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rock boulders are typical features of the surfaces of many airless bodies, so the possibility of estimating their potential survival times may provide insights into the rates of surface-modification processes. as an opening point of this study we employ estimates of the survival times of meter-sized boulders on the surface of the moon based on analysis of the spatial density of boulders on the rims of small lunar craters of known absolute age (basilevsky et al., 2013), and apply them, with necessary corrections, to boulders on other bodies. in this approach the major factor of rock destruction is considered to be impacts of meteorites. however another factor of the rock destruction, thermal fatigue due to day-night cycling, does exist and it was claimed by delbo et al. (2014) as being more important than meteorite impacts. they concluded this on the basis of known presence of fine material on the surface of small asteroids, claiming that due to extremely low gravity on those bodies, the products of meteorite bombardment should leave these bodies, and thus their presence indicates that the process of thermal fatigue should be much more effective there. delbo et al. (2014) made laboratory experiments on heating-cooling centimeter-sized samples of chondrites and, applying some assumptions and theoretical modeling concluded that, for example, at 1 au distance from the sun, the lifetime of 10 cm rock fragments on asteroids with period of rotation from 2.2 to 6 h should be only ~103 to 104 years (that is ~3.5×106 to 1.5×107 thermal cycles) and the larger the rock, the faster it should be destroyed. in response to those conclusions we assessed the results of earlier laboratory experiments, which show that only a part of comminuted material produced by high-velocity impacts into solid rocks is ejected from the crater while another part is not ejected but stays exposed on the target surface and is present in its subsurface. this means that the presence of granulometrically fine material on the surface of small asteroids does not prove the predominance of thermal stresses over rupture by meteorite impacts as a factor in the comminution of the surface material. we then analyzed images of lunar rocks of decimeters- to meters-size whose lunar surface exposure ages were radiometrically dated. this analysis shows that the presence of the fragment on the lunar surface for a time period 26-400 ma (that is, ~3×108 to 5×109 day-night thermal cycles) did not lead to the formation of any features conclusively supporting rock destruction by thermal cycles. in turn, this means that on the lunar surface as well as on the surface of other bodies at 1 au and further from the sun, the destruction of rocks by thermal fatigue is secondary compared to rock rupture by the meteorite impacts. the possible implications of the difference in environments on fast spinning asteroids and on the moon require additional analysis then utilizing the entire catalog of inner solar system minor planet orbits out to jupiter as a proxy for the distribution of potential impactors throughout the inner solar system, we calculated the meteorite flux and impact velocities for a number of airless bodies to use them for estimates of survival times of rock boulders on their surfaces (normalized to those for lunar boulders). we found that if the average survival time for meter-size rock boulders on the surface of the moon is 1, then considering rupture by the meteorite impacts as the major process of rock destruction, for phobos it is ~0.8, for deimos ~0.7, for asteroid itokawa ~1, for eros ~0.3, for vesta and ceres ~0.03 and for the average of the first 150 trojans discovered is ~12.5. implications of these findings are that on the surfaces of vesta and ceres, compared to the moon, the regolith layer should generally have a larger thickness and higher maturity, while small craters with rocky ejecta are rare. on the typical trojans, where impact flux is closer to that on the moon, but the impact velocities are by factor 4 lower, the situation should be the opposite: thinner layer of regolith, lower maturity and a larger percentage of small craters with rocky ejecta. these predictions and observations can be tested with future robotic and human exploration of the moon and small bodies. | survival times of meter-sized rock boulders on the surface of airless bodies |
we present a paleomagnetic study of seven cm carbonaceous chondrites. cm chondrites are believed to be some of the most chemically primitive materials available in our solar system and may sample the continuum of transitional objects between asteroids and comets formed in the outer solar system. as such, cm chondrites can help us to understand primordial aspects of the history of the early solar system including protoplanetary disk and planetesimal magnetism. the ferromagnetic assemblage of cm chondrites is composed of a mixture of primary metallic iron, pyrrhotite, and magnetite. the remanent properties are usually dominated by secondary pyrrhotite. paleomagnetic analyses using thermal and alternating field demagnetization identified a stable origin-trending component of magnetization in the seven studied cm chondrites. in each meteorite, this component is homogeneous in direction at least at the cm scale and is therefore post-accretional. we interpret this stable component as a pre-terrestrial chemical remanent magnetization acquired during crystallization of magnetite and pyrrhotite during parent body aqueous alteration in a field of at least a few μ t (2 ± 1.5 μ t). considering the timescale and intensities of primordial magnetic fields, both internally generated fields from a putative dynamo and external fields, generated in the protoplanetary disk, may have been recorded by cm chondrites. it is presently difficult to discriminate between the two hypotheses. regardless, cm chondrites likely contain the oldest paleomagnetic record yet identified. | an early solar system magnetic field recorded in cm chondrites |
the mascot camera (mascam) is part of the mobile asteroid surface scout (mascot) lander's science payload. mascot has been launched to asteroid (162173) ryugu onboard jaxa's hayabusa 2 asteroid sample return mission on dec 3rd, 2014. it is scheduled to arrive at ryugu in 2018, and return samples to earth by 2020. mascam was designed and built by dlr's institute of planetary research, together with airbus-ds germany. the scientific goals of the mascam investigation are to provide ground truth for the orbiter's remote sensing observations, provide context for measurements by the other lander instruments (radiometer, spectrometer and magnetometer), the orbiter sampling experiment, and characterize the geological context, compositional variations and physical properties of the surface (e.g. rock and regolith particle size distributions). during daytime, clear filter images will be acquired. during night, illumination of the dark surface is performed by an led array, equipped with 4×36 monochromatic light-emitting diodes (leds) working in four spectral bands. color imaging will allow the identification of spectrally distinct surface units. continued imaging during the surface mission phase and the acquisition of image series at different sun angles over the course of an asteroid day will contribute to the physical characterization of the surface and also allow the investigation of time-dependent processes and to determine the photometric properties of the regolith. the mascam observations, combined with the mascot hyperspectral microscope (mmega) and radiometer (mara) thermal observations, will cover a wide range of observational scales and serve as a strong tie point between hayabusa 2's remote-sensing scales (103-10^{-3} m) and sample scales (10^{-3}-10^{-6} m). the descent sequence and the close-up images will reveal the surface features over a broad range of scales, allowing an assessment of the surface's diversity and close the gap between the orbital observations and those made by the in-situ measurements. the mascam is mounted inside the lander slightly tilted, such that the center of its 54.8° square field-of-view is directed towards the surface at an angle of 22° with respect to the surface plane. this is to ensure that both the surface close to the lander and the horizon are observable. the camera optics is designed according to the scheimpflug principle, thus that the entire scene along the camera's depth of field (150 mm to infinity) is in focus. the camera utilizes a 1024×1024 pixel cmos sensor sensitive in the 400-1000 nm wavelength range, peaking at 600-700 nm. together with the f-16 optics, this yields a nominal ground resolution of 150 micron/px at 150 mm distance (diffraction limited). the camera flight model has undergone standard radiometric and geometric calibration both at the component and system (lander) level. mascam relies on the use of wavelet compression to maximize data return within stringent mission downlink limits. all calibration and flight data products will be generated and archived in the planetary data system in pds image format. | the camera of the mascot asteroid lander on board hayabusa 2 |
asteroid (3200) phaethon is an active near-earth asteroid and the parent body of the geminid meteor shower. because of its small perihelion distance, phaethon's surface reaches temperatures sufficient to destabilize hydrated materials. we conducted rotationally resolved spectroscopic observations of this asteroid, mostly covering the northern hemisphere and the equatorial region, beyond 2.5-µm to search for evidence of hydration on its surface. here we show that the observed part of phaethon does not exhibit the 3-µm hydrated mineral absorption (within 2σ). these observations suggest that phaethon's modern activity is not due to volatile sublimation or devolatilization of phyllosilicates on its surface. it is possible that the observed part of phaethon was originally hydrated and has since lost volatiles from its surface via dehydration, supporting its connection to the pallas family, or it was formed from anhydrous material. | near-infrared observations of active asteroid (3200) phaethon reveal no evidence for hydration |
near earth asteroids are attractive targets for new space missions; firstly, because of their scientific importance, but also because of their impact threat and prospective resources. the asteroid retrieval mission concept has thus arisen as a synergistic approach to tackle these three facets of interest in one single mission. this paper reviews the methodology used by the authors (2013) in a previous search for objects that could be transported from accessible heliocentric orbits into the earth's neighbourhood at affordable costs (or easily retrievable objects, a.k.a. eros). this methodology consisted of a heuristic pruning and an impulsive manoeuvre trajectory optimisation. low thrust propulsion on the other hand clearly enables the transportation of much larger objects due to its higher specific impulse. hence, in this paper, low thrust retrieval transfers are sought using impulsive trajectories as first guesses to solve the optimal control problem. gpops-ii is used to transcribe the continuous-time optimal control problem to a nonlinear programming problem (nlp). the latter is solved by ipopt, an open source software package for large-scale nlps. finally, a natural continuation procedure that increases the asteroid mass allows to find out the largest objects that could be retrieved from a given asteroid orbit. if this retrievable mass is larger than the actual mass of the asteroid, the asteroid retrieval mission for this particular object is said to be feasible. the paper concludes with an updated list of 17 eros, as of april 2016, with their maximum retrievable masses by means of low thrust propulsion. this ranges from 2000 tons for the easiest object to be retrieved to 300 tons for the least accessible of them. | asteroid retrieval missions enabled by invariant manifold dynamics |
nasa's osiris-rex asteroid sample return mission spacecraft includes the touch and go camera system (tagcams) three camera-head instrument. the purpose of tagcams is to provide imagery during the mission to facilitate navigation to the target asteroid, confirm acquisition of the asteroid sample, and document asteroid sample stowage. the cameras were designed and constructed by malin space science systems (msss) based on requirements developed by lockheed martin and nasa. all three of the cameras are mounted to the spacecraft nadir deck and provide images in the visible part of the spectrum, 400-700 nm. two of the tagcams cameras, navcam 1 and navcam 2, serve as fully redundant navigation cameras to support optical navigation and natural feature tracking. their boresights are aligned in the nadir direction with small angular offsets for operational convenience. the third tagcams camera, stowcam, provides imagery to assist with and confirm proper stowage of the asteroid sample. its boresight is pointed at the osiris-rex sample return capsule located on the spacecraft deck. all three cameras have at their heart a 2592 × 1944 pixel complementary metal oxide semiconductor (cmos) detector array that provides up to 12-bit pixel depth. all cameras also share the same lens design and a camera field of view of roughly 44° × 32° with a pixel scale of 0.28 mrad/pixel. the stowcam lens is focused to image features on the spacecraft deck, while both navcam lens focus positions are optimized for imaging at infinity. a brief description of the tagcams instrument and how it is used to support critical osiris-rex operations is provided. | touch and go camera system (tagcams) for the osiris-rex asteroid sample return mission |
context. the esa euclid mission has been designed to map the geometry of the dark universe. scheduled for launch in 2020, it will conduct a six-year visible and near-infrared imaging and spectroscopic survey over 15 000 deg2 down to vab ~ 24.5. although the survey will avoid ecliptic latitudes below 15°, the survey pattern in repeated sequences of four broadband filters seems well-adapted to detect and characterize solar system objects (ssos).aims: we aim at evaluating the capability of euclid of discovering ssos and of measuring their position, apparent magnitude, and spectral energy distribution. we also investigate how the sso orbits, morphology (activity and multiplicity), physical properties (rotation period, spin orientation, and 3d shape), and surface composition can be determined based on these measurements.methods: we used the current census of ssos to extrapolate the total amount of ssos that will be detectable by euclid, that is, objects within the survey area and brighter than the limiting magnitude. for each different population of sso, from neighboring near-earth asteroids to distant kuiper-belt objects (kbos) and including comets, we compared the expected euclid astrometry, photometry, and spectroscopy with the sso properties to estimate how euclid will constrain the ssos dynamical, physical, and compositional properties.results: with the current survey design, about 150 000 ssos, mainly from the asteroid main-belt, should be observable by euclid. these objects will all have high inclination, which is a difference to many sso surveys that focus on the ecliptic plane. euclid may be able to discover several 104 ssos, in particular, distant kbos at high declination. the euclid observations will consist of a suite of four sequences of four measurements and will refine the spectral classification of ssos by extending the spectral coverage provided by gaia and the lsst, for instance, to 2 microns. combined with sparse photometry such as measured by gaia and the lsst, the time-resolved photometry will contribute to determining the sso rotation period, spin orientation, and 3d shape model. the sharp and stable point-spread function of euclid will also allow us to resolve binary systems in the kuiper belt and detect activity around centaurs.conclusions: the depth of the euclid survey (vab ~ 24.5), its spectral coverage (0.5 to 2.0 μm), and its observation cadence has great potential for solar system research. a dedicated processing for ssos is being set up within the euclid consortium to produce astrometry catalogs, multicolor and time-resolved photometry, and spectral classification of some 105 ssos, which will be delivered as legacy science. | solar system science with esa euclid |
we describe castalia, a proposed mission to rendezvous with a main belt comet (mbc), 133p/elst-pizarro. mbcs are a recently discovered population of apparently icy bodies within the main asteroid belt between mars and jupiter, which may represent the remnants of the population which supplied the early earth with water. castalia will perform the first exploration of this population by characterising 133p in detail, solving the puzzle of the mbc's activity, and making the first in situ measurements of water in the asteroid belt. in many ways a successor to esa's highly successful rosetta mission, castalia will allow direct comparison between very different classes of comet, including measuring critical isotope ratios, plasma and dust properties. it will also feature the first radar system to visit a minor body, mapping the ice in the interior. castalia was proposed, in slightly different versions, to the esa m4 and m5 calls within the cosmic vision programme. we describe the science motivation for the mission, the measurements required to achieve the scientific goals, and the proposed instrument payload and spacecraft to achieve these. | the castalia mission to main belt comet 133p/elst-pizarro |
hypervelocity impacts cause significant heating of planetary bodies. such events are recorded by a reset of 40ar-36ar ages and/or impact melts. here we investigate the influence of friction and plastic deformation in shock-generated comminuted rocks on the degree of impact heating using the isale shock-physics code. we demonstrate that conversion from kinetic to internal energy in the targets with strength occurs during pressure release, and additional heating becomes significant for low-velocity impacts (<10 km s-1). this additional heat reduces the impact-velocity thresholds required to heat the targets with the 0.1 projectile mass to temperatures for the onset of ar loss and melting from 8 and 10 km s-1, respectively, for strengthless rocks to 2 and 6 km s-1 for typical rocks. our results suggest that the impact conditions required to produce the unique features caused by impact heating span a much wider range than previously thought. | effects of friction and plastic deformation in shock-comminuted damaged rocks on impact heating |
asteroids can be classified into several groups based on their spectral reflectance. among these groups, the one belonging to the l-class in the taxonomic classification based on visible and near-infrared spectra exhibit several peculiar properties. first, their near-infrared spectrum is characterized by a strong absorption band interpreted as the diagnostic of a high content of the feo bearing spinel mineral. this mineral is one of the main constituents of calcium-aluminum-rich inclusions (cai) the oldest mineral compounds found in the solar system. in polarimetry, they possess an uncommonly large value of the inversion angle incompatible with all known asteroid belonging to other taxonomical classes. asteroids found to possess such a high inversion angle are commonly called barbarians based on the first asteroid on which this property was first identified, (234) barbara. in this paper we present the results of an extensive campaign of polarimetric and spectroscopic observations of l-class objects. we have derived phase-polarization curves for a sample of 7 barbarians, finding a variety of inversion angles ranging between 25 and 30°. spectral reflectance data exhibit variations in terms of spectral slope and absorption features in the near-infrared. we analyzed these data using a hapke model to obtain some inferences about the relative abundance of cai and other mineral compounds. by combining spectroscopic and polarimetric results, we find evidence that the polarimetric inversion angle is directly correlated with the presence of cai, and the peculiar polarimetric properties of barbarians are primarily a consequence of their anomalous composition. | new polarimetric and spectroscopic evidence of anomalous enrichment in spinel-bearing calcium-aluminium-rich inclusions among l-type asteroids |
we report a petrography, mineral chemistry, oxygen and chromium isotopic study of grove mountains (grv) 020043 together with a subset of other acapulcoites and lodranites. grv 020043 is a petrologic type 4 chondrite, with chondrules of diverse types and sizes, and is composed of low-ca pyroxene (40 vol.%), olivine (24 vol.%), diopside (8 vol.%), plagioclase (10 vol.%), fe-ni metal (kamacite and taenite), troilite and some accessory minerals (chromite and apatite). the olivine in grv 020043 has an average fayalite content (fa) of 10.7 mol.% with the low-ca pyroxene having an average ferrosilite content (fs) of 10.8 mol.%. the whole rock oxygen isotopic composition of grv 020043 is +3.226 ± 0.267‰, +0.797 ± 0.131‰, and -0.927 ± 0.017‰ for δ18o, δ17o, and δ17o, respectively, with a bulk chromium isotopic compositions of ɛ54cr = -0.48 ± 0.10. these characteristics of grv 020043 are different from all established or ungrouped chondrites but agree with those of the acapulcoite-lodranite clan. we therefore suggest that grv 020043 represents the chondritic precursor of acapulcoite-lodranite parent body. the similarity of bulk oxygen and chromium isotopic compositions among grv 020043, acapulco, northwest africa (nwa) 468 (metal-rich lodranite), nwa 8118 (lodranite), nwa 8287 (acapulcoite), and nwa 8422 (lodranite) indicates that they originated from a common oxygen and chromium reservoir in the protoplanetary disk or may have derived from a parent body with a differentiated multilayer structure. | evidence for a multilayered internal structure of the chondritic acapulcoite-lodranite parent asteroid |
context. the sloan digital sky survey (sdss) and wide-field infrared survey explorer (wise) provide information about the surface composition of about 100 000 minor planets. the resulting visible colors and albedos enabled us to group them in several major classes, which are a simplified view of the diversity shown by the few existing spectra. a large set of data in the 0.8-2.5 μm, where wide spectral features are expected, is required to refine and complement the global picture of these small bodies of the solar system.aims: we aim to obtain the near-infrared colors for a large sample of solar system objects using the observations made during the vista-vhs survey.methods: we performed a serendipitous search in vista-vhs observations using a pipeline developed to retrieve and process the data that corresponds to solar system objects (sso). the resulting photometric data is analyzed using color-color plots and by comparison with the known spectral properties of asteroids.results: the colors and the magnitudes of the minor planets observed by the vista survey are compiled into three catalogs that are available online: the detections catalog (movis-d), the magnitudes catalog (movis-m), and the colors catalog (movis-c). they were built using the third data release of the survey (vista vhs-dr3). a total of 39 947 objects were detected, including 52 neas, 325 mars crossers, 515 hungaria asteroids, 38 428 main-belt asteroids, 146 cybele asteroids, 147 hilda asteroids, 270 trojans, 13 comets, 12 kuiper belt objects and neptune with its four satellites. the colors found for asteroids with known spectral properties reveal well-defined patterns corresponding to different mineralogies. the distributions of movis-c data in color-color plots shows clusters identified with different taxonomic types. all the diagrams that use (y - j) color separate the spectral classes more effectively than the (j - h) and (h - ks) plots used until now: even for large color errors (<0.1), the plots (y - j) vs. (y - ks) and (y - j) vs. (j - ks) provide the separation between s-complex and c-complex. the end members a, d, r, and v-types occupy well-defined regions. the catalogs are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/591/a115 | near-infrared colors of minor planets recovered from vista-vhs survey (movis) |
white dwarf wd 1145+017 is orbited by several clouds of dust, possibly emanating from actively disintegrating bodies. these dust clouds reveal themselves through deep, broad, and evolving transits in the star's light curve. here, we report two epochs of multiwavelength photometric observations of wd 1145+017, including several filters in the optical, ks and 4.5 μm bands in 2016 and 2017. the observed transit depths are different at these wavelengths. however, after correcting for excess dust emission at ks and 4.5 μm, we find the transit depths for the white dwarf itself are the same at all wavelengths, at least to within the observational uncertainties of ∼5-10 per cent. from this surprising result, and under the assumption of low optical depth dust clouds, we conclude that there is a deficit of small particles (with radii s ≲ 1.5 μm) in the transiting material. we propose a model wherein only large particles can survive the high equilibrium temperature environment corresponding to 4.5 h orbital periods around wd 1145+017, while small particles sublimate rapidly. in addition, we evaluate dust models that are permitted by our measurements of infrared emission. | a dearth of small particles in the transiting material around the white dwarf wd 1145+017 |
we present new observational data for selected main-belt asteroids of different compositional types. the detailed magnitude-phase dependences including small phase angles (<1°) were obtained for these asteroids, namely: (10) hygiea (down to the phase angle of 0.3°, c-type), (176) iduna (0.2°, g-type), (214) aschera (0.2°, e-type), (218) bianca (0.3°, s-type), (250) bettina (0.3°, m-type), (419) aurelia (0.1°, f-type), (596) scheila (0.2°, d-type), (635) vundtia (0.2°, b-type), (671) carnegia (0.2°, p-type), (717) wisibada (0.1°, t-type), (1021) flammario (0.6°, b-type), and (1279) uganda (0.5°, e-type). for several asteroids, the dependences of brightness on the phase angle were investigated in the bvri bands. we found a great diversity in the opposition-effect behavior both in the magnitude and the width of the opposition surges, especially for low-albedo asteroids. some low-albedo asteroids (e.g., (10) hygiea) display a broad opposition effect with an amplitude of 0.15-0.20 mag relative to the extrapolation of the linear part of the phase curve. other asteroids (e.g., (596) scheila, (1021) flammario) show linear magnitude-phase dependences down to small phase angles (0.1-0.2°). using numerous data sets on the magnitude-phase dependences with extensive phase-angle coverage, we examined in more detail the new three-parameter h, g1, g2 magnitude system. we determined the values of the g1 and g2 parameters for magnitude phase dependences of individual asteroids and obtained the average parameters for main asteroid compositional types. the values obtained can be used for the estimation of the absolute magnitude of an asteroid from a single observed magnitude when the magnitude-phase dependency is unknown and/or to calculate a visible magnitude for the ephemerides. | asteroid observations at low phase angles. iv. average parameters for the new h, g1, g2 magnitude system |
we observed the l4 jupiter trojans (jts) swarm using the hyper suprime-cam attached to the 8.2 m subaru telescope on 2015 march 30 (ut). the survey covered ∼26 deg2 of sky area near the opposition and around the ecliptic plane with a 240 s exposure time in the r-band filter through the entire survey. we detected 631 l4 jts in the survey field with a detection limit of mr= 24.4 mag. we selected 481 objects with absolute magnitude hr< 17.4 mag and heliocentric distance r < 5.5 au as an unbiased sample and then used them to estimate the size distribution. assuming a geometric albedo of 0.07, the size range of our unbiased sample is ∼2-20 km in diameter (d). we fit a single-slope power law to the cumulative size distribution and found that the best-fit index (b) is b = 1.84 ± 0.05 in n(> d) \propto {d}-b. the slope value (α) of the corresponding absolute magnitude distribution (n(h) \propto {10}α h) is 0.37 ± 0.01. this α is consistent with that of the faint-end slope presented by wong & brown. the size distribution obtained from this survey is slightly different from the results of previous surveys with a similar size range, which reported broken power-law or double power-law slopes in their cumulative size distribution. our results insist that the slope of b = 1.84 continues from h = 14.0 to at least h = 17.4. since this work contains the largest l4 jt samples and is 1 mag deeper than the study by wong & brown, we believe that our study has obtained the most robust size distribution of small jts so far. combining the cataloged l4 jts and our survey, we show the entire size distribution of l4 jts up to hr= 17.4 mag. based on data collected at the subaru telescope, which is operated by the national astronomical observatory of japan. | small jupiter trojans survey with the subaru/hyper suprime-cam |
the recently discovered object p/2019 ld2 (by the asteroid terrestrial-impact last alert system) was initially thought to be a jupiter trojan asteroid, until dynamical studies and the appearance of persistent cometary activity revealed that this object is actually an active centaur. however, the dynamical history, thermal environment, and impact of such environments on the activity of 2019 ld2 are poorly understood. here we conduct dynamical simulations to constrain its orbital history and resulting thermal environment over the past 3000 yr. we find that 2019 ld2 is currently in the vicinity of a dynamical "gateway" that facilitates the majority of transitions from the centaur population into the jupiter family of comets (jfc population). our calculations show that it is unlikely to have spent significant amounts of time in the inner solar system, suggesting that its nucleus is relatively pristine in terms of physical, chemical, and thermal processing through its history. this could explain its relatively high level of distant activity as a recently activated primordial body. finally, we find that the median frequency of transition from the gateway population into the jfc population varies from once every ∼3 yr to less than once every 70 yr, if 2019 ld2's nucleus is ∼1 km in radius or greater than 3 km in radius. forward modeling of 2019 ld2 shows that it will transition into the jfc population in 2063, representing the first known opportunity to observe the evolution of an active centaur nucleus as it experiences this population-defining transition. | p/2019 ld2 (atlas): an active centaur in imminent transition to the jupiter family |
how rare are extreme-spin primordial black holes? we show how, from an underlying distribution of primordial black hole (pbh) spin, extreme-value statistics can be used to quantify the rarity of spinning pbhs with kerr parameter close to 1. using the peaks-over-threshold method, we show how the probability that a pbh forms with spin exceeding a sufficiently high threshold can be calculated using the generalized pareto distribution. this allows us to estimate the average number of pbhs amongst which we can find a single pbh that formed with spin exceeding a high threshold. we found that the primordial spin distribution gives rise to exceedingly rare near-extremal spin pbhs at formation time: for typical parameter values, roughly up to one in a hundred million pbhs would be formed with spin exceeding the thorne limit. we discuss conditions under which even more extreme-spin pbhs may be produced, including modifying the skewness and kurtosis of the spin distribution via a smooth transformation. we deduce from our calculations that, if indeed asteroid-mass pbhs above the current observational limit on evaporating pbhs of mass ∼1017 g contribute significantly to the dark matter, it is very likely that some of them at somewhat lower masses could be long-lived near-extremal pbhs. | extreme-value statistics of the spin of primordial black holes |
context. the hubble space telescope (hst) archives constitute a rich dataset of high-resolution images to mine for strong gravitational lenses. while many hst programmes specifically target strong lenses, they can also be present by coincidence in other hst observations.aims: our aim is to identify non-targeted strong gravitational lenses, without any prior selection on the lens properties, in almost two decades of images from the esa hst archive (ehst).methods: we used crowdsourcing on the hubble asteroid hunter (hah) citizen science project to identify strong lenses, along with asteroid trails, in publicly available large field-of-view hst images. we visually inspected 2354 objects tagged by citizen scientists as strong lenses to clean the sample and identify the genuine lenses.results: we report the detection of 252 strong gravitational lens candidates, which were not the primary targets of the hst observations. a total of 198 of them are new, not previously reported by other studies, consisting of 45 a grades, 74 b grades and 79 c grades. the majority are galaxy-galaxy configurations. the newly detected lenses are, on average, 1.3 magnitudes fainter than previous hst searches. this sample of strong lenses with high-resolution hst imaging is ideal to follow up with spectroscopy for lens modelling and scientific analyses.conclusions: this paper presents the unbiased search of lenses that enabled us to find a wide variety of lens configurations, including exotic lenses. we demonstrate the power of crowdsourcing in visually identifying strong lenses and the benefits of exploring large archival datasets. this study shows the potential of using crowdsourcing in combination with artificial intelligence for the detection and validation of strong lenses in future large-scale surveys such as esa's euclid mission or in james webb space telescope (jwst) archival images. appendix tables are also available at the cds via anonymous ftp to cdsarc.cds.unistra.fr (ftp://130.79.128.5) or via https://cdsarc.cds.unistra.fr/viz-bin/cat/j/a+a/667/a141 | hubble asteroid hunter. ii. identifying strong gravitational lenses in hst images with crowdsourcing |
as part of the international asteroid warning network's observational exercises, we conducted a campaign to observe near-earth asteroid 2019 xs around its close approach to earth on 2021 november 9. the goal of the campaign was to characterize errors in the observation times reported to the minor planet center, which become an increasingly important consideration as astrometric accuracy improves and more fast-moving asteroids are observed. as part of the exercise, a total of 957 astrometric observations of 2019 xs during the encounter were reported and subsequently were analyzed to obtain the corresponding residuals. while the timing errors are typically smaller than 1 s, the reported times appear to be negatively biased, i.e., they are generally earlier than they should be. we also compared the observer-provided position uncertainty with the cross-track residuals, which are independent of timing errors. a large fraction of the estimated uncertainties appear to be optimistic, especially when <0.″2. we compiled individual reports for each observer to help identify and remove the root cause of any possible timing error and improve the uncertainty quantification process. we suggest possible sources of timing errors and describe a simple procedure to derive reliable, conservative position uncertainties. | international asteroid warning network timing campaign: 2019 xs |
we present an update to the first white-light detections of a dust trail observed closely following the orbit of asteroid (3200) phaethon, as seen by the wide-field imager for the parker solar probe instrument on the nasa parker solar probe mission. here, we provide a summary and analysis of observations of the dust trail over nine separate mission encounters between 2018 october and 2021 august that saw the spacecraft approach to within 0.0277 au of the orbit of phaethon. we find the photometric and estimated dust mass properties to be in line with those in the initial publication, with a visual (v) magnitude of v ~ 16.1 ± 0.3 pixel-1, corresponding to a surface brightness of 26.1 mag arcsec-2, and an estimated mass of dust within the range 1010-1012 kg depending on the assumed dust properties. however, the key finding of this survey is the discovery that the dust trail does not perfectly follow the orbit of phaethon, with a clear separation noted between them that increases as a function of true anomaly, though the trail may differ from phaethon's orbit by as little as 1° in periapsis. | continued psp/wispr observations of a phaethon-related dust trail |
the statistics of nonlinear processes in avalanching systems, based on the self-organized criticality (soc) concept of bak et al. (1988), predicts power-law-like size (or occurrence frequency) distribution functions. following up on previous work, we define a standard soc model in terms of six assumptions: (i) area fractality, (ii) volume fractality, (iii) the flux-volume proportionality, (iv) classical diffusion, (v) the euclidean maximum at the event peak time, and (vi) the spatiotemporal fluence or energy of an avalanche event. we gather data of the fractal dimension and power-law slopes from 162 publications and assemble them in 28 groups (for instance, solar flare energies, or stellar flare energies), from which we find that 75% of the groups are consistent with the standard soc model. alternative soc models (lévy flight, flat-world, nonfractal) are slightly less correlated with the data. outliers are attributed to small number statistics, background definition problems, inadequate fitting ranges, and deviations from ideal power laws. | the fractality and size distributions of astrophysical self-organized criticality systems |
the touch and go camera system (tagcams) is a three-camera-head instrument onboard nasa's osiris-rex asteroid sample return mission spacecraft. the purpose of tagcams is to facilitate navigation to the target asteroid, (101955) bennu; confirm acquisition of the asteroid sample; document asteroid sample stowage; and provide supplementary imaging for osiris-rex science investigations. | in-flight calibration and performance of the osiris-rex touch and go camera system (tagcams) |
the abundant phyllosilicate and carbonate minerals characterizing most of the returned particles from asteroid ryugu suggest a history of extensive aqueous alteration on its parent body, similar to the rare mineralogically altered, but chemically primitive, ci (ivuna-type) chondrite meteorites. particle c0009 differs mineralogically from other ryugu particles examined so far by containing anhydrous silicates at a level of ~0.5 vol%, and thus can help shed light on the unaltered original materials that constituted ryugu's protolith. in situ oxygen isotope measurements of the most mg-rich olivine and pyroxene in c0009 reveal two populations of δ17o: −25‰ to −15‰ and −8‰ to −3‰. the former and the latter populations correlate well with silicate morphologies similar to those seen in amoeboid olivine aggregates and chondrule phenocrysts, respectively, both of which are abundant in less aqueously altered carbonaceous chondrites. this result also highlights the presence of olivine with δ17o close to the solar value in either a ci chondrite or an asteroid with ci-chondrite characteristics, and provides strong evidence that amoeboid olivine aggregates and mg-rich chondrules accreted into ryugu's protolith. our data also raise the possibility that the protoliths of ci and other carbonaceous chondrites incorporated similar anhydrous silicates. | incorporation of 16o-rich anhydrous silicates in the protolith of highly hydrated asteroid ryugu |
dynamic models of solar system evolution suggest that d-type asteroids formed beyond saturn's orbit and represent invaluable witnesses of the prevailing conditions in the outer solar system. here, we report a comprehensive petrographic and isotopic characterization of the carbonaceous chondrite tarda, a recent fall recovered in the moroccan sahara. we show that tarda shares strong similarities with the d-type-derived chondrite tagish lake, implying that tarda represents a rare sample of d-type asteroids. both tarda and tagish lake are characterized by the presence of rare 16o-rich chondrules and chondrule fragments, high c/h ratios, and enrichments in deuterium, 15n, and 13c. by combining our results with literature data on carbonaceous chondrites related to c-type asteroids, we show that the outer solar system 4.56 gy ago was characterized by large-scale oxygen isotopic homogeneities in (i) the water-ice grains accreted by asteroids and (ii) the gas controlling the formation of feo-poor chondrules. conversely, the zone in which d-type asteroids accreted was significantly enriched in deuterium relative to the formation regions of c-type asteroids, features likely inherited from unprocessed, d-rich, molecular-cloud materials. | the tarda meteorite: a window into the formation of d-type asteroids |
nasa sent the double asteroid redirection test (dart) mission to impact dimorphos, the satellite of the asteroid binary system (65803) didymos. dart will release liciacube prior to impact to obtain high-resolution post-impact images. the impact will produce a crater and a large amount of material ejected at high speed (several tens of m s-1), producing an ejecta cone that will quickly disperse. we analysed an additional effect: the lofting of material at low velocity due to the generation of seismic waves that propagate inside dimorphos, producing surface shaking far from the impact point. we divide the process into different stages: from the generation of impact-induced waves, the interaction of them with surface particles, the ejection of dust particles at velocities, and the prediction of the observability of the dust coma and trail. we anticipate the following observable effects: (i) generation of a dust cloud that will produce a hazy appearance of dimorphos' surface, detectable by liciacube; (ii) brightness increase of the binary system due to enhancement of the cross-section produced by the dust cloud; (iii) generation of a dust trail, similar to those observed in some active asteroids, which can last for several weeks after impact. numerical prediction of the detectability of these effects depends on the amount and size distribution of ejected particles, which are largely unknown. in case these effects are observable, an inversion method can be applied to compute the amount of ejected material and its velocity distribution, and discuss the relevance of the shaking process. | lofting of low-speed ejecta produced in the dart experiment and production of a dust cloud |
ground-based radar systems are critical for physical and dynamical characterization of near-earth objects (neos) and space debris. the operational aspect and applications of radar for planetary defense and space situational/domain awareness (ssa/sda) are similar, but there are some factors that should be taken into account for an instrument to support both areas: planetary defense is focused on asteroids and comets in heliocentric orbit with perihelion distance <1.3 au. special attention is given to potentially hazardous objects (phos), which are neos larger than 140 m that can come within 0.05 au (∼20 lunar distances) of earth. radar can quickly and accurately determine neos' future trajectory, therefore, the sooner an object can be observed, the safer it is to assess any possible threat. radar is also useful to help obtaining information about the objects' properties to plan for an impact mitigation mission if needed. for ssa, the focus is artificial objects orbiting earth. this document presents the radar capabilities of the legacy arecibo telescope, and explores synergistic future concepts for planetary defense and ssa. | the arecibo observatory's legacy and future radar capabilities |
this paper presents a method for rapid generation of three-dimensional low-thrust trajectories that utilizes fourier series for shaping the position vector. the generated trajectories are feasible with respect to the given thrust acceleration constraints. an objective function is defined representing the overall mission cost, i.e. minimum δv . four missions from earth to mars, the near earth asteroid 1989ml, comet tempel 1 and asteroid dionysus are considered for assessing the performance of the algorithm. the selected missions present a range of various difficulties with different levels of thrust acceleration constraints. the fourier series technique is flexible in generating various shapes rather than using one global shape. the proposed method is capable of rapid generation of sub-optimal feasible trajectories that are totally different from and comparable to the solutions of the state-of-the-art three-dimensional shape-based methods. this feature is quite favorable at the preliminary stages of low-thrust mission designs where various trajectory alternatives are required. the results also show that the obtained trajectories can be used as initial guesses for high fidelity optimal control tools. | initial three-dimensional low-thrust trajectory design |
olivine occurs across the galaxy, from earth to extraterrestrial bodies including the moon, mars, and asteroids, to particles of comet dust and distant debris disks. the mineral is critical to our understanding of early solar system chronology, planetary formation processes (e.g., magma ocean solidification), crustal evolution (e.g., volcanic eruptions), and surface weathering. olivine's ability to shed light on these processes lies in the linkage of small, physical samples and satellite-derived data. laboratory spectra become the basis for olivine detection and compositional interpretation in remotely sensed spectra ranging from high-resolution planetary maps to single extra-solar datapoints. in turn, petrologic studies of olivine underpin the geologic interpretations of these spectral datasets. finally, olivine chemistry records solar system formation conditions and relative chronology. olivine is our bridge across time and space. | galaxy of green |
in this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (sirm) paleointensity calibration experiments were conducted for the returned samples from c-type asteroid (162173) ryugu and two carbonaceous chondrites (orgueil and tagish lake) to evaluate the remanence carriers of the ryugu sample and its ability as a paleomagnetic recorder. our magnetic measurements show that ryugu samples exhibit signatures for framboidal magnetite, coarse-grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of ryugu samples in the middle-coercivity range. the sirm paleointensity constant was obtained for two ryugu samples, and the median value was 3,318 ± 1,038 μt, which is close to the literature's value based on the average among magnetite, titanomagnetite, pyrrhotite, and feni alloys and is widely used for sirm paleointensity experiments. the paleointensity values estimated using the obtained sirm paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that sun's protoplanetary disk existed at the disk location of ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid. | rock magnetic characterization of returned samples from asteroid (162173) ryugu: implications for paleomagnetic interpretation and paleointensity estimation |
interstellar objects are a category of comets and asteroids that offer a unique scientific opportunity to answer fundamental scientific questions about the origin of solar system volatiles, the compositions of exo-solar systems, and the transfer rates of material between solar systems. however, they are also difficult to reach due to their high energy and the minimal lead time afforded by current detection infrastructure. this investigation presents the stationary satellite, or statite, concept as a method to enable rendezvous missions with extended stays at these important targets of study. through the use of a high-performance solar sail, the statite spacecraft is able to maintain a stationary position with respect to the sun, thus maintaining a state with a high potential energy. upon detection, it reorients its sail and enters into a controlled fall towards the sun, by which it obtains a high velocity to match the trajectory of the target. the applicability of this approach is assessed on rendezvous missions to the two known interstellar objects: 'oumuamua and borisov. counter examples based upon electrically propelled spacecraft characterize the potential improvement in response time and mission duration offered by the statite concept. based on the expected population of detectable objects, conclusions are drawn regarding flight times to the target population. the analysis includes trajectories that transfer the statite from the earth to strategic locations to await interstellar targets. | high-performance solar sails for interstellar object rendezvous |
the double asteroid redirection test (dart) is the first planetary defense test mission. it will demonstrate the kinetic impactor technique by intentionally colliding the dart spacecraft with the near-earth asteroid dimorphos. the main dart spacecraft is accompanied by the italian space agency light italian cubesat for imaging of asteroids (liciacube). shape modeling efforts will estimate the volume of dimorphos and constrain the nature of the impact site. the dart mission uses stereophotoclinometry (spc) as its primary shape modeling technique. dart is essentially a worst-case scenario for any image-based shape modeling approach because images taken by the camera on board the dart spacecraft, called the didymos reconnaissance and asteroid camera for optical navigation (draco), possess little stereo and no lighting variation; they simply zoom in on the asteroid. liciacube images add some stereo, but the images are substantially lower in resolution than the draco images. despite the far-from-optimal imaging conditions, our tests indicate that we can identify the impact site to an accuracy and precision better than 10% the size of the spacecraft core, estimate the volume of dimorphos to better than 25%, and measure tilts at the impact site over the scale of the spacecraft with an accuracy better than 7°. in short, we will know with excellent accuracy where the dart spacecraft hit, with reasonable knowledge of local tilt, and determine the volume well enough that uncertainties in the density of dimorphos will be comparable to or dominate the uncertainty in the estimated mass. the tests reported here demonstrate that spc is a robust technique for shape modeling, even with suboptimal images. | shape modeling of dimorphos for the double asteroid redirection test (dart) |
in this work, we divide the classic "lunar megaregolith" layer into three distinct regions: (1) a surficial regolith layer, about 5-20 m in depth, consisting of loose, unconsolidated fines and breccia, and characterized by frequent overturn and comminution caused by small impacts; (2) an upper megaregolith layer, about 1-3 km in depth, consisting of depositional layers of brecciated and/or melted material, and characterized by the transport and deposition of material via either transient crater gravitational collapse or impact ejecta ballistic sedimentation; and (3) a lower megaregolith layer, about 20-25 km in depth, consisting of bedrock that has been fractured in place, and characterized by a fracture-density and fragment-size distribution that decreases rapidly with increasing depth. the objective of this study is to model the formation of the lunar upper megaregolith layer, the least well characterized of these three layers, using modern scaling relationships and a three-dimensional terrain, monte carlo cratering model. we first developed a model impactor population that accurately reproduces the lunar highlands crater population, which is assumed to originate in the main asteroid belt. we then applied this impactor population in multiple full-scale lunar surface simulations, producing an upper megaregolith depth of 1.4 ± 1.0 km at the point of best χ2 fit between model and actual crater counts. this upper megaregolith layer consists of ∼60% crater collapse deposits and ∼40% impact ejecta deposits. we find that a total delivered impactor mass of 3.72 ± 1.14 × 1019 kg, or 0.0506 ± 0.0156 lunar weight percent (wt%), is required to reproduce the observed lunar highlands cratering record. | modeling the formation of the lunar upper megaregolith layer |
previous observations suggested that ceres has active, but possibly sporadic, water outgassing as well as possibly varying spectral characteristics over a timescale of months. we used all available data of ceres collected in the past three decades from the ground and the hubble space telescope, as well as the newly acquired images by the dawn framing camera, to search for spectral and albedo variability on ceres, on both a global scale and in local regions, particularly the bright spots inside the occator crater, over timescales of a few months to decades. our analysis has placed an upper limit on the possible temporal albedo variation on ceres. sporadic water vapor venting, or any possibly ongoing activity on ceres, is not significant enough to change the albedo or the area of the bright features in the occator crater by >15%, or the global albedo by >3% over the various timescales that we searched. recently reported spectral slope variations can be explained by changing sun-ceres-earth geometry. the active area on ceres is less than 1 km2, too small to cause global albedo and spectral variations detectable in our data. impact ejecta due to impacting projectiles of tens of meters in size like those known to cause observable changes to the surface albedo on asteroid scheila cannot cause detectable albedo change on ceres due to its relatively large size and strong gravity. the water vapor activity on ceres is independent of ceres’ heliocentric distance, ruling out the possibility of the comet-like sublimation process as a possible mechanism driving the activity. | surface albedo and spectral variability of ceres |
main-belt asteroid (6478) gault unexpectedly sprouted two tails in late 2018 and early 2019, identifying it as a new active asteroid. here we present observations obtained by the 1.2 m zwicky transient facility survey telescope that provide detailed time-series coverage of the onset and evolution of gault’s activity. gault exhibited two brightening events, with the first one starting on 2018 october 18 ± 5 days and a second one starting on 2018 december 24 ± 1 days. the amounts of mass released are 2 × 107 kg and 1 × 106 kg, respectively. based on photometric measurements, each event persisted for about a month. gault’s color has not changed appreciably over time, with a pre-outburst color of g ps1 - r ps1 = 0.50 ± 0.04 and g ps1 - r ps1 = 0.46 ± 0.04 during the two outbursts. simulations of dust dynamics shows that the ejecta consists of dust grains of up to 10 μm in size that are ejected at low velocities below 1 {{m}} {{{s}}}-1 regardless of particle sizes. this is consistent with non-sublimation-driven ejection events. the size distribution of the dust exhibits a broken power law, with particles at 10-20 μm following a power law of -2.5 to -3.0, while larger particles follow a steeper slope of -4.0. the derived properties can be explained by either rotational excitation of the nucleus or a merger of a near-contact binary, with the latter scenario to be statistically more likely. . | multiple outbursts of asteroid (6478) gault |
a heliogyro is a rotating solar sail with the reflecting surface divided into a number of long and slender blades, which are stiffened by a spin-induced centrifugal force. each blade can rotate around its own longitudinal axis so as to change the pitch angle and allow the thrust vector to be effectively controlled. the aim of this paper is to analyze the optimal heliocentric transfers of a sun-facing heliogyro, that is, a heliogyro whose fundamental plane is always perpendicular to the sun-spacecraft line. a simplified analytical model of the thrust and torque vectors provided by a sun-facing heliogyro is illustrated, using the characteristic acceleration as a performance parameter. the proposed thrust vector model is then exploited to calculate the minimum flight times in a set of two-dimensional heliocentric transfers. using an indirect method and a semi-analytical approach for trajectory optimization, some exemplary cases are discussed, such as circle-to-circle earth-mars and earth-venus transfers or a simplified mission to the asteroid 25143 itokawa. | optimal heliocentric transfers of a sun-facing heliogyro |
in the dusk of the mesozoic, advanced duck-billed dinosaurs (hadrosauridae) were so successful that they likely outcompeted other herbivores, contributing to declines in dinosaur diversity. from laurasia, hadrosaurids dispersed widely, colonizing africa, south america, and, allegedly, antarctica. here, we present the first species of a duck-billed dinosaur from a subantarctic region, gonkoken nanoi , of early maastrichtian age in magallanes, chile. unlike duckbills further north in patagonia, gonkoken descends from north american forms diverging shortly before the origin of hadrosauridae. however, at the time, non-hadrosaurids in north america had become replaced by hadrosaurids. we propose that the ancestors of gonkoken arrived earlier in south america and reached further south, into regions where hadrosaurids never arrived: all alleged subantarctic and antarctic remains of hadrosaurids could belong to non-hadrosaurid duckbills like gonkoken . dinosaur faunas of the world underwent qualitatively different changes before the cretaceous-paleogene asteroid impact, which should be considered when discussing their possible vulnerability. subantarctic fossils rewrite the biogeographic history of duck-billed dinosaurs and their role in pre-extinction ecosystems. | relict duck-billed dinosaurs survived into the last age of the dinosaurs in subantarctic chile |
this paper presents methodologies for constructing control barrier functions (cbfs) for nonlinear, control-affine systems, in the presence of input constraints and bounded disturbances. more specifically, given a constraint function with high-relative-degree with respect to the system dynamics, the paper considers three methodologies, two for relative-degree 2 and one for higher relative-degrees, for creating cbfs whose zero sublevel sets are subsets of the constraint function's zero sublevel set. three special forms of robust cbfs (rcbfs) are developed as functions of the input constraints, system dynamics, and disturbance bounds, such that the resultant rcbf condition on the control input is always feasible for states in the rcbf zero sublevel set. the rcbf condition is then enforced in a switched fashion, which allows the system to operate safely without enforcing the rcbf condition when far from the safe set boundary and allows tuning of how closely trajectories approach the safe set boundary. the proposed methods are verified in simulations demonstrating the developed rcbfs in an asteroid flyby scenario for a satellite with low-thrust actuators, and in asteroid proximity operations for a satellite with high-thrust actuators. | robust control barrier functions under high relative degree and input constraints for satellite trajectories |
we show that a number of claims made in myhrvold (2018) (hereafter m2018b) regarding the wise data and thermal modeling of asteroids are incorrect. that paper provides thermal fit parameter outputs for only two of the about 150,000 object dataset and does not make a direct comparison to asteroids with diameters measured by other means to assess the quality of that work's thermal model. we are unable to reproduce the results for the two objects for which m2018b published its own thermal fit outputs, including diameter, albedo, beaming, and infrared albedo. in particular, the infrared albedos published in m2018b are unphysically low. [...] while there were some minor issues with consistency between tables due to clerical errors in the wise/neowise team's various papers and data release in the planetary data system, and a software issue that slightly increased diameter uncertainties in some cases, these issues do not substantially change the results and conclusions drawn from the data. we have shown in previous work and with updated analyses presented here that the effective spherical diameters for asteroids published to date are accurate to within the previously quoted minimum systematic 1-sigma uncertainty of about 10 percent when data of appropriate quality and quantity are available. moreover, we show that the method used by m2018b to compare diameters between various asteroid datasets is incorrect and overestimates their differences. in addition, among other misconceptions in m2018b, we show that the wise photometric measurement uncertainties are appropriately characterized and used by the wise data processing pipeline and neowise thermal modeling software. we show that the near-earth asteroid thermal model (harris 1998) employed by the neowise team is a very useful model for analyzing infrared data to derive diameters and albedos when used properly. | response to "an empirical examination of wise/neowise asteroid analysis and results" |
the influence of lineaments, lineament intersections and geology on the groundwater yield of the basement terrain of ondo state was investigated using optical remote sensing data, aster dem, geology, and borehole yield data. landsat-7 etm+ and aster dem were processed to generate composite lineament map. the study area was traversed by five (5) main lineament populations trending n-s, ne-sw, e-w, ene-wsw, nnw-sse. boreholes sited on lineament exhibited a yield range of between 0.8 and 1.28 l/s with an average yield of 1.04 l/s. boreholes sited close to lineament gave groundwater yield values of between 0.5 and 1.28 l/s and an average yield of 1 l/s, while boreholes located outside lineament gave groundwater yield range of between 0.2 and 1.26 l/s with an average yield of 0.98 l/s. the investigation of the hydrogeological characteristics of the lithologies by superimposing the yield data showed average yield of 0.98 l/s for migmatite gneiss biotite granite undifferentiated (m), 1.01 l/s for porphyritic granite (ogp), 1.03 l/s for medium- to coarse-grained (oge), 1.17 l/s for pelitic schist undifferentiated (su), 1.24 l/s for quartz schist and quartzite (eq), 1.12 l/s for older granite undifferentiated (ogu), 0.5 l/s for slightly migmatised medium-grained granite-gneiss (gg) and 1.23 l/s for fine-grained flaggy quartzite and schists (sf). the study concluded that borehole data located on or near lineaments or at intersection of lineaments gave higher yields more than those located before lineaments or outside lineaments, while quartz schist and quartzite exhibited the highest average groundwater yield of all the lithological units. | investigation of the influence of lineaments, lineament intersections and geology on groundwater yield in the basement complex terrain of ondo state, southwestern nigeria |
the osiris-rex laser altimeter (ola) is a scanning lidar instrument with a high measurement rate of 10 khz and a dexterous two-axis mirror. ola is optimized for proximity operations (< 7 km range) around a small asteroid. the high repetition rate and scanning capability of the instrument give ola the ability to rapidly obtain high-density topographic scans of the surface of the near-earth asteroid (101955) bennu. we describe our approach to creating a global shape model using overlapping high-fidelity raster scans of the asteroid surface, demonstrated here with simulated data in advance of the asteroid encounter. this approach minimizes the dependence of the shape model on absolute position and pointing knowledge while taking advantage of the excellent short-term relative pointing stability of the instrument. it also provides a computationally efficient method of dealing with a dataset consisting of ≈ 1 billion data points through the use of keypoints and rigid transformations. the keypoint approach, in which matching features in overlapping scans are assigned a direct correspondence, mitigates against issues such as convergence into local minima, or dependence on initial conditions that methods such as icp have. we explain how we generate maps, digital elevation models, and digital terrain models for determining the sampleability and safety of potential sample sites and for the scientific interpretation of the asteroid. | global shape modeling using the osiris-rex scanning laser altimeter |
we report the detection of a large-amplitude mir outburst in the white dwarf (wd) 0145+234 in the neowise survey data. the source had a stable mir flux before 2018, and was brightened by about 1.0 magnitude in the w1 and w2 bands within half a year and has been continuously brightening since then. no significant variations are found in the optical photometry data during the same period. this suggests that this mir outburst is caused by recent replenishing or redistribution of dust, rather than intrinsic variations of the wd. spectral energy distribution modeling of 0145+234 suggests that there was already a dust disk around the wd in the quiescent state, and both of the temperature and surface area of the disk evolved rapidly since the outburst. the dust temperature was ≃1770 k in the initial rising phase, close to the sublimation temperature of silicate grains, and gradually cooled down to around 1150 k, while the surface area increased by a factor of about six during the same period. the inferred closest distance of dust to the wd is within the tidal disruption radius of a gravitationally bounded asteroid. we estimated the dust mass to be between 3 × 1015 and 3 × 1017 ρ/(1 g cm-3) kg for silicate grains of a power-law size distribution with a high cutoff size from 0.1 to 1000 μm. we interpret this as a possible tidal breakup of an exoasteroid by the wd. further follow-up observations of this rare event may provide insights on the origin of dust disk and metal pollution in some wds. | an ongoing mid-infrared outburst in the white dwarf 0145+234: catching in action the tidal disruption of an exoasteroid? |
motions of spacecraft in non-synchronized binary asteroid systems are facing significant dynamics problems due to the irregular-shaped primaries and time-varying gravitational field. this paper presents a novel method for the design and maintenance of bounded trajectory in the vicinity of non-synchronized binary systems. a non-synchronized model with considering both the planar full two-body problem and the elliptic restricted three-body problem is developed for the bounded motion design. this model can better reflect the properties of motion in non-synchronized binary systems. based on this non-synchronized model, bounded motions are designed with predetermined stability using the modified grid search and two-level correction strategy. further, considering the model uncertainty and unmodeled perturbations in the high-fidelity model, a self-adaptive control method is proposed to maintain the trajectories. simulations for the binary asteroid 1999 kw4 validate the stability and robustness of the proposed controller. compared with periodic orbits using the synchronized model, the proposed strategy by taking the bounded trajectories as reference trajectories can effectively improve the tracking accuracy and reduce the fuel consumption. this provides a more effective solution for mission trajectory design in future explorations to binary asteroid systems. | bounded trajectory design and self-adaptive maintenance control near non-synchronized binary systems comprised of small irregular bodies |
by investigating the petrology and chemical composition of type ii (feo-rich) chondrules in the mighei-like carbonaceous (cm) chondrites we constrain their thermal histories and relationship to the ornans-like carbonaceous (co) chondrites. we identified feo-rich relict grains in type ii chondrules by their fe/mn ratios; their presence indicates chondrule recycling among type ii chondrules. the majority of relict grains in type ii chondrules are feo-poor olivine grains. consistent with previous studies, chemical similarities between cm and co chondrite chondrules indicate that they had similar formation conditions and that their parent bodies probably formed in a common region within the protoplanetary disk. however, important differences such as mean chondrule size and the lower abundance of feo-poor relicts in cm chondrite type ii chondrules than in co chondrites suggest cm and co chondrules did not form together and they likely originate from distinct parent asteroids. despite being aqueously altered, many cm chondrites contain pre-accretionary anhydrous minerals (i.e., olivine) that are among the least thermally metamorphosed materials in chondrites according to the cr2o3 content of their ferroan olivine. the presence of these minimally altered pre-accretionary chondrule silicates suggests that samples to be returned from aqueously altered asteroids by the hayabusa2 and osiris-rex asteroid sample return missions, even highly hydrated, may contain silicates that can provide information about the pre-accretionary histories and conditions of asteroids ryugu and bennu, respectively. | cm and co chondrites: a common parent body or asteroidal neighbors? insights from chondrule silicates |
we present dual-band herschel/pacs imaging for 59 main-sequence stars with known warm dust (t warm ∼ 200 k), characterized by spitzer. of 57 debris disks detected at herschel wavelengths (70 and/or 100 and 160 μm), about half have spectral energy distributions (seds) that suggest two-ring disk architectures mirroring that of the asteroid-kuiper belt geometry; the rest are consistent with single belts of warm, asteroidal material. herschel observations spatially resolve the outer/cold dust component around 14 a-type and 4 solar-type stars with two-belt systems, 15 of which for the first time. resolved disks are typically observed with radii >100 au, larger than expected from a simple blackbody fit. despite the absence of narrow spectral features for ice, we find that the shape of the continuum, combined with resolved outer/cold dust locations, can help constrain the grain size distribution and hint at the dust’s composition for each resolved system. based on the combined spitzer/irs+multiband imaging photometer (5-to-70 μm) and herschel/pacs (70-to-160 μm) data set, and under the assumption of idealized spherical grains, we find that over half of resolved outer/cold belts are best fit with a mixed ice/rock composition. minimum grain sizes are most often equal to the expected radiative blowout limit, regardless of composition. three of four resolved systems around the solar-type stars, however, tend to have larger minimum grains compared to expectation from blowout (f mb = a min/a bos ∼ 5). we also probe the disk architecture of 39 herschel-unresolved systems by modeling their seds uniformly, and find them to be consistent with 31 single- and 8 two-belt debris systems. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia, with important participation from nasa. | herschel-resolved outer belts of two-belt debris disks—evidence of icy grains |
the vega planetary system hosts the archetype of extrasolar kuiper belts and is rich in dust from the sub-astronomical unit region out to hundreds of astronomical units, suggesting intense dynamical activity. we present atacama large millimeter/submillimeter array (alma) millimeter observations that detect and resolve the outer dust belt from the star for the first time. the interferometric visibilities show that the belt can be fit by a gaussian model or by power-law models with a steep inner edge (at 60-80 au). the belt is very broad, extending out to at least 150-200 au. we strongly detect the star and set a stringent upper limit to warm dust emission previously detected in the infrared. we discuss three scenarios that could explain the architecture of vega's planetary system, including the new alma constraints: no outer planets, a chain of low-mass planets, and a single giant planet. the planetless scenario is only feasible if the outer belt was born with the observed sharp inner edge. if, instead, the inner edge is currently being truncated by a planet, then the planet must be $\gtrsim 6$ ${m}_{\oplus }$ and at $\lesssim 71\,\mathrm{au}$ to have cleared its chaotic zone within the system age. in the planet chain scenario, outward planet migration and inward scattering of planetesimals could produce the hot and warm dust observed in the inner regions of the system. in the single giant planet scenario, an asteroid belt could be responsible for the warm dust, and mean motion resonances with the planet could put asteroids on star-grazing orbits, producing the hot dust. | dust populations in the iconic vega planetary system resolved by alma |
aims: trojans are defined as objects that share the orbit of a planet at the stable lagrangian points l4 and l5. in the solar system, these bodies show a broad size distribution ranging from micrometer (μm) to centimeter (cm) particles (trojan dust) and up to kilometer (km) rocks (trojan asteroids). it has also been theorized that earth-like trojans may be formed in extra-solar systems. the trojan formation mechanism is still under debate, especially theories involving the effects of dissipative forces from a viscous gaseous environment.methods: we perform hydro-simulations to follow the evolution of a protoplanetary disk with an embedded 1-10 jupiter-mass planet. on top of the gaseous disk, we set a distribution of μm-cm dust particles interacting with the gas. this allows us to follow dust dynamics as solids get trapped around the lagrangian points of the planet.results: we show that large vortices generated at the lagrangian points are responsible for dust accumulation, where the leading lagrangian point l4 traps a larger amount of submillimeter (submm) particles than the trailing l5, which traps mostly mm-cm particles. however, the total bulk mass, with typical values of ~mmoon, is more significant in l5 than in l4, in contrast to what is observed in the current solar system a few gigayears later. furthermore, the migration of the planet does not seem to affect the reported asymmetry between l4 and l5.conclusions: the main initial mass reservoir for trojan dust lies in the same co-orbital path of the planet, while dust migrating from the outer region (due to drag) contributes very little to its final mass, imposing strong mass constraints for the in situ formation scenario of trojan planets. | dust trapping around lagrangian points in protoplanetary disks |
computer-aided polyp detection (cade) is becoming a standard, integral part of any modern colonoscopy system. a typical colonoscopy cade detects a polyp in a single frame and does not track it through the video sequence. yet, many downstream tasks including polyp characterization (cadx), quality metrics, automatic reporting, require aggregating polyp data from multiple frames. in this work we propose a robust long term polyp tracking method based on re-identification by visual appearance. our solution uses an attention-based self-supervised ml model, specifically designed to leverage the temporal nature of video input. we quantitatively evaluate method's performance and demonstrate its value for the cadx task. | self-supervised polyp re-identification in colonoscopy |
the discovery of 1i/‘oumuamua confirmed that planetesimals must exist in great numbers in interstellar space. originally generated during planet formation, they are scattered from their original systems and subsequently drift through interstellar space. as a consequence they should seed molecular clouds with at least hundred-meter-scale objects. we consider how the galactic background density of planetesimals, enriched from successive generations of star and system formation, can be incorporated into forming stellar systems. we find that at a minimum of the order of 107 ‘oumuamua-sized and larger objects, plausibly including hundred-kilometer-scale objects, should be present in protoplanetary disks. at such initial sizes, the growth process of these seed planetesimals in the initial gas- and dust-rich protoplanetary disks is likely to be substantially accelerated. this could resolve the tension between accretionary timescales and the observed youth of fully fledged planetary systems. our results strongly advocate that the population of interstellar planetesimals should be taken into account in future studies of planet formation. as not only the galaxy’s stellar metallicity increased over time but also the density of interstellar objects, we hypothesize that this enriched seeding accelerates and enhances planetary formation after the first couple of generations of planetary systems. | a hypothesis for the rapid formation of planets |
we study imaging of point sources with a quadrupole gravitational lens while focusing on the formation and evolution of the einstein cross formed on the image sensor of an imaging telescope. for this, we consider the optical properties of an oblate gravitational lens that is characterized, in addition to a monopole potential, by the presence of a quadrupole zonal harmonic. we use a new type of a diffraction integral that we developed to study generic, opaque, weakly aspherical gravitational lenses. to evaluate this integral, we use the method of stationary phase that yields a quartic equation with respect to a cartesian projection of the observer's position vector with respect to the vector of the impact parameter. the resulting quartic equation can be solved analytically using the method first published by cardano in 1545. we find that the resulting solution provides a good approximation of the electromagnetic (em) field almost everywhere in the image plane, yielding the well-known astroid caustic of the quadrupole lens. the sole exception is the immediate vicinity of the caustic boundary, where a numerical treatment of the diffraction integral yields better results. we also convolve the quartic solution for the em field on the image plane with the point-spread function of a thin lens imaging telescope. by doing so, we are able to explore the direct relationship between the algebraic properties of the quartic solution for the em field, the geometry of the astroid caustic, and the geometry and shape of the resulting einstein cross that appear on the image plane of the thin lens telescope. the new quartic solution leads to significant improvements in numerical modeling as an evaluation of this solution is computationally far less expensive than a direct numerical treatment of the new diffraction integral. in the case of the solar gravitational lens, the new results drastically improve the speed of numerical simulations related to sensitivity analysis performed in the context of high-resolution imaging of exoplanets. | wave-optical study of the einstein cross formed by a quadrupole gravitational lens |
the gravitational coupling of nearby massive bodies to test masses in a gravitational wave (gw) detector cannot be shielded and gives rise to "gravity gradient noise" (ggn) in the detector. in this paper we show that for any gw detector using local test masses in the inner solar system, the ggn from the motion of the field of ∼105 inner solar system asteroids presents an irreducible noise floor for the detection of gw that rises exponentially at low frequencies. this severely limits prospects for gw detection using local test masses for frequencies fgw≲(few )×10-7 hz . at higher frequencies, we find that the asteroid ggn falls rapidly enough that detection may be possible; however, the incompleteness of existing asteroid catalogs with regard to small bodies makes this an open question around fgw∼μ hz , and further study is warranted. we show that a detector network placed in the outer solar system would not be overwhelmed by this noise above ∼10 nhz , and make comments on alternative approaches that could overcome the limitations of local test masses for gw detection in the ∼10 nhz - μ hz band. | gravity gradient noise from asteroids |
we develop a shape model of asteroid 16 psyche using observations acquired in a wide range of wavelengths: arecibo s-band delay-doppler imaging, atacama large millimeter array (alma) plane-of-sky imaging, adaptive optics (ao) images from keck and the very large telescope (vlt), and a recent stellar occultation. our shape model has dimensions 278 (-4/+8 km) × 238(-4/+6 km) × 171 km (-1/+5 km), an effective spherical diameter deff = 222-1/+4 km, and a spin axis (ecliptic lon, lat) of (36°, -8°) ± 2°. we survey all the features previously reported to exist, tentatively identify several new features, and produce a global map of psyche. using 30 calibrated radar echoes, we find psyche's overall radar albedo to be 0.34 ± 0.08 suggesting that the upper meter of regolith has a significant metal (i.e., fe-ni) content. we find four regions of enhanced or complex radar albedo, one of which correlates well with a previously identified feature on psyche, and all of which appear to correlate with patches of relatively high optical albedo. based on these findings, we cannot rule out a model of psyche as a remnant core, but our preferred interpretation is that psyche is a differentiated world with a regolith composition analogous to enstatite or ch/cb chondrites and peppered with localized regions of high metal concentrations. the most credible formation mechanism for these regions is ferrovolcanism as proposed by johnson et al. (2020). | asteroid 16 psyche: shape, features, and global map |
we present deep hubble space telescope/space telescope imaging spectrograph coronagraphic images of the β pic debris disk obtained at two epochs separated by 15 yr. the new images and the re-reduction of the 1997 data provide the most sensitive and detailed views of the disk at optical wavelengths as well as the yet smallest inner working angle optical coronagraphic image of the disk. our observations characterize the large-scale and inner-disk asymmetries and we identify multiple breaks in the disk radial surface brightness profile. we study in detail the radial and vertical disk structure and show that the disk is warped. we explore the disk at the location of the β pic b super-jupiter and find that the disk surface brightness slope is continuous between 0.''5 and 2.''0, arguing for no change at the separations where β pic b orbits. the two epoch images constrain the disk's surface brightness evolution on orbital and radiation pressure blow-out timescales. we place an upper limit of 3% on the disk surface brightness change between 3'' and 5'', including the locations of the disk warp, and the co and dust clumps. we discuss the new observations in the context of high-resolution multi-wavelength images and divide the disk asymmetries in two groups: axisymmetric and non-axisymmetric. the axisymmetric structures (warp, large-scale butterfly, etc.) are consistent with disk structure models that include interactions of a planetesimal belt and a non-coplanar giant planet. the non-axisymmetric features, however, require a different explanation. | the inner disk structure, disk-planet interactions, and temporal evolution in the β pictoris system: a two-epoch hst/stis coronagraphic study |
context. information about shapes and spin states of individual asteroids is important for the study of the whole asteroid population. for asteroids from the main belt, most of the shape models available now have been reconstructed from disk-integrated photometry by the lightcurve inversion method.aims: we want to significantly enlarge the current sample (~350) of available asteroid models.methods: we use the lightcurve inversion method to derive new shape models and spin states of asteroids from the sparse-in-time photometry compiled in the lowell photometric database. to speed up the time-consuming process of scanning the period parameter space through the use of convex shape models, we use the distributed computing project asteroids@home, running on the berkeley open infrastructure for network computing (boinc) platform. this way, the period-search interval is divided into hundreds of smaller intervals. these intervals are scanned separately by different volunteers and then joined together. we also use an alternative, faster, approach when searching the best-fit period by using a model of triaxial ellipsoid. by this, we can independently confirm periods found with convex models and also find rotation periods for some of those asteroids for which the convex-model approach gives too many solutions.results: from the analysis of lowell photometric data of the first 100 000 numbered asteroids, we derived 328 new models. this almost doubles the number of available models. we tested the reliability of our results by comparing models that were derived from purely lowell data with those based on dense lightcurves, and we found that the rate of false-positive solutions is very low. we also present updated plots of the distribution of spin obliquities and pole ecliptic longitudes that confirm previous findings about a non-uniform distribution of spin axes. however, the models reconstructed from noisy sparse data are heavily biased towards more elongated bodies with high lightcurve amplitudes.conclusions: the lowell photometric database is a rich and reliable source of information about the spin states of asteroids. we expect hundreds of other asteroid models for asteroids with numbers larger than 100 000 to be derivable from this data set. more models will be able to be reconstructed when lowell data are merged with other photometry. tables 1 and 2 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/587/a48 | asteroid models from the lowell photometric database |
context. asteroids smaller than about 100 m in diameter are observed to rotate very fast, with periods often much shorter than the critical spin limit of 2.2 h. some of these super-fast rotators can also achieve a very large semimajor axis drift induced by the yarkovsky effect, which, in turn, is determined by internal and surface physical properties.aims: we consider here a small super-fast-rotating near-earth asteroid, designated as 2016 ge1. this object rotates in just about 34 s, and a large yarkovsky effect has been determined from astrometry. by using these results, we aim to constrain the thermal inertia of the surface of this extreme object.methods: we used a recently developed statistical method to determine the thermal properties of near-earth asteroids. the method is based on the comparison between the observed and the modeled yarkovsky effect, and the thermal conductivity (inertia) is determined via a monte carlo approach. parameters of the yarkovsky effect model are fixed if their uncertainty is negligible, modeled with a gaussian distribution of the errors if they are measured, or deduced from general properties of the population of near-earth asteroids when they are unknown.results: using a well-established orbit determination procedure, we determined the yarkovsky effect on 2016 ge1 and confirm a significant semimajor axis drift rate. using a statistical method, we show that this semimajor axis drift rate can only be explained by low thermal inertia values below 100 j m−2 k−1 s−1/2. we benchmarked our statistical method using the well-characterized asteroid bennu and find that only knowing the semimajor axis drift rate and the rotation period is generally insufficient for determining the thermal inertia. however, when the statistical method is applied to super-fast rotators, we find that the measured yarkovsky effect can be achieved only for very low values of thermal inertia: namely, 90% of the probability density function of the model outcomes is contained at values smaller than 100 j m−2 k−1 s−1/2.conclusions: we propose two possible interpretations for the extremely low thermal inertia of 2016 ge1: a high porosity or a cracked surface, or a thin layer of fine regolith on the surface. though both possibilities seem somewhat unexpected, this opens up the possibility of a subclass of low-inertia, super-fast-rotating asteroids. | the low surface thermal inertia of the rapidly rotating near-earth asteroid 2016 ge1 |
the first known interstellar object ’oumuamua exhibited a nongravitational acceleration that appeared inconsistent with cometary outgassing, leaving radiation pressure as the most likely force. barring the alien lightsail hypothesis, an ultra-low density due to a fractal structure might also explain the acceleration of ’oumuamua by radiation pressure. in this letter we report a decrease in ’oumuamua’s rotation period based on ground-based observations, and show that this spin-down can be explained by the yorp effect if ’oumuamua is indeed a fractal body with the ultra-low density of 10-2 kg m-3. we also investigate the mechanical consequences of ’oumuamua as a fractal body subjected to rotational and tidal forces, and show that a fractal structure can survive these mechanical forces. | the interstellar object ’oumuamua as a fractal dust aggregate |
anisotropic outgassing from comets exerts a torque sufficient to rapidly change the angular momentum of the nucleus, potentially leading to rotational instability. here, we use empirical measures of spin changes in a sample of comets to characterize the torques, and to compare them with expectations from a simple model. both the data and the model show that the characteristic spin-up timescale, τs, is a strong function of nucleus radius, rn. empirically, we find that the timescale for comets (most with perihelion 1-2 au and eccentricity ∼0.5) varies as ${\tau }_{s}\sim 100{r}_{{\rm{n}}}^{2}$ , where rn is expressed in kilometers, and τs is in years. the fraction of the nucleus surface that is active varies as ${f}_{{\rm{a}}}\sim 0.1{r}_{{\rm{n}}}^{-2}$ . we find that the median value of the dimensionless moment arm of the torque is kt = 0.007 (i.e., ∼0.7% of the escaping momentum torques the nucleus), with weak (<3σ) evidence for a size dependence ${k}_{t}\sim {10}^{-3}{r}_{{\rm{n}}}^{2}$ . sub-kilometer nuclei have spin-up timescales comparable to their orbital periods, confirming that outgassing torques are quickly capable of driving small nuclei toward rotational disruption. torque-induced rotational instability likely accounts for the paucity of sub-kilometer short-period cometary nuclei, and for the pre-perihelion destruction of sungrazing comets. torques from sustained outgassing on small active asteroids can rival yorp torques, even for very small (≲1 g s-1) mass-loss rates. finally, we highlight the important role played by observational biases in the measured distributions of τs, fa, and kt. | systematics and consequences of comet nucleus outgassing torques |
this study presents the analysis of forced photometry data in the o and c filters of centaurs 29p/schwassmann-wachmann and (2060) chiron obtained by the atlas network between 2015 and 2022. centaur 29p had 24 outbursts with a median peak brightness of -3.0 and a range of -3.7 mag, regardless of spectral band. some of these outbursts exhibited an asymmetric light curve with respect to peak brightness, with brightness decreases ranging from -0.22 to -7.6 mag h-1 and durations from 2.8 min to 1.4 d. the slope m of the photometric profile of the coma after/before and during an outburst was ≤1 and >1, respectively, reflecting an increase in brightness at the optocenter of the object. without the outbursts, 29p has an absolute magnitudes h0 of 9.3 ± 0.2 and 9.10 ± 0.01 in the c and o filters, respectively, and activity indices of n = 11.56 ± 0.08 and 2.1 ± 0.1. using the lomb-scargle periodogram, a periodicity of 0.97 d was found in the c magnitudes after perihelion, probably related to nuclear rotation. the absolute magnitude of chiron in the hg1g2 system in the o filter is nearly constant between 2017 and 2020, with a weighted mean of 5.35 ± 0.03. in 2021, the brightness increases to h = 4.54 ± 0.03 and decreases to 5.04 ± 0.04 in 2022. this increase in 2021 is not due to outbursts that did not occur during the entire observing campaign, but is related to the increase in opposition effect. | a photometric study of centaurs 29p/schwassmann-wachmann and (2060) chiron |
the first large interstellar object discovered near earth by the pan starrs telescope, `oumuamua, showed half a dozen anomalies relative to comets or asteroids in the solar system. all natural-origin interpretations of `oumuamua's anomalies contemplated objects of a type never seen before, such as a porous cloud of dust particles, a tidal disruption fragment or exotic icebergs made of pure hydrogen or pure nitrogen. each of these natural-origin models has major quantitative shortcomings, and so the possibility of an artificial origin for `oumuamua must be considered. `oumuamua's anomalies suggest that it might have been a thin craft—with a large area per unit mass—pushed by the reflection of sunlight; sharing qualities with the thin artifact 2020 so—launched by nasa in 1966 and discovered by pan starrs in 2020 to exhibit a push away from the sun with no cometary tail. the galileo project aims to collect new data that will identify the nature of `oumuamua-like objects in the coming years. | on the possibility of an artificial origin for `oumuamua |
the galileo project is the first systematic scientific research program in the search for potential astro-archaeological artifacts or remnants of extraterrestrial technological civilizations (etcs) or potentially active equipment near earth. taking a path not taken, it conceivably may pick some low-hanging fruit, and without asserting probabilities — make discoveries of etc-related objects, which would have far-reaching implications for science and our worldview. | overview of the galileo project |
cosmologies in which dark matter clumps strongly on small scales are unfavorable to terrestrial detectors that are as yet unexposed to the clumps. i show that sub-hectometer clumps could trigger thermonuclear runaways by scattering on nuclei in white dwarf cores (carbon and oxygen) and neutron star oceans (carbon), setting off type ia-like supernovae and x-ray superbursts respectively. i consider two scenarios: ``dark clusters" that are essentially microhalos, and ``long-range dark nuggets", essentially macroscopic composites, with long-range yukawa baryonic interactions that source the energy for igniting explosions. i constrain dark clusters weighing between the planck mass and asteroid masses, and long-range dark nuggets over a wider mass range spanning forty orders of magnitude. these limits greatly complement searches i had co-proposed in 2109.04582 for scattering interactions of dark clumps in neutron stars, cosmic rays, and pre-historic minerals. | supernovae and superbursts by dark matter clumps |
the sariçiçek howardite meteorite shower consisting of 343 documented stones occurred on september 2, 2015 in turkey and is the first documented howardite fall. cosmogenic isotopes show that sariçiçek experienced a complex cosmic-ray exposure history, exposed during 12-14 ma in a regolith near the surface of a parent asteroid, and that an 1 m sized meteoroid was launched by an impact 22 ± 2 ma ago to earth (as did one-third of all hed meteorites). sims dating of zircon and baddeleyite yielded 4550.4 ± 2.5 ma and 4553 ± 8.8 ma crystallization ages for the basaltic magma clasts. the apatite u-pb age of 4525 ± 17 ma, k-ar age of 3.9 ga, and the u,th-he ages of 1.8 ± 0.7 and 2.6 ± 0.3 ga are interpreted to represent thermal metamorphic and impact-related resetting ages, respectively. petrographic; geochemical; and o-, cr-, and ti-isotopic studies confirm that sariçiçek belongs to the normal clan of hed meteorites. petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the sariçiçek regolith and organic contamination of the meteorite after a few days on soil. video observations of the fall show an atmospheric entry at 17.3 ± 0.8 km s-1 from nw; fragmentations at 37, 33, 31, and 27 km altitude; and provide a pre-atmospheric orbit that is the first dynamical link between the normal hed meteorite clan and the inner main belt. spectral data indicate the similarity of sariçiçek with the vesta asteroid family (v-class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) vesta. dynamical modeling of meteoroid delivery to earth shows that the complete disruption of a 1 km sized vesta family asteroid or a 10 km sized impact crater on vesta is required to provide sufficient meteoroids ≤4 m in size to account for the influx of meteorites from this hed clan. the 16.7 km diameter antionia impact crater on vesta was formed on terrain of the same age as given by the 4he retention age of sariçiçek. lunar scaling for crater production to crater counts of its ejecta blanket show it was formed 22 ma ago. | the sariçiçek howardite fall in turkey: source crater of hed meteorites on vesta and impact risk of vestoids |
in the last two decades, new computational tools have been developed in order to aid space missions to orbit around irregular small bodies. one of the techniques consists in rebuilding their shape in tetrahedral polyhedron. this method is well suited to determine the shape and estimate certain physical features of asteroids. however, a large computational effort is necessary depending on the quantity of triangular faces chosen. another method is based on a representation of the central body in terms of mascons (discrete spherical masses). the main advantage of the method is its simplicity which makes the calculation faster. nevertheless, the errors are non-negligible when the attraction expressions are calculated near the surface of the body. in this work, we carry out a study to develop a new code that determines the centre of mass of each tetrahedron of a shaped polyhedral source and evaluates the gravitational potential function and its first- and second-order derivatives. we performed a series of tests and compared the results with the classical polyhedron method. we found good agreement between our determination of the attraction expressions close to the surface, and the same determination by the classical polyhedron method. however, this agreement does not occur inside the body. our model appears to be more accurate in representing the potential very close to the body's surface when we divide the tetrahedron in three parts. finally, we have found that in terms of cpu time requirements, the execution of our code is much faster compared with the polyhedron method. | mascon gravitation model using a shaped polyhedral source |
to improve the autonomy and reliability of asteroid landing control, a fast solution continuation approach for time-optimal asteroid landing trajectories is presented in this study. the contributions of this study are threefold. first, a deep neural network (dnn) is developed to approximate the gravitational field of asteroids, and the corresponding time consumption of gravity calculation in trajectory propagation is significantly reduced. second, the original 3-dimensional (3d) landing control problem is connected to a simplified 2d one according to the continuation relationship between these model dynamics. third, the 2d control problem is further transformed into a multi-variable root-finding problem with analytical shooting equations with the help of a gauss-legendre integral method and could be quickly solved by shooting methods. taking the solution of this root-finding problem as an initial guess, the accurate solution of the original time-optimal landing problem can be quickly obtained through a backward solution continuation process. finally, numerical simulations of landings on 443 eros are given to verify the effectiveness of the proposed techniques and thus to illustrate the excellent performance on rapidity, convergence and solution accuracy of the developed algorithm for the generation of time-optimal landing trajectories. | fast solution continuation of time-optimal asteroid landing trajectories using deep neural networks |
theory and previous space missions indicate there are several populations of zodiacal dust. the most prominent populations are grains on bound elliptic orbits (α-meteoroids), and β-meteoroids on hyperbolic escape trajectories governed largely by their size and composition. yet, there may be other populations not yet confirmed by observation. the parker solar probe (psp) spacecraft is able to observe in situ dust populations in the densest part of the zodiacal cloud. over the first seven orbits, dust count rates are well organized by orbital groups based on orbital parameters of psp's shrinking orbit. in particular, the first three orbits and the sixth orbit have a single, preperihelion peak in count rate with a gradual drop off postperihelion, while orbits 4, 5, and 7 have two distinct count rate peaks on either side of perihelion. the secondary peaks in orbits 4, 5, and 7 are inconsistent with current zodiacal dust models that account for only two dust populations: α- and β-meteoroids. in examining the directionality of dust impacts on the psp spacecraft, the presence of an anti-ram impactor anomaly postperihelion during orbit 4 is evident. this anomaly may indicate another dust population beyond the nominal α- and β-meteoroids, and its origin may be related to the geminids meteoroid stream associated with the asteroid 3200 phaethon. | dust directionality and an anomalous interplanetary dust population detected by the parker solar probe |
in order to understand the geological evolution of asteroids eros, itokawa and ryugu and their collisional history, previous studies investigated boulder size distributions on their surfaces. however, quantitative comparison of these size distributions is hampered by numerous differences between these studies regarding the definition of a boulder's size, measuring technique and the fitting method to determine the power-index of the boulder size distributions. we provide a consistent and coherent model of boulder size distributions by remeasuring the boulders on the entire surfaces of eros and itokawa using the small body mapping tool (sbmt) and combining our observations with the ryugu data of michikami et al. (2019). we derived power-indices of the boulder size distributions of -3.25 ± 0.14 for eros, -3.05 ± 0.14 for itokawa and -2.65 ± 0.05 for ryugu. the asteroid with the highest number density of boulders ≥ 5 m turns out to be ryugu, not itokawa, as suggested by an earlier study. we show that the appearance of the boulders tends towards more elongated shapes as the size of an asteroid decreases, which can be explained by differences in asteroid gravity and boulder friction angles. our quantitative observational results indicate that boulder migration preferentially affects smaller boulders, and tends to occur on larger asteroids. | boulder sizes and shapes on asteroids: a comparative study of eros, itokawa and ryugu |
the surface of the rubble-pile asteroid (101955) bennu has been characterized in detail by the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission. by examining global and local digital terrain models, we observed that bennu possesses terraces, that is, a series of roughly latitude-parallel, step-like slope breaks. these partially circumscribe the poles and extend east-west over several longitudinal quadrants at mid- to high (≥30°) latitudes. the terraces are subtle in amplitude, with heights ranging from 1 to 5 m. they often exhibit back-wasting that results in v-shaped scarps that open downslope in some locations. when boulders >5-10 m are absent at or near a terrace, the steeper portion (the drop) of the terrace lacks rocks, whereas the flatter portion (the bench) of the terrace has accumulations of rocks at its crest. when boulders >5-10 m are present, their steep downslope faces often make up the drop from the terrace crest, and they retain debris upslope, thereby enhancing the terrace structure. a geotechnical stability analysis indicates that bennu's surface is likely unstable and that surface cohesion is <0.6 pa. bennu's terraces strongly resemble scarps generated in laboratory and numerical simulations of a cohesionless granular bed as the slope of the bed increases quasi-statically. we conclude that terraces are probably actively forming on bennu as its surface slowly fails owing to creep induced by spin acceleration. | the formation of terraces on asteroid (101955) bennu |
the sun-earth triangular lagrange point, l 5, offers an ideal location to monitor the space weather. furthermore, l 4, l 5 may harbor earth `trojan' asteroids and space dust that are of significant interest to the scientific community. no spacecraft has, thus far, entered an orbit in the vicinity of sun-earth triangular points in part because of high propellant costs. by incorporating solar sail dynamics in the model representing cr3bp, the concept of a mission to l 4, l 5 can be re-evaluated and the total δv can be reconsidered. a solar sail is employed to increase the energy of the spacecraft and deliver the spacecraft to an orbit about an artificial lagrange point by leveraging solar radiation pressure and, potentially, without any insertion δv. | solar sail transfers and trajectory design to sun-earth l 4, l 5: solar observations and potential earth trojan exploration |
laser ablation inductively coupled plasma-mass spectrometry (la-icp-ms) u-pb geochronology of shocked zircon grains in a vesicular-fluidal impact melt rock from the ≥54 km charlevoix impact structure, québec, canada, suggests an ordovician to silurian age of 450 ± 20 ma for the impact. this age is anchored by concordant u-pb results of 450 ma for a u-rich, cryptocrystalline zircon grain in the melt rock, interpreted as a recrystallized metamict zircon crystal; the u-th-pb system of the metamict grain was seemingly chronometrically reset by the charlevoix impact, but withstood later tectonometamorphic events. the new zircon age for charlevoix is in agreement with a stratigraphically constrained late ordovician maximum age of 453 ma and corroborates earlier suggestions that the impact occurred most likely in the ordovician, and not 100 myr later, as indicated by previous k/ar and 40ar/39ar geochronologic results. the latter may reflect postimpact thermal overprint of impactites during the salinian (late silurian to early devonian) and/or acadian (late devonian) orogenies. u-pb geochronology of zircon crystals in anorthosite exposed in the central uplift of the impact structure yielded a grenvillian crystallization age of 1062 ± 11 ma. the preferred ordovician age for the charlevoix impact structure, which is partially overthrusted by the appalachian front, suggests the impact occurred during a phase of taconian tectonism and an episode of enhanced asteroid bombardment of the earth. our results, moreover, demonstrate that (recrystallized) metamict zircon grains may be of particular interest in impact geochronology. | in situ u-pb analysis of shocked zircon from the charlevoix impact structure, québec, canada |
we present the results of "snapshot" numerical integrations of test particles representing comet-like and asteroid-like objects in the inner solar system aimed at investigating the short-term dynamical evolution of objects close to the dynamical boundary between asteroids and comets as defined by the tisserand parameter with respect to jupiter, tj (i.e., tj = 3). as expected, we find that tj for individual test particles is not always a reliable indicator of initial orbit types. furthermore, we find that a few percent of test particles with comet-like starting elements (i.e., similar to those of jupiter-family comets) reach main-belt-like orbits (at least temporarily) during our 2 myr integrations, even without the inclusion of non-gravitational forces, apparently via a combination of gravitational interactions with the terrestrial planets and temporary trapping by mean-motion resonances with jupiter. we estimate that the fraction of real jupiter-family comets occasionally reaching main-belt-like orbits on myr timescales could be on the order of ∼ 0.1-1%, although the fraction that remain on such orbits for appreciable lengths of time is certainly far lower. for this reason, the number of jfc-like interlopers in the main-belt population at any given time is likely to be small, but still non-zero, a finding with significant implications for efforts to use apparently icy yet dynamically asteroidal main-belt comets as tracers of the primordial distribution of volatile material in the inner solar system. the test particles with comet-like starting orbital elements that transition onto main-belt-like orbits in our integrations appear to be largely prevented from reaching low eccentricity, low inclination orbits, suggesting that the real-world population of main-belt objects with both low eccentricities and inclinations may be largely free of this potential occasional jupiter-family comet contamination. we therefore find that low-eccentricity, low-inclination main-belt comets may provide a more reliable means for tracing the primordial ice content of the main asteroid belt than the main-belt comet population as a whole. | potential jupiter-family comet contamination of the main asteroid belt |
differentiated asteroids are rare in the main asteroid belt despite evidence for ∼ 100 distinct differentiated bodies in the meteorite record. we have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. using the sloan digital sky survey (sdss) to search for a needle in a haystack we identify spectral a-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. we have performed a near-infrared spectral survey with spex on the nasa irtf and fire on the magellan telescope. we report results from having doubled the number of known a-type asteroids. we deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. we find a-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of ∼ 600 a-type asteroids above that size. they are found rather evenly distributed throughout the main belt, are even detected at the distance of the cybele region, and have no statistically significant concentration in any asteroid family. we conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere. | olivine-dominated a-type asteroids in the main belt: distribution, abundance and relation to families |
the jaxa/isas spacecraft destiny+ will be launched to the active asteroid (3200) phaethon in 2022. among the proposed core payload is the destiny+ dust analyzer (dda) which is an upgrade of the cosmic dust analyzer flown on the cassini spacecraft to saturn (srama et al., 2011). we use two up-to-date computer models, the esa interplanetary meteoroid engineering model (imem, dikarev et al., 2005a, c), and the interstellar dust module of the interplanetary meteoroid environment for exploration model (imex;sterken et al. 2013; strub et al., 2019) to study the detection conditions and fluences of interplanetary and interstellar dust with dda. our results show that a statistically significant number of interplanetary and interstellar dust particles will be detectable with dda during the 4-years interplanetary cruise of destiny+. the particle impact direction and speed can be used to descriminate between interstellar and interplanetary particles and likely also to distinguish between cometary and asteroidal particles. | modelling destiny+ interplanetary and interstellar dust measurements en route to the active asteroid (3200) phaethon |
it has been hypothesized that the impactors that created the majority of the observable craters on the ancient lunar highlands were derived from the main asteroid belt in such a way that preserved their size-frequency distribution (strom, r.g., malhotra, r., ito, t., yoshida, f., kring, d.a. [2005]. science 309, 1847-1850). a more limited version of this hypothesis, dubbed the e-belt hypothesis, postulates that a destabilized contiguous inner extension of the main asteroid belt produced a bombardment limited to those craters younger than nectaris basin (bottke, w.f., vokrouhlický, d., minton, d., nesvorný, d., morbidelli, a., brasser, r., simonson, b., levison, h.f. [2012]. nature 485, 78-81). we investigate these hypotheses with a monte carlo code called the cratered terrain evolution model (ctem), which models the topography of a terrain that has experienced bombardment due to an input impactor population. we detail our effort to calibrate the code with a human crater counter. we also take advantage of recent advances in understanding the scaling relationships between impactor size (di) and final crater size (dc) for basin-sized impact craters (dc > 300 km) in order to use large impact basins as a constraint on the ancient impactor population of the moon. we find that matching the observed number of lunar highlands craters with dc ≃ 100 km requires that the total number of impacting asteroids with di > 10 km be no fewer than 4 ×10-6km-2 . however, this required mass of impactors has <1% chance of producing only a single basin larger than the ∼1200 km imbrium basin; instead, these simulations are likely to produce more large basins than are observed on the moon. this difficulty in reproducing the lunar highlands cratering record with a main asteroid belt sfd arises because the main belt is relatively abundant in the objects that produce these "megabasins" that are larger than imbrium. we also find that the main asteroid belt sfd has <16% chance of producing nectarian densities of dc > 64 km craters while not producing a crater larger than imbrium, as required by the e-belt hypothesis. these results suggest that the lunar highlands were unlikely to have been bombarded by a population whose size-frequency distribution resembles that of the currently observed main asteroid belt. we suggest that the population of impactors that cratered the lunar highlands had a somewhat similar size-frequency distribution as the modern main asteroid belt, reflecting a similar rocky composition and collisional history, but had a smaller ratio of objects capable of producing megabasins compared to objects capable of producing ∼100 km craters. we estimate that the impactor population required to match the lunar highlands had n>5.5km /n>70km ≃ 630 , while the modern main asteroid belt ratio is n>5.5km /n>70km ≃ 100 . | re-examining the main asteroid belt as the primary source of ancient lunar craters |
this paper presents transition of the failure mode of a cohesive, spherical body due to the yarkovsky-o'keefe-radzievskii-paddack (yorp) spin-up. on the assumption that the distribution of materials in the body is homogeneous, failed regions first appearing in the body at different spin rates are predicted by comparing the yield condition of an elastic stress in the body. it is found that as the spin rate increases, the locations of the failed regions move from the equatorial surface to the central region. to avoid such failure modes, the body should have higher cohesive strength. the results by this model are consistent with those by a plastic finite element model. then, this model and a two-layered-cohesive model first proposed by hirabayashi et al. are used to classify possible evolution and disruption of a spherical body. there are three possible pathways to disruption. first, because of a strong structure, failure of the central region is dominant and eventually leads to a breakup into multiple components. secondly, a weak surface and a weak interior make the body oblate. thirdly, a strong internal core prevents the body from failing and only allows surface shedding. this implies that observed failure modes may highly depend on the internal structure of an asteroid, which could provide crucial information for giving constraints on the physical properties. | failure modes and conditions of a cohesive, spherical body due to yorp spin-up |
we analyzed the warm spitzer/irac data of kic 8462852. we found no evidence of infrared excess at 3.6 μm and a small excess of 0.43 ± 0.18 mjy at 4.5 μm below the 3σ threshold necessary to claim a detection. the lack of strong infrared excess 2 years after the events responsible for the unusual light curve observed by kepler further disfavors the scenarios involving a catastrophic collision in a kic 8462852 asteroid belt, a giant impact disrupting a planet in the system or a population of dust-enshrouded planetesimals. the scenario invoking the fragmentation of a family of comets on a highly elliptical orbit is instead consistent with the lack of strong infrared excess found by our analysis. | kic 8462852: the infrared flux |
the innermost section of the solar system has not been extensively studied because minor bodies moving inside earth's orbit tend to spend most of their sidereal orbital periods at very low solar elongation, well away from the areas more frequently observed by programs searching for near-earth objects. the survey carried out from the zwicky transient facility (ztf) is the first one that has been able to detect multiple asteroids well detached from the direct gravitational perturbation of the earth-moon system. ztf discoveries include 2019 aq3 and 2019 lf6, two atiras with the shortest periods among known asteroids. here, we perform an assessment of the orbital evolution of 2020 av2, an atira found by ztf with a similarly short period but following a path contained entirely within the orbit of venus. this property makes it the first known member of the elusive vatira population. genuine vatiras, those long-term dynamically stable, are thought to be subjected to the so-called von zeipel-lidov-kozai oscillation that protects them against close encounters with both mercury and venus. however, 2020 av2 appears to be a former atira that entered the vatira orbital domain relatively recently. it displays an anticoupled oscillation of the values of eccentricity and inclination, but the value of the argument of perihelion may circulate. simulations show that 2020 av2 might reach a 3:2 resonant orbit with venus in the future, activating the von zeipel-lidov-kozai mechanism, which in turn opens the possibility to the existence of a long-term stable population of vatiras trapped in this configuration. | on the orbital evolution of 2020 av2, the first asteroid ever observed to go around the sun inside the orbit of venus |
active asteroids behave dynamically like asteroids but display comet-like comae. these objects are poorly understood, with only about 30 identified to date. we have conducted one of the deepest systematic searches for asteroid activity by making use of deep images from the dark energy camera (decam) ideally suited to the task. we looked for activity indicators among 11,703 unique asteroids extracted from 35,640 images. we detected three previously identified active asteroids ((62412), (1) ceres and (779) nina), though only (62412) showed signs of activity. our activity occurrence rate of 1 in 11,703 is consistent with the prevailing 1 in 10,000 activity occurrence rate estimate. our proof of concept demonstrates (1) our novel informatics approach can locate active asteroids and (2) decam data are well-suited to the search for active asteroids. | safari: searching asteroids for activity revealing indicators |
asteroid 162173 ryugu and asteroid 101955 bennu, which were recently visited by spacecraft hayabusa2 and osiris-rex, respectively, are spinning top-shaped rubble piles. other axisymmetric top-shaped near-earth asteroids have been observed with ground-based radar, most of which rotate near breakup rotation periods of ∼ 3 h. this suggests that rotation-induced deformation of asteroids through rotational spinup produces top shapes. although some previous simulations using the discrete element method showed that spinup of rubble piles may produce oblate top shapes, it is still unclear what kinds of conditions such as friction angles of constituent materials and spinup timescales are required for top-shape formation. here we show, through smoothed particle hydrodynamics simulations of granular bodies spinning-up at different rates, that the rotation-induced deformation of spherical rubble piles before breakup can be classified into three modes according to the friction angle ϕd: quasi-static and internal deformation for ϕd ≤ 40 ° , dynamical and internal deformation for 50 ° ≤ϕd ≤ 60 ° , and a set of surface landslides for ϕd ≥ 70 ° . note that these apparent large values of friction angle can be acceptable if we consider the effect of cohesion among blocks of a rubble pile under weak gravity. bodies with ϕd ≤ 60 ° evolve into oblate spheroids through internal deformation, but never form pronounced equators defining a top shape. in contrast, bodies with ϕd ≥ 70 ° deform into axisymmetric top shapes through an axisymmetric set of surface landslides if spinup timescales are ≲ a few days. in addition, through slow spinups with timescales ≳ 1 month, bodies with ϕd ≥ 70 ° deform into non-axisymmetric shapes via localized sets of landslides. we suggest that rapid spinup mechanisms are preferable for the formation of axisymmetric top shapes. | sph simulations for shape deformation of rubble-pile asteroids through spinup: the challenge for making top-shaped asteroids ryugu and bennu |
context. the vast majority of the geophysical and geological constraints (e.g., internal structure, cratering history) for main-belt asteroids have so far been obtained via dedicated interplanetary missions (e.g., esa rosetta, nasa dawn). the high angular resolution of sphere/zimpol, the new-generation visible adaptive-optics camera at eso vlt, implies that these science objectives can now be investigated from the ground for a large fraction of d ≥ 100 km main-belt asteroids. the sharp images acquired by this instrument can be used to accurately constrain the shape and thus volume of these bodies (hence density when combined with mass estimates) and to characterize the distribution and topography of d ≥ 30 km craters across their surfaces.aims: here, via several complementary approaches, we evaluated the recently proposed hypothesis that the s-type asteroid (89) julia is the parent body of a small compact asteroid family that formed via a cratering collisional event.methods: we observed (89) julia with vlt/sphere/zimpol throughout its rotation, derived its 3d shape, and performed a reconnaissance and characterization of the largest craters. we also performed numerical simulations to first confirm the existence of the julia family and to determine its age and the size of the impact crater at its origin. finally, we utilized the images/3d shape in an attempt to identify the origin location of the small collisional family.results: on the one hand, our vlt/sphere observations reveal the presence of a large crater (d ~ 75 km) in julia's southern hemisphere. on the other hand, our numerical simulations suggest that (89) julia was impacted 30-120 myrs ago by a d ~ 8 km asteroid, thereby creating a d ≥ 60 km impact crater at the surface of julia. given the small size of the impactor, the obliquity of julia and the particular orientation of the family in the (a,i) space, the imaged impact crater is likely to be the origin of the family.conclusions: new doors into ground-based asteroid exploration, namely, geophysics and geology, are being opened thanks to the unique capabilities of vlt/sphere. also, the present work may represent the beginning of a new era of asteroid-family studies. in the fields of geophysics, geology, and asteroid family studies, the future will only get brighter with the forthcoming arrival of 30-40 m class telescopes like elt, tmt, and gmt. based on observations made with eso telescopes at the paranal observatory under program id 199.c-0074 (pi: p. vernazza). the reduced images are only available available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/618/a154 | the impact crater at the origin of the julia family detected with vlt/sphere? |
the migrations of solid objects throughout the solar system are thought to have played key roles in disk evolution and planet formation. however, our understanding of these migrations is limited by a lack of quantitative constraints on their timings and distances recovered from laboratory measurements of meteorites. the protoplanetary disk supported a magnetic field that decreased in intensity with heliocentric distance. as such, the formation distances of the parent asteroids of ancient meteorites can potentially be constrained by paleointensity measurements of these samples. here, we find that the wis 91600 ungrouped c2 chondrite experienced an ancient field intensity of 4.4 ± 2.8 μt. combined with the thermal history of this meteorite, magnetohydrodynamical models suggest the disk field reached 4.4 μt at ∼9.8 au, indicating that the wis 91600 parent body formed in the distal solar system. because wis 91600 likely came to earth from the asteroid belt, our recovered formation distance argues that this body previously traveled from ∼10 au to 2-3 au, supporting the migration of asteroid-sized bodies throughout the solar system. wis 91600 also contains chondrules, calcium-aluminum-rich inclusions and amoeboid olivine aggregates, indicating that some primitive millimeter-sized solids that formed in the innermost solar system migrated outward to ∼10 au within ∼3-4 myr of solar system formation. moreover, the oxygen isotopic compositions of proposed distal meteorites (wis 91600, tagish lake and ci chondrites) argue that the cm, co, and cr chondrites contain micrometer-scale dust and ice that originated in the distal solar system. | constraints on the distances and timescales of solid migration in the early solar system from meteorite magnetism |
white dwarfs (wds) often show metal lines in their spectra, indicating accretion of asteroidal material. our sun is to become a wd in several gigayears. here, we examine how the solar wd accretes from the three major small body populations: the main belt asteroids (mbas), jovian trojan asteroids (jtas), and trans-neptunian objects (tnos). owing to the solar mass loss during the giant branch, 40% of the jtas are lost but the vast majority of mbas and tnos survive. during the wd phase, objects from all three populations are sporadically scattered onto the wd, implying ongoing accretion. for young cooling ages ≲100 myr, accretion of mbas predominates; our predicted accretion rate ~106 g s-1 falls short of observations by two orders of magnitude. on gigayear timescales, thanks to the consumption of the tnos that kicks in ≳100 myr, the rate oscillates around 106-107 g s-1 until several gigayears and drops to ~105 g s-1 at 10 gyr. our solar wd accretion rate from 1 gyr and beyond agrees well with those of the extrasolar wds. we show that for the solar wd, the accretion source region evolves in an inside-out pattern. moreover, in a realistic small body population with individual sizes covering a wide range as wd pollutants, the accretion is dictated by the largest objects. as a consequence, the accretion rate is lower by an order of magnitude than that from a population of bodies of a uniform size and the same total mass and shows greater scatter. | metal pollution of the solar white dwarf by solar system small bodies |
small asteroids are often considered to be rubble-pile objects, and such asteroids may be the most likely type of near earth objects (neos) to pose a threat to earth. however, impact cratering on such bodies is complex and not yet understood. we perform three low-velocity (≈ 400 m/s) impact experiments in granular targets with and without projectile-size boulders. we conducted sph simulations that closely reproduced the impact experiments. our results suggest that cratering on heterogeneous targets displaces and ejects boulders, rather than fragmenting them, unless directly hit. we also see indications that as long as the energy required to disrupt the boulder is small compared to the kinetic energy of the impact, the disruption of boulders directly hit by the projectile may have minimal effect on the crater size. the presence of boulders within the target causes ejecta curtains with higher ejection angles compared to homogeneous targets. at the same time, there is a segregation of the fine ejecta from the boulders, resulting in boulders landing at larger distances than the surrounding fine grained material. however, boulders located in the target near the maximum extent of the expanding excavation cavity are merely exhumed and distributed radially around the crater rim, forming ring patterns similar to the ones observed on asteroids itokawa, ryugu and bennu. altogether, on rubble-pile asteroids this process will redistribute boulders and finer-grained material heterogeneously, both areally around the crater and vertically in the regolith. in the context of a kinetic impactor on a rubble-pile asteroid and the dart mission, our results indicate that the presence of boulders will reduce the momentum transfer compared to a homogeneous, fine-grained target. | boulder exhumation and segregation by impacts on rubble-pile asteroids |
indirect optimization methods convert optimal control problems (ocps) into two- or multi-point boundary-value problems. a highly desirable feature of indirect methods, specifically for space applications, is that high-resolution trajectories can be generated, which satisfy the first-order necessary conditions of optimality. a recently developed composite smoothing control (csc) framework is utilized to formulate and solve the problem of simultaneous trajectory optimization and propulsion sub-system design of spacecraft. a reasonable parameterized breakdown of the spacecraft mass is adopted, which captures the impact of power produced by the solar arrays and its contribution to the total spacecraft mass. thus, the implicit trade-offs can be considered in the indirect optimization approach. the function space co-optimization problem of spacecraft power subsystem parameters along with the main trajectory is solved with the objective to maximize the payload delivered. the proposed framework amounts to an invariant embedding that reduces the original, difficult-to-solve, multi-point boundary-value problem into a two-point boundary-value problem with continuous, differentiable control inputs. utility of the proposed construct is demonstrated through a low-thrust, multi-revolution, multi-year rendezvous maneuver to asteroid dionysus with a variable-specific-impulse, variable-thrust modeled engine. this is the first time that indirect optimization methods have tackled such a complex co-optimization problem using the csc framework. | a composite framework for co-optimization of spacecraft trajectory and propulsion system |
context. on september 26, 2022, the double asteroid redirection test (dart) successfully changed the trajectory of the asteroid dimorphos (i.e. 65803 didymos i), a satellite circling (65803) didymos.aims: we aim to characterize the consequence of this collision and derive the physical properties of the ejecta features based on ground-based observations in east asia.methods: filtered photometric observations were made between september 21 2022 (~5 days before dart impact) and january 5 2023 using the lulin 1-m telescope to identify the taxonomy, size, and rotational period of didymos. the finson-probstein dust dynamical models were used to determine the grain sizes (mm-cm) released after the dart impact and the date of the activity.results: we report a rapid increase in the brightness by about one order of magnitude after the impact, to be followed by a gradual 0.07 mag decrease over the first two weeks producing a relatively shallow brightness slope at the end of october. the size and rotation period at post-impact were 0.7−0.10+0.12 km and 2.27 h, respectively. the principal component index (pci), relative reflectance, and colors were all classified as s-complex. the dydimos system became bluer after the collision before returning to its original color. the formation of a comet-like trail containing debris in the anti-sunward direction can be explained by expansion driven by the pressure of solar radiation. a finson-probstein modeling approach led to an estimate of the grain size in the mm-cm range. the splitting of the tail into two components is shown in the image acquired on october 12, which may possibly be interpreted as being due to the secondary impact of fallback ejecta about a week after dart. | physical properties of the didymos system before and after the dart impact |
the shower database (sd) of the meteor data center (mdc) had been operating on the basis of stream-naming rules which were too complex and insufficiently precise for 15 years. with a gradual increase in the number of discovered meteor showers, the procedure for submitting new showers to the database and naming them led to situations that were inconsistent with the fundamental role of the sd - the disambiguation of stream names in the scientific literature. our aim was to simplify the meteor shower nomenclature rules. we proposed a much simpler set of meteor shower nomenclature rules, based on a two-stage approach, similar to those used in the case of asteroids. the first stage applies to a new shower just after its discovery. the second stage concerns a repeatedly observed shower, the existence of which no longer raises any doubts. our proposed new procedure was approved by a vote of the commission f1 of the iau in july 2022. | new nomenclature rules for meteor showers adopted |
near-earth asteroid (101955) bennu is an active asteroid experiencing mass loss. the activity manifests itself in the form of ejection events emitting up to hundreds of millimeter- to centimeter-scale particles. the origins, spectral interpretation, resource identification, and security-regolith explorer spacecraft monitored particle activity for a 10-month period that included bennu's perihelion and aphelion. novel and classical methods were utilized to detect the particles and characterize their orbital and physical properties. roughly 30% of the observed particle mass escaped to heliocentric orbit. a majority of particles fell back onto the surface of bennu after ejection, with the longest-lived particle surviving for 6 days on a temporary orbit. particle ejection events appear to preferentially take place in the afternoon and evening and from low latitudes, although they can occur at any time or latitude. the reaccumulation of material is biased toward low latitudes resulting in the possible in-fill of craters and growth of bennu's equatorial bulge. of the potential mechanisms behind this activity that were investigated in focused studies, meteoroid impacts, thermal fracturing, and ricochet—but not water ice sublimation—were found to be consistent with observations. while phyllosilicate dehydration was not investigated with a focused study, it remains a possible mechanism. these mechanisms are not unique to bennu, suggesting that many near-earth asteroids may exhibit activity that has gone undetected thus far. spacecraft missions with wide-field imagers are encouraged to further characterize this phenomenon. | introduction to the special issue: exploration of the activity of asteroid (101955) bennu |
following the report of a new hard x-ray transient swift j1727.8-1613 (grb 230824a, gcn #34537, atel #16205), we obtained forced photometry measurements at the location reported in gcn #34543 on images taken by the asteroid terrestrial-impact last alert system (atlas; tonry et al. 2018). | atlas constraints on the optical onset of new x-ray transient swift j1727.8-1613 |
in space operation of the microwave discharge ion thruster μ10 on the asteroid explorers hayabusa and hayabusa2, the propellant utilization efficiency deteriorated much more than in the ground endurance test. in this study, a fault tree analysis and experimental simulations of space operation were performed, focusing on the grid-derived internal carbon contamination. it was found that the performance deterioration due to the waveguide contamination matched that in hayabusa2 qualitatively and quantitatively. based on the experimental verification, the future performance is experimentally predicted. | investigation and experimental simulation of performance deterioration of microwave discharge ion thruster μ10 during space operation |
paleomagnetic measurements of ancient terrestrial and extraterrestrial samples indicate that numerous planetary bodies generated magnetic fields through core dynamo activity during the early solar system. the existence, timing, intensity and stability of these fields are governed by the internal transfer of heat throughout their parent bodies. thus, paleomagnetic records preserved in natural samples can contain key information regarding the accretion and thermochemical history of the rocky bodies in our solar system. however, models capable of predicting these field properties across the entire active lifetime of a planetary core that could relate the processes occurring within these bodies to features in these records and provide such information are limited. here, we perform asteroid thermal evolution models across suites of radii, accretion times and thermal diffusivities with the aim of predicting when fully and partially differentiated asteroids generated magnetic fields. we find that dynamo activity in both types of asteroid is delayed until ∼4.5-5.5 myr after calcium-aluminium-rich inclusion formation due to the partitioning of 26al into the silicate portion of the body during differentiation and large early surface heat fluxes, followed by a brief period (<12.5 myr for bodies with radii <500 km) of thermally-driven dynamo activity as heat is convected from the core across a partially-molten magma ocean. we also expect that gradual core solidification produced compositionally-driven dynamo activity in these bodies, the timing of which could vary by tens to hundreds of millions of years depending on the s concentration of the core and the radius of the body. there was likely a pause in core cooling and dynamo activity following the cessation of convection in the magma ocean. our predicted periods of magnetic field generation and quiescence match eras of high and low paleointensities in the asteroid magnetic field record compiled from paleomagnetic measurements of multiple meteorites, providing the possible origins of the remanent magnetisations carried by these samples. we also compare our predictions to paleomagnetic results from different meteorite groups to constrain the radii of the angrite, cv chondrite, h chondrite, iie iron meteorite and bjürbole (l/ll chondrite) parent bodies and identify a likely nebula origin for the remanent magnetisation carried by the cm chondrites. | constraints on asteroid magnetic field evolution and the radii of meteorite parent bodies from thermal modelling |
the biogenic elements, h, c, n, o, p and s, have a long cosmic history, whose evolution can still be observed in diverse locales of the known universe, from interstellar clouds of gas and dust, to pre-stellar cores, nebulas, protoplanetary discs, planets and planetesimals. the best analytical window into this cosmochemical evolution as it neared earth has been provided so far by the small bodies of the solar system, some of which were not significantly altered by the high gravitational pressures and temperatures that accompanied the formation of larger planets and may carry a pristine record of early nebular chemistry. asteroids have delivered such records, as their fragments reach the earth frequently and become available for laboratory analyses. the carbonaceous chondrite meteorites (cc) are a group of such fragments with the further distinction of containing abundant organic materials with structures as diverse as kerogen-like macromolecules and simpler compounds with identical counterparts in earth's biosphere. all have revealed a lineage to cosmochemical synthetic regimes. several cc show that asteroids underwent aqueous alteration of their minerals or rock metamorphism but may yet yield clues to the reactivity of organic compounds during parent-body processes, on asteroids as well as larger ocean worlds and planets. whether the exogenous delivery by meteorites held an advantage in earth's molecular evolution remains an open question as many others regarding the origins of life are. nonetheless, the natural samples of meteorites allow exploring the physical and chemical processes that might have led to a selected chemical pool amenable to the onset of life. [figure not available: see fulltext.] | carbonaceous chondrite meteorites: the chronicle of a potential evolutionary path between stars and life |
carbonaceous chondrites are fragments from primitive parent asteroids, which represent some of the most primitive meteorites accessible for laboratory analysis and offer therefore the best opportunity to explore the chemical and physical conditions in the early solar system. here, we report the identification of presolar grains, which are circumstellar condensates that date back from before the formation of our solar system, in fine-grained dust rims around chondrules in carbonaceous chondrites. average presolar grain abundances in the rims of aqueously altered chondrites (petrologic type 2) are three times higher than in the respective interchondrule matrices, while for the most pristine specimens (petrologic type 3), the opposite is observed. the presence of these grains implies a nebular origin of the rim material, and gives evidence for differing alteration pathways for different reservoirs of fine-grained material found in primitive meteorites. moreover, our findings indicate formation of the fine-grained rims in the solar nebula prior to parent-body accretion, giving support to accretionary scenarios for parent-bodies in the presence of dust-rimmed chondrules. | ancient stardust in fine-grained chondrule dust rims from carbonaceous chondrites |
asteroid anchoring is the premise for the spacecraft to conduct in-situ scientific exploration on the surface of a weak gravitational asteroid. there is not any precedent for successful anchoring on the asteroid surface all over the world. ultrasonic drill actuated by the piezoelectric ceramic is especially suitable for drilling on the surface of a weak gravitational asteroid, showing outstanding advantages such as low power consumption, low required drilling pressure and wide temperature range. in order to solve the technical problem of anchoring, a novel anchoring device based on multiple ultrasonic drill cross-drilling geometric force closure is proposed. firstly, the structure and working principle of the anchoring device are introduced. then the edem software based on the discrete element method is used to simulate the influencing factors of the anchoring force. finally, the effectiveness of the anchoring device is proved by experiments. the results show that the ultrasonic drill is effective for the anchoring device; the anchoring device can provide an anchoring force of 60-250 n for the spacecraft; its structure is simple, compact and adaptable. | an asteroid anchoring method based on cross-drilling geometric force closure of ultrasonic drill |
the resurfacing process on ryugu accompanying the artificial impact crater formation by hayabusa2's small carry-on impactor (sci) was studied by comparing pre- and post-impact images of this region captured by an optical navigation camera. three different aspects of the resurfacing process were examined: the crater rim profiles, the motion of boulders and the appearance of new boulders, and the motion vectors of ryugu's surface around the sci crater. the averaged crater rim height, h, was derived as follows: h = hr exp [-(r/rrim - 1)/λrim], where rrim is the sci crater rim radius of 8.8 m, the fitted parameter, hr, is 0.475 m, and the λrim is 0.245. the ejecta blanket thickness of the sci crater was thinner than that estimated from both the observation of natural craters and the crater formation theory. however, this discrepancy of the ejecta blanket thickness was resolved by taking into account the new boulders appearing in the post-impact images in the volume. the motion of the discovered boulders could be classified by its mechanisms as follows: a dragging motion created by excavation flow during the crater formation, a pushing motion created by falling-back ejecta, a dragging motion created by the slight motion of the okamoto boulder, and a motion caused by seismic shaking induced by the sci impact itself. the seismic shaking caused boulders to move farther than 3 cm from the original site in most of the region within 15 m distance from the sci crater center, where the maximum acceleration of the impact induced seismic waves 7 times larger than the surface gravity of ryugu based on the laboratory experiments (matsue et al. [2020] icarus, 338, 113520), and the evidence of the seismic shaking for boulders with a movement of >3 cm was detected in about 10% of the boulders in the region between 15 m and 30 m from the crater center, which region was inferred to experience acceleration larger than the ryugu's surface gravity based on previous laboratory experiments (matsue et al. [2020] icarus, 338, 113520). | resurfacing processes on asteroid (162173) ryugu caused by an artificial impact of hayabusa2's small carry-on impactor |
we have conducted a nanosims-based search for presolar material in samples recently returned from c-type asteroid ryugu as part of jaxa's hayabusa2 mission. we report the detection of all major presolar grain types with o- and c-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 o-anomalous supernova grain of ambiguous phase, 38 sic, and 16 carbonaceous grains. at least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate c isotopic anomalies are probably organics. the presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered ryugu matrix. the matrix-normalized presolar grain abundances in ryugu are ${4.8}_{-2.6}^{+4.7}$ ppm for o-anomalous grains, ${25}_{-5}^{+6}$ ppm for sic grains, and ${11}_{-3}^{+5}$ ppm for carbonaceous grains. ryugu is isotopically and petrologically similar to carbonaceous ivuna-type (ci) chondrites. to compare the in situ presolar grain abundances of ryugu with ci chondrites, we also mapped ivuna and orgueil samples and found a total of 15 sic grains and 6 carbonaceous grains. no o-anomalous grains were detected. the matrix-normalized presolar grain abundances in the ci chondrites are similar to those in ryugu: ${23}_{-6}^{+7}$ ppm sic and ${9.0}_{-3.6}^{+5.4}$ ppm carbonaceous grains. thus, our results provide further evidence in support of the ryugu-ci connection. they also reveal intriguing hints of small-scale heterogeneities in the ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material. | presolar stardust in asteroid ryugu |
the small carry-on impactor (sci) equipped on hayabusa2 was developed to produce an artificial impact crater on the primitive near-earth asteroid (nea) 162173 ryugu (ryugu) in order to explore the asteroid subsurface material unaffected by space weathering and thermal alteration by solar radiation. an exposed fresh surface by the impactor and/or the ejecta deposit excavated from the crater will be observed by remote sensing instruments, and a subsurface fresh sample of the asteroid will be collected there. the sci impact experiment will be observed by a deployable camera 3-d (dcam3-d) at a distance of ∼1 km from the impact point, and the time evolution of the ejecta curtain will be observed by this camera to confirm the impact point on the asteroid surface. as a result of the observation of the ejecta curtain by dcam3-d and the crater morphology by onboard cameras, the subsurface structure and the physical properties of the constituting materials will be derived from crater scaling laws. moreover, the sci experiment on ryugu gives us a precious opportunity to clarify effects of microgravity on the cratering process and to validate numerical simulations and models of the cratering process. | scientific objectives of small carry-on impactor (sci) and deployable camera 3 digital (dcam3-d): observation of an ejecta curtain and a crater formed on the surface of ryugu by an artificial high-velocity impact |
carbonaceous chondrites are meteorites believed to preserve our planet's source materials, but the precise nature of these materials still remains uncertain. to uncover pristine planetary materials, we performed synchrotron radiation-based x-ray computed nanotomography of a primitive carbonaceous chondrite, acfer 094, and found ultraporous lithology (upl) widely distributed in a fine-grained matrix. upls are porous aggregates of amorphous and crystalline silicates, fe-ni sulfides, and organics. the porous texture must have been formed by removal of ice previously filling pore spaces, suggesting that upls represent fossils of primordial ice. the ice-bearing upls formed through sintering of fluffy icy dust aggregates around the h2o snow line in the solar nebula and were incorporated into the acfer 094 parent body, providing new insight into asteroid formation by dust agglomeration. | discovery of fossil asteroidal ice in primitive meteorite acfer 094 |
by investigating the in situ chemical and o-isotope compositions of olivine in lightly sintered dust agglomerates from the early solar system, we constrain their origins and the retention of dust in the protoplanetary disk. the grain sizes of silicates in these agglomeratic olivine (ao) chondrules indicate that the grain sizes of chondrule precursors in the renazzo-like carbonaceous (cr) chondrites ranged from <1 to 80 μm. we infer this grain size range to be equivalent to the size range for dust in the early solar system. ao chondrules may contain, but are not solely composed of, recycled fragments of earlier formed chondrules. they also contain 16o-rich olivine related to amoeboid olivine aggregates and represent the best record of chondrule-precursor materials. ao chondrules contain one or more large grains, sometimes similar to feo-poor (type i) and/or feo-rich (type ii) chondrules, while others contain a type ii chondrule core. these morphologies are consistent with particle agglomeration by electrostatic charging of grains during collision, a process that may explain solid agglomeration in the protoplanetary disk in the micrometer size regime. the petrographic, isotopic, and chemical compositions of ao chondrules are consistent with chondrule formation by large-scale shocks, bow shocks, and current sheets. the petrographic, isotopic, and chemical similarities between ao chondrules in cr chondrites and chondrule-like objects from comet 81p/wild 2 indicate that comets contain ao chondrules. we infer that these ao chondrules likely formed in the inner solar system and migrated to the comet forming region at least 3 ma after the formation of the first solar system solids. observations made in this study imply that the protoplanetary disk retained a dusty disk at least ∼3.7 ma after the formation of the first solar system solids, longer than half of the dusty accretion disks observed around other stars. | the retention of dust in protoplanetary disks: evidence from agglomeratic olivine chondrules from the outer solar system |
here were report on a laboratory study aiming to reproduce specificities of near-earth asteroid. we study how the elevated surface temperature, their surface roughness (rock or regolith), as well as observation geometry can affect the absorption features detected on asteroids. for that purpose, we selected a recent carbonaceous chondrite fall, the mukundpura cm2 chondrite which fell in india in june 2017. bidirectional reflectance spectroscopy was performed to analyze the effect of the geometrical configuration (incidence, emergence and azimuth angle) on the measurement. our results show that reflectance spectra obtained under warm environment (nea-like) tends to show shallower absorption bands compared to low-temperature conditions (mba-like), but still detectable in our experiments under laboratory timescales. irreversible alteration of the sample because of the warm environment (from room temperature to 250 °c) has been detected as an increase of the spectral slope and a decrease of the band depths (at 0.7 μm, 0.9 μm and 2.7 μm). comparing the meteoritic chip and the powdered sample, we found that surface texture strongly affects the shape of the reflectance spectra of meteorites and thus of asteroids, where a dust-covered surface presents deeper absorption features. we found that all spectral parameters, such as the reflectance value, spectral slope and possible absorption bands are affected by the geometry of measurement. we observed the disappearance of the 0.7 μm absorption feature at phase angle larger than 120°, but the 3 μm band remains detectable on all measured spectra. | some things special about neas: geometric and environmental effects on the optical signatures of hydration |
following its flyby and first imaging of the pluto-charon binary, the new horizons spacecraft visited the kuiper belt object (kbo) 2014 mu69 (also known as (486958) arrokoth). the imaging showed mu69 to be a contact binary that rotates at a low spin period (15.92 hours), is made of two individual lobes connected by a narrow neck and has a high obliquity (about 98 degrees)1, properties that are similar to those of other kbo contact binaries inferred through photometric observations2. however, all scenarios suggested so far for the origins of such configurations3-5 have failed to reproduce these properties and their probable frequent occurrence in the kuiper belt. here we show that semi-secular perturbations6,7 operating on only ultrawide kbo binaries close to their stability limit can robustly lead to gentle, slow binary mergers at arbitrarily high obliquities but low rotational velocities, reproducing the characteristics of mu69 and other similar oblique contact binaries. using n-body simulations, we find that approximately 15 per cent of all ultrawide binaries with a cosine-uniform inclination distribution5,9 are likely to merge through this process. moreover, we find that such mergers are sufficiently gentle to deform the shape of the kbo only slightly. the semi-secular contact binary formation channel not only explains the observed properties of mu69, but may also apply to other kuiper belt or asteroid belt binaries and in the solar system and extra-solar moon systems. | the wide-binary origin of (2014) mu69-like kuiper belt contact binaries |
context. the population of near-earth asteroids (neas) shows a large variety of objects in terms of physical and dynamical properties. they are subject to planetary encounters and to strong solar wind and radiation effects. their study is also motivated by practical reasons regarding space exploration and long-term probability of impact with the earth.aims: we aim to spectrally characterize a significant sample of neas with sizes in the range of 0.25-5.5 km (categorized as large), and search for connections between their spectral types and the orbital parameters.methods: optical spectra of neas were obtained using the isaac newton telescope (int) equipped with the ids spectrograph. these observations are analyzed using taxonomic classification and by comparison with laboratory spectra of meteorites.results: a total number of 76 neas were observed. we spectrally classified 44 of them as q/s-complex, 16 as b/c-complex, eight as v-types, and another eight belong to the remaining taxonomic classes. our sample contains 27 asteroids categorized as potentially hazardous and 31 possible targets for space missions including (459872) 2014 ek24, (436724) 2011 uw158, and (67367) 2000 ly27. the spectral data corresponding to (276049) 2002 ce26 and (385186) 1994 aw1 shows the 0.7 μm feature which indicates the presence of hydrated minerals on their surface. we report that q-types have the lowest perihelia (a median value and absolute deviation of 0.797 ± 0.244 au) and are systematically larger than the s-type asteroids observed in our sample. we explain these observational evidences by thermal fatigue fragmentation as the main process for the rejuvenation of nea surfaces.conclusions: in general terms, the taxonomic distribution of our sample is similar to the previous studies and matches the broad groups of the inner main belt asteroids. nevertheless, we found a wide diversity of spectra compared to the standard taxonomic types. all optical data from int 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/627/a124 | near-earth asteroids spectroscopic survey at isaac newton telescope |
observed hyperbolic minor bodies might have an interstellar origin, but they can be natives of the solar system as well. fly-bys with the known planets or the sun may result in the hyperbolic ejection of an originally bound minor body; in addition, members of the oort cloud could be forced to follow inbound hyperbolic paths as a result of secular perturbations induced by the galactic disc or, less frequently, due to impulsive interactions with passing stars. these four processes must leave distinctive signatures in the distribution of radiants of observed hyperbolic objects, both in terms of coordinates and velocity. here, we perform a systematic numerical exploration of the past orbital evolution of known hyperbolic minor bodies using a full n-body approach and statistical analyses to study their radiants. our results confirm the theoretical expectations that strong anisotropies are present in the data. we also identify a statistically significant overdensity of high-speed radiants towards the constellation of gemini that could be due to the closest and most recent known fly-by of a star to the solar system, that of the so-called scholz's star. in addition to and besides 1i/2017 u1 (`oumuamua), we single out eight candidate interstellar comets based on their radiants' velocities. | where the solar system meets the solar neighbourhood: patterns in the distribution of radiants of observed hyperbolic minor bodies |
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