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phobos and deimos occupy unique positions both scientifically and programmatically on the road to the exploration of the solar system. japan aerospace exploration agency (jaxa) plans a phobos sample return mission (mmx: martian moons exploration). the mmx spacecraft is scheduled to be launched in 2024, orbit both phobos and deimos (multiple flybys), and retrieve and return >10 g of phobos regolith back to earth in 2029. the phobos regolith represents a mixture of endogenous phobos building blocks and exogenous materials that contain solar system projectiles (e.g., interplanetary dust particles and coarser materials) and ejecta from mars and deimos. under the condition that the representativeness of the sampling site(s) is guaranteed by remote sensing observations in the geologic context of phobos, laboratory analysis (e.g., mineralogy, bulk composition, o-cr-ti isotopic systematics, and radiometric dating) of the returned sample will provide crucial information about the moon's origin: capture of an asteroid or in-situ formation by a giant impact. if phobos proves to be a captured object, isotopic compositions of volatile elements (e.g., d/h, 13c/12c, 15n/14n) in inorganic and organic materials will shed light on both organic-mineral-water/ice interactions in a primitive rocky body originally formed in the outer solar system and the delivery process of water and organics into the inner rocky planets. | the importance of phobos sample return for understanding the mars-moon system |
carbonaceous chondrites (ccs) are important materials for understanding the early evolution of the solar system and delivery of volatiles and organic material to the early earth. presumed cc-like asteroids are also the targets of two current sample return missions: osiris-rex to asteroid bennu and hayabusa-2 to asteroid ryugu, and the dawn orbital mission at asteroid ceres. to improve our ability to identify and characterize cm2 cc-type parent bodies, we have examined how factors such as particle size, particle packing, and viewing geometry affect reflectance spectra of the murchison cm2 cc. the derived relationships have implications for disc-resolved examinations of dark asteroids and sampleability. it has been found that reflectance spectra of slabs are more blue-sloped (reflectance decreasing toward longer wavelengths as measured by the 1.8/0.6 μm reflectance ratio), and generally darker, than powdered sample spectra. decreasing the maximum grain size of a powdered sample results in progressively brighter and more red-sloped spectra. decreasing the average grain size of a powdered sample results in a decrease in diagnostic absorption band depths, and redder and brighter spectra. decreasing porosity of powders and variations in surface texture result in spectral changes that may be different as a function of viewing geometry. increasing thickness of loose dust on a denser powdered substrate leads to a decrease in absorption band depths. changes in viewing geometry lead to different changes in spectral metrics depending on whether the spectra are acquired in backscatter or forward-scatter geometries. in backscattered geometry, increasing phase angle leads to an initial increase and then decrease in spectral slope, and a general decrease in visible region reflectance and absorption band depths, and frequent decreases in absorption band minima positions. in forward scattering geometry, increasing phase angle leads to small non-systematic changes in spectral slope, and general decreases in visible region reflectance, and absorption band depths. the highest albedos and larger band depths are generally seen in the lowest phase angle backscattering geometry spectra. the reddest spectra are generally seen in the lowest phase angle backscatter geometry spectra. for the same phase angle, spectra acquired in forward scatter geometry are generally redder and darker and have shallower absorption bands than those acquired in backscatter geometry. overall, backscatter geometry-acquired spectra are flatter, brighter, and have deeper 0.7 μm region absorption band depths than forward scatter geometry-acquired spectra. it was also found that the 0.7, 0.9, and 1.1 μm absorption bands in murchison spectra, which are attributable to various fe electronic processes, are ubiquitous and can be used to recognize cm2 chondrites regardless of the physical properties of the meteorite and viewing geometry. | spectral reflectance "deconstruction" of the murchison cm2 carbonaceous chondrite and implications for spectroscopic investigations of dark asteroids |
a number of earth co-orbital asteroids experience repeated transitions between the quasi-satellite and horseshoe dynamical states. asteroids 2001 go2, 2002 aa29, 2003 yn107 and 2015 so2 are well-documented cases of such a dynamical behaviour. these transitions depend on the gravitational influence of other planets, owing to the overlapping of a multiplicity of secular resonances. here, we show that the recently discovered asteroid (469219) 2016 ho3 is a quasi-satellite of our planet - the fifth one, joining the ranks of (164207) 2004 gu9, (277810) 2006 fv35, 2013 lx28, and 2014 ol339. this new earth co-orbital also switches repeatedly between the quasi-satellite and horseshoe configurations. its current quasi-satellite episode started nearly 100 yr ago and it will end in about 300 yr from now. the orbital solution currently available for this object is very robust and our full n-body calculations show that it may be a long-term companion (time-scale of myr) to our planet. among the known earth quasi-satellites, it is the closest to our planet and as such, a potentially accessible target for future in situ study. due to its presumably lengthy dynamical relationship with the earth and given the fact that at present and for many decades this transient object remains well positioned with respect to our planet, the results of spectroscopic studies of this small body, 26-115 m, may be particularly useful to improve our understanding of the origins - local or captured - of earth's co-orbital asteroid population. the non-negligible effect of the uncertainty in the value of the mass of jupiter on the stability of this type of co-orbitals is also briefly explored. | asteroid (469219) 2016 ho3, the smallest and closest earth quasi-satellite |
since 2017, two macroscopic interstellar objects have been discovered in the inner solar system, both of which are distinct in nature. the first interstellar object, 1i/`oumuamua, passed within $\sim63$ lunar distances of the earth, appeared asteroidal lacking detectable levels of gas or dust loss, yet exhibited a nongravitational acceleration. 1i/`oumuamua's brief visit left open questions regarding its provenance which has given rise to many theoretical hypotheses, including an icy comet lacking a dust coma, an elongated fragment of a planet or planetesimal that was tidally disrupted, and an ultra-porous fractal aggregate. the second interstellar object, 2i/borisov, was distinct from 1i/`oumuamua in terms of its bulk physical properties and displayed a definitive cometary tail. we review the discoveries of these objects, the subsequent observations and characterizations, and the theoretical hypotheses regarding their origins. we describe 1i/`oumuamua and 2i/borisov in the context of active asteroids and comets in the solar system. the discovery of these two objects implies a galactic-wide population of $\sim10^{26}$ similar bodies. forthcoming observatories should detect many more interstellar planetesimals which may offer new insights into how planetary formation processes vary throughout the galaxy. | interstellar objects |
wd j204713.76-125908.9 is a new addition to the small class of white dwarfs with helium-dominated photospheres that exhibit strong balmer absorption lines and atmospheric metal pollution. the exceptional abundances of hydrogen observed in these stars may be the result of accretion of water-rich rocky bodies. we obtained far-ultraviolet and optical spectroscopy of wd j204713.76-125908.9 using the cosmic origin spectrograph on-board the hubble space telescope and x-shooter on the very large telescope, and identify photospheric absorption lines of nine metals: c, o, mg, si, p, s, ca, fe, and ni. the abundance ratios are consistent with the steady-state accretion of exo-planetesimal debris rich in the volatile elements carbon and oxygen, and the transitional element sulphur, by factors of 17, 2, and 4, respectively, compared to the bulk earth. the parent body has a composition akin to solar system carbonaceous chondrites, and the inferred minimum mass, 1.6 × 1020 g, is comparable to an asteroid 23 km in radius. we model the composition of the disrupted parent body, finding from our simulations a median water mass fraction of 8 per cent. | white dwarf pollution by hydrated planetary remnants: hydrogen and metals in wd j204713.76-125908.9 |
we provide a scheme to correct asteroid astrometric observations for star catalog systematic errors due to inaccurate star positions and proper motions. as reference we select the most accurate stars in the ppmxl catalog, i.e., those based on 2mass astrometry. we compute position and proper motion corrections for 19 of the most used star catalogs. the use of these corrections provides better ephemeris predictions and improves the error statistics of astrometric observations, e.g., by removing most of the regional systematic errors previously seen in pan-starrs ps1 asteroid astrometry. the correction table is publicly available at ftp://ssd.jpl.nasa.gov/pub/ssd/debias/debias_2014.tgz and can be freely used in orbit determination algorithms to obtain more reliable asteroid trajectories. | star catalog position and proper motion corrections in asteroid astrometry |
we examined two decades of spex/nasa infrared telescope facility observations from the small main-belt asteroid spectroscopic survey (smass) and the mit-hawaii near-earth object spectroscopic survey (mithneos) to investigate uncertainties and systematic errors in reflectance spectral slope measurements of asteroids. from 628 spectra of 11 solar analogs used for calibration of the asteroid spectra, we derived an uncertainty of on slope measurements over 0.8-2.4 μm. air mass contributes to -0.92% μm-1 per 0.1 unit air mass difference between the asteroid and the solar analog and therefore for an overall 2.8% μm-1 slope variability in smass and mithneos designed to operate within 1.0-1.3 air mass. no additional observing conditions (including the parallactic angle, seeing, and humidity) were found to contribute systematically to slope change. we discuss implications for asteroid taxonomic classification works. uncertainties provided in this study should be accounted for in future compositional investigation of small bodies to distinguish intrinsic heterogeneities from possible instrumental effects. | twenty years of spex: accuracy limits of spectral slope measurements in asteroid spectroscopy |
in this paper, the methods and results from tsinghua university and shanghai institute of satellite engineering for the 11th global trajectory optimization competition (gtoc11) are presented. to deal with the complicated "dyson sphere" building problem, a three-stage procedure is conducted. first, the pre-analysis is performed to reduce search space. it is found that two-impulse maneuvers between asteroid flybys are near-optimal, the semi-major axis of the "dyson ring" should be better at 1.0-1.5 au, and the larger arrival mass asteroids tend to be selected. second, the globally optimal trajectory design problem is further divided into two sub-problems, the mothership trajectory design and the asteroid assignment to the "dyson ring" power stations. for the first problem, beam search is used to obtain numerous single mothership trajectories based on a pre-constructed flyby trajectory database of 3-8 asteroids. the overall trajectories and asteroids visited are obtained by selecting 10 mothership trajectories with a genetic algorithm. for the second problem, we build a database of optimal rendezvous times for all the 83,453 asteroids at different phase angles to reach power stations of different radii and phase angles, then a greedy algorithm is proposed to obtain the asteroid arrival schedule based on all the asteroids visited by motherships. finally, local optimization of asteroid sequence and flyby epochs is conducted. the activation time adjustment in combination with indirect continuous-thrust trajectory optimization is used based on the global optimization result. in the final submission, motherships fly by 388 asteroids, and the minimum mass of twelve power stations reaches 94% of the theoretical upper bound, which is defined using the minimum-time orbital transfers with free initial and target phases. | gtoc 11: results from tsinghua university and shanghai institute of satellite engineering |
we consider how qcd axions produced by the misalignment mechanism could form galactic dark matter halos. we recall that stationary, gravitationally stable axion field configurations have the size of an asteroid with masses of order 10-13m⊙ (because gradient pressure is insufficient to support a larger object). we call such field configurations "drops." we explore whether rotating drops could be larger, and find that their mass could increase by a factor ∼10 . this mass is comparable to the mass of miniclusters generated from misalignment axions in the scenario where the axion is born after inflation. we speculate that misalignment axions today are in the form of drops, contributing to dark matter like a distribution of asteroids (and not as a coherent oscillating background field). we consider some observational signatures of the drops, which seem consistent with a galactic halo made of axion dark matter. | rotating drops of axion dark matter |
unravelling the origin of organic compounds that were accreted into asteroids requires better constraining the impact of asteroidal hydrothermal alteration on their isotopic signatures, molecular structures, and spatial distribution. here, we conducted a multi-scale/multi-technique comparative study of the organic matter (om) from two cm chondrites (that originate from the same parent body or from identical parent bodies that accreted the same mixture of precursors) and underwent a different degree of hydrothermal alteration: paris (a weakly altered cm chondrite - cm 2.8) and murchison (a more altered one - cm 2.5). the paris insoluble organic matter (iom) shows a higher aliphatic/aromatic carbon ratio, a higher radical abundance and a lower oxygen content than the murchison iom. analysis of the om in situ shows that two texturally distinct populations of organic compounds are present within the paris matrix: sub-micrometric individual om particles and diffuse om finely distributed within phyllosilicates and amorphous silicates. these results indicate that hydrothermal alteration on the cm parent body induced aromatization and oxidation of the iom, as well as a decrease in radical and nitrogen contents. some of these observations were also reported by studies of variably altered fragment of tagish lake (c2), although the hydrothermal alteration of the om in tagish lake was apparently much more severe. finally, comparison with data available in the literature suggests that the parent bodies of other chondrite petrologic groups could have accreted a mixture of organic precursors different from that accreted by the parent body of cms. | paris vs. murchison: impact of hydrothermal alteration on organic matter in cm chondrites |
with a hyperbolic trajectory around the sun, ‘oumuamua is the first confirmed interstellar object. however, its origin is poorly known. by simulating the orbits of 0.23 million local stars, we find 109 encounters with periastron less than 5 pc. ‘oumuamua’s low peculiar velocity is suggestive of its origin from a young stellar association with similar velocity. in particular, we find that ’oumuamua would have had slow encounters with at least five young stars belonging to the local association, thus suggesting these as plausible sites for formation and ejection. in addition to an extremely elongated shape, the available observational data for ‘oumuamua indicates a red color, suggestive of a potentially organic-rich and activity-free surface. these characteristics seem consistent with formation through energetic collisions between planets and debris objects in the middle part of a young stellar system. we estimate an abundance of at least 6.0 × 10-3 au-3 for such interstellar objects with mean diameter larger than 100 m and find that it is likely that most of them will be ejected into the galactic halo. our bayesian analysis of the available light curves indicates a rotation period of {6.96}-0.39+1.45 {hr}, which is consistent with the estimation by meech et al. and shorter than those in other literature. the codes and results are available on github (https://github.com/phillippro/oumuamua). | ‘oumuamua as a messenger from the local association |
chondrules formed by the melting of dust aggregates in the solar protoplanetary disk and as such provide unique insights into how solid material was transported and mixed within the disk. here, we show that chondrules from enstatite and ordinary chondrites show only small 50ti variations and scatter closely around the 50ti composition of their host chondrites. by contrast, chondrules from carbonaceous chondrites have highly variable 50ti compositions, which, relative to the terrestrial standard, range from the small 50ti deficits measured for enstatite and ordinary chondrite chondrules to the large 50ti excesses known from ca-al-rich inclusions (cais). these 50ti variations can be attributed to the addition of isotopically heterogeneous cai-like material to enstatite and ordinary chondrite-like chondrule precursors. the new ti isotopic data demonstrate that isotopic variations among carbonaceous chondrite chondrules do not require formation over a wide range of orbital distances, but can instead be fully accounted for by the incorporation of isotopically anomalous “nuggets” into chondrule precursors. as such, these data obviate the need for disk-wide transport of chondrules prior to chondrite parent body accretion and are consistent with formation of chondrules from a given chondrite group in localized regions of the disk. finally, the ubiquitous presence of 50ti-enriched material in carbonaceous chondrites and the lack of this material in the non-carbonaceous chondrites support the idea that these two meteorite groups derive from areas of the disk that remained isolated from each other, probably through the formation of jupiter. | mixing and transport of dust in the early solar nebula as inferred from titanium isotope variations among chondrules |
one of the major unresolved problems in cosmochemistry is the origin of chondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2 mm. chondrules are an essential component of primitive meteorites and perhaps of all early solar system materials including the terrestrial planets. numerous hypotheses have been proposed for their origin. many carbonaceous chondrites are composed of about equal amounts of chondrules and fine-grained matrix. recent data confirm that matrix in carbonaceous chondrites has high si/mg and fe/mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. chondrules have the opposite signature, low si/mg and fe/mg ratios. in some carbonaceous chondrites chondrules have low al/ti ratios, matrix has the opposite signature and the bulk is chondritic. it is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. they reflect preaccretionary processes. both chondrules and matrix must have formed from a single, solar-like reservoir. consequences of complementarity for chondrule formation models are discussed. an independent origin and/or random mixing of chondrules and matrix can be excluded. hence, complementarity is a strong constraint for all astrophysical-cosmochemical models of chondrule formation. although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components. | the origin of chondrules: constraints from matrix composition and matrix-chondrule complementarity |
we discuss problems of planetesimal migration in the emerging solar system and exoplanetary systems. protoplanetary disk evolution models and the formation of planets are considered. the formation of the moon and of the asteroid and trans-neptunian belts is studied. we show that earth and venus could acquire more than half of their mass in 5 million years, and their outer layers could accumulate the same material from different parts of the feeding zone of these planets. the migration of small bodies toward the terrestrial planets from various regions of the solar system is simulated numerically. based on these computations, we conclude that the mass of water delivered to the earth by planetesimals, comets, and carbonaceous chondrite asteroids from beyond the ice line could be comparable to the mass of earth's oceans. the processes of dust migration in the solar system and sources of the zodiacal cloud are considered. | migration processes in the solar system and their role in the evolution of the earth and planets |
complexity theory traditionally studies the hardness of solving classical computational problems. in the quantum setting, it is also natural to consider a different notion of complexity, namely the complexity of physically preparing a certain quantum state. we study the relation between two such state complexity classes: statepspace, which contains states that can be generated by space-uniform polynomial-space quantum circuits, and stateqip, which contains states that a polynomial-time quantum verifier can generate by interacting with an all-powerful untrusted quantum prover. the latter class was recently introduced by rosenthal and yuen (itcs 2022), who proved that statepspace $\subseteq$ stateqip. our main result is the reverse inclusion, stateqip $\subseteq$ statepspace, thereby establishing equality of the two classes and providing a natural state-complexity analogue to the celebrated qip = pspace theorem of jain, et al. (j. acm 2011). to prove this, we develop a polynomial-space quantum algorithm for solving a large class of exponentially large "pspace-computable" semidefinite programs (sdps), which also prepares an optimiser encoded in a quantum state. our sdp solver relies on recent block-encoding techniques from quantum algorithms, demonstrating that these techniques are also useful for complexity theory. using similar techniques, we also show that optimal prover strategies for general quantum interactive protocols can be implemented in quantum polynomial space. we prove this by studying an algorithmic version of uhlmann's theorem and establishing an upper bound on the complexity of implementing uhlmann transformations. | stateqip = statepspace |
we study the abstract problem of rounding fractional bipartite $b$-matchings online. the input to the problem is an unknown fractional bipartite $b$-matching, exposed node-by-node on one side. the objective is to maximize the \emph{rounding ratio} of the output matching $\mathcal{m}$, which is the minimum over all fractional $b$-matchings $\mathbf{x}$, and edges $e$, of the ratio $\pr[e\in \mathcal{m}]/x_e$. in offline settings, many dependent rounding schemes achieving a ratio of one and strong negative correlation properties are known (e.g., gandhi et al., j.acm'06 and chekuri et al., focs'10), and have found numerous applications. motivated by online applications, we present \emph{online dependent-rounding schemes} (odrses) for $b$-matching. for the special case of uniform matroids (single offline node), we present a simple online algorithm with a rounding ratio of one. interestingly, we show that our algorithm yields \emph{the same distribution} as its classic offline counterpart, pivotal sampling (srinivasan, focs'01), and so inherits the latter's strong correlation properties. in arbitrary bipartite graphs, an online rounding ratio of one is impossible, and we show that a combination of our uniform matroid odrs with repeated invocations of \emph{offline} contention resolution schemes (crses) yields a rounding ratio of $1-1/e\approx 0.632$. our main technical contribution is an odrs breaking this pervasive bound, yielding rounding ratios of $0.646$ and $0.652$ for $b$-matchings and simple matchings, respectively. we obtain these results by grouping nodes and using crses for negatively-correlated distributions, together with a new method we call \emph{group discount and individual markup}, analyzed using the theory of negative association. we present a number of applications of our odrses to online edge coloring, several stochastic optimization problems, and algorithmic fairness. | online dependent rounding schemes |
primordial black holes (pbhs) are predicted in many models via different formation mechanisms. identifying the origin of pbhs is of the same importance as probing their existence. we propose to probe the asteroid-mass pbhs [𝒪(1017) g ≲ m ≲ 𝒪 (1022) g] with gamma-rays from hawking radiation and the stochastic gravitational waves (gws) from the early universe. we consider four concrete formation mechanisms, including collapse from primordial curvature perturbations, first-order phase transitions, or cosmic strings, and derive the extended pbh mass functions of each mechanism for phenomenological study. the results demonstrate that by combining gamma-rays and gw signals we can probe pbhs up to 𝒪(1019) g and identify their physical origins. | pinning down the primordial black hole formation mechanism with gamma-rays and gravitational waves |
the geology in the wuliji area (including the enger us and quagan qulu areas) is important for understanding the late paleozoic tectonics of the solonker zone. ultramafic/mafic rocks in the enger us area, previously interpreted as an ophiolitic suture, are actually lava flows and sills in a permian turbiditic sequence and a small body of fault breccia containing serpentinite. subduction zone features, such as accretionary complexes, magmatic arc volcanics or lp/hp metamorphism are absent. early permian n-morb mafic rocks and late permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting. in the quagan qulu area, outcrops of the late carboniferous to permian amushan formation are composed of volcano-sedimenary rocks and guyot-like reef limestone along with a late permian volcano-sedimentary unit. a dacite lava in the late permian volcano-sedimentary unit yields a zircon u-pb age of 254 ma. the gabbros in the quagan qulu area are intruded into the amushan formation and caused contact metamorphism of country rocks. sandstones in the upper member of the amushan formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks (i.e. biotite, muscovite and garnet). geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc (cia) and active continental margin (acm) tectonic settings. a late permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the wuliji area. the volcano-sedimentary rocks in the wuliji area experienced a nearly n-s shortening that was probably related to the early mesozoic nearly n-s compression well developed in other areas close to the wuliji area. | late paleozoic tectonics of the solonker zone in the wuliji area, inner mongolia, china: insights from stratigraphic sequence, chronology, and sandstone geochemistry |
asteroids provide fundamental clues to the formation and evolution of planetesimals. collisional models based on the depletion of the primordial main belt of asteroids predict 10-15 craters >400 km should have formed on ceres, the largest object between mars and jupiter, over the last 4.55 gyr. likewise, an extrapolation from the asteroid vesta would require at least 6-7 such basins. however, ceres' surface appears devoid of impact craters >~280 km. here, we show a significant depletion of cerean craters down to 100-150 km in diameter. the overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that ceres experienced protracted widespread resurfacing. | the missing large impact craters on ceres |
this paper presents the robust planning of the hayabusa2-ryugu proximity operation and landing site selection process considering unknown asteroid environment and the spacecraft constraints. the proximity operation scenario is described together with the relationship between the selection process and the in-situ observation. the mission constraints are summarized for the possible asteroid environment, including the rotation state, thermal condition and gravity. | hayabusa2-ryugu proximity operation planning and landing site selection |
resolving the timing of crustal processes and meteorite impact events is central to understanding the formation, evolution and habitability of planetary bodies. however, identifying multi-stage events from complex planetary materials is highly challenging at the length scales of current isotopic techniques. here we show that accurate u-pb isotopic analysis of nanoscale domains of baddeleyite can be achieved by atom probe tomography. within individual crystals of highly shocked baddeleyite from the sudbury impact structure, three discrete nanostructural domains have been isolated yielding average 206pb/238u ages of 2,436+/-94 ma (protolith crystallization) from homogenous-fe domains, 1,852+/-45 ma (impact) from clustered-fe domains and 1,412+/-56 ma (tectonic metamorphism) from planar and subgrain boundary structures. baddeleyite is a common phase in terrestrial, martian, lunar and asteroidal materials, meaning this atomic-scale approach holds great potential in establishing a more accurate chronology of the formation and evolution of planetary crusts. | atomic-scale age resolution of planetary events |
deciphering the spatial and temporal evolution of chondrules allows for a better understanding of how asteroidal seeds formed, migrated, and eventually accreted into parent asteroids. here we report high precision al-mg ages and oxygen three-isotope ratios of fifteen feo-poor chondrules from the least metamorphosed mighei-like (cm) and ornans-like (co) carbonaceous chondrites, asuka 12236 (cm2.9), dominion range 08006 (co3.01), and yamato 81020 (co3.05). this is the first report of al-mg ages of chondrules from the cm chondrite group. all but one of the fifteen chondrules exhibit a restricted range of inferred initial 26al/27al ratios, and all ratios are ≤ 6.0 × 10-6, which is systematically lower than those of the majority of ordinary chondrite (oc) chondrules. these observations indicate that the majority of chondrules in the outer solar system were produced ≥2.2 ma after the formation of ca-al-rich inclusions (cais), which postdates oc chondrule formation in the inner solar system (≤2.2 ma after cai formation). we propose that the discrete chondrule-forming events in different disk regions reflect a time difference in growth and orbital evolution of planetesimals within the first 4 ma of the solar system. one chondrule from asuka 12236 has an age of 1.9 ma after cai formation and is therefore significantly older than the other fourteen chondrules, meaning this chondrule formed contemporaneously with the majority of oc chondrules. this old chondrule also exhibits 16o-depleted oxygen isotope characteristics compared to the other chondrules, suggesting a distinct formation region, probably inside the disk region relative to where the majority of cm and co chondrules formed. our results indicate that this old chondrule has migrated from the inner to the outer part of the protoplanetary disk within ∼1 ma and then accreted into the cm parent asteroid >3 ma after cai formation, although its formation exterior to the accretion region of the cm parent asteroid and subsequent inward migration cannot be ruled out completely. | a temporal shift of chondrule generation from the inner to outer solar system inferred from oxygen isotopes and al-mg chronology of chondrules from primitive cm and co chondrites |
natural hazards include a wide range of high-impact phenomena that affect socioeconomic and natural systems. landslides are a natural hazard whose destructive power has caused a significant number of victims and substantial damage around the world. remote sensing provides many data types and techniques that can be applied to monitor their effects through landslides inventory maps. three unsupervised change detection methods were applied to the advanced spaceborne thermal emission and reflection radiometer (aster)-derived images from an area prone to landslides in the south of mexico. linear regression (lr), chi-square transformation, and change vector analysis were applied to the principal component and the normalized difference vegetation index (ndvi) data to obtain the difference image of change. the thresholding was performed on the change histogram using two approaches: the statistical parameters and the secant method. according to previous works, a slope mask was used to classify the pixels as landslide/no-landslide; a cloud mask was used to eliminate false positives; and finally, those landslides less than 450 m2 (two aster pixels) were discriminated. to assess the landslide detection accuracy, 617 polygons (35,017 pixels) were sampled, classified as real landslide/no-landslide, and defined as ground-truth according to the interpretation of color aerial photo slides to obtain omission/commission errors and kappa coefficient of agreement. the results showed that the lr using ndvi data performs the best results in landslide detection. change detection is a suitable technique that can be applied for the landslides mapping and we think that it can be replicated in other parts of the world with results similar to those obtained in the present work. | evaluation of unsupervised change detection methods applied to landslide inventory mapping using aster imagery |
high-pressure minerals in meteorites are important records of shock events that have affected the surfaces of planets and asteroids. a widespread distribution of impact craters has been observed on the vestan surface. however, very few high-pressure minerals have been discovered in howardite-eucrite-diogenite (hed) meteorites. here we present the first evidence of tissintite, vacancy-rich clinopyroxene, and super-silicic garnet in the eucrite northwest africa (nwa) 8003. combined with coesite and stishovite, the presence of these high-pressure minerals and their chemical compositions reveal that solidification of melt veins in nwa 8003 began at a pressure of >~10 gpa and ceased when the pressure dropped to <~8.5 gpa. the shock temperature in the melt veins exceeded 1900 °c. simulation results show that shock events that create impact craters of ~3 km in diameter (subject to a factor of 2 uncertainty) are associated with sufficiently high pressures to account for the occurrence of the high-pressure minerals observed in nwa 8003. this indicates that hed meteorites containing similar high-pressure minerals should be observed more frequently than previously thought. | high-pressure minerals in eucrite suggest a small source crater on vesta |
a model for fragmentation in bench blasting is developed from dimensional analysis adapted from asteroid collision theory, to which two factors have been added: one describing the discontinuities spacing and orientation and another the delay between successive contiguous shots. the formulae are calibrated by nonlinear fits to 169 bench blasts in different sites and rock types, bench geometries and delay times, for which the blast design data and the size distributions of the muckpile obtained by sieving were available. percentile sizes of the fragments distribution are obtained as the product of a rock mass structural factor, a rock strength-to-explosive energy ratio, a bench shape factor, a scale factor or characteristic size and a function of the in-row delay. the rock structure is described by means of the joints' mean spacing and orientation with respect to the free face. the strength property chosen is the strain energy at rupture that, together with the explosive energy density, forms a combined rock strength/explosive energy factor. the model is applicable from 5 to 100 percentile sizes, with all parameters determined from the fits significant to a 0.05 level. the expected error of the prediction is below 25% at any percentile. these errors are half to one-third of the errors expected with the best prediction models available to date. | a distribution-free description of fragmentation by blasting based on dimensional analysis |
many boulders on (101955) bennu, a near-earth rubble pile asteroid, show signs of in situ disaggregation and exfoliation, indicating that thermal fatigue plays an important role in its landscape evolution. observations of particle ejections from its surface also show it to be an active asteroid, though the driving mechanism of these events is yet to be determined. exfoliation has been shown to mobilize disaggregated particles in terrestrial environments, suggesting that it may be capable of ejecting material from bennu's surface. we investigate the nature of thermal fatigue on the asteroid, and the efficacy of fatigue-driven exfoliation as a mechanism for generating asteroid activity, by performing finite element modeling of stress fields induced in boulders from diurnal cycling. we develop a model to predict the spacing of exfoliation fractures and the number and speed of particles that may be ejected during exfoliation events. we find that crack spacing ranges from ~1 mm to 10 cm and disaggregated particles have ejection speeds up to ~2 m/s. exfoliation events are most likely to occur in the late afternoon. these predictions are consistent with observed ejection events at bennu and indicate that thermal fatigue is a viable mechanism for driving asteroid activity. crack propagation rates and ejection speeds are greatest at perihelion when the diurnal temperature variation is largest, suggesting that events should be more energetic and more frequent when closer to the sun. annual thermal stresses that arise in large boulders may influence the spacing of exfoliation cracks or frequency of ejection events. | thermal fatigue as a driving mechanism for activity on asteroid bennu |
measurements of the low-temperature thermodynamic and physical properties of meteorites provide fundamental data for the study and understanding of asteroids and other small bodies. of particular interest are the cm carbonaceous chondrites, which represent a class of primitive meteorites that record substantial chemical information concerning the evolution of volatile-rich materials in the early solar system. most cm chondrites are petrographic type 2 and contain anhydrous minerals such as olivine and pyroxene, along with abundant hydrous phyllosilicates contained in the meteorite matrix interspersed between the chondrules. using a quantum design physical property measurement system, we have measured the thermal conductivity, heat capacity, and thermal expansion of five cm2 carbonaceous chondrites (murchison, murray, cold bokkeveld, northwest africa 7309, jbilet winselwan) at low temperatures (5-300 k) which span the range of possible surface temperatures in the asteroid belt and outer solar system. the thermal expansion measurements show a substantial and unexpected decrease in cm2 volume as temperature increases from 210 to 240 k followed by a rapid increase in cm2 volume as temperature rises from 240 to 300 k. this transition has not been seen in anhydrous cv or co carbonaceous chondrites. thermal diffusivity and thermal inertia as a function of temperature are calculated from measurements of density, thermal conductivity, and heat capacity. our thermal diffusivity results compare well with previous estimates for similar meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of higher precision and cover a wider range of temperatures. | the surprising thermal properties of cm carbonaceous chondrites |
graham et al. reported a periodically varying quasar and supermassive black hole binary candidate, pg1302-102 (hereafter pg1302), which was discovered in the catalina real-time transient survey (crts). its combined lincoln near-earth asteroid research (linear) and crts optical light curve is well fitted to a sinusoid of an observed period of ≈1884 days and well modeled by the relativistic doppler boosting of the secondary mini-disk. however, the linear+crts light curve from mjd ≈52,700 to mjd ≈56,400 covers only ∼2 cycles of periodic variation, which is a short baseline that can be highly susceptible to normal, stochastic quasar variability. in this letter, we present a reanalysis of pg1302 using the latest light curve from the all-sky automated survey for supernovae (asas-sn), which extends the observational baseline to the present day (mjd ≈58,200), and adopting a maximum likelihood method that searches for a periodic component in addition to stochastic quasar variability. when the asas-sn data are combined with the previous linear+crts data, the evidence for periodicity decreases. for genuine periodicity one would expect that additional data would strengthen the evidence, so the decrease in significance may be an indication that the binary model is disfavored. | did asas-sn kill the supermassive black hole binary candidate pg1302-102? |
context. asteroid (16) psyche is the target of the nasa psyche mission. it is considered one of the few main-belt bodies that could be an exposed proto-planetary metallic core and that would thus be related to iron meteorites. such an association is however challenged by both its near- and mid-infrared spectral properties and the reported estimates of its density.aims: here, we aim to refine the density of (16) psyche to set further constraints on its bulk composition and determine its potential meteoritic analog.methods: we observed (16) psyche with eso vlt/sphere/zimpol as part of our large program (id 199.c-0074). we used the high angular resolution of these observations to refine psyche's three-dimensional (3d) shape model and subsequently its density when combined with the most recent mass estimates. in addition, we searched for potential companions around the asteroid.results: we derived a bulk density of 3.99 ± 0.26 g cm-3 for psyche. while such density is incompatible at the 3-sigma level with any iron meteorites (∼7.8 g cm-3), it appears fully consistent with that of stony-iron meteorites such as mesosiderites (density ∼4.25 g cm-3). in addition, we found no satellite in our images and set an upper limit on the diameter of any non-detected satellite of 1460 ± 200 m at 150 km from psyche (0.2% × rhill, the hill radius) and 800 ± 200 m at 2000 km (3% × rhill).conclusions: considering that the visible and near-infrared spectral properties of mesosiderites are similar to those of psyche, there is merit to a long-published initial hypothesis that psyche could be a plausible candidate parent body for mesosiderites. based on observations made with 1) eso telescopes at the la silla paranal observatory under programs 086.c-0785 (pi carry) and 199.c-0074 (pi vernazza); and 2) the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california and the national aeronautics and space administration. the observatory was made possible by the generous financial support of the w. m. keck foundation.tables a1 and a2 and reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/619/l3 | (16) psyche: a mesosiderite-like asteroid? |
the restricted planar elliptic three body problem (rpetbp) describes the motion of a massless particle (a comet or an asteroid) under the gravitational field of two massive bodies (the primaries, say the sun and jupiter) revolving around their center of mass on elliptic orbits with some positive eccentricity. the aim of this paper is to show the existence of orbits whose angular momentum performs arbitrary excursions in a large region. in particular, there exist diffusive orbits, that is, with a large variation of angular momentum. the leading idea of the proof consists in analyzing parabolic motions of the comet. by a well-known result of mcgehee, the union of future (resp. past) parabolic orbits is an analytic manifold {p^+} (resp. {p^-}). in a properly chosen coordinate system these manifolds are stable (resp. unstable) manifolds of a manifold at infinity p_∞, which we call the manifold at parabolic infinity. on p_∞ it is possible to define two scattering maps, which contain the map structure of the homoclinic trajectories to it, i.e. orbits parabolic both in the future and the past. since the inner dynamics inside p_∞ is trivial, two different scattering maps are used. the combination of these two scattering maps permits the design of the desired diffusive pseudo-orbits. using shadowing techniques and these pseudo orbits we show the existence of true trajectories of the rpetbp whose angular momentum varies in any predetermined fashion. | global instability in the restricted planar elliptic three body problem |
observations of debris disks offer a window into the physical and dynamical properties of planetesimals in extrasolar systems through the size distribution of dust grains. in particular, the millimeter spectral index of thermal dust emission encodes information on the grain size distribution. we have made new vla observations of a sample of seven nearby debris disks at 9 mm, with 3\prime\prime resolution and ∼5 μjy beam-1rms. we combine these with archival atca observations of eight additional debris disks observed at 7 mm, together with up-to-date observations of all disks at (sub)millimeter wavelengths from the literature, to place tight constraints on the millimeter spectral indices and thus grain size distributions. the analysis gives a weighted mean for the slope of the power-law grain size distribution, n(a)\propto {a}-q, of < q> =3.36+/- 0.02, with a possible trend of decreasing q for later spectral type stars. we compare our results to a range of theoretical models of collisional cascades, from the standard self-similar, steady-state size distribution (q = 3.5) to solutions that incorporate more realistic physics such as alternative velocity distributions and material strengths, the possibility of a cutoff at small dust sizes from radiation pressure, and results from detailed dynamical calculations of specific disks. such effects can lead to size distributions consistent with the data, and plausibly the observed scatter in spectral indices. for the au mic system, the vla observations show clear evidence of a highly variable stellar emission component; this stellar activity obviates the need to invoke the presence of an asteroid belt to explain the previously reported compact millimeter source in this system. | constraints on planetesimal collision models in debris disks |
this study exploited the multispectral advanced spaceborne thermal emission and reflection radiometer (aster) and landsat 8 operational land imager (oli) data in order to map lithological units and structural map in the south high atlas of marrakech. the method of analysis was used by principal component analysis (pca), band ratios (br), minimum noise fraction (mnf) transformation. we performed a support vector machine (svm) classification method to allow the joint use of geomorphic features, textures and multispectral data of the advanced space-borne thermal emission and reflection radiometer (aster) satellite. svm based on ground truth in addition to the results of pca and br show an excellent correlation with the existing geological map of the study area. consequently, the methodology proposed demonstrates a high potential of aster and landsat 8 oli data in lithological units discrimination. the application of the svm methods on aster and landsat satellite data show that these can be used as a powerful tool to explore and improve lithological mapping in mountainous semi-arid, the overall classification accuracy of landsat8 oli data is 97.28% and the kappa coefficient is 0.97. the overall classification accuracy of aster using nine bands (vnir-swir) is 74.88% and the kappa coefficient is 0.71. | lithological mapping using landsat 8 oli and aster multispectral data in imini-ounilla district south high atlas of marrakech |
the isotopic composition of water in earth's oceans is challenging to recreate using a plausible mixture of known extraterrestrial sources such as asteroids—an additional isotopically light reservoir is required. the sun's solar wind could provide an answer to balance earth's water budget. we used atom probe tomography to directly observe an average ~1 mol% enrichment in water and hydroxyls in the solar-wind-irradiated rim of an olivine grain from the s-type asteroid itokawa. we also experimentally confirm that h+ irradiation of silicate mineral surfaces produces water molecules. these results suggest that the itokawa regolith could contain ~20 l m−3 of solar-wind-derived water and that such water reservoirs are probably ubiquitous on airless worlds throughout our galaxy. the production of this isotopically light water reservoir by solar wind implantation into fine-grained silicates may have been a particularly important process in the early solar system, potentially providing a means to recreate earth's current water isotope ratios. | solar wind contributions to earth's oceans |
collected by mars rovers and orbiters data allowed to reconstruct the possible stages in the development on the planet mars. it is believed that the first geological era of the planet - fillotsian - started 4.5 billion years ago. it lasted for 500-700 million years. at that time, mars was a wet planet. today mars is a desert. however, when about 4 billion years ago there began an eruption of numerous volcanoes. the planet slowly cooled, volcanic activity has decreased - and ejection of gases into the atmosphere has decreased. evidence of the impact of a large asteroid on mars is the hellas planitia, which is located near the southern polar region. thanks to the theory, methods of calculation and programs that are designed for tasks of penetration projectiles - managed to reconstruct the shape of hellas and determine the parameters of asteroids. upon impact, could have formed a powerful shock wave that has passed to the opposite hemisphere, and was focused symmetrically to the crater of hellas. as a result by the shock wave was formed the highest volcano in solar system - olympus | processes on the "young" mars: possible developments of events |
availability of multispectral remote sensing data cheaply and its higher spectral resolution compared to remote sensing data with higher spatial resolution has proved valuable for geological mapping exploitation and mineral mapping. this has benefited applications such as landslide quantification, fault pattern mapping, rock and lineament mapping especially with advanced remote sensing techniques and the use of short wave infrared bands. while landsat and aster data have been used to map geology in arid areas and band ratios suiting the application established, mapping in geology in highland regions has been challenging due to vegetation land cover. the aim of this study was to map geology and investigate bands suited for geological applications in a study area containing semi arid and highland characteristics. therefore, landsat 7 (etm+, 2000) and landsat 8 (oli, 2014) were compared in determining suitable bands suited for geological mapping in the study area. the methodology consist performing principal component and factor loading analysis, ihs transformation and decorrelation stretch of the fcc with the highest contrast, band rationing and examining fcc with highest contrast, and then performing knowledge base classification. pca factor loading analysis with emphasis on geological information showed band combination (5, 7, 3) for landsat 7 and (6, 7, 4) for landsat 8 had the highest contrast and more contrast was enhanced by performing decorrelation stretch. band ratio combination (3/2, 5/1, 7/3) for landsat 7 and (4/3, 6/2, 7/4) for landsat 8 had more contrast on geologic information and formed the input data in knowledge base classification. lineament visualisazion was achieved by performing ihs transformation of fcc with highest contrast and its saturation band combined as follows: landsat 7 (ic1, pc2, saturation band), landsat 8 (ic1, pc4, saturation band). the results were compared against existing geology maps and were superior and could be used to update the existing maps. | a comparison of landsat 8 (oli) and landsat 7 (etm+) in mapping geology and visualising lineaments: a case study of central region kenya |
we measured 3-μm reflectance spectra of 21 meteorites that represent all carbonaceous chondrite types available in terrestrial meteorite collections. the measurements were conducted at the laboratory for spectroscopy under planetary environmental conditions (labspec) at the johns hopkins university applied physics laboratory (jhu apl) under vacuum and thermally-desiccated conditions (asteroid-like conditions). this is the most comprehensive 3-μm dataset of carbonaceous chondrites ever acquired in environments similar to the ones experienced by asteroids. the 3-μm reflectance spectra are extremely important for direct comparisons with and appropriate interpretations of reflectance data from ground-based telescopic and spacecraft observations of asteroids. we found good agreement between 3-μm spectral characteristics of carbonaceous chondrites and carbonaceous chondrite classifications. the 3-μm band is diverse, indicative of varying composition, thus suggesting that these carbonaceous chondrites experienced distinct parent body aqueous alteration and metamorphism environments. the spectra of ci chondrites, from which significant amount of water adsorbed under ambient conditions was removed, are consistent with mg-serpentine and clay minerals. the high abundances of organics in ci chondrites is also associated with the mineralogy of these chondrites, oxyhydroxides- and complex clay minerals-rich. cm chondrites, which are cronstedtite-rich, have shallower 3-μm band than ci chondrites, suggesting they experienced less aqueous alteration. cr chondrites showed moderate aqueous alteration relative to ci and cm chondrites. cv chondrites, except for efremovka, have a very shallow 3-μm band, consistent with their lower phyllosilicate proportions. co chondrites, like most cvs, have a very shallow 3-μm band that suggest they experienced minor aqueous alteration. the 3-μm band in ch/cbb is deep and broad centered 3.11 μm, possibly due to the high abundance of feni metal and presence of heavily hydrated clasts in these chondrites. the 3-μm spectra of essebi (c2-ung) and eet 83226 are more consistent with cm chondrites' spectra. the 3-μm spectra of tagish lake (c2-ung), on the other hand, are consistent with ci chondrites. none of these spectral details could have been resolved without removing the adsorbed water before acquiring spectra. | 3-μm reflectance spectroscopy of carbonaceous chondrites under asteroid-like conditions |
two extremely red main-belt asteroids, 203 pompeja and 269 justitia, were identified from combined visible and near-infrared spectroscopic observations collected at the infra-red telescope facility (irtf) and seoul national university astronomical observatory (sao). these two asteroids have a redder spectral slope than any other d-type body, which are the reddest objects in the asteroid belt, and similar to rr and ir-class objects found in the outer solar system among trans-neptunian objects (tnos) and centaurs. spectroscopic results suggest the presence of complex organic materials on the surface layer of these asteroids, implying that they could have formed in the vicinity of neptune and been transplanted to the main belt region during a phase of planetary migration. 203 pompeja is the only very red asteroid known so far among the ~250 bodies with diameter larger than 110 km (i.e., presumably structurally intact) found in the asteroid belt. these discoveries provide more evidence that the main asteroid belt hosts a population of bodies that were formed in the outskirts of the solar system. | discovery of two tno-like bodies in the asteroid belt |
cubesats offer a flexible and low-cost option to increase the scientific and technological return of small-body exploration missions. esa's hera mission, the european component of the asteroid impact and deflection assessment (aida) international collaboration, plans on deploying two cubesats in the proximity of binary system 65803 didymos, after arrival in 2027. in this work, we discuss the feasibility and preliminary mission profile of hera's milani cubesat. the cubesat mission is designed to achieve both scientific and technological objectives. we identify the design challenges and discuss design criteria to find suitable solutions in terms of mission analysis, operational trajectories, and guidance, navigation, & control (gnc) design. we present initial trajectories and gnc baseline, as a result of trade-off analyses. we assess the feasibility of the milani cubesat mission and provide a preliminary solution to cover the operational mission profile of milani in the close-proximity of didymos system. | preliminary mission profile of hera's milani cubesat |
a simple phenomenological fit for the power spectrum of scalar (curvature) perturbations during inflation is proposed to analytically describe slow roll of inflaton and formation of primordial black holes (pbh) in the early universe, in the framework of single-field models. the fit is given by a sum of the power spectrum of slow-roll inflation, needed for a viable description of the cosmic microwave background (cmb) radiation in agreement with planck/bicep/keck measurements, and the log-normal (gaussian) fit for the power spectrum enhancement (peak) needed for efficient pbh production, in the leading (model-independent) approximation. the t-type α-attractor models are used to get the simple cmb power spectrum depending upon the e-folds as the running variable. the location and height of the peak are chosen to yield the pbh masses in the asteroid-size window allowed for the whole (current) dark matter. we find the restrictions on the peak width. | fitting power spectrum of scalar perturbations for primordial black hole production during inflation |
volatile compositions of asteroids provide information on the solar system history and the origins of earth's volatiles. visible to near-infrared observations at wavelengths of <2.5 µm have suggested a genetic link between outer main belt asteroids located at 2.5-4 au and carbonaceous chondrite meteorites (ccs) that show isotopic similarities to volatile elements on earth. however, recent longer wavelength data for large outer main belt asteroids show 3.1 μm absorption features of ammoniated phyllosilicates that are absent in ccs and cannot easily form from materials stable at those present distances. here, by combining data collected by the akari space telescope and hydrological, geochemical, and spectral models of water-rock reactions, we show that the surface materials of asteroids having 3.1 μm absorption features and ccs can originate from different regions of a single, water-rock-differentiated parent body. ammoniated phyllosilicates form within the water-rich mantles of the differentiated bodies containing nh3 and co2 under high water-rock ratios (>4) and low temperatures (<70°c). ccs can originate from the rock-dominated cores, that are likely to be preferentially sampled as meteorites by disruption and transport processes. our results suggest that multiple large main belt asteroids formed beyond the nh3 and co2 snow lines (currently >10 au) and could be transported to their current locations. earth's high hydrogen to carbon ratio may be explained by accretion of these water-rich progenitors. | distant formation and differentiation of outer main belt asteroids and carbonaceous chondrite parent bodies |
the cm carbonaceous chondrite meteorites experienced aqueous alteration in the early solar system. they range from mildly altered type 2 to almost completely hydrated type 1 chondrites, and offer a record of geochemical conditions on water-rich asteroids. we show that cm1 chondrites contain abundant (84-91 vol%) phyllosilicate, plus olivine (4-8 vol%), magnetite (2-3 vol%), fe-sulfide (<5 vol%), and calcite (<2 vol%). the cm1/2 chondrites contain phyllosilicate (71-88 vol%), olivine (4-20 vol%), enstatite (2-6 vol%), magnetite (2-3 vol%), fe-sulfides (1-2 vol%), and calcite ( 1 vol%). as aqueous alteration progressed, the abundance of mg-serpentine and magnetite in the cm chondrites increased. in contrast, calcite abundances in the cm1/2 and cm1 chondrites are often depleted relative to the cm2s. the modal data support the model, whereby metal and fe-rich matrix were the first components to be altered on the cm parent body(ies), before further hydration attacked the coarser mg-rich silicates found in chondrules and fragments. based on the absence of tochilinite, we suggest that cm1 chondrites experienced increased alteration due to elevated temperatures (>120 °c), although higher water/rock ratios may also have played a role. the modal data provide constraints for interpreting the composition of asteroids and the mineralogy of samples returned from these bodies. we predict that "cm1-like" asteroids, as has been proposed for bennu—target for the osiris-rex mission—will have a high abundance of mg-rich phyllosilicates and fe-oxides, but be depleted in calcite. | type 1 aqueous alteration in cm carbonaceous chondrites: implications for the evolution of water-rich asteroids |
most navigation solutions which make use of lidar for proximity operations with respect to non-cooperative objects rely on the iterative closest point, or icp, algorithm. for correct convergence, icp requires a good initial guess as to the 6 degree-of-freedom relative pose of a client object. some solutions require manual pose initialization; and template matching - refined by icp - was recently demonstrated as an automated solution for initialization. additionally, some have used the output of one icp iteration as the initial guess for the next, which is inherently dangerous (since bad icp poses are propagated forward in time by the filter, by icp, or by both; and because it introduces measurement errors that are correlated with the a priori state errors). we demonstrate the use of a method borrowed from personal robotics, our-cvfh (for oriented, unique, and repeatable clustered viewpoint feature histograms), for rendezvous with a tumbling object in low earth orbit as well as an asteroid in a heliocentric orbit. our strategy requires no initial pose estimate, and refines our-cvfh results with icp; we demonstrate its utility as part of a full navigation solution with a dual-state inertial extended kalman filter. | lidar-based relative navigation with respect to non-cooperative objects |
tir, the thermal infrared imager on hayabusa2, acquired high-resolution thermal images of the asteroid 162173 ryugu for one asteroid rotation period on august 1, 2018 to investigate the thermophysical properties of the asteroid. the surface temperatures of ryugu suggest that the surface has a low thermal inertia, indicating the presence of porous materials. thermophysical models that neglect or oversimplify surface roughness cannot reproduce the flat diurnal temperature profiles observed during daytime. we performed numerical simulations of a thermophysical model, including the effects of roughness on the diurnal brightness temperature, the predictions of which successfully reproduced the observed diurnal variation of temperature. the global thermal inertia was obtained with a standard deviation of 225 ± 45 j m-2 s-0.5 k-1, which is relatively low but still within the range of the value estimated in our previous study (okada et al., nature 579, 518-522, 2020), confirming that the boulders on ryugu are more porous in nature than typical carbonaceous chondrites. the global surface roughness (the ratio of the variance of the height relative to a local horizontal surface length) was determined as 0.41 ± 0.08, corresponding to a rms surface slope of 47 ± 5°. we identified a slightly lower roughness distributed along the equatorial ridge, implying a mass movement of boulders from the equatorial ridge to the mid-latitudes. | thermophysical properties of the surface of asteroid 162173 ryugu: infrared observations and thermal inertia mapping |
the asteroid 101955 bennu is the target asteroid of the ongoing asteroid sample return mission osiris-rex from nasa. in the mission, the spacecraft is scheduled to rendezvous with bennu in august 2018. investigating the dynamics of surface motion can offer guidance for further hopping landers or even sample return missions regarding bennu or similarly irregular-shaped asteroids. this paper presents the free motion of sample particles on and above the surface of bennu. the concepts and equations that govern the motion of a particle on and above the surface of an asteroid are briefly introduced. trajectories of a number of particles' free motion are numerically calculated by considering four scenarios with different restitution coefficients. initial positions of those particles are all randomly given on the surface of bennu and their initial velocities are set as zero. the distribution of final locations of those sample particles is summarized and analyzed. both the gravitational potential and its effective potential on the surface of bennu are calculated to give a possible reason for the distributing characteristics. | the motion of surface particles for the asteroid 101955 bennu |
the presence of h2o within differentiated terrestrial bodies in the inner solar system is well established; however, the source(s) of this h2o and the time of its arrival to the inner solar system is an area of active study. at present, the prevailing model for the origin of inner solar system h2o calls upon carbonaceous chondrites as the source. this is largely based on reported observations that h- and n-isotopic compositions of differentiated planetary bodies are largely the same and within a range of values that overlaps with carbonaceous chondrites as opposed to comets or the sun. in this contribution, we evaluate the efficacy of this model and other models for the origin of inner solar system h2o by considering geochronological constraints on early solar system history, constraints on primary building blocks of differentiated bodies based on nucleosynthetic isotope anomalies, and constraints from dynamical models of planet formation. in addition to h- and n-isotopic data, these constraints indicate that an interstellar source of h2o was present in the inner solar system within the first 4 ma of cai formation. furthermore, the most h2o-rich carbonaceous chondrites are unlikely to be the source of h2o for the earliest-formed differentiated bodies based on their minimally overlapping primary accretion windows and the separation of their respective isotopic reservoirs by jupiter in the timespan of about 1-4 ma after cai formation. the presence of deuterium-rich, non-nebular h2o sources in the inner solar system prior to the formation of carbonaceous chondrites or comets implies early contributions of interstellar ices to both the inner and outer solar system portions of the protoplanetary disk. evidence for this interstellar ice component in the inner solar system may be preserved in ll chondrites and in the mantle of mars. in contrast to the earlier-formed bodies within the inner solar system, earth's protracted accretion window may have facilitated incorporation of h2o in its interior from both the inner and outer solar system, helping the earth to become a habitable planet. | origin and abundances of h2o in the terrestrial planets, moon, and asteroids |
carbonaceous chondrites (cc) contain a diversity of organic compounds. no definitive evidence for a genetic relationship between these complex organic molecules and the simple organic molecules detected in the interstellar medium (ism) has yet been reported. one of the many difficulties arises from the transformations of organic compounds during accretion and hydrothermal alteration on asteroids. here, we report results of hydrothermal alteration experiments conducted on a common constituent of interstellar ice analogs, hexamethylenetetramine (hmt - c6h12n4). we submitted hmt to asteroidal hydrothermal conditions at 150 °c, for various durations (up to 31 days) and under alkaline ph. organic products were characterized by gas chromatography mass spectrometry, infrared spectroscopy and synchrotron-based x-ray absorption near edge structure spectroscopy. results show that, within a few days, hmt has evolved into (1) a very diverse suite of soluble compounds dominated by n-bearing aromatic compounds (> 150 species after 31 days), including for instance formamide, pyridine, pyrrole and their polymers (2) an aromatic and n-rich insoluble material that forms after only 7 days of experiment and then remains stable through time. the reaction pathways leading to the soluble compounds likely include hmt dissociation, formose and maillard-type reactions, e.g. reactions of sugar derivatives with amines. the present study demonstrates that, if interstellar organic compounds such as hmt had been accreted by chondrite parent bodies, they would have undergone chemical transformations during hydrothermal alteration, potentially leading to the formation of high molecular weight insoluble organic molecules. some of the diversity of soluble and insoluble organic compounds found in cc may thus result from asteroidal hydrothermal alteration. | evolution of interstellar organic compounds under asteroidal hydrothermal conditions |
chondrules, mm-sized igneous-textured spherules, are the dominant bulk silicate constituent of chondritic meteorites and originate from highly energetic, local processes during the first million years after the birth of the sun. so far, an astrophysically consistent chondrule formation scenario explaining major chemical, isotopic and textural features, in particular fe,ni metal abundances, bulk fe/mg ratios and intra-chondrite chemical and isotopic diversity, remains elusive. here, we examine the prospect of forming chondrules from impact splashes among planetesimals heated by radioactive decay of short-lived radionuclides using thermomechanical models of their interior evolution. we show that intensely melted planetesimals with interior magma oceans became rapidly chemically equilibrated and physically differentiated. therefore, collisional interactions among such bodies would have resulted in chondrule-like but basaltic spherules, which are not observed in the meteoritic record. this inconsistency with the expected dynamical interactions hints at an incomplete understanding of the planetary growth regime during the lifetime of the solar protoplanetary disk. to resolve this conundrum, we examine how the observed chemical and isotopic features of chondrules constrain the dynamical environment of accreting chondrite parent bodies by interpreting the meteoritic record as an impact-generated proxy of early solar system planetesimals that underwent repeated collision and reaccretion cycles. using a coupled evolution-collision model we demonstrate that the vast majority of collisional debris feeding the asteroid main belt must be derived from planetesimals which were partially molten at maximum. therefore, the precursors of chondrite parent bodies either formed primarily small, from sub-canonical aluminum-26 reservoirs, or collisional destruction mechanisms were efficient enough to shatter planetesimals before they reached the magma ocean phase. finally, we outline the window in parameter space for which chondrule formation from planetesimal collisions can be reconciled with the meteoritic record and how our results can be used to further constrain early solar system dynamics. | impact splash chondrule formation during planetesimal recycling |
we fit 54,296 sparsely sampled asteroid light curves in the palomar transient factory survey to a combined rotation plus phase-function model. each light curve consists of 20 or more observations acquired in a single opposition. using 805 asteroids in our sample that have reference periods in the literature, we find that the reliability of our fitted periods is a complicated function of the period, amplitude, apparent magnitude, and other light-curve attributes. using the 805-asteroid ground-truth sample, we train an automated classifier to estimate (along with manual inspection) the validity of the remaining ∼53,000 fitted periods. by this method we find that 9033 of our light curves (of ∼8300 unique asteroids) have “reliable” periods. subsequent consideration of asteroids with multiple light-curve fits indicates a 4% contamination in these “reliable” periods. for 3902 light curves with sufficient phase-angle coverage and either a reliable fit period or low amplitude, we examine the distribution of several phase-function parameters, none of which are bimodal though all correlate with the bond albedo and with visible-band colors. comparing the theoretical maximal spin rate of a fluid body with our amplitude versus spin-rate distribution suggests that, if held together only by self-gravity, most asteroids are in general less dense than ∼2 g cm-3, while c types have a lower limit of between 1 and 2 g cm-3. these results are in agreement with previous density estimates. for 5-20 km diameters, s types rotate faster and have lower amplitudes than c types. if both populations share the same angular momentum, this may indicate the two types’ differing ability to deform under rotational stress. lastly, we compare our absolute magnitudes (and apparent-magnitude residuals) to those of the minor planet center’s nominal (g = 0.15, rotation-neglecting) model; our phase-function plus fourier-series fitting reduces asteroid photometric rms scatter by a factor of ∼3. | asteroid light curves from the palomar transient factory survey: rotation periods and phase functions from sparse photometry |
we present recent improvements of the modeling of the disruption of strength dominated bodies using the smooth particle hydrodynamics (sph) technique. the improvements include an updated strength model and a friction model, which are successfully tested by a comparison with laboratory experiments. in the modeling of catastrophic disruptions of asteroids, a comparison between old and new strength models shows no significant deviation in the case of targets which are initially non-porous, fully intact and have a homogeneous structure (such as the targets used in the study by benz and asphaug, 1999). however, for many cases (e.g. initially partly or fully damaged targets and rubble-pile structures) we find that it is crucial that friction is taken into account and the material has a pressure dependent shear strength. our investigations of the catastrophic disruption threshold <mml:msubsup> q d * as a function of target properties and target sizes up to a few 100 km show that a fully damaged target modeled without friction has a <mml:msubsup> q d * which is significantly (5-10 times) smaller than in the case where friction is included. when the effect of the energy dissipation due to compaction (pore crushing) is taken into account as well, the targets become even stronger (<mml:msubsup> q d * is increased by a factor of 2-3). on the other hand, cohesion is found to have an negligible effect at large scales and is only important at scales ≲ 1 km. our results show the relative effects of strength, friction and porosity on the outcome of collisions among small (≲ 1000 km) bodies. these results will be used in a future study to improve existing scaling laws for the outcome of collisions (e.g. leinhardt and stewart, 2012). | sph calculations of asteroid disruptions: the role of pressure dependent failure models |
we compare primitive near-earth asteroid spectral properties to the irradiated carbonaceous chondrite samples of lantz et al. (2017) in order to assess how space weathering processes might influence taxonomic classification. using the same eigenvectors from the asteroid taxonomy by demeo et al. (2009), we calculate the principal components for fresh and irradiated meteorites and find that change in spectral slope (blueing or reddening) causes a corresponding shift in the two first principal components along the same line that the c- and x-complexes track. using a sample of b-, c-, x-, and d-type neos with visible and near-infrared spectral data, we further investigated the correlation between prinicipal components and the spectral curvature for the primitive asteroids. we find that space weathering effects are not just slope and albedo, but also include spectral curvature. we show how, through space weathering, surfaces having an original "c-type" reflectance can thus turn into a redder p-type or a bluer b-type, and that space weathering can also decrease (and disguise) the d-type population. finally we take a look at the case of osiris-rex target (101955) bennu and propose an explanation for the blue and possibly red spectra that were previously observed on different locations of its surface: parts of bennu's surface could have become blue due to space weathering, while fresher areas are redder. no clear prediction can be made on hayabusa-2 target (162173) ryugu. | space weathering trends on carbonaceous asteroids: a possible explanation for bennu's blue slope? |
we report the discovery of a stripped giant + lower giant algol-type binary, 2m04123153+6738486 (2m0412), identified during a search for non-interacting compact object - star binaries. 2m0412 is an evolved (teff, giant ≃ 4000 k), luminous (lgiant ≃ 150 l⊙) red giant in a circular p = 81.2 d binary. 2m0412 is a known variable star previously classified as a semiregular variable. the cross-correlation functions of follow-up keck/hires and lbt/potsdam echelle polarimetric and spectroscopic instrument (pepsi) spectra show an radial velocity variable second component with implied mass ratio q = mgiant/mcomp ≃ 0.20 ± 0.01. the all-sky automated survey for supernovae (asas-sn), asteroid terrestrial-impact last alert system (atlas), transiting exoplanet survey telescope ( tess), and zwicky transient facility (ztf) light curves show that the giant is a roche lobe filling ellipsoidal variable with an inclination of 49.4 ± 0.3°, and a giant mass of mgiant = 0.38 ± 0.01 m⊙ for a distance of ≃ 3.7 kpc. the mass of the giant indicates that its envelope has been partially stripped. the giant companion on the lower red giant branch has a mass of mcomp = 1.91 ± 0.03 m⊙ with teff, comp ≃ 5000 k, lcomp ≃ 60 l⊙, and rcomp ≃ 11 r⊙. the lower giant contributes ${\sim }35{{\ \rm per\ cent}}$ of the flux in the v band. we also identify an orbital phase dependent, broad $\rm h\,\alpha$ emission line which could indicate ongoing accretion from the stripped red giant on to the companion. | the 'giraffe': discovery of a stripped red giant in an interacting binary with an 2 m⊙ lower giant |
the new horizons spacecraft fly-through of the pluto system in july 2015 will provide humanity's first data for the crater populations on pluto and its binary companion, charon. in principle, these surfaces could be dated in an absolute sense, using the observed surface crater density (# craters/km2 larger than some threshold crater diameter d). success, however, requires an understanding of both the cratering physics and absolute impactor flux. the canada-france ecliptic plane survey (cfeps) l7 synthetic model of classical and resonant kuiper belt populations (petit, j.m. et al. [2011]. astron. j. 142, 131-155; gladman, b. et al. [2012]. astron. j. 144, 23-47) and the scattering object model of kaib et al. (kaib, n., roškar, r., quinn, t. [2011]. icarus 215, 491-507) calibrated by shankman et al. (shankman, c. et al. [2013]. astrophys. j. 764, l2-l5) provide such impact fluxes and thus current primary cratering rates for each dynamical sub-population. we find that four sub-populations (the q < 42au hot and stirred main classicals, the classical outers, and the plutinos) dominate pluto's impact flux, each providing ≈ 15- 25 % of the total rate. due to the uncertainty in how the well-characterized size distribution for kuiper belt objects (with impactor diameter d > 100km) connects to smaller projectiles, we compute cratering rates using five model impactor size distributions: a single power-law, a power-law with a knee, a power-law with a divot, as well as the "wavy" size distributions described in minton et al. (minton, d.a. et al. [2012]. asteroids comets meteors conf. 1667, 6348) and schlichting et al. (schlichting, h.e., fuentes, c.i., trilling, d.e. [2013]. astron. j. 146, 36-42). we find that there is only a small chance that pluto has been hit in the past 4 gyr by even one impactor with a diameter larger than the known break in the projectile size distribution (d ≈ 100km) which would create a basin on pluto (d ⩾ 400km in diameter). we show that due to present uncertainties in the impactor size distribution between d = 1- 100km , computing absolute ages for the surface of pluto is entirely dependent on the extrapolation to small sizes and thus fraught with uncertainty. we show, however, what the ages would be for several cases and illustrate the relative importance of each kuiper belt sub-population to the cratering rate, both now and integrated into the past. in addition, we compute the largest "fresh" crater expected to have formed in 1 gyr on the surface of pluto and in 3 gyr on charon (to 95% confidence) and use the "wavy" size distribution models to predict whether these largest "fresh" craters will provide surfaces for which portions of the crater production function can be measured should most of the target's surface appear saturated. the fly-through results coupled with telescopic surveys that bridge current uncertainties in the d = 10- 100km regime should eventually result in the population estimate uncertainties for the kuiper belt sub-populations, and thus the impact fluxes onto pluto and charon, dipping to < 30 % . we also compute "disruption timescales" (to a factor of three accuracy) for pluto's smaller satellites: styx, nix, kerberos, and hydra. we find that none of the four satellites have likely undergone a catastrophic disruption and reassembly event in the past ≈ 4gyr . in addition, we find that for a knee size distribution with αfaint ⩽ 0.4 (down to sub-km diameters), satellites of all sizes are able to survive catastrophic disruption over the past 4 gyr. | impact and cratering rates onto pluto |
the thermal infrared imager tir onboard hayabusa2 has been developed to investigate thermo-physical properties of c-type, near-earth asteroid 162173 ryugu. tir is one of the remote science instruments on hayabusa2 designed to understand the nature of a volatile-rich solar system small body, but it also has significant mission objectives to provide information on surface physical properties and conditions for sampling site selection as well as the assessment of safe landing operations. tir is based on a two-dimensional uncooled micro-bolometer array inherited from the longwave infrared camera lir on akatsuki (fukuhara et al., 2011). tir takes images of thermal infrared emission in 8 to 12 μm with a field of view of 16 × 12° and a spatial resolution of 0.05° per pixel. tir covers the temperature range from 150 to 460 k, including the well calibrated range from 230 to 420 k. temperature accuracy is within 2 k or better for summed images, and the relative accuracy or noise equivalent temperature difference (netd) at each of pixels is 0.4 k or lower for the well-calibrated temperature range. tir takes a couple of images with shutter open and closed, the corresponding dark frame, and provides a true thermal image by dark frame subtraction. data processing involves summation of multiple images, image processing including the starpixel compression (hihara et al., 2014), and transfer to the data recorder in the spacecraft digital electronics (de). we report the scientific and mission objectives of tir, the requirements and constraints for the instrument specifications, the designed instrumentation and the pre-flight and in-flight performances of tir, as well as its observation plan during the hayabusa2 mission. | thermal infrared imaging experiments of c-type asteroid 162173 ryugu on hayabusa2 |
we performed pulsed-laser irradiation of a chip of the cm2 murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. optical reflectance spectroscopy and transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. the spectrum of the deposit on the glass slide shows a red slope between 0.35-2.5 μm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. we identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. extracted focused ion beam (fib) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (stem). microstructural and chemical analyses based on the stem observations show widespread melting and the formation of fe-bearing nanoparticles (including prevalent fe-ni-sulfides) across the surface of the meteorite. the section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. these analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic space weathered samples. we discuss the implications these results have for the space weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies. | spectral and chemical effects of simulated space weathering of the murchison cm2 carbonaceous chondrite |
discovery of the first interstellar asteroid (isa)—1i/2017 ’oumuamua—raised natural questions regarding its origin, some related to its lack of cometary activity, suggesting refractory composition. here we explore the possibility that ’oumuamua-like isas are produced in tidal disruption events (tdes) of refractory planetoids (asteroids, terrestrial planets, etc.) by white dwarfs (wds). this idea is supported by spectroscopic observations of metal-polluted wds, indicating the predominantly volatile-poor composition of the accreted material. we show that such tdes sourced by realistic planetary systems (including a population of ≳103 km planetoids and massive perturbers—neptune-to-saturn mass planets) can eject up to 30% of planetary mass involved in tdes to interstellar space. collisional fragmentation, caused by vertical collapse of the disrupted planetoid’s debris inside the wd roche sphere, channels most of its mass into 0.1-1 km fragments, similar to ’oumuamua. such a size spectrum of isas (very different from the top-heavy distributions expected in other scenarios) implies that planetary tdes can account for a significant fraction (up to ∼30%) of isas. this figure is based on existing observations of wd metal pollution, which are de-biased using realistic models of circum-wd planetary systems. such isas should exhibit kinematic characteristics of old, dynamically hot galactic populations. isa ejection in individual planetary tdes is highly anisotropic, resulting in large fluctuations of their space density. we also show that other isa production channels involving stellar remnants—direct ejection by massive planets around the wds and supernova explosions—have difficulty explaining ’oumuamua-like isas. | 1i/2017 ’oumuamua-like interstellar asteroids as possible messengers from dead stars |
the formation of cold gas giants similar to jupiter and saturn in orbit and mass is a great challenge for planetesimal-driven core accretion models because the core growth rates far from the star are low. here we model the growth and migration of single protoplanets that accrete planetesimals and gas. we integrated the core growth rate using fits in the literature to n-body simulations, which provide the efficiency of accreting the planetesimals that a protoplanet migrates through. we take into account three constraints from the solar system and from protoplanetary discs: (1) the masses of the terrestrial planets and the comet reservoirs in neptune's scattered disc and the oort cloud are consistent with a primordial planetesimal population of a few earth masses per au, (2) evidence from the asteroid belt and the kuiper belt indicates that the characteristic planetesimal diameter is 100 km, and (3) observations of protoplanetary discs indicate that the dust is stirred by weak turbulence; this gas turbulence also excites the inclinations of planetesimals. our nominal model built on these constraints results in maximum protoplanet masses of 0.1 earth masses. ignoring constraint (1) above, we show that even a planetesimal population of 1000 earth masses, corresponding to 50 earth masses per au, fails to produce cold gas giants (although it successfully forms hot and warm gas giants). we conclude that a massive planetesimal reservoir is in itself insufficient to produce cold gas giants. the formation of cold gas giants by planetesimal accretion additionally requires that planetesimals are small and that the turbulent stirring is very weak, thereby violating all three above constraints. | exploring the conditions for forming cold gas giants through planetesimal accretion |
context. debris discs are a consequence of the planet formation process and constitute the fingerprints of planetesimal systems. their counterparts in the solar system are the asteroid and edgeworth-kuiper belts.aims: the aim of this paper is to provide robust numbers for the incidence of debris discs around fgk stars in the solar neighbourhood.methods: the full sample of 177 fgk stars with d ≤ 20 pc proposed for the dust around nearby stars (dunes) survey is presented. herschel/pacs observations at 100 and 160 μm were obtained, and were complemented in some cases with data at 70 μm and at 250, 350, and 500 μm spire photometry. the 123 objects observed by the dunes collaboration were presented in a previous paper. the remaining 54 stars, shared with the disc emission via a bias-free reconnaissance in ir and sub-mm (debris) consortium and observed by them, and the combined full sample are studied in this paper. the incidence of debris discs per spectral type is analysed and put into context together with other parameters of the sample, like metallicity, rotation and activity, and age.results: the subsample of 105 stars with d ≤ 15 pc containing 23 f, 33 g, and 49 k stars is complete for f stars, almost complete for g stars, and contains a substantial number of k stars from which we draw solid conclusions on objects of this spectral type. the incidence rates of debris discs per spectral type are 0.26+0.21-0.14 (6 objects with excesses out of 23 f stars), 0.21+0.17-0.11 (7 out of 33 g stars), and 0.200.14-0.09 (10 out of 49 k stars); the fraction for all three spectral types together is 0.22+0.08-0.07 (23 out of 105 stars). the uncertainties correspond to a 95% confidence level. the medians of the upper limits of ldust/l∗ for each spectral type are 7.8 × 10-7 (f), 1.4 × 10-6 (g), and 2.2 × 10-6 (k); the lowest values are around 4.0 × 10-7. the incidence of debris discs is similar for active (young) and inactive (old) stars. the fractional luminosity tends to drop with increasing age, as expected from collisional erosion of the debris belts. herschel is an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa. | incidence of debris discs around fgk stars in the solar neighbourhood |
land surface temperature (lst) is a vital physical parameter of earth surface system. estimating high-resolution lst precisely is essential to understand heat change processes in urban environments. existing lst products with coarse spatial resolution retrieved from satellite-based thermal infrared imagery have limited use in the detailed study of surface energy balance, evapotranspiration, and climatic change at the urban spatial scale. downscaling lst is a practicable approach to obtain high accuracy and high-resolution lst. in this study, a machine learning-based geostatistical downscaling method (rfatpk) is proposed for downscaling lst which integrates the advantages of random forests and area-to-point kriging methods. the rfatpk was performed to downscale the 90 m advanced spaceborne thermal emission and reflection radiometer (aster) lst 10 m over two representative areas in guangzhou, china. the 10 m multi-type independent variables derived from the sentinel-2a imagery on 1 november 2017, were incorporated into the rfatpk, which considered the nonlinear relationship between lst and independent variables and the scale effect of the regression residual lst. the downscaled results were further compared with the results obtained from the normalized difference vegetation index (ndvi) based thermal sharpening method (tsharp). the experimental results showed that the rfatpk produced 10 m lst with higher accuracy than the tsharp; the tsharp showed poor performance when downscaling lst in the built-up and water regions because ndvi is a poor indicator for impervious surfaces and water bodies; the rfatpk captured lst difference over different land coverage patterns and produced the spatial details of downscaled lst on heterogeneous regions. more accurate lst data has wide applications in meteorological, hydrological, and ecological research and urban heat island monitoring. | downscaling aster land surface temperature over urban areas with machine learning-based area-to-point regression kriging |
deflecting potentially dangerous asteroids may not be an easy task due to the complexity of the system, as well as challenges such as monitoring and defining their future orbit, which can often be very sensitive to encounters with massive planets. over the years, many proposals have been made to face the challenges and even deflect the asteroid from a possible collision with earth. within this scenario, we are proposing the use of the kinetic impact deflection technique combined with gravitational perturbations from the earth. we assume the following scenario: the asteroid will have a closest approach to earth and will move away again; however, in its next closest approach to earth, it will collide with it. the proposal is to take advantage of the first maximum approach between the asteroid and the earth, to apply a velocity variation on the asteroid that will have its effect intensified by the swing-by with earth. we will take the opportunity to understand how the planets can influence the results. our results show that planets can change the results significantly. another interesting result is that the minimum impulse to avoid apophis collision has the magnitude of − 5 mm/s. | studying the prevention of collision of asteroid apophis with earth by kinetic impact |
milani is a 6u cubesat that will be released in the didymos binary asteroid system by esa's hera spacecraft. its objectives are to study and characterize the system's asteroids, thus demonstrating the use of miniaturized technologies for asteroid science. milani adopts sophisticated vision-based technologies for the guidance, navigation, and control system in the asteroid's close-proximity environment. this work elaborates on the architecture design and on the performance analysis of the image processing and the guidance, navigation, and control system of milani, showing that they can successfully assure adequate pointing and control of the cubesat in the didymos environment. | the vision-based guidance, navigation, and control system of hera's milani cubesat |
we consider a simplified model to study some types of elongated asteroids with three protuberances, two at the ends and one in the middle. an example considered in this work is the asteroid holiday. to model these bodies, we consider a tripolar system with a segment, which consists of a massive segment and three spheres, two at the ends of the segment and one between them, rotating around their center of mass with uniform angular velocity. in particular, we restrict our case to variations in masses and their positions, as well as variations in the mass of the segment or rod. for this problem, we obtain the potential and calculate families of symmetric periodic orbits, analyzing asymptotic points that may represent heteroclinic orbits as well as orbits that may represent possible collisions with the studied body. furthermore, it was possible to obtain zero velocity curves and equilibrium points of the system. the analysis of symmetric periodic orbits can contribute to improve the efficiency of space missions, prolonging the useful life of satellites or spacecraft, in addition to collaborating for a better understanding of the dynamics of a satellite around an asteroid. the asteroid holiday was chosen due to its degree of importance, both for its proximity to our planet and its periodicity, which led nasa to classify it as potentially dangerous. | analysis of symmetric periodic orbits in a tripolar system with a segment |
part v of the evolutionary system of mineralogy explores phases produced by aqueous alteration, metasomatism, and/or thermal metamorphism—relicts of ancient processes that affected virtually all asteroids and that are preserved in the secondary mineralogy of meteorites. we catalog 166 historical natural kinds of minerals that formed by alteration in the parent bodies of chondritic and non-chondritic meteorites within the first 20 ma of the solar system. secondary processes saw a dramatic increase in the chemical and structural diversity of minerals. these phases incorporate 41 different mineral-forming elements, including the earliest known appearances of species with essential co, ge, as, nb, ag, sn, te, au, hg, pb, and bi. among the varied secondary meteorite minerals are the earliest known examples of halides, arsenides, tellurides, sulfates, carbonates, hydroxides, and a wide range of phyllosilicates. | an evolutionary system of mineralogy, part v: aqueous and thermal alteration of planetesimals ( 4565 to 4550 ma) |
this study aims to investigate the location and stability of equilibrium points in the potential field of the the asteroid (87) sylvia. the potential series expansion method is used, which involves decomposing the asteroid into homogeneous tetrahedral elements with a constant rotation speed. the results are compared with those obtained using the classical polyhedral method, and we found good agreement outside the body, even in close to its surface. our model can be applied to any polyhedral-shaped body as it expresses the potential analytically, which makes it easier to manipulate algebraically for determining acceleration and velocity components. moreover, it significantly reduces computational costs in terms of cpu time requirements, keeping the accuracy at a very acceptable level. | the potential series expansion method: application to the asteroid (87) sylvia |
mining asteroids will soon be a reality; the technology for this venture is almost off the shelf depending on the development of artificial intelligence for autonomous robotic spacecraft. in this work, we treat the problem of transporting ores to earth, mainly to the vicinity of the moon to avoid any accident of a colliding asteroid. we explore the database for near-earth objects (neos) and choose the best asteroid candidates for mining, based on their orbit. we studied apollos and atens groups since they are earth orbit crossing objects. the main strategy of this work is to obtain trajectories that could lead to a transfer orbit from the current orbit of the asteroid to the vicinity of the lunar orbit. we use the relative two body energy between the moon and the asteroid to find the best orbit candidates. the best point of the asteroid trajectory is the point that could lead to a less expensive maneuver. we found that there are less than 1 000 asteroids from the apollo group, and less than 350 asteroids from the aten group, which could be transferred to a temporary orbit around the moon with a variation in velocity smaller than 447 m/s. we found a temporary capture of an apollo asteroid (2015 do215) around the moon in the year ∼2063 . we also identified, from our numerical simulations, that an asteroid of the aten group may collide with earth. therefore, we propose two mitigation maneuvers to change the probability of collision. | trajectories for mining space mission on asteroids in near-earth orbit |
chondrites are fragments of asteroids that avoided melting and, thus, provide a record of the material that accreted to form protoplanets. the dominant constituent of chondrites are millimeter-sized chondrules formed by transient heating events in the protoplanetary disk. some chondritic components, including chondrules, contain evidence of the extinct short-lived radionuclide 26al (half-life of 0.73 myr). the decay of 26al is postulated to have been an important heat source promoting asteroidal melting and differentiation. thus, understanding the 26al inventory in the accretion regions of differentiated asteroids is critical to constrain the accretion timescales of protoplanets. the current paradigm asserts that the canonical 26al/27al ratio of ∼ 5 × 10-5 recorded by the oldest dated solids, calcium-aluminium refractory inclusions, represents that of the bulk solar system. we report, for the first time, the 26al-26mg systematics of chondrules from the north west africa (nwa) 5697 l 3.10 ordinary chondrite and allende cv3oxa (vigarano type) carbonaceous chondrite that have been previously dated by u-corrected pb-pb dating. eight chondrules, which record absolute ages ranging from 4567.57 ± 0.56 to 4565.84 ± 0.72 ma, define statistically-significant internal isochron relationships corresponding to initial (26al/27al) ([26al/27al]0) ratios in their precursors at the time of cai formation at 4567.3 ± 0.16 ma ranging from (3.92+4.53-2.95) × 10-6 to (2.74+1.30-1.09) × 10-5. these initial ratios are much lower than those predicted by the pb-pb ages, corresponding to age mismatches between the pb-pb and 26al-26mg systems ranging from 0.69+0.54-0.44 to 2.71+0.66-0.59 myr. all chondrules record 54cr/52cr compositions indicating an origin from inner solar system precursor material and, as such, we interpret the age mismatch to reflect a reduced initial abundance of 26al in the chondrule precursors, similar to that proposed for the angrite parent body. in particular, the range of [26al/27al]0 ratios essentially defines two groups, which are apparently correlated with the absolute ages of the chondrules. a first group, charactertized by chondrules with absolute pb-pb ages identical to cais, defines a mean [26al/27al]0 value of (4.75+1.99-1.21) × 10-6, whereas a second group, with absolute ages ∼1 myr younger than cais, record a mean mean [26al/27al]0 of (1.82+0.57-0.40) × 10-5. we interpret this systematic variability in [26al/27al]0 values as reflecting progressive inward transport and admixing of dust of solar composition and 26al content from the outer disk during chondrule recycling and remelting. finally, a reduced [26al/27al]0 ratio in chondrule precursors impacts our understanding of the accretion timescales of differentiated planetesimals if chondrules are indeed representative of inner disk material. using the average [26al/27al]0 ratio of (1.36 ± 0.72) × 10-5 defined by the eight chondrules, thermal modelling constrains the accretion of differentiated planetesimals formed with this 26al inventory from ∼0.1 to ∼0.9 myr after solar system formation to ensure melting by 26al decay. | combined u-corrected pb-pb dating and 26al-26mg systematics of individual chondrules - evidence for a reduced initial abundance of 26al amongst inner solar system chondrules |
it is in the interest of astronomy and engineering to find orbits for spacecraft that allow a good observation of the orbited body and, at the same time, to reduce expenses with fuel consumption for correction and maintenance maneuvers. considering the current scenario, many of the small bodies in the solar system have been shown to be good candidates for future study missions, such as planetary moons, asteroids, and dwarf planets, beyond the orbit of neptune. in this sense, the search for methods that aim to locate favorable orbital configurations for the placement of a spacecraft is an important point to be studied. in particular, it is important to search for orbits with high inclinations and circular or quasi-circular, since these orbits allow the observation of the entire body during its natural rotation. however, these orbits are subject to strong perturbations due to the presence of effects, such as those caused by mother planets and the inhomogeneity of the mass and the shape of the satellites. so, the goal of the present paper is to search for orbital configurations for a spacecraft around small satellites. therefore, in this paper, we study the perturbations given by planet saturn in a spacecraft orbiting the satellite iapetus. | searching for orbits to observe iapetus |
this work proposes a numerical investigation for periodic orbits in the restricted three-body problem to observe the smaller primary of the system. periodic orbits are very important for observation missions, because they do not need station-keeping maneuvers and allow predicted passages by the main bodies. so, they allow a better observation of the body under study. for this verification, the grid search method will be used [(barrio and blesa, chaos solit fractals, 41, 560-582 (2009)]. for each set of conditions, the differential equations of the motion of the spacecraft will be numerically integrated using tides [abad et al., acm trans math softw (toms) 39, 1-28 (2012)]. in case of occurrence of periodic orbits, the characteristics of these orbits will be analyzed and the families found will be identified and classified. in particular, it is important to avoid effects from the close approach with the secondary body (swing-by), because this effect may destroy the periodicity of the orbit. this can be done using angle of approaches of 0∘ or 180∘ for the close approach, because they allow passages very close to the smaller body but with zero variations in energy and angular momentum. this aspect of the swing-by maneuver is very important in the present research. | periodic orbits in the restricted three-body problem for observations of the smaller primary |
the assessment of flash flood hazards in the coastal zone of ras ghareb city (rgc), red sea, egypt, was accomplished through the use of gis tools and the spatial multi-criteria approach. the presented work aims to assess, integrate, and generate potential flash flood hazard maps. the analytic hierarchy process was utilized to calculate weights of hazard and vulnerability of flash flood controlling factors and their parameters such as topographical, geological, and hydrological factors. in addition, the risk degree of each specific basin and its sub-basins is estimated by combining standardized parameter values. despite its location in an arid region, the basin may receive a large amount of rainwater, which can cause flash floods at the basin's outlet. recently, flash flooding took place in the coastal region of rgc in october 2016 and september 2020, resulting in the loss of many human lives and catastrophic effects on local infrastructure and surrounding environments. according to reports from hurghada, red sea governorate, the rgc experienced exceptional flooding that exceeded 120 million cubic meters as a result of 51 mm of rainfall. based on the remote sensing satellite data such as aster digital elevation model (gdem) and the gis tools, the basin and sub-basin drainage patterns were delineated and compared with reference topographical map sheets of a scale of 1: 50,000. the sub-basins have been isolated and morphometrically studied to determine vulnerability to flash flooding. in addition, the flash flood threat model was developed using geoprocessing tools provided by arcgis software to incorporate all contributing factors spatially. the flash flood risk in the ras ghareb (rg) basins and their sub-basins has been identified and classified into three classes (high, medium, and low hazard degree). high and moderate flood-risk basins require comprehensive studies to introduce measures to protect certain areas from flood danger. finally, the gis and the spatial multi-criteria analyses were effective ways to carry out a flash flood management system in order to support the decision-makers by recommendations to conserve and mitigate the possible flash flood hazards in the study areas. | flash flooding hazard assessment, modeling, and management in the coastal zone of ras ghareb city, gulf of suez, egypt |
the world's meteorite collections contain a very rich picture of what the early solar system would have been made of, however the lack of spatial context with respect to their parent population for these samples is an issue. the asteroid population is equally as rich in surface mineralogies, and mapping these two populations (meteorites and asteroids) together is a major challenge for planetary science. directly probing asteroids achieves this at a high cost. observing meteorite falls and calculating their pre-atmospheric orbit on the other hand, is a cheaper way to approach the problem. the global fireball observatory (gfo) collaboration was established in 2017 and brings together multiple institutions (from australia, usa, canada, morocco, saudi arabia, the uk, and argentina) to maximise the area for fireball observation time and therefore meteorite recoveries. the members have a choice to operate independently, but they can also choose to work in a fully collaborative manner with other gfo partners. this efficient approach leverages the experience gained from the desert fireball network (dfn) pathfinder project in australia. the state-of-the art technology (dfn camera systems and data reduction) and experience of the support teams is shared between all partners, freeing up time for science investigations and meteorite searching. with all networks combined together, the gfo collaboration already covers 0.6% of the earth's surface for meteorite recovery as of mid-2019, and aims to reach 2% in the early 2020s. we estimate that after 5 years of operation, the gfo will have observed a fireball from virtually every meteorite type. this combined effort will bring new, fresh, extra-terrestrial material to the labs, yielding new insights about the formation of the solar system. | a global fireball observatory |
the mascot radiometer mara is a multi-spectral instrument which measures net radiative flux in six wavelength bands. mara uses thermopile sensors as sensing elements, and the net flux between the instrument and the surface in the 18° field of view is determined by evaluating the thermoelectric potential between the sensors' absorbing surface and the thermopile's cold-junction. mara houses 4 bandpass channels in the spectral range of 5.5-7, 8-9.5, 9.5-11.5, and 13.5-15.5 μm, as well as one long-pass channel, which is sensitive in the >3 μm range. in addition, one channel is similar to that used by the hayabusa 2 orbiter thermal mapper, which uses a wavelength range of 8-12 μm. the primary science objective of the mara instrument it the determination of the target asteroid's surface brightness temperature, from which surface thermal inertia can be derived. in addition, the spectral bandpass channels will be used to estimate the spectral slope of the surface in the thermal infrared wavelength range. the instrument has been calibrated using a cavity blackbody, and the temperature uncertainty is 1 k in the long pass channel for target temperatures of >173 k. measurement uncertainty in the spectral bandpasses is 1 k for target temperatures above 273 k. | the mascot radiometer mara for the hayabusa 2 mission |
nirs3: the near infrared spectrometer is installed on the hayabusa2 spacecraft to observe the target c-type asteroid 162173 ryugu at near infrared wavelengths of 1.8 to 3.2 μm. it aims to obtain reflectance spectra in order to detect absorption bands of hydrated and hydroxide minerals in the 3 μm-band. we adopted a linear-image sensor with indium arsenide (inas) photo diodes and a cooling system with a passive radiator to achieve an optics temperature of 188 k (-85°c), which enables to retaining sufficient sensitivity and noise level in the 3 μm wavelength region. we conducted ground performance tests for the nirs3 flight model (fm) to confirm its baseline specifications. the results imply that the properties such as the signal-to-noise ratio (snr) conform to scientific requirements to determine the degree of aqueous alteration, such as cm or ci chondrite, and the stage of thermal metamorphism on the asteroid surface. | nirs3: the near infrared spectrometer on hayabusa2 |
focused on asteroid soft-landing mission scenario, this paper investigates the methods of online gravity field modeling and trajectory optimization. since the gravity field near asteroids and its surface topography are irregular, accurate asteroid soft-landing can be a challenging problem to solve, especially in the case of limited gravity data. with an actual asteroid soft-landing mission in mind, this study constructs a dataset based on the gravity field data collected in the limited area through which a soft-landing probe passed, and conducts online modeling of the asteroid inhomogeneous gravity field at the same time, using a transfer learning deep neural network (tl-dnn). to achieve fuel optimization and an accurate landing, a fast trajectory optimization method based on bezier shape approach is implemented to achieve fast online robust re-trajectory optimization. numerical simulation results show that the adopted tl-dnn can quickly reconstruct the gravitational field near the asteroid online, based only on the limited gravity data collected by the probe. compared with the situation without online gravity field reconstruction and multiple online trajectory optimization, the proposed online gravity field modeling and re-trajectory optimization method can reduce the final position and velocity error between the multi-planned ideal optimal trajectory and the actual trajectory from 2396.367 m and 3.870 m/s to 14.152 m and 0.075 m/s, respectively. in other words, the soft-landing accuracy is improved by about two orders of magnitude. | a framework of gravity field online modeling and trajectory optimization in asteroid soft-landing mission scenarios |
this paper presents the low-thrust (lt) trajectory design for near-earth asteroid (nea) supply delivery and resource transportation mission using high-power solar electric propulsion (sep). nea low-thrust roundtrip accessibility is investigated through a numerical approach and new knowledge of the mass transportation capability of sep systems in nea missions is provided. a number of powerful deep neural networks (dnns) were trained and optimized for 60 kw, 150 kw, 300 kw and 500 kw sep-based lt trajectory design. dnns are used as the surrogate of the conventional optimization process. a new low thrust trajectory roundtrip opportunity search algorithm is developed, which integrates the dnn models and allows an efficient roundtrip search process. compared to the conventional approach, the dnn-based search algorithm reduces the search time by 99.96%. the sep mass transportation capabilities were numerically studied. it was found the 60 kw sep can deliver 5 tons of supply to up to 40% of neas. considering refueling on neas, the accessible neas can be further increased by 16.2%. it is suggested that the 150 kw, 300 kw, 500 kw sep to be used to transport 10-30 tons, 30-70 tons, 70-120 tons resources from neas respectively. these mass ranges ensure about 4,000 or more targets to be accessible. in all the case studies, the roundtrip accessible boundaries were constructed using polynomial regression. these boundaries were numerically obtained, which could be useful for mission designers to rapidly determine the lt roundtrip accessibility of newly found neas. | low-thrust trajectory design for near-earth asteroid supply delivery and resource transportation mission using high-power solar electric propulsion |
the terminal tracking camera system (ttcam) on the nasa lucy trojan asteroid discovery mission consists of a pair of block redundant cameras and their associated electronics that are mounted on the spacecraft's instrument pointing platform and co-boresighted with the rest of the mission's science payload instruments. the primary function of the ttcams is as a navigation system designed to provide an autonomous onboard late pre-encounter update of the location of each asteroid flyby target relative to the spacecraft. however, once the terminal tracking function is complete, the ttcam system will also provide 11.0°×8.2° field of view broadband (425-675 nm) images during the close approach phase of each asteroid flyby that will be used for scientific analyses like shape modeling and assessment of each target's geology and topography. this paper provides an overview of the ttcam cameras and electronics, the science-focused requirements that the system is designed to meet, pointers to pre-flight calibration and in-flight calibration details for the cameras, as well as a high-level summary of the kinds of science that these images will enable for the mission. | the terminal tracking camera system on the nasa lucy trojan asteroid discovery mission |
context. the movis catalog contains the largest set of near-infrared (nir) colors for solar system objects. these data were obtained from the observations performed by vista-vhs survey using the y, j, h, and ks filters. the taxonomic classification of objects in this catalog allows us to obtain large-scale distributions for the asteroidal population, to study faint objects, and to select targets for detailed spectral investigations.aims: we aim to provide a taxonomic classification for asteroids observed by vista-vhs survey. we derive a method for assigning a compositional type to an object based on its (y - j), (j - ks), and (h - ks) colors.methods: we present a taxonomic classification for 18 265 asteroids from the movis catalog, using a probabilistic method and the k-nearest neighbors algorithm. because our taxonomy is based only on nir colors, several classes from bus-demeo were clustered into groups and a slightly different notation was used: i.e., the superscript indicates that the classification was obtained based on the nir colors and the subscript indicates possible misidentifications with other types. our results are compared with the information provided by the sloan digital sky survey (sdss) and wide-field infrared survey explorer (wise).results: the two algorithms used in this study give a taxonomic type for all objects having at least (y - j) and (j - ks) observed colors. a final classification is reported for a set of 6496 asteroids based on the criteria that knn and probabilistic algorithms gave the same result, and the color errors are within the limits (y - j)err ≤ 0.118 and (j - ks)err ≤ 0.136. this set includes 144 bodies classified as bkni, 613 as cni, 197 as cgxni, 91 as xtni, 440 as dsni, 665 as klni, 233 as adni, 3315 as sni, and 798 as vni. we report the albedo distribution for each taxonomic group and we compute new median values for the main types. we found that v-type and a-type candidates have identical size frequency distributions, but v types are five times more common than a types. several particular cases, such as the a-type asteroid (11616) 1996 bq2 and the s-type (3675) kematsch, both in the cybele population, are discussed. classification table for 18 265 asteroids is 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/617/a12 | taxonomic classification of asteroids based on movis near-infrared colors |
this paper presents a comprehensive review of the science and technology of accessing near-earth asteroids (neas), or making them accessible, for obtaining both information and resources. the survey is divided into four major groups of nea study, namely a) discovery (population estimation and detection), b) exploration (identification and characterization), c) deflection and redirection, and d) mining (prospecting, excavation, processing, refining, storage.). recent research and development advancements from both industry and academia are discussed in each group, and certain specific future directions are highlighted. some concluding remarks are made at the end, including the need for creating new educational programs to train competent engineers and researchers for the taskforce in the new field of asteroid engineering in near future. | asteroid engineering: the state-of-the-art of near-earth asteroids science and technology |
primordial black holes (pbhs) remain a viable dark matter candidate in the asteroid-mass range. we point out that in this scenario, the pbh abundance would be large enough for at least one object to cross through the inner solar system per decade. since solar system ephemerides are modeled and measured to extremely high precision, such close encounters could produce detectable perturbations to orbital trajectories with characteristic features. we evaluate this possibility with a suite of simple solar system simulations, and we argue that the abundance of asteroid-mass pbhs can plausibly be probed by existing and near-future data. | close encounters of the primordial kind: a new observable for primordial black holes as dark matter |
eclipsing post-common-envelope binaries are highly important for resolving the poorly understood, very short-lived common-envelope phase of stellar evolution. most hot subdwarfs (sdo/bs) are the bare helium-burning cores of red giants that have lost almost all of their hydrogen envelope. this mass loss is often triggered by common-envelope interactions with close stellar or even substellar companions. cool companions to hot subdwarf stars such as late-type stars and brown dwarfs are detectable from characteristic light-curve variations - reflection effects and often eclipses. in the recently published catalog of eclipsing binaries in the galactic bulge and in the asteroid terrestrial-impact last alert system (atlas) survey, we discovered 125 new eclipsing systems showing a reflection effect seen by visual inspection of the light curves and using a machine-learning algorithm, in addition to the 36 systems previously discovered by the optical gravitational lesing experiment (ogle) team. the eclipsing reflection effect binaries from optical surveys (erebos) project aims at analyzing all newly discovered eclipsing binaries of the hw vir type (hot subdwarf + close, cool companion) based on a spectroscopic and photometric follow up to derive the mass distribution of the companions, constrain the fraction of substellar companions, and determine the minimum mass needed to strip off the red-giant envelope. to constrain the nature of the primary we derived the absolute magnitude and the reduced proper motion of all our targets with the help of the parallaxes and proper motions measured by the gaia mission and compared those to the gaia white-dwarf candidate catalog. it was possible to derive the nature of a subset of our targets, for which observed spectra are available, by measuring the atmospheric parameter of the primary, confirming that less than 10% of our systems are not sdo/bs with cool companions but are white dwarfs or central stars of planetary nebula. this large sample of eclipsing hot subdwarfs with cool companions allowed us to derive a significant period distribution for hot subdwarfs with cool companions for the first time showing that the period distribution is much broader than previously thought and is ideally suited to finding the lowest-mass companions to hot subdwarf stars. the comparison with related binary populations shows that the period distribution of hw vir systems is very similar to wd+dm systems and central stars of planetary nebula with cool companions. in the future, several new photometric surveys will be carried out, which will further increase the sample of this project, providing the potential to test many aspects of common-envelope theory and binary evolution. | the erebos project: investigating the effect of substellar and low-mass stellar companions on late stellar evolution. survey, target selection, and atmospheric parameters |
the lucy mission accomplishes its science during a series of five flyby encounters with seven trojan asteroid targets. this mission architecture drives a concept of operations design that maximizes science return, provides redundancy in observations where possible, features autonomous fault protection, and utilizes onboard target tracking near closest approach. these design considerations reduce risk during the relatively short time-critical periods when science data is collected. the payload suite consists of a color camera and infrared imaging spectrometer, a high-resolution panchromatic imager, and a thermal infrared spectrometer. the mission design allows for concurrent observations of all instruments. additionally, two spacecraft subsystems will also contribute to the science investigations: the terminal tracking cameras will obtain wide field-of-view imaging near closest approach to determine the shape of each of the trojan targets and the telecommunication subsystem will carry out doppler tracking of the spacecraft to determine the mass of each of the trojan targets. | lucy mission to the trojan asteroids: instrumentation and encounter concept of operations |
reproducing the large earth/mars mass ratio requires a strong mass depletion in solids within the protoplanetary disc between 1 and 3 au. the grand tack model invokes a specific migration history of the giant planets to remove most of the mass initially beyond 1 au and to dynamically excite the asteroid belt. however, one could also invoke a steep density gradient created by inward drift and pile-up of small particles induced by gas drag, as has been proposed to explain the formation of close-in super-earths. here we show that the asteroid belt's orbital excitation provides a crucial constraint against this scenario for the solar system. we performed a series of simulations of terrestrial planet formation and asteroid belt evolution starting from discs of planetesimals and planetary embryos with various radial density gradients and including jupiter and saturn on nearly circular and coplanar orbits. discs with shallow density gradients reproduce the dynamical excitation of the asteroid belt by gravitational self-stirring but form mars analogues significantly more massive than the real planet. in contrast, a disc with a surface density gradient proportional to r-5.5 reproduces the earth/mars mass ratio but leaves the asteroid belt in a dynamical state that is far colder than the real belt. we conclude that no disc profile can simultaneously explain the structure of the terrestrial planets and asteroid belt. the asteroid belt must have been depleted and dynamically excited by a different mechanism such as, for instance, in the grand tack scenario. | terrestrial planet formation constrained by mars and the structure of the asteroid belt |
we report observations of the didymos-dimorphos binary asteroid system using the atacama large millimeter/submillimeter array (alma) and the atacama compact array (aca) in support of the double asteroid redirection test mission. our observations on ut 2022 september 15 provided a preimpact baseline and the first measure of didymos-dimorphos's spectral emissivity at λ = 0.87 mm, which was consistent with the handful of siliceous and carbonaceous asteroids measured at millimeter wavelengths. our postimpact observations were conducted using four consecutive executions each of alma and the aca spanning from t+3.52 to t+8.60 hr, sampling thermal emission from the asteroids and the impact ejecta. we scaled our preimpact baseline measurement and subtracted it from the postimpact observations to isolate the flux density of millimeter-sized grains in the ejecta. ejecta dust masses were calculated for a range of materials that may be representative of dimorphos's s-type asteroid material. the average ejecta mass over our observations is consistent with 1.3-6.4 × 107 kg, with the lower and higher values calculated for amorphous and crystalline silicates, respectively. owing to the likely crystalline nature of s-type asteroid material, the higher value is favored. these ejecta masses represent 0.3%-1.5% of dimorphos's total mass and are in agreement with lower limits on the ejecta mass based on measurements at optical wavelengths. our results provide the most sensitive measure of millimeter-sized material in the ejecta and demonstrate the power of alma for providing supporting observations to spaceflight missions. | alma observations of the dart impact: characterizing the ejecta at submillimeter wavelengths |
the asteroid 99942 apophis is a near earth asteroid, which was just recently removed from the potentially hazardous asteroids list, since there is no risk of collision with the earth for the next 100 years. although, its importance to dynamical astronomy remains evidenced due to other further close encounters that will happen. in the current work, we analyze the dynamics of a hypothetical disc with massless particles around apophis that produce a complex structure in terms of possible fates (survivors, collisions, and ejections). the gravitational potential due to the highly irregular shape of apophis produces asymmetries in the dynamics around it. commensurabilities between the particle's orbital motion frequencies and apophis' spin generate resonances that dominate the observed complex structure. the results show that the orbital evolution in the third dimension is affected by a combination of the resonances and the gravitational field elongated asymmetry, which helps explain most structure details. | the dynamical structure of a hypothetical disc of particles around the asteroid 99942 apophis |
hawking proposed that the sun may harbor a primordial black hole (bh) whose accretion supplies some of the solar luminosity. such an object would have formed within the first 1 s after the big bang with the mass of a moon or an asteroid. these light bhs are a candidate solution to the dark matter problem, and could grow to become stellar-mass bhs if captured by stars. here we compute the evolution of stars having such a bh at their center. we find that such objects can be surprisingly long-lived, with the lightest bhs having no influence over stellar evolution, while more massive ones consume the star over time to produce a range of observable consequences. models of the sun born about a bh whose mass has since grown to approximately 10-6 m ⊙ are compatible with current observations. in this scenario, the sun would first dim to half its current luminosity over a span of 100 myr as the accretion starts to generate enough energy to quench nuclear reactions. the sun would then expand into a fully convective star, where it would shine luminously for potentially several gigayears with an enriched surface helium abundance, first as a sub-subgiant star, and later as a red straggler, before becoming a subsolar-mass bh. we also present results for a range of stellar masses and metallicities. the unique internal structures of stars harboring bhs may make it possible for asteroseismology to discover them, should they exist. we conclude with a list of open problems and predictions. | solar evolution models with a central black hole |
the nasa double asteroid redirection test (dart) spacecraft will impact the secondary member of the [65803] didymos binary in order to perform the first demonstration of asteroid deflection by kinetic impact. determination of the momentum transfer to the target body from the kinetic impact is a primary planetary defense objective, using ground-based telescopic observations of the orbital period change of didymos and imaging of the dart impact ejecta plume by the liciacube cubesat, along with modeling and simulation of the dart impact. liciacube, contributed by the italian space agency, will perform a flyby of didymos a few minutes after the dart impact, to resolve the ejecta plume spatial structure and to study the temporal evolution. liciacube ejecta plume images will help determine the vector momentum transfer from the dart impact, by determining or constraining the direction and the magnitude of the momentum carried by ejecta. a model is developed for the impact ejecta plume optical depth, using a point source scaling model of the dart impact. the model is applied to expected liciacube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. the ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. the evolution of the plume optical depth profiles determined from liciacube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. liciacube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly strength and porosity, thereby allowing inference of these properties to improve the determination of momentum transfer. | dart mission determination of momentum transfer: model of ejecta plume observations |
context. the recent estimates of the 3d shape of the m/xe-type triple asteroid system (216) kleopatra indicated a density of ~5 g cm−3, which is by far the highest for a small solar system body. such a high density implies a high metal content as well as a low porosity which is not easy to reconcile with its peculiar "dumbbell" shape.aims: given the unprecedented angular resolution of the vlt/sphere/zimpol camera, here, we aim to constrain the mass (via the characterization of the orbits of the moons) and the shape of (216) kleopatra with high accuracy, hence its density.methods: we combined our new vlt/sphere observations of (216) kleopatra recorded during two apparitions in 2017 and 2018 with archival data from the w. m. keck observatory, as well as lightcurve, occultation, and delay-doppler images, to derive a model of its 3d shape using two different algorithms (adam, mpcd). furthermore, an n-body dynamical model allowed us to retrieve the orbital elements of the two moons as explained in the accompanying paper.results: the shape of (216) kleopatra is very close to an equilibrium dumbbell figure with two lobes and a thick neck. its volume equivalent diameter (118.75 ± 1.40) km and mass (2.97 ± 0.32) × 1018 kg (i.e., 56% lower than previously reported) imply a bulk density of (3.38 ± 0.50) g cm−3. such a low density for a supposedly metal-rich body indicates a substantial porosity within the primary. this porous structure along with its near equilibrium shape is compatible with a formation scenario including a giant impact followed by reaccumulation. (216) kleopatra's current rotation period and dumbbell shape imply that it is in a critically rotating state. the low effective gravity along the equator of the body, together with the equatorial orbits of the moons and possibly rubble-pile structure, opens the possibility that the moons formed via mass shedding.conclusions: (216) kleopatra is a puzzling multiple system due to the unique characteristics of the primary. this system certainly deserves particular attention in the future, with the extremely large telescopes and possibly a dedicated space mission, to decipher its entire formation history. reduced images are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/653/a57 based on observations made with eso telescopes at the la silla paranal observatory under program 199.c-0074 (pi: vernazza). | (216) kleopatra, a low density critically rotating m-type asteroid |
in our solar system, spin-orbit resonances are common under sun--planet, planet--satellite and binary asteroid configurations. in this work, high-order and secondary spin-orbit resonances are investigated by taking numerical and analytical approaches. poincaré sections as well as two types of dynamical maps are produced, showing that there are complicated structures in the phase space. to understand numerical structures, we adopt the theory of perturbative treatments to formulate resonant hamiltonian for describing spin-orbit resonances. results show that there is an excellent agreement between analytical and numerical structures. it is concluded that the main v-shape structure arising in the parameter space $(\dot\theta,\alpha)$ is sculpted by the synchronous primary resonance, those minute structures inside the v-shape region are dominated by secondary resonances and those structures outside the v-shape region are governed by high-order resonances. at last, the analytical approach is applied to binary asteroid systems (65803) didymos and (4383) suruga to reveal their phase-space structures. | dynamical structures associated with high-order and secondary resonances in the spin-orbit problem |
we report a statistically significant detection of nongravitational acceleration on the subkilometer near-earth asteroid (523599) 2003 rm. due to its orbit, 2003 rm experiences favorable observing apparitions every 5 yr. thus, since its discovery, 2003 rm has been extensively tracked with ground-based optical facilities in 2003, 2008, 2013, and 2018. we find that the observed plane-of-sky positions cannot be explained with a purely gravity-driven trajectory. including a transverse nongravitational acceleration allows us to match all observational data, but its magnitude is inconsistent with perturbations typical of asteroids such as the yarkovsky effect or solar radiation pressure. after ruling out that the orbital deviations are due to a close approach or collision with another asteroid, we hypothesize that this anomalous acceleration is caused by unseen cometary outgassing. a detailed search for evidence of cometary activity with archival and deep observations from the panoramic survey telescope and rapid response system and the very large telescope does not reveal any detectable dust production. however, the best-fitting h2o sublimation model allows for brightening due to activity consistent with the scatter of the data. we estimate the production rate required for h2o outgassing to power the acceleration and find that, assuming a diameter of 300 m, 2003 rm would require q(h2o) ~ 1023 molec s-1 at perihelion. we investigate the recent dynamical history of 2003 rm and find that the object most likely originated in the mid-to-outer main belt (~86% probability) as opposed to from the jupiter-family comet region (~11% probability). further observations, especially in the infrared, could shed light on the nature of this anomalous acceleration. | (523599) 2003 rm: the asteroid that wanted to be a comet |
current gravitational-wave observations set the most stringent bounds on the abundance of primordial black holes (pbhs) in the solar mass range. this constraint, however, inherently relies on the merger rate predicted by pbh models. previous analyses have focused mainly on two binary formation mechanisms: early universe assembly out of decoupling from the hubble expansion and dynamical capture in present-day dark matter structures. using reaction rates of three-body processes studied in the astrophysical context, we show that, under conservative assumptions, three-body interactions in pbh halos efficiently produce binaries. those binaries form at high redshift in poisson-induced pbh small-scale structures and a fraction is predicted to coalesce and merge within the current age of the universe, at odds with the dynamical capture scenario where they merge promptly. in general, we find that this channel predicts rates comparable to the dynamical capture scenario. however, binaries formed from three-body interactions do not significantly contribute to the overall pbh merger rate unless pbhs made up a dominant fraction of the dark matter above the solar mass range, a scenario that is ruled out by current constraints. our results support strong bounds on the pbh abundance in the stellar mass range derived from laser interferometer gravitational-wave observatory/virgo/kagra observations. finally, we show that both dynamical channels are always subdominant compared to early universe assembly for pbh mergers in the asteroid mass range, while we expect it to become relevant in scenarios where pbhs are initially strongly clustered. | primordial black hole mergers from three-body interactions |
we report statistically significant detections of nonradial, nongravitational accelerations based on astrometric data in the photometrically inactive objects 1998 ky26, 2005 vl1, 2016 nj33, 2010 vl65, 2016 rh120, and 2010 rf12. the magnitudes of the nongravitational accelerations are greater than those typically induced by the yarkovsky effect, and there is no radiation-based, nonradial effect that can be so large. therefore, we hypothesize that the accelerations are driven by outgassing and calculate implied h2o production rates for each object. we attempt to reconcile outgassing-induced acceleration with the lack of visible comae or photometric activity via the absence of surface dust and low levels of gas production. although these objects are small, and some are rapidly rotating, the surface cohesive forces are stronger than the rotational forces, and rapid rotation alone cannot explain the lack of surface debris. it is possible that surface dust was removed previously, perhaps via outgassing activity that increased the rotation rates to their present-day value. we calculate dust production rates of order ~10-4 g s-1 in each object, assuming that the nuclei are bare, within the upper limits of dust production from a sample stacked image of 1998 ky26 of ${\dot{m}}_{\mathrm{dust}}\lt 0.2$ g s-1. this production corresponds to brightness variations of order ~0.0025%, which are undetectable in extant photometric data. we assess the future observability of each of these targets and find that the orbit of 1998 ky26-which is also the target of the extended hayabusa2 mission-exhibits favorable viewing geometry before 2025. | dark comets? unexpectedly large nongravitational accelerations on a sample of small asteroids |
nasa's lucy mission spacecraft was launched on 16 october 2021 and will perform the initial in situ investigation of the jovian trojan asteroids (levison et al. 2021, 2024). the lucy long range reconnaissance imager (l'lorri) is a panchromatic visible light (420-795 nm, 50% qe points), narrow-angle (field of view = 0.29°), high spatial resolution (1.0'' pixel−1) imager used on the lucy mission for both science observations and optical navigation. l'lorri is designed to provide maps of the sunlit portions of the trojan surfaces to a resolution of ∼10 m (after deconvolution), which will enable crater counting to constrain the surface ages. l'lorri's high sensitivity and large dynamic range permits imaging of the low albedo trojans at moderately large phase angles (down to i/f values of ∼0.0014 with snr ≈ 30 using an exposure time of 100 ms), as well as providing early acquisitions of the trojans during the approach phase, searches for trojan activity that are ∼10× better than can be obtained from earth, and deep searches for potential trojan satellites down to v ≈20.4 at spatial resolutions far surpassing that available from earth. this paper describes the l'lorri instrument design and the requirements that drove the design. we present results from l'lorri's ground calibration campaign, summarize the l'lorri in-flight calibration plan, and describe typical l'lorri operations scenarios during the trojan flybys. we also present an analysis of in-flight data taken during the first year of lucy operations, which show that most aspects of l'lorri's performance are nominal (i.e., as predicted), but the telescope's point spread function is slightly degraded relative to pre-flight predictions. nevertheless, l'lorri is still expected to fulfill all of its scientific objectives, which should revolutionize our view of the jovian trojans. | the lucy long range reconnaissance imager (l'lorri) |
mars is the next planet from the sun after earth. the minimum distance between the planets, due to the significant eccentricity of the orbit, in opposition varies from 55 to 101 million km. on the surface of mars, light continents, dark seas and very light polar caps are observed in the polar regions. the rotation of mars is direct with a period of 24h37m22.6679s. short-lived (days) light condensation clouds were recorded over the continents and volcanoes of the planet. darker dust clouds appeared over the seas. their life span ranges from days to months. it is believed that mars may once have had an almost terrestrial oxygen atmosphere, and water reserves in the form of seas and rivers. topographic data on the surface and features of planitia hellas indicate that in the past mars had a catastrophic collision with an asteroid of large size and high density. the resulting shock wave in the opposite hemisphere could lead to the formation of, among other things, the highest volcano in the solar system, mount olympus. before this event, atmospheric pressure could be up to 0.4 bar. such a collision in a short period of time led to the fact that mars got rid of water reserves on the surface. during its existence, it passed through three large-scale geological eras. the first phyllocian geological era began 4.5 billion years ago; it was wet and lasted more than 500 million years. after global climate change caused by volcanic activity, the theiikian era began; it lasted from 4 to 3.5 billion years ago. about 3.5 billion years ago, the third, siderikan era began. now mars is a desert. although volcanoes were active there 4 billion years ago, the planet was surrounded by a dense gas atmosphere, and water in the form of rain and snow fed lakes and seas. | history of possible climate change on mars |
we present preliminary diameters and albedos for 7956 asteroids detected in the first year of the neowise reactivation mission. of those, 201 are near-earth asteroids and 7755 are main belt or mars-crossing asteroids. 17% of these objects have not been previously characterized using the near-earth object wide-field infrared survey explorer, or “neowise” thermal measurements. diameters are determined to an accuracy of ∼20% or better. if good-quality h magnitudes are available, albedos can be determined to within ∼40% or better. | neowise reactivation mission year one: preliminary asteroid diameters and albedos |
this report summarizes observations of returned apollo rocks and soils, lunar surface images, orbital observations, and experimental impacts related to the erosion and comminution of rocks exposed at the lunar surface. the objective is to develop rigorous criteria for the recognition of impact processes that assist in distinguishing "impact" from other potential erosional processes, particularly thermal fatigue, which has recently been advocated specifically for asteroids. impact in rock is a process that is centrally to bilaterally symmetric, resulting in highly crushed, high-albedo, quasicircular depressions surrounded by volumetrically prominent spall zones. containing central glass-lined pits in many cases, such features provide distinctive evidence of impact that is not duplicated by any other process. additional evidence of impact can include radial fracture systems in the target that emanate from the impact point and clusters of fragments that attest to the lateral acceleration and displacement of each one. it is also important to note that impact produces a wide variety of fragment shapes that might totally overlap with those produced by thermal fatigue; we consider fragment shape to be an unreliable criterion for either process. the stochastic nature of the impact process will result in exponential survival times of surface rocks; that is, rock destruction initially is relatively efficient, but it is followed by ever increasing surface times for the last rock remnants. thermal fatigue, however, is essentially a thermal-equilibrium process. the corresponding distribution of survival times should be much more peaked in comparison, presumably gaussian, and diagnostically different from that due to impact. given the abundance of evidence that has been gleaned from returned apollo rocks and soils, it is surprising how little has been learned about the impact process from the photography of rocks and boulders taken by the astronauts on the lunar surface. this suggests that it will require rocks and soils returned from asteroids to evaluate the relative roles of thermal versus impact-triggered rock erosion, particularly when both processes are likely to be operating. | erosion of lunar surface rocks by impact processes: a synthesis |
we performed pulse-laser irradiation experiments of a primitive meteorite to simulate space weathering by micrometeorite bombardments on c-type asteroids. pellets of powdered murchison cm2 chondrite were set in vacuum and exposed to pulse laser with a diameter of 0.5 mm and delivered energies of 5, 10, and 15 mj. we measured reflectance spectra of unirradiated and irradiated surfaces of the pellets. during analysis the pellet was heated to approximately 100 °c and purged in n2 gas in order to reduce absorption of ambient water. the spectra become darker and bluer with increasing laser energies. their uv reflectance increases and 0.7- and 3-μm band depths decrease from 0 to 15 mj. the spectral bluing observed in our experiments reproduces the bluing occurred during space weathering of c-type asteroids. high-resolution observation by a transmission electron microscope showed that the laser heating causes preferential melting and evaporation in fes-rich fine-grained portions, which results in dispersion and deposition of numerous fes-rich amorphous silicate particles 20-1000 nm in size on the surface of the pellet. in addition, at the laser-irradiated but unmelted areas, heat-induced amorphization and decomposition of serpentine occur. these mineralogical changes make the reflectance spectra of the murchison cm chondrite darker and bluer. | pulse-laser irradiation experiments of murchison cm2 chondrite for reproducing space weathering on c-type asteroids |
context. planets orbiting low-mass stars such as m dwarfs are now considered a cornerstone in the search for planets with the potential to harbour life. gj 273 is a planetary system orbiting an m dwarf only 3.75 pc away, which is composed of two confirmed planets, gj 273b and gj 273c, and two promising candidates, gj 273d and gj 273e. planet gj 273b resides in the habitable zone. currently, due to a lack of observed planetary transits, only the minimum masses of the planets are known: mb sin ib = 2.89 m⊕, mc sin ic = 1.18 m⊕, md sin id = 10.80 m⊕, and me sin ie = 9.30 m⊕. despite its interesting character, the gj 273 planetary system has been poorly studied thus far.aims: we aim to precisely determine the physical parameters of the individual planets, in particular, to break the mass-inclination degeneracy to accurately determine the mass of the planets. moreover, we present a thorough characterisation of planet gj 273b in terms of its potential habitability.methods: first, we explored the planetary formation and hydration phases of gj 273 during the first 100 myr. secondly, we analysed the stability of the system by considering both the two- and four-planet configurations. we then performed a comparative analysis between gj 273 and the solar system and we searched for regions in gj 273 which may harbour minor bodies in stable orbits, that is, the main asteroid belt and kuiper belt analogues.results: from our set of dynamical studies, we find that the four-planet configuration of the system allows us to break the mass-inclination degeneracy. from our modelling results, the masses of the planets are unveiled as: 2.89 ≤ mb ≤ 3.03 m⊕, 1.18 ≤ mc ≤ 1.24 m⊕, 10.80 ≤ md ≤ 11.35 m⊕, and 9.30 ≤ me ≤ 9.70 m⊕. these results point to a system that is likely to be composed of an earth-mass planet, a super-earth and two mini-neptunes. based on planetary formation models, we determine that gj 273b is likely an efficient water captor while gj 273c is probably a dry planet. we find that the system may have several stable regions where minor bodies might reside. collectively, these results are used to offer a comprehensive discussion about the habitability of gj 273b. | gj 273: on the formation, dynamical evolution, and habitability of a planetary system hosted by an m dwarf at 3.75 parsec |
here, primordial black holes (pbhs) creation from exponential potential has been inquired, through gravitationally raised friction emanated from the nonminimal coupling between gravity and field derivative setup. setting a two-parted exponential function of inflaton field as coupling parameter, and fine-tuning of four parameter cases of our model, we could sufficiently slow down the inflaton owing to high friction during an ultra slow-roll phase. this empowers us to achieve enough enhancement in the amplitude of curvature perturbations power spectra, via numerical solving of mukhanov-sasaki equation. thereafter, we illustrate the generation of four pbhs with disparate masses in rd era, corresponding to our four parameter cases. two specimens of these pbhs with stellar 𝒪(10)m ⊙ and earth 𝒪(10-6)m ⊙ masses can be appropriate to explicate the ligo-virgo events, and the ultrashort-timescale microlensing events in ogle data, respectively. another two cases of pbhs have asteroid masses around 𝒪(10-13)m ⊙ and 𝒪(10-15)m ⊙ with abundance of 96% and 95% of the dark matter (dm) content of the universe. furthermore, we scrutinize the induced gravitational waves (gws) ensued from pbhs production in our model. subsequently, we elucidate that their contemporary density parameter spectra (ωgw0 ) for all predicted cases have acmes which lie in the sensitivity scopes of the gws detectors, thereupon the verity of our conclusions can be verified in view of deduced data from these detectors. at length, our numerical outcomes exhibit a power-law behavior for the spectra of ωgw0with respect to frequency as ωgw0(f) ~ (f/fc ) n in the proximity of acmes position. as well, in the infrared regime f ≪ fc , the log-reliant form of power index as n = 3 - 2/ln(fc /f) is attained. | primordial black holes ensued from exponential potential and coupling parameter in nonminimal derivative inflation model |
nasa's double asteroid redirection test (dart) mission intentionally impacted the asteroid dimorphos on september 26, 2022, and this kinetic impact changed dimorphos' orbit around its binary companion didymos. this first planetary defense test explored technological readiness for this method of asteroid deflection. | planetary defense with the double asteroid redirection test (dart) mission and prospects |
the osiris-rex mission collected a sample from the surface of the asteroid (101955) bennu in 2020 october. here, we study the impact of the osiris-rex touch-and-go sampling acquisition mechanism (tagsam) interacting with the surface of an asteroid in the framework of granular physics. traditional approaches to estimating the penetration depth of a projectile into a granular medium include force laws and scaling relationships formulated from laboratory experiments in terrestrial-gravity conditions. however, it is unclear that these formulations extend to the osiris-rex scenario of a 1300-kg spacecraft interacting with regolith in a microgravity environment. we studied the tagsam interaction with bennu through numerical simulations using two collisional codes, pkdgrav and gdc-i. we validated their accuracy by reproducing the results of laboratory impact experiments in terrestrial gravity. we then performed tagsam penetration simulations varying the following geotechnical properties of the regolith: packing fraction (p), bulk density, inter-particle cohesion (σc), and angle of friction (ϕ). we find that the outcome of a spacecraft-regolith impact has a non-linear dependence on packing fraction. closely packed regolith (p ≳ 0.6) can effectively resist the penetration of tagsam if ϕ ≳ 28° and/or σc ≳ 50 pa. for loosely packed regolith (p ≲ 0.5), the penetration depth is governed by a drag force that scales with impact velocity to the 4/3 power, consistent with energy conservation. we discuss the importance of low-speed impact studies for predicting and interpreting spacecraft-surface interactions. we show that these low-energy events also provide a framework for interpreting the burial depths of large boulders in asteroidal regolith. | modified granular impact force laws for the osiris-rex touchdown on the surface of asteroid (101955) bennu |
context. on september 26, 2022, the nasa dart mission impacted the asteroid dimorphos, the smaller component of the didymos binary asteroid system. this provided a unique opportunity to observe, in real time, the evolution of the ejecta cloud produced by the impact and the formation of a tail.aims: we present observations performed with the muse instrument at the very large telescope to characterise the morphology, spectral properties, and evolution of the ejecta. the didymos system was observed with muse on 11 nights from just before impact to almost one month post-impact, using both wide-field observations without adaptive optics and narrow-field observations with adaptive optics.methods: we produced white light images that were used to study the morphology of the ejecta at different spatial scales. the spectral information was used to search for gas emission from either exposed ice or propellant, and to study the spatial and temporal variation of the ejecta dust reflectance through reflectance maps.results: we searched for, but did not detect, emission from [oi], xe, nh2, and h2o+ in a 1'×1' field of view in our observations starting almost 4h after impact. we detected a number of morphological features, including a short-lived ejecta cloud visible on september 27 towards the east, spirals, clumps, and a tail that started forming only a few hours after impact. the analysis of the reflectance maps showed that the initial ejecta was bluer than the system before impact, while the tail and spirals were redder than the initial ejecta, consistent with them being made of larger particles. over the few weeks following impact, the tail became redder. no significant colour differences could be seen between the clumps and the initial ejecta. | morphology and spectral properties of the dart impact ejecta with vlt/muse |
we present here the decam ecliptic exploration project (deep), a three year noao/noirlab survey that was allocated 46.5 nights to discover and measure the properties of thousands of trans-neptunian objects (tnos) to magnitudes as faint as vr~27, corresponding to sizes as small as 20 km diameter. in this paper we present the science goals of this project, the experimental design of our survey, and a technical demonstration of our approach. the core of our project is "digital tracking," in which all collected images are combined at a range of motion vectors to detect unknown tnos that are fainter than the single exposure depth of vr~23 mag. through this approach we reach a depth that is approximately 2.5 magnitudes fainter than the standard lsst "wide fast deep" nominal survey depth of 24.5 mag. deep will more than double the number of known tnos with observational arcs of 24 hours or more, and increase by a factor of 10 or more the number of known small (<50 km) tnos. we also describe our ancillary science goals, including measuring the mean shape distribution of very small main belt asteroids, and briefly outline a set of forthcoming papers that present further aspects of and preliminary results from the deep program. | the decam ecliptic exploration project (deep): i. survey description, science questions, and technical demonstration |
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