the secondary appears to exhibit a larger circular polarization ratio than the primary, suggesting a rougher surface or subsurface at radar wavelength scales. | radar imaging and characterization of the binary near-earth asteroid (185851) 2000 dp107 |
here, we evaluate the extent of aqueous alteration among five pristine specimens of the ungrouped tagish lake carbonaceous chondrite (tl5b, tl11h, tl11i, tl4, and tl10a) using thermogravimetric analysis (tga) and infrared (ir) transmission spectroscopy. both tga and ir spectroscopy have proven to be reliable methods for determining the extent of aqueous alteration among different carbonaceous chondrites, in particular the cm chondrites (e.g., garenne et al. 2014), with which tagish lake shares some affinities. using these two methods, our goal is to incorporate tl4 and tl10a into the known alteration sequence of tl5b < tl11h < tl11i (herd et al. 2011; blinova et al. 2014a). this study highlights the compositional variability of the tagish lake specimens, which we ascribe to its brecciated nature. our tga and ir spectroscopy results are congruent with the reported alteration sequence, allowing us to introduce the tl4 and tl10a specimens in the following order: tl4 < tl5b ≤ tl10a < tl 11h < tl11i. notably, these two specimens appear to be similar to the least altered lithologies previously reported, and the alteration of tagish lake is similar to that experienced by lesser altered members of the cm chondrites (>cm1.6). based on these findings, tagish lake could be considered a 1.6-2.0 ungrouped carbonaceous chondrite. visible and near-ir reflectance measurements of tagish lake were also acquired in this study to revisit the tagish lake parent body connection. while other studies have paired tagish lake with d- and t-type asteroid parent bodies, the reflectance spectra acquired in this study are variable among the different tagish lake specimens in relation to their alteration sequences; results match with spectra characteristic of c-, x-, xc-, and d-type asteroids. the heterogeneity of tagish lake coupled with its low albedo makes the parent body connection a challenge. | water abundance in the tagish lake meteorite from tga and ir spectroscopy: evaluation of aqueous alteration |
the detached object sedna is likely at the inner edge of the oort cloud, more precisely the inner oort cloud (ioc). until recently it was the sole member of this population. the recent discovery of the detached object 2012 vp113 has confirmed that there should be more objects in this region. three additional ioc candidates with orbits much closer to neptune have been proposed in the past decade since sedna's discovery: 2000 cr105, 2004 vn112 and 2010 gb174. sedna and 2012 vp113 have perhelia near 80 au and semimajor axes over 250 au. the latter three have perihelia between 44 and 50 au and semimajor axes between 200 and 400 au. here we determine whether the latter three objects belong to the ioc or are from the kuiper belt's extended scattered disc (esd) using numerical simulations. we assume that the ioc was formed when the sun was in its birth cluster. we analyse the evolution of the ioc and the scattered disc (sd) during an episode of late giant planet migration. we examine the impact of giant planet migration in the context of four and five planets. we report that the detached objects 2004 vn112 and 2010 gb174 are likely members of the ioc that were placed there while the sun was in its birth cluster or during an episode of solar migration in the galaxy. the origin of 2000 cr105 is ambiguous but it is likely that it belongs to the esd. based on our simulations, we find that the maximum perihelion distance of sd objects is 41 au when the semimajor axis is higher than 250 au. objects closer in are subject to mean-motion resonances with neptune that may raise their perihelia. the five-planet model yields the same outcome. we impose a conservative limit and state that all objects with perihelion distance q > 45 au and semimajor axis a > 250 au belong to the ioc. | re-assessing the formation of the inner oort cloud in an embedded star cluster - ii. probing the inner edge |
we review previously published and newly obtained crater size-frequency distributions in the inner solar system. these data indicate that the moon and the terrestrial planets have been bombarded by two populations of objects. population 1, dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. population 2, dominating since about 3.8-3.7 gyr, had the same size distribution as near-earth objects (neos) and a much lower impact flux, and produced a crater size distribution characterized by a differential -3 single-slope power law in the crater diameter range 0.02 km to 100 km. taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. the neo population is the source of population 2 and it has been in near-steady state over the past ∼ 3.7-3.8 gyr; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. however, population 1 was composed of main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during orbit migration of giant planets; this caused the so-called late heavy bombardment (lhb). the lhb began some time before ∼3.9 gyr, peaked and declined rapidly over the next ∼ 100 to 300 myr, and possibly more slowly from about 3.8-3.7 gyr to ∼2 gyr. a third crater population (population s) consisted of secondary impact craters that can dominate the cratering record at small diameters. | the inner solar system cratering record and the evolution of impactor populations |
since 1996, the nasa/jet propulsion laboratory on-line horizons system has provided open access to the latest jpl orbit solutions through customizable ephemeris generation and searches. currently, high-precision ephemerides for more than 683,000 objects are available: all known solar system bodies, several dozen spacecraft, system barycenters, and some libration points.since inception, horizons has produced 150 million ephemeris products in response to 70.4 million connections by 800,000 unique ip addresses. recent usage is typically 6000 unique users requesting 4,000,000 ephemeris products per month.horizons is freely accessible without an account and may be used and automated through any of three interfaces: interactive telnet connection, web-browser form, or by sending e-mail command-files.asteroid and comet ephemerides are numerically integrated on request using jpl's dastcom5 database of initial conditions which is kept current by a separate process; as new measurements and discoveries are reported by the minor planet center, they are automatically processed into new jpl orbit solutions. radar targets and other objects of high interest have their orbit solutions manually examined and updated into the database.for asteroids and comets, spk files may be dynamically created using horizons. this is effectively a recording of the integrator output. the binary files may then be efficiently interpolated by user software to exactly reproduce the trajectory without having to duplicate the numerically integrated n-body dynamical model or ppn equations of motion.other horizons output is numerical and in the form of plain-text observer, vector, osculating element, and close-approach tables. more than one hundred quantities can be requested in various time-scales and coordinate systems. for asteroids and comets, statistical uncertainties can be mapped to output times to assess position and motion uncertainties.horizons is consistent with the de431 solar system solution, the iau 1976 ecliptic, itrf93, and the iau2009 planetary rotational and cartographic models. | status of the jpl horizons ephemeris system |
the first multimodal emotion recognition challenge (mer 2023) was successfully held at acm multimedia. the challenge focuses on system robustness and consists of three distinct tracks: (1) mer-multi, where participants are required to recognize both discrete and dimensional emotions; (2) mer-noise, in which noise is added to test videos for modality robustness evaluation; (3) mer-semi, which provides a large amount of unlabeled samples for semi-supervised learning. in this paper, we introduce the motivation behind this challenge, describe the benchmark dataset, and provide some statistics about participants. to continue using this dataset after mer 2023, please sign a new end user license agreement and send it to our official email address merchallenge.contact@gmail.com. we believe this high-quality dataset can become a new benchmark in multimodal emotion recognition, especially for the chinese research community. | mer 2023: multi-label learning, modality robustness, and semi-supervised learning |
from small seeds falling from trees to asteroids colliding with planets and moons, the impact of projectiles onto granular targets occurs in nature at different scales. in this paper, we investigate open questions in the mechanics of granular cratering, in particular, the forces acting on the projectile and the roles of granular packing, grain-grain friction, and projectile spin. for that, we carried out discrete element method computations of the impact of solid projectiles on a cohesionless granular medium, where we varied the projectile and grain properties (diameter, density, friction, and packing fraction) for different available energies (within relatively small values). we found that a denser region forms below the projectile, pushing it back and causing its rebound by the end of its motion, and that solid friction affects considerably the crater morphology. besides, we show that the penetration length increases with the initial spin of the projectile, and that differences in initial packing fractions can engender the diversity of scaling laws found in the literature. finally, we propose an ad hoc scaling that collapsed our data for the penetration length and can perhaps unify existing correlations. our results provide new insights into the formation of craters in granular matter. | roles of packing fraction, microscopic friction, and projectile spin in cratering by impact |
c-type asteroids are the source of the carbonaceous chondrite meteorites and represent remnants of primitive planetesimals that formed at the outer margins of the early solar system and may have delivered volatiles to the inner solar system, in particular the early earth. however, the nature of carbonaceous chondrites is not well understood owing to terrestrial alteration. here, we present the petrology and mineral chemistry of surface materials collected by the japan aerospace exploration agency (jaxa) hayabusa2 spacecraft from the c-type asteroid ryugu. the ryugu particles we studied are similar to ci (ivuna-type) chondrites but with some important differences, such as the presence of na-mg phosphates and na-rich phases and the lack of ferrihydrite and gypsum. ryugu particles experienced several steps of aqueous alteration, metasomatism and brecciation under variable conditions. these materials represent mixed lithologies and formed at different locations within their parent asteroid. the evidence presented here demonstrates that the c-type asteroid ryugu experienced a complex geologic evolution shortly after its formation. | insight into multi-step geological evolution of c-type asteroids from ryugu particles |
hayabusa2 spacecraft successfully collected rock samples from the surface of c-type near-earth asteroid 162173 ryugu through two touchdowns and brought them back to earth in 2020. at the extraterrestrial sample curation center in jaxa, we performed initial description of all samples to obtain fundamental information and prepare the database for sample allocation. we propose morphological classifications for the returned samples based on the initial description of 205 grains described in the first 6 months. the returned samples can be distinguished by four morphological characteristics: dark, glossy, bright, and white. according to coordinated study to provide an initial description and detailed investigation by scanning electron microscopy and x-ray diffraction analysis in this study, these features reflect the differences in the degree of space weathering and mineral assemblages. the degree of space weathering of the four studied grain types is heterogeneous: weak for a0042 (dark group) and c0041 (white group); moderate for c0094 (glossy); and severe for a0017 (bright). the white phase, which is the mineral characteristic of the white group grains, is identified as large carbonate minerals. this is the first effort to classify ryugu returned samples into distinct categories. based on these results, researchers can estimate sample characteristics only from the information on the jaxa curation public database. it will be an important reference for sample selection for further investigation. | variations of the surface characteristics of ryugu returned samples |
context. asteroid families are the outcomes of disruption or cratering events on a size and energy scales that are not reproducible in laboratory experiments. overall structure, as well as properties of individual members, in the old families could have been changed since their formation. therefore young families preserve best the characteristics of the initial event.aims: we study the most suitable known asteroid family with an age of less than 1 myr, the datura family. we aim (i) to obtain information about rotation state and shape of the largest members in the family; and (ii) to constrain its debiased population down to couple of hundreds of meters in size.methods: we have analyzed the up-to-date catalog of orbital elements of main belt asteroids. we evaluated the detection efficiency of catalina sky survey (css) in regard to detections of members in the datura family, and we have used our photometric observations and lightcurve inversion methods to determine the rotation states and shapes of the largest members of the family.results: we determined rotation periods of the seven largest members of the datura family, and we also derived accurate mean absolute magnitudes for six of them. except for the largest fragment (1270) datura, the asteroids tend to have long rotation periods and large amplitude of the lightcurve, witnessing an elongated shape. for the four largest asteroids, our observations allow us to resolve rotation pole and a rough shape. all of them are prograde-rotating and have the latitude of the rotation pole >50°. our search in orbital catalogs resulted in the discovery of many small, sub-kilometer members of the datura family. using the css detection efficiency, we inverted this information into the debiased population of datura family members. we show that the mass and angular momentum content in small fragments is negligible compared to the largest fragment (1270) datura. these findings may help to constrain the formation mechanism of the family. | the young datura asteroid family. spins, shapes, and population estimate |
the samples returned from a c-type asteroid (ryugu) by the hayabusa2 mission constitute unprecedented access to carbonaceous material never exposed to earth's atmosphere that may still contain phases formed in the earliest stages of the solar system. we present an extensive analysis of a large set of grains and bulks of the ryugu samples, performed directly within the japan aerospace exploration agency curation center in japan with the near-infrared hyperspectral microscope micromega, to identify and characterize the carbonate component of the samples, which has recorded early evolutionary steps. we reveal a large presence of carbonates within the collection distributed over two main size-dependent populations: generally small (<100 µm) dolomite-rich and larger (up to hundreds of µm) breunnerite-rich areas, some with complex elongated morphologies. similarities with c-chondrites suggest that such characteristics may emerge as a general property of primitive materials in the outer part of the asteroid belt. these two carbonate populations likely translate distinct processes and stages of formation in the early solar system that might have taken place while co2 ice was still present (possibly before accretion of the ryugu parent body) and/or from c-rich phases. | constraints on solar system early evolution by micromega analysis of ryugu carbonates |
we found that sdss j094002.56+274942.0 underwent a superoutburst in 2019 february based on our observations and zwicky transient facility (ztf) data. this object showed shallow eclipses during this superoutburst and we established the orbital period to be 0.1635015(1) d in combination with the ztf and asteroid terrestrial-impact last alert system (atlas) data in quiescence. superhumps apparently started to develop soon after the object reached the plateau phase and fully grown superhumps were recorded within the initial 6 d of the plateau phase. using the superhump and orbital periods, we obtained a mass ratio (q) of 0.39(3) and obtained an inclination of 70.5(5) deg by eclipse modeling. these values reproduced the quiescent ellipsoidal variations very well. using the gaia parallax and 2mass observations, we confirmed that the secondary is indistinguishable from an unevolved main-sequence star. the resultant mass ratio and orbital period were the highest among su uma stars, and this provided a proof that the 3:1 resonance can develop in less than 6 d even in q=0.39(3). the superoutburst faded relatively rapidly and was followed by a rebrightening, suggesting that the tidal effect in a large-q system was insufficient to maintain a long superoutburst and the remnant matter caused a rebrightening. the presence of such a system among dwarf novae is against the conventional idea that outbursts in dwarf novae are not long enough to develop superhumps, in contrast to novalike variables, under a weak tidal effect. the present observation also supports that the 3:1 resonance is the cause of a long outburst, and not its consequence, even under extreme q. the rapid growth of the 3:1 resonance in a high-q system challenges the generally accepted results of hydrodynamic simulations. | sdss j094002.56+274942.0: an su uma star with an orbital period of 3.92 hours and an apparently unevolved secondary |
near-earth asteroid 99942 apophis presents a unique opportunity to study the dynamics, bulk properties, and interior structure of a rubble-pile asteroid when it makes its close encounter with the earth in 2029. in order to better understand the potential outcomes of a tidal encounter between earth and apophis, and to support a potential future mission to apophis, we perform numerical simulations of the encounter. we represent earth as a single rigid sphere and the target body as a cohesionless, self-gravitating granular aggregate of identical spheres in a hexagonal-close-packed configuration subject only to gravitational and soft-sphere (elastic) contact forces. we use a radar-derived shape model for the asteroid, along with current best estimates for the orbital solution of apophis to simulate the encounter trajectory, and perform a large parameter sweep over different potential encounter orientations and bulk densities for the body. we find that the median change in the rotational period for apophis, sampled for a range of different initial body and spin orientations, is -1.9 h (mean -0.1 ± 6.0 (1-σ) hours) during the encounter. additionally, we measure that the mean of the largest change in axis length among the 3 primary body axes, also sampled over trials with different initial body and spin orientations, is 0.132 ± 0.066 mm during the encounter, assuming a bulk young's modulus of 106 pa. such strains on the timescale of peak stress during the encounter may be large enough to be detected by an in-situ seismometer. | using a discrete element method to investigate seismic response and spin change of 99942 apophis during its 2029 tidal encounter with earth |
aims: we investigate the spectra, material properties, and orbital distribution of millimeter- to decimeter-sized meteoroids. our study aims to distinguish the characteristics of populations of differently sized meteoroids and reveal the heterogeneity of identified meteoroid streams. we verify the surprisingly large ratio of pure iron meteoroids on asteroidal orbits detected among mm-sized bodies.methods: emission spectra and multi-station meteor trajectories were collected within the amos network observations. the sample is based on 202 meteors of -1 to -14 magnitude, corresponding to meteoroids of mm to dm sizes. meteoroid composition is studied by spectral classification based on relative intensity ratios of na, mg, and fe and corresponding monochromatic light curves. heliocentric orbits, trajectory parameters, and material strengths inferred from empirical kb and pe parameters were determined for 146 meteoroids.results: an overall increase of na content compared to the population of mm-sized meteoroids was detected, reflecting weaker effects of space weathering processes on larger meteoroids. the preservation of volatiles in larger meteoroids is directly observed. we report a very low ratio of pure iron meteoroids and the discovery of a new spectral group of fe-rich meteors. the majority of meteoroids on asteroidal orbits were found to be chondritic. thermal processes causing na depletion and physical processes resulting in na-rich spectra are described and linked to characteristically increased material strengths. numerous major and minor shower meteors were identified in our sample, revealing various degrees of heterogeneity within halley-type, ecliptical, and sungrazing meteoroid streams. our results imply a scattered composition of the fragments of comet 2p/encke and 109p/swift-tuttle. the largest disparities were detected within α-capricornids of the inactive comet 169p/neat and δ-aquarids of the sungrazing 96p/machholz. we also find a spectral similarity between κ-cygnids and taurids, which could imply a similar composition of the parent objects of the two streams. tables 5 and 6 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/629/a71 | spectral and orbital survey of medium-sized meteoroids |
context. over the past decades, several interplanetary missions have studied small bodies in situ, leading to major advances in our understanding of their geological and geophysical properties. these missions, however, have had a limited number of targets. among them, the nasa dawn mission has characterised in detail the topography and albedo variegation across the surface of asteroid (4) vesta down to a spatial resolution of ~20 m pixel-1 scale.aims: here our aim was to determine how much topographic and albedo information can be retrieved from the ground with vlt/sphere in the case of vesta, having a former space mission (dawn) providing us with the ground truth that can be used as a benchmark.methods: we observed vesta with vlt/sphere/zimpol as part of our eso large programme (id 199.c-0074) at six different epochs, and deconvolved the collected images with a parametric point spread function (psf). we then compared our images with synthetic views of vesta generated from the 3d shape model of the dawn mission, on which we projected vesta's albedo information.results: we show that the deconvolution of the vlt/sphere images with a parametric psf allows the retrieval of the main topographic and albedo features present across the surface of vesta down to a spatial resolution of ~20-30 km. contour extraction shows an accuracy of ~1 pixel (3.6 mas). the present study provides the very first quantitative estimate of the accuracy of ground-based adaptive-optics imaging observations of asteroid surfaces.conclusions: in the case of vesta, the upcoming generation of 30-40 m telescopes (elt, tmt, gmt) should in principle be able to resolve all of the main features present across its surface, including the troughs and the north-south crater dichotomy, provided that they operate at the diffraction limit. reduced images of table a.1 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/623/a6 based on observations made with eso telescopes at the paranal observatory under programme id 199.c-0074 (pi: p. vernazza). | closing the gap between earth-based and interplanetary mission observations: vesta seen by vlt/sphere |
we present "tracklet-less heliocentric orbit recovery" (thor), an algorithm for linking of observations of solar system objects across multiple epochs that does not require intranight tracklets or a predefined cadence of observations within a search window. by sparsely covering regions of interest in the phase space with "test orbits," transforming nearby observations over a few nights into the corotating frame of the test orbit at each epoch, and then performing a generalized hough transform on the transformed detections followed by orbit determination filtering, candidate clusters of observations belonging to the same objects can be recovered at moderate computational cost and with little to no constraint on cadence. we validate the effectiveness of this approach by running on simulations as well as on real data from the zwicky transient facility (ztf). applied to a short, two-week slice of ztf observations, we demonstrate thor can recover 97.4% of all previously known and discoverable objects in the targeted (a > 1.7 au) population with five or more observations and with purity between 97.7% and 100%. this includes 10 likely new discoveries, and a recovery of an e ~ 1 comet c/2018 u1 (the comet would have been a ztf discovery had thor been running in 2018 when the data were taken). the thor package and demo jupyter notebooks are open source and available at https://github.com/moeyensj/thor. | thor: an algorithm for cadence-independent asteroid discovery |
aeolian erosion is a destructive process that can erode small-size planetary objects through their interaction with a gaseous environment. aeolian erosion operates in a wide range of environments and under various conditions. aeolian erosion has been extensively explored in the context of geophysics in terrestrial planets. here we show that aeolian erosion of cobbles, boulders, and small planetesimals in protoplanetary discs can constitute a significant barrier for the early stages of planet formation. we use analytic calculations to show that under the conditions prevailing in protoplanetary discs small bodies ( $10\!-\!10^4 \, \rm {m}$ ) are highly susceptible to gas-drag aeolian erosion. at this size-range aeolian erosion can efficiently erode the planetesimals down to tens-cm size and quench any further growth of such small bodies. it thereby raises potential difficulties for channels suggested to alleviate the metre-size barrier. nevertheless, the population of ∼decimetre-size cobbles resulting from aeolian erosion might boost the growth of larger (>km size) planetesimals and planetary embryos through increasing the efficiency of pebble-accretion, once/if such large planetesimals and planetary embryos exist in the disc. | the aeolian-erosion barrier for the growth of metre-size objects in protoplanetary discs |
aims: to interpret adaptive-optics observations of (216) kleopatra, we need to describe an evolution of multiple moons orbiting an extremely irregular body and include their mutual interactions. such orbits are generally non-keplerian and orbital elements are not constants.methods: consequently, we used a modified n-body integrator, which was significantly extended to include the multipole expansion of the gravitational field up to the order ℓ = 10. its convergence was verified against the `brute-force' algorithm. we computed the coefficients cℓm, sℓm for kleopatra's shape, assuming a constant bulk density. for solar system applications, it was also necessary to implement a variable distance and geometry of observations. our χ2 metric then accounts for the absolute astrometry, the relative astrometry (second moon with respect to the first), angular velocities, and silhouettes, constraining the pole orientation. this allowed us to derive the orbital elements of kleopatra's two moons.results: using both archival astrometric data and new vlt/sphere observations (eso lp 199.c-0074), we were able to identify the true periods of the moons, p1 = (1.822359 ± 0.004156) d, p2 = (2.745820 ± 0.004820) d. they orbit very close to the 3:2 mean-motion resonance, but their osculating eccentricities are too small compared to other perturbations (multipole, mutual), meaning that regular librations of the critical argument are not present. the resulting mass of kleopatra, m1 = (1.49 ± 0.16) × 10−12 m⊙ or 2.97 × 1018 kg, is significantly lower than previously thought. an implication explained in the accompanying paper is that (216) kleopatra is a critically rotating body. based on observations made with eso telescopes at the la silla paranal observatory under program 199.c-0074 (pi vernazza). | an advanced multipole model for (216) kleopatra triple system |
object detection and tracking are challenging tasks for resource-constrained embedded systems. while these tasks are among the most compute-intensive tasks from the artificial intelligence domain, they are only allowed to use limited computation and memory resources on embedded devices. in the meanwhile, such resource-constrained implementations are often required to satisfy additional demanding requirements such as real-time response, high-throughput performance, and reliable inference accuracy. to overcome these challenges, we propose skynet, a hardware-efficient neural network to deliver the state-of-the-art detection accuracy and speed for embedded systems. instead of following the common top-down flow for compact dnn (deep neural network) design, skynet provides a bottom-up dnn design approach with comprehensive understanding of the hardware constraints at the very beginning to deliver hardware-efficient dnns. the effectiveness of skynet is demonstrated by winning the competitive system design contest for low power object detection in the 56th ieee/acm design automation conference (dac-sdc), where our skynet significantly outperforms all other 100+ competitors: it delivers 0.731 intersection over union (iou) and 67.33 frames per second (fps) on a tx2 embedded gpu; and 0.716 iou and 25.05 fps on an ultra96 embedded fpga. the evaluation of skynet is also extended to got-10k, a recent large-scale high-diversity benchmark for generic object tracking in the wild. for state-of-the-art object trackers siamrpn++ and siammask, where resnet-50 is employed as the backbone, implementations using our skynet as the backbone dnn are 1.60x and 1.73x faster with better or similar accuracy when running on a 1080ti gpu, and 37.20x smaller in terms of parameter size for significantly better memory and storage footprint. | skynet: a hardware-efficient method for object detection and tracking on embedded systems |
we report on the first polarimetric study of (3200) phaethon, the target of jaxa's destiny+ mission, in the negative branch to ensure its anhydrous nature and to derive an accurate geometric albedo. we conducted observations at low phase angles (sun-target-observer angle, α = 8.8-32.4°) from 2021 october to 2022 january and found that phaethon has a minimum polarization degree pmin = -1.3 ± 0.1 per cent, a polarimetric slope h = 0.22 ± 0.02 per cent deg-1, and an inversion angle α0 = 19.9 ± 0.3°. the derived geometric albedo is pv = 0.11 (in the range of 0.08-0.13). these polarimetric properties are consistent with anhydrous chondrites, contradict hydrous chondrites, and typical cometary nuclei. | (3200) phaethon polarimetry in the negative branch: new evidence for the anhydrous nature of the destiny+ target asteroid |
in this paper, we show that the constant-dimensional weisfeiler-leman algorithm for groups (brachter & schweitzer, lics 2020) can be fruitfully used to improve parallel complexity upper bounds on isomorphism testing for several families of groups. in particular, we show: - groups with an abelian normal hall subgroup whose complement is $o(1)$-generated are identified by constant-dimensional weisfeiler-leman using only a constant number of rounds. this places isomorphism testing for this family of groups into $\textsf{l}$; the previous upper bound for isomorphism testing was $\textsf{p}$ (qiao, sarma, & tang, stacs 2011). - we use the individualize-and-refine paradigm to obtain a $\textsf{quasisac}^{1}$ isomorphism test for groups without abelian normal subgroups, previously only known to be in $\textsf{p}$ (babai, codenotti, & qiao, icalp 2012). - we extend a result of brachter & schweitzer (arxiv, 2021) on direct products of groups to the parallel setting. namely, we also show that weisfeiler-leman can identify direct products in parallel, provided it can identify each of the indecomposable direct factors in parallel. they previously showed the analogous result for $\textsf{p}$. we finally consider the count-free weisfeiler-leman algorithm, where we show that count-free wl is unable to even distinguish abelian groups in polynomial-time. nonetheless, we use count-free wl in tandem with bounded non-determinism and limited counting to obtain a new upper bound of $\beta_{1}\textsf{mac}^{0}(\textsf{foll})$ for isomorphism testing of abelian groups. this improves upon the previous $\textsf{tc}^{0}(\textsf{foll})$ upper bound due to chattopadhyay, torán, & wagner (acm trans. comput. theory, 2013). | on the parallel complexity of group isomorphism via weisfeiler-leman |
the cm carbonaceous chondrites provide unique insights into the composition of the protoplanetary disk, and the accretion and geological history of their parent c complex asteroid(s). of the hundreds of cms that are available for study, the majority are finds and so may have been compromised by terrestrial weathering. nineteen falls have been recovered between 1838 and 2020, and there is a hint of two temporal clusters: 1930-1942 and 2009-2020. falls are considered preferable to finds to study because they should be near pristine, and here this assumption is tested by investigating their susceptibility to alteration before recovery and during curation. cms falling on the land surface are prone to contamination by organic compounds from soil and vegetation. where exposed to liquid water prior to collection, minerals including oldhamite can be dissolved and most fluid mobile elements leached. within days of recovery, cms adsorb water from the atmosphere and are commonly contaminated by airborne hydrocarbons. interaction with atmospheric water and oxygen during curation over year to decadal timescales can produce fe oxyhydroxides from fe,ni metal and gypsum from indigenous gypsum and oldhamite. relationships between the petrologic (sub)types of pre 1970 falls and their terrestrial age could be due to extensive but cryptic alteration during curation, but are more likely a sampling bias. the terrestrial history of a cm fall, including circumstances of its collection and conditions of its curation, must be taken into account before it is used to infer processes on c complex parent bodies such as ryugu and bennu. | cm carbonaceous chondrite falls and their terrestrial alteration |
implantation of ions in minerals by high energy radiation is an important process in planetary and materials sciences. for example, the solar wind is a multi-ion flux that progressively modifies the composition and structure of near-surface domains in solar objects, like asteroids. a bombardment of a target by different elements like hydrogen (h) at various energies causes, among other things, the implantation of these particles in crystalline and amorphous materials. it is important to understand the mechanisms and features of this process (e.g., how much is implanted and retained), to constrain its contribution to the chemical budget of solar objects or for planning various material-science applications. yet, there has been no detailed study on h implantation into olivine (e.g., the quantification of maximum retainable h), a major mineral in this context. we performed experiments on h implantation in san carlos olivine at 10 and 20 kev with increasing fluences (up to 3×1018 at/cm2). nanoscale h profiles that result from implantation were analyzed using nuclear resonance reaction analysis after each implantation to observe the evolution of the h distribution as a function of fluence. we observed that after a systematic growth of the characteristic, approximately gaussian shaped, h profiles with increasing fluences, a maximum concentration at h ~ 20 at% is attained. the maximum concentration is approximately independent of ion energy, but the maximum penetration depth is a function of beam energy and is greater at higher energies. the shapes of the profiles as well as the maximum concentrations deviate from those predicted by currently available models and point to the need for direct experimental measurements. we compared the depth profiles with predictions by srim. based on observations from this study, we were able to constrain the maximum retainable h in olivine as a function of ion energy. | an experimental study of proton implantation in olivine |
we report on the mineralogy, petrography, and o and al-mg isotopic systematics of secondary mineralization in the metasomatically altered igneous ca,al-rich inclusions (cais) [compact type a (cta), b1, b2, forsterite-bearing b (fob), and c] from the cv3 carbonaceous chondrite allende. this alteration affected mainly melilite, and to a lesser degree anorthite, and resulted in the formation of a variety of secondary minerals, including adrianite, al-diopside, andradite, anorthite, calcite, celsian, clintonite, corundum, dmisteinbergite, ferroan olivine, ferroan monticellite, ferroan al-diopside, forsterite, grossular, heazlewoodite, hedenbergite, hutcheonite, kushiroite, margarite, monticellite, na-melilite, nepheline, pentlandite, pyrrhotite, sodalite, spinel, tilleyite, wadalite, and wollastonite. the secondary mineral assemblages are mainly defined by chemical compositions of the primary melilite replaced and elements introduced by an aqueous fluid. gehlenitic melilite (åk<35) in ctas and mantles of b1s is mainly replaced by anorthite + grossular; clintonite, corundum, spinel, and al-diopside are minor. åkermanitic melilite (åk35-90) in type b2s, fobs, and cores of b1s is replaced by the grossular + monticellite + wollastonite, grossular + monticellite, and grossular + al-diopside assemblages; forsterite, spinel, clintonite, and na-melilite are minor. in type cs, lacy melilite (åkermanitic melilite with rounded inclusions of anorthite) is pseudomorphically replaced by the grossular + forsterite + monticellite and grossular + al-diopside assemblages; na-melilite is minor. primary and secondary anorthites in the peripheral portions of cais are replaced by nepheline, sodalite, and ferromagnesian olivine. some cais contain voids and cracks filled by andradite, hedenbergite, wollastonite, ±sodalite, ±grossular, ±monticellite, ±tilleyite, and ±calcite. all cais studied are surrounded by wark-lovering rims, fine-grained matrix-like rims composed of lath-shaped ferroan olivine and abundant nepheline grains, and a layer of salite-hedenbergite pyroxenes + andradite + wollastonite. grossular associating with monticellite, al-diopside, and forsterite and replacing åkermanitic melilite (27al/24mg ~ 2) has high 27al/24mg ratios (30−100) and shows no resolvable excess of radiogenic 26mg (26mg*). the 27al/24mg ratios (7−10) and 26mg* (2−3‰) in the nearly monomineralic grossular veins crosscutting gehlenitic melilite are similar to those of the host melilite and plot along a regression line with 26al/27al ratio of ~5×10−5. oxygen isotopic compositions of secondary minerals in the most type bs measured in situ with the uh cameca ims-1280 and matrix-matched standards plot along mass-dependent fractionation line with ∆17o of ~ −3±2‰ with δ18o ranging from ~0 to ~10‰. primary melilite and anorthite in the host cais are similarly 16o-depleted, whereas spinel, forsterite, and most al,ti-diopside grains have 16o-rich compositions (∆17o ~ −25±2‰). secondary grossular and forsterite in type cs and type b1 cai ts-34 show a range of ∆17o, from ~ −15 to ~ −1‰; the 16o-enriched compositions of grossular and forsterite plot along the carbonaceous chondrite anhydrous mineral line. the similar ranges of ∆17o and positions on the three-isotope oxygen diagram are observed for primary anorthite; melilite is generally 16o-depleted compared to anorthite (∆17o ~ −5 to −1±2‰); spinel and fassaite are 16o-rich (except very ti-rich fassaite in ts-34 and cta cais). we conclude that allende cais experienced an open-system in situ metasomatic alteration at relatively high temperatures (200-250 °c) in the presence of co2- and h2o-bearing fluid with ∆17o of ~ −3±2‰ followed by thermal metamorphism at ~ 500 °c on the cv chondrite parent asteroid. during the alteration, most elements were mobile: si, na, cl, k, fe, s, and ni were introduced; al, ti, mg, and ba were locally mobilized; ca and some mg and al were lost from the host inclusions. the alteration occurred after nearly complete decay of 26al, >3 ma after crystallization of cais with the canonical (26al/27al)0 of (5.25±0.02)×10-5; 26mg* in grossular was inherited from the primary melilite and provide no chronological significance. oxygen isotopic heterogeneity of primary minerals in the allende cais at least partly is due to isotopic exchange with an aqueous fluid that largely affected melilite, anorthite, perovskite, zr- and sc-rich oxides and silicates, and possibly very ti-rich fassaite. | infiltration metasomatism of the allende coarse-grained calcium-aluminum-rich inclusions |
asteroid-sized bodies are predicted to have been scattered throughout the solar system following gravitational interactions with the giant planets. this process could have delivered water-rich small bodies to the inner solar system. however, evidence from the meteorite record supporting this scattering is limited due to difficulties in recovering the formation distance of meteorite parent bodies from laboratory measurements. moreover, ancient millimeter-sized solids that formed in the inner solar system (calcium-aluminum-rich inclusions (cais) and chondrules) have also been proposed to have migrated throughout the solar system, which could have been key to their survival. our understanding of the driving mechanisms, distances, and timings involved in this motion is also restricted for the same reasons. here, we address these limitations by recovering the formation distance of the parent asteroid of the tagish lake meteorite from measurements of its natural remanent magnetization. we find that this meteorite experienced an ancient field intensity <0.15 μt. accounting for the average effect of a tilted parent body rotation axis and possible uncertainties associated with the remanence acquisition mechanism, this result argues that the tagish lake parent body formed at >8-13 au, suggesting this body originates from the distal solar system. tagish lake came to earth from the asteroid belt which, combined with our recovered formation distance, suggests that some small bodies traveled large distances throughout the solar system. moreover, tagish lake contains cais and chondrules, indicating that these solids were capable of traveling to the distal solar system within just a few million years. | evidence for asteroid scattering and distal solar system solids from meteorite paleomagnetism |
we present a fast method to calculate an asteroid survey's 'bias' - essentially a correction factor from the observed number of objects to the actual number in the population. the method builds upon the work of jedicke and metcalfe (jedicke, r., metcalfe, t.s. [1998]. icaurs 131, 245-260) and granvik et al. (granvik, m., vaubaillon, j., jedicke, r. [2012]. icarus 218, 262-277) and essentially efficiently maps out the phase space of orbit elements that can appear in a field-of-view. it does so by 'integrating' outwards in geocentric distance along a field's boresite from the topocentric location of the survey and calculating the allowable angular elements for each desired combination of semi-major axis, eccentricity and inclination. we then use a contour algorithm to map out the orbit elements that place an object at the edge of the field-of-view. we illustrate the method's application to calculate the bias correction for near earth objects detected with the catalina sky survey (christensen, e. et al. [2012]. aas/division for planetary sciences meeting abstracts, vol. 44, p. 210.13; larson, s. et al. [1998]. bulletin of the american astronomical society, vol. 30, p. 1037). | a fast method for quantifying observational selection effects in asteroid surveys |
k. w. smith, queen's university, belfast; and l. denneau, university of hawaii, on behalf of the "asteroid terrestrial-impact last alert system" (atlas) team, report the serendipitous discovery of unusual activity associated with the inner main-belt minor planet (6478), which appears to have developed a lengthening tail or trail that was first identified in individual atlas exposures by taken by smith. a median combination of seven 30-s exposures on 2019 jan. 5 shows a tail or trail 135" long in p.a. 290 degrees. the tail/trail first appears in individual atlas exposures on 2018 dec. 8, as identified by denneau, with a median combined 120-s exposure showing a tail 30" long in p.a. 290 degrees. there is no evidence of a tail in previous atlas imaging in january 2018. an initial analysis using a cometary finson- probstein model (cf. website url http://comet-toolbox.com/fp.html, as per j.-b. vincent) shows that both the dec. 2018 and jan. 2019 data are consistent with the ejection of material or commencement of activity in early nov. 2018. recent observations in pan-starrs1 imagery obtained by r. weryk show a tail or trail consistent with the atlas observations and confirm no prior activity as far back as 2010. further observations of this object are highly encouraged. | (6478) gault |
observational evidence of white dwarf planetary systems is dominated by the remains of exo-asteroids through accreted metals, debris discs, and orbiting planetesimals. however, exo-planets in these systems play crucial roles as perturbing agents, and can themselves be perturbed close to the white dwarf roche radius. here, we illustrate a procedure for computing the tidal interaction between a white dwarf and a near-spherical solid planet. this method determines the planet's inward and/or outward drift, and whether the planet will reach the roche radius and be destroyed. we avoid constant tidal lag formulations and instead employ the self-consistent secular darwin-kaula expansions from boué & efroimsky (2019), which feature an arbitrary frequency dependence on the quality functions. we adopt wide ranges of dynamic viscosities and spin rates for the planet in order to straddle many possible outcomes, and provide a foundation for the future study of individual systems with known or assumed rheologies. we find that (i) massive super-earths are destroyed more readily than minor planets (such as the ones orbiting wd 1145+017 and sdss j1228+1040), (ii) low-viscosity planets are destroyed more easily than high-viscosity planets, and (iii) the boundary between survival and destruction is likely to be fractal and chaotic. | orbital relaxation and excitation of planets tidally interacting with white dwarfs |
though rare, asteroid impacts are inevitable, and with the current state of technology, kinetic impactors are the preferred but not the complete solution. if the time to impact is short, or the threatening body too large, nuclear deflection serves as a final option. this work is part of an integrated study by national aeronautics and space administration (nasa) and the national nuclear security administration (nnsa) to better determine the relative efficacy of these complimentary approaches. in particular, we examine the important material properties that affect each approach, to improve critical characterization efforts, and reduce uncertainty in the limits of the impactor technology. impact speeds for kinetic impactors on near-earth object (neo) intercept trajectories commonly range from 5 to 20 km/s, resulting in significant crater ejecta and a momentum enhancement above that carried by the impactor. this enhancement depends substantially on the strength and porosity of the asteroid, as well as the impact speed. here simulations from different codes are presented, along with constraints from experimental measurements. the uncertainties due to ignorance of the strength and porosity of the impact point are significant in determining the limits of impactor sufficiency. the nuclear approach is considered within the context of current capabilities, posing no need to test, as extant and well-understood devices are sufficient for the largest known potentially hazardous objects (phos). results of x-ray sources with realistic spectra as well as blackbody spectra are given, along with some assessment on composition dependence. | options and uncertainties in planetary defense: impulse-dependent response and the physical properties of asteroids |
multiple sources of evidence suggest that asteroids ranging from hundreds meters to few kilometers in size are rubble piles, i.e. gravitational aggregates of loosely consolidated material. however, no direct data on their internal structure is available to date. cohesion between rubble-pile building blocks has been invoked in the past to explain the stability of top-shaped asteroids, which in most cases would not be capable of maintaining their large-scale shape features (low flattening, and a pronounced equatorial ridge) otherwise. however, the physical origin of cohesion is unclear and there is no direct evidence of it. recent close-range imaging and local sampling of the surfaces of top-shaped near earth asteroids (nea) suggest the presence of very porous surface structure with minimal strength and nearly no cohesion. this raises new questions about the internal structure of such objects, with important implications on their origin and evolution. here we show by numerically simulating the dynamics of irregular rocky fragments, that the presence of a rigid core within the asteroid's rubble-pile structure can explain the top shape and surface features observed recently on bennu and ryugu, without the need of cohesion between building blocks. also, we find that the rigid core model produces more easily equatorial mass shedding, which is thought to be responsible for satellite formation. the presence of a rigid core has never been revealed so far, but is consistent with the accretion history of those objects, and with recent estimates of their internal mass distribution. our findings will be tested directly by esa's hera mission, which will scan the interior of dimorphos, the small moon of didymos binary system, providing for the first time direct data on the interior of a nea. | interior of top-shaped asteroids with cohesionless surface |
for those with access to even a modest telescope and ccd camera, this new and improved guide delivers all the information needed to take part in the scientific study of asteroids and variable stars. new techniques in photometry continue to be refined, and expert brian warner covers the developing territory in detail for those both new and experienced. updated to reflect changes in telescope and ccd technology, it also includes an expanded chapter on the analysis of asteroid lightcurves to cover some of the common pitfalls that lead to incorrect answers as well as how to discover an asteroid satellite via lightcurves. with this information, amateur astronomers can use commercially available equipment to determine the rotation rate, size, and shape of asteroids. similarly, it is possible to discover the size, temperature, and orbits of stars in binary systems by using this powerful technique. brian warner yet again delivers all the material needed for readers to understand the theory, and avoid the practical pitfalls of lightcurve photometry. detailed examples are given for obtaining data, and of course for the exciting and rewarding task of analyzing the data to determine the physical properties of the objects. it also includes many detailed finder charts with magnitudes for reference and detailed steps on how to go about gathering data for specific projects without misinterpretation. any college student or amateur astronomer who wants to go beyond mere imaging with a ccd camera and enter the challenging world of "real science" via the lightcurves of asteroids and binary stars will find everything necessary in this updated book. | a practical guide to lightcurve photometry and analysis |
the design of an attitude control system for an asteroid-orbiting satellite via immersion and invariance is the subject of this paper. it is assumed that the asteroid is rotating with a constant rate, and that the inertia parameters of the satellite and the coefficients in the spherical harmonic gravitational potential of the asteroid are not known. the objective is to regulate the quaternion trajectory of the satellite orbiting in an equatorial orbit. based on the immersion and invariance (i&i) theory, a noncertainty-equivalence adaptive (ncea) attitude control law is derived. for the design, a backstepping design process involving two steps is used, and filtered signals are constructed to overcome the difficulty in solving certain matrix inequalities of the i&i methodology. the control law includes a stabilizer and an identifier - designed separately. unlike the classical certainty-equivalence adaptive (cea) systems, here the estimated parameters include not only the signals obtained from an integral type update law, but also judiciously chosen nonlinear algebraic signals that yield stronger stability properties. by the lyapunov stability analysis, it is shown that the quaternion trajectories of the disturbance input-free closed-loop system asymptotically converge to the equilibrium point. the control law is effective in regulating the attitude to the equilibrium point with minimal rotation of spacecraft. also, for the model with disturbance input, uniform ultimate boundedness of system trajectories is established. simulation results for the attitude control of spacecraft in orbit around asteroid 433 eros are presented for illustration. these results show that the spacecraft achieves nadir pointing attitude despite uncertainties in the system dynamics. | quaternion-based adaptive attitude control of asteroid-orbiting spacecraft via immersion and invariance |
most of the major planets in the solar system support populations of co-orbiting bodies, known as trojans, at their l4 and l5 lagrange points. in contrast, earth has only one known co-orbiting companion. this paper presents the results from a search for earth trojans (ets) using the decam instrument on the blanco telescope at ctio. this search found no additional trojans in spite of greater coverage compared to previous surveys of the l5 point. therefore, the main result of this work is to place the most stringent constraints to date on the population of ets. these constraints depend on assumptions regarding the underlying population properties, especially the slope of the magnitude distribution (which in turn depends on the size and albedo distributions of the objects). for standard assumptions, we calculate upper limits to a 90 per cent confidence limit on the l5 population of net < 1 for magnitude h < 15.5, net = 60-85 for h < 19.7, and net = 97 for h = 20.4. this latter magnitude limit corresponds to trojans ∼300 m in size for albedo 0.15. at h = 19.7, these upper limits are consistent with previous l4 et constraints and significantly improve l5 constraints. | search for l5 earth trojans with decam |
ammonium-bearing minerals have been suggested to be present on mars, ceres, and various asteroids and comets. we undertook a systematic study of the spectral reflectance properties of ammonium-bearing minerals and compounds that have possible planetary relevance (i.e., ammonium carbonates, chlorides, nitrates, oxalates, phosphates, silicates, and sulfates). various synthetic and natural nh4+-bearing minerals were analyzed using reflectance spectroscopy in the long-wave ultraviolet, visible, near-infrared, and mid-infrared regions (0.35-8 μm) in order to identify spectral features characteristic of the nh4+ molecule, and to evaluate if and how these features vary among different species. mineral phases were confirmed through structural and compositional analyses using x-ray diffraction, x-ray fluorescence, and elemental combustion analysis. characteristic absorption features associated with nh4 can be seen in the reflectance spectra at wavelengths as short as ∼1 μm. in the near-infrared region, the most prominent absorption bands are located near 1.6, 2.0, and 2.2 μm. absorption features characteristic of nh4+ occurred at slightly longer wavelengths in the mineral-bound nh4+ spectra than for free nh4+ for most of the samples. differences in wavelength position are attributable to various factors, including differences in the type and polarizability of the anion(s) attached to the nh4+, degree and type of hydrogen bonding, molecule symmetry, and cation substitutions. multiple absorption features, usually three absorption bands, in the mid-infrared region between ∼2.8 and 3.8 μm were seen in all but the most nh4-poor sample spectra, and are attributed to fundamentals, combinations, and overtones of stretching and bending vibrations of the nh4+ molecule. these features appear even in reflectance spectra of water-rich samples which exhibit a strong 3 μm region water absorption feature. while many of the samples examined in this study have nh4 absorption bands at unique wavelength positions, in order to discriminate between different nh4+-bearing phases, absorption features corresponding to molecules other than nh4+ should be included in spectral analysis. a qualitative comparison of the laboratory results to telescopic spectra of asteroids 1 ceres, 10 hygiea, and 324 bamberga for the 3 μm region demonstrates that a number of nh4-bearing phases are consistent with the observational data in terms of exhibiting an absorption band in the 3.07 μm region. | reflectance spectroscopy (0.35-8 μm) of ammonium-bearing minerals and qualitative comparison to ceres-like asteroids |
microtektites represent high-velocity/distal meteorite impact ejecta. demonstrating that microtektites found at several locations throughout east-antarctica consist of a homogeneous class of geological objects belonging to the australasian tektite/microtektite strewn field is fundamental to define the actual extent of the largest and youngest known tektite field on earth produced by an asteroidal impact ∼0.8 ma ago. this study presents new 40ar/39ar analyses performed by multi-collector noble gas mass spectrometry on individual microtektites from two key locations in the transantarctic mountains: miller butte, in northern victoria land, and mount raymond, over 1,000 km further south, in the grosvenor mountains. results indicate that particles are heavily contaminated by at least one extraneous ar component, which is not correlated with size nor with bulk chemical composition, and precludes a straightforward interpretation of 40ar/39ar data. analysis of data from step-heating and total fusion analyses in three-isotope correlation diagrams yielded indistinguishable isochron ages from the two locations, with a combined isochron average of 800 ± 89 ka (95% confidence level). these age results improve by more than one order of magnitude previously published 40ar/39ar age determinations and improve by ∼4 times a previous fission track date, thus providing conclusive evidence that microtektites found throughout the transantarctic mountains of antarctica belong to a single source - the australasian field. this study strengthens the southward extension of the australasian field (∼4,000 km southward with respect to australasian microtektites recovered at lower latitudes from deep sea sediments), thus implying a launch distance of nearly 12,000 km from the putative impact location in indochina. from a broad perspective, results also reveal a contrasting behavior between microtektites from the transantarctic mountains, highly contaminated by extraneous ar, and australasian macroscopic tektites, weakly or negligibly contaminated. although future dedicated experimental work, aimed at the definition of physical homogeneity of microtektites at the submicroscale and at the understanding of the true intra-particle spatial distribution of ar isotopes are necessary, we speculatively hypothesize that the contrasting behavior between tektites and microtektites may reflect displacement in different environments. | multi-collector 40ar/39ar dating of microtektites from transantarctic mountains (antarctica): a definitive link with the australasian tektite/microtektite strewn field |
we obtained thorough photometric observations of two binary near-earth asteroids (66391) moshup = 1999 kw4 and (88710) 2001 sl9 taken from 2000 to 2019. we modeled the data and derived physical and dynamical properties of the binary systems. for (66391) 1999 kw4, we derived its mutual orbit's pole, semimajor axis and eccentricity that are in agreement with radar-derived values (ostro et al., 2006. science, 314, 1276-1280). however, we found that the data are inconsistent with a constant orbital period and we obtained unique solution with a quadratic drift of the mean anomaly of the satellite of -0.65 ± 0.16 deg./yr2 (all quoted uncertainties correspond to 3σ). this means that the semimajor axis of the mutual orbit of the components of this binary system, determined a = 2.548 ± 0.015 km by ostro et al. (2006), increases in time with a mean rate of 1.2 ± 0.3 cm/yr. for (88710) 2001 sl9, we determined that the mutual orbit has a pole within 10° of (l, b) = (302∘, -73∘) (ecliptic coordinates), and is close to circular (eccentricity < 0.07). the data for this system are also inconsistent with a constant orbital period and we obtained two solutions for the quadratic drift of the mean anomaly: 2.8 ± 0.2 and 5.2 ± 0.2 deg./yr2, implying that the semimajor axis of the mutual orbit of the components (estimated a ~ 1.6 km) decreases in time with a mean rate of -2.8 ± 0.2 or -5.1 ± 0.2 cm/yr for the two solutions, respectively. the expanding orbit of (66391) 1999 kw4 may be explained by mutual tides interplaying with binary yorp (byorp) effect (mcmahon and scheeres, 2010a. icarus 209, 494-509). however, a modeling of the byorp drift using radar-derived shapes of the binary components predicted a much higher value of the orbital drift than the observed one. it suggests that either the radar-derived shape model of the secondary is inadequate for computing the byorp effect, or the present theory of byorp overestimates it. it is possible that the byorp coefficient has instead an opposite sign than predicted; in that case, the system may be moving into an equilibrium between the byorp and the tides. in the case of (88710) 2001 sl9, the byorp effect is the only known physical mechanism that can cause the inward drift of its mutual orbit. together with the binary (175706) 1996 fg3 which has a mean anomaly drift consistent with zero, implying a stable equilibrium between the byorp effect and mutual body tides (scheirich et al., 2015. icarus 245, 56-63), we now have three distinct cases of well observed binary asteroid systems with their long-term dynamical models inferred. they indicate a presence of all the three states of the mutual orbit evolution - equilibrium, expanding and contracting - in the population of near-earth binary asteroids. | a satellite orbit drift in binary near-earth asteroids (66391) 1999 kw4 and (88710) 2001 sl9 - indication of the byorp effect |
every year, around 28,100 journals publish 2.5 million research publications. search engines, digital libraries, and citation indexes are used extensively to search these publications. when a user submits a query, it generates a large number of documents among which just a few are relevant. due to inadequate indexing, the resultant documents are largely unstructured. publicly known systems mostly index the research papers using keywords rather than using subject hierarchy. numerous methods reported for performing single-label classification (slc) or multi-label classification (mlc) are based on content and metadata features. content-based techniques offer higher outcomes due to the extreme richness of features. but the drawback of content-based techniques is the unavailability of full text in most cases. the use of metadata-based parameters, such as title, keywords, and general terms, acts as an alternative to content. however, existing metadata-based techniques indicate low accuracy due to the use of traditional statistical measures to express textual properties in quantitative form, such as bow, tf, and tfidf. these measures may not establish the semantic context of the words. the existing mlc techniques require a specified threshold value to map articles into predetermined categories for which domain knowledge is necessary. the objective of this paper is to get over the limitations of slc and mlc techniques. to capture the semantic and contextual information of words, the suggested approach leverages the word2vec paradigm for textual representation. the suggested model determines threshold values using rigorous data analysis, obviating the necessity for domain expertise. experimentation is carried out on two datasets from the field of computer science (jucs and acm). in comparison to current state-of-the-art methodologies, the proposed model performed well. experiments yielded average accuracy of 0.86 and 0.84 for jucs and acm for slc, and 0.81 and 0.80 for jucs and acm for mlc. on both datasets, the proposed slc model improved the accuracy up to 4%, while the proposed mlc model increased the accuracy up to 3%. | multi-label classification of research articles using word2vec and identification of similarity threshold |
interactions of the solar wind and emitted photoelectrons with airless bodies have been studied extensively. however, the details of how charged particles interact with the regolith at the scale of a single grain have remained largely uncharacterized. recent efforts have focused upon determining total surface charge under photoemission and solar wind bombardment and the associated electric field and potential. in this work, theory and simulations are used to show that grain-grain charge differences can exceed classical sheath predictions by several orders of magnitude, sometimes reaching dielectric breakdown levels. temperature-dependent electrical conductivity works against supercharging by allowing current to leak through individual grains; the balance between internal conduction and surface charging controls the maximum possible grain-to-grain electric field. understanding the finer details of regolith grain charging, conductive equilibrium, and dielectric breakdown will improve future numerical studies of space weathering and dust levitation on airless bodies. | grain-scale supercharging and breakdown on airless regoliths |
destiny+ is a flyby mission of asteroid phaethon proposed for jaxa/isas epsilon class small program with a launch target in 2022. mission overview is presented. | destiny+ mission: flyby of geminids parent asteroid (3200) phaethon and in-situ analyses of dust accreting on the earth |
simulated space weathering experiments on volatile-rich carbonaceous chondrites (ccs) have resulted in contrasting spectral behaviors (e.g. reddening vs bluing). the aim of this work is to investigate the origin of these contrasting trends by simulating space weathering on a subset of minerals found in these meteorites. we use pulsed laser irradiation to simulate micrometeorite impacts on aqueously altered minerals and observe their spectral and physical evolution as a function of irradiation time. irradiation of the mineral lizardite, a mg-phyllosilicate, produces a small degree of reddening and darkening, but a pronounced reduction in band depths with increasing irradiation. in comparison, irradiation of an fe-rich aqueously altered mineral assemblage composed of cronstedtite, pyrite and siderite, produces significant darkening and band depth suppression. the spectral slopes of the fe-rich assemblage initially redden then become bluer with increasing irradiation time. post-irradiation analyses of the fe-rich assemblage using scanning and transmission electron microscopy reveal the presence of micron sized carbon-rich particles that contain notable fractions of nitrogen and oxygen. radiative transfer modeling of the fe-rich assemblage suggests that nanometer sized metallic iron (npfe0) particles result in the initial spectral reddening of the samples, but the increasing production of micron sized carbon particles (μpc) results in the subsequent spectral bluing. the presence of npfe0 and the possible catalytic nature of cronstedtite, an fe-rich phyllosilicate, likely promotes the synthesis of these carbon-rich, organic-like compounds. these experiments indicate that space weathering processes may enable organic synthesis reactions on the surfaces of volatile-rich asteroids. furthermore, mg-rich and fe-rich aqueously altered minerals are dominant at different phases of the aqueous alteration process. thus, the contrasting spectral slope evolution between the fe- and mg-rich samples in these experiments may indicate that space weathering trends of volatile-rich asteroids have a compositional dependency that could be used to determine the aqueous histories of asteroid parent bodies. | simulated space weathering of fe- and mg-rich aqueously altered minerals using pulsed laser irradiation |
the four massive galilean satellites are believed to have formed within a circumplanetary disk during the last stages of jupiter’s formation. while the existence of a circum-jovian disk is supported by hydrodynamic simulations, no consensus exists regarding the origin and delivery mechanisms of the building blocks of the forming satellites. the opening of a gap in the circumsolar disk would have efficiently isolated jupiter from the main sources of solid material. however, a reservoir of planetesimals should have existed at the outer edge of jupiter’s gap, where solids were trapped and accumulated over time. here we show that the formation of saturn’s core within this reservoir, or its prompt inward migration, allows planetesimals to be redistributed from this reservoir toward jupiter and the inner solar system, thereby providing enough material to form the galilean satellites and to populate the main belt with primitive asteroids. we find that the orbit of planetesimals captured within the circum-jovian disk are circularized through friction with gas in a compact system comparable to the current radial extent of the galilean satellites. the decisive role of saturn in the delivery mechanism has strong implications for the occurrence of massive moons around extrasolar giant planets as they would preferentially form around planets within multiple planet systems. | saturn’s formation and early evolution at the origin of jupiter’s massive moons |
aims: asteroid (31) euphrosyne is one of the biggest objects in the asteroid main belt and it is also the largest member of its namesake family. the euphrosyne family occupies a highly inclined region in the outer main belt and contains a remarkably large number of members, which is interpreted as an outcome of a disruptive cratering event.methods: the goals of this adaptive-optics imaging study are threefold: to characterize the shape of euphrosyne, to constrain its density, and to search for the large craters that may be associated with the family formation event.results: we obtained disk-resolved images of euphrosyne using sphere/zimpol at the eso 8.2 m vlt as part of our large program (id: 199.c-0074, pi: vernazza). we reconstructed its 3d shape via the adam shape modeling algorithm based on the sphere images and the available light curves of this asteroid. we analyzed the dynamics of the satellite with the genoid meta-heuristic algorithm. finally, we studied the shape of euphrosyne using hydrostatic equilibrium models.conclusions: our sphere observations show that euphrosyne has a nearly spherical shape with the sphericity index of 0.9888 and its surface lacks large impact craters. euphrosyne's diameter is 268 ± 6 km, making it one of the top ten largest main belt asteroids. we detected a satellite of euphrosyne - s/2019 (31) 1 - that is about 4 km across, on a circular orbit. the mass determined from the orbit of the satellite together with the volume computed from the shape model imply a density of 1665 ± 242 kg m-3, suggesting that euphrosyne probably contains a large fraction of water ice in its interior. we find that the spherical shape of euphrosyne is a result of the reaccumulation process following the impact, as in the case of (10) hygiea. however, our shape analysis reveals that, contrary to hygiea, the axis ratios of euphrosyne significantly differ from those suggested by fluid hydrostatic equilibrium following reaccumulation. the reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/641/a80 based on observations made with eso telescopes at the la silla paranal observatory under program 199.c-0074 (pi vernazza). | binary asteroid (31) euphrosyne: ice-rich and nearly spherical |
this paper describes a new, analytic, and mechanistic model for calculating the effective thermal conductivity (keff) of planetary regolith, or any porous granular medium consisting of solid particles and gas (or vacuum). the model computes keff as a function of the physical properties of its components (e.g., intrinsic thermal conductivities), particle size and shape, bulk porosity, pore gas density, temperature, cohesive force, and lithostatic pressure (or depth). a simplified version of the model for the case of regolith in vacuum is also presented. model predictions are compared to laboratory measurements from previous studies for a wide range of particle properties and temperature/pressure conditions. the model is based on the maxwell-eucken theoretical expressions for the upper and lower bounds for keff of heterogeneous, isotropic material. these equations provide tighter bounds than the parallel and series approximations often used to estimate keff for porous media. the effect of interparticle contact is modeled using an semi-empirical parameter fsc that represents the fractional continuity of the solid phase. an expression for this parameter is proposed with a functional dependence on the relative size and number of contacts between particles. the actual size of the contacts is estimated based on hertzian mechanics of elastic deformation including the effects of cohesive surface forces (jkr theory). an effective contact radius is determined that also takes into account the heat transfer through the pore space in the immediate vicinity of the contact based on theoretical work by batchelor and o'brien (1977), as well as lower limits due to plastic deformation. particle shape is quantified in terms of its sphericity and roundness. the effects of sphericity are explicitly included in calculations of the maxwell-eucken bounds, the effective pore size and, along with roundness, the average local radius of curvature at the contacts. the effect of radiative heat transfer is included, as well as the dependence of gas conductivity on temperature and knudsen number from kinetic theory. the only free parameters in the model are two constant coefficients in the hypothesized expressions for fsc and pore size which are empirically determined by least-squares fits to laboratory measurements of keff for glass beads over a wide range of particle size and pore gas pressure. using these best-fit values for the coefficients, the model is then shown to predict values of keff which are in close agreement (σ ≤ 20%) with previous laboratory measurements for basalt and quartz powders, crushed kyanite, and apollo lunar soil samples. a key finding of the model is that keff does depend on the instrinsic conductivity of the solid particles (and therefore on their composition and temperature) to a greater degree than indicated in previous studies, and is especially important for regolith on airless bodies. finally, for cohesive particulates, a method is presented for estimating the porosity as a function of particle size, surface energy, density, and gravitational force. | a mechanistic model for the thermal conductivity of planetary regolith: 1. the effects of particle shape, composition, cohesion, and compression at depth |
we have identified a star, epic 249706694 (hd 139139), that was observed during k2 campaign 15 with the kepler extended mission that appears to exhibit 28 transit-like events over the course of the 87-d observation. the unusual aspect of these dips, all but two of which have depths of 200 ± 80 ppm, is that they exhibit no periodicity, and their arrival times could just as well have been produced by a random number generator. we show that no more than four of the events can be part of a periodic sequence. we have done a number of data quality tests to ascertain that these dips are of astrophysical origin, and while we cannot be absolutely certain that this is so, they have all the hallmarks of astrophysical variability on one of two possible host stars (a likely bound pair) in the photometric aperture. we explore a number of ideas for the origin of these dips, including actual planet transits due to multiple or dust emitting planets, anomalously large ttvs, s- and p-type transits in binary systems, a collection of dust-emitting asteroids, `dipper-star' activity, and short-lived starspots. all transit scenarios that we have been able to conjure up appear to fail, while the intrinsic stellar variability hypothesis would be novel and untested. | the random transiter - epic 249706694/hd 139139 |
the orbit-attitude hovering means that both the position and attitude of the spacecraft are kept to be stationary in the asteroid body-fixed frame. the orbit-attitude hovering is discussed in the framework of the gravitationally coupled orbit-attitude dynamics, also called the full dynamics, in which the spacecraft is modeled as a rigid body to take into account the gravitational orbit-attitude coupling naturally. a feedback hovering control law is proposed by using the non-canonical hamiltonian structure of the problem, which is consisted of two potential shapings and one energy dissipation. the first potential shaping is to create an artificial equilibrium at the desired hovering position-attitude. then, the second potential shaping modifies the potential further so that the artificial equilibrium is a minimum of the modified hamiltonian on the invariant manifold. finally, the energy dissipation leads the motion to converge asymptotically to the minimum of the modified hamiltonian, i.e., the artificial equilibrium for hovering. the feasibility of the hovering control law is verified through numerical simulations. the proposed hovering control law has a simple form and can be implemented by the spacecraft autonomously with little computation. this feature can be attributed to the utilization of the hamiltonian structure and natural dynamical behaviors of the system in the control law design. | body-fixed orbit-attitude hovering control over an asteroid using non-canonical hamiltonian structure |
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