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the near-earth object wide-field infrared survey explorer (neowise) reactivation mission has completed its third year of surveying the sky in the thermal infrared for near-earth asteroids and comets. neowise collects simultaneous observations at 3.4 and 4.6 μm of solar system objects passing through its field of regard. these data allow for the determination of total thermal emission from bodies in the inner solar system, and thus the sizes of these objects. in this paper, we present thermal model fits of asteroid diameters for 170 neos and 6110 main belt asteroids (mbas) detected during the third year of the survey, as well as the associated optical geometric albedos. we compare our results with previous thermal model results from neowise for overlapping sample sets, as well as diameters determined through other independent methods, and find that our diameter measurements for neos agree to within 26% (1σ) of previously measured values. diameters for the mbas are within 17% (1σ). this brings the total number of unique near-earth objects characterized by the neowise survey to 541, surpassing the number observed during the fully cryogenic mission in 2010. | neowise reactivation mission year three: asteroid diameters and albedos |
we use data from five stellar occultations observed between 2013 and 2016 to constrain chariklo’s size and shape, and the ring reflectivity. we consider four possible models for chariklo (sphere, maclaurin spheroid, triaxial ellipsoid, and jacobi ellipsoid), and we use a bayesian approach to estimate the corresponding parameters. the spherical model has a radius r = 129 ± 3 km. the maclaurin model has equatorial and polar radii a=b={143}-6+3 {km} and c={96}-4+14 {km}, respectively, with density {970}-180+300 {kg} {{{m}}}-3. the ellipsoidal model has semiaxes a={148}-4+6 {km}, b={132}-5+6 {km}, and c={102}-8+10 {km}. finally, the jacobi model has semiaxes a = 157 ± 4 km, b = 139 ± 4 km, and c = 86 ± 1 km, and density {796}-4+2 {kg} {{{m}}}-3. depending on the model, we obtain topographic features of 6-11 km, typical of saturn icy satellites with similar size and density. we constrain chariklo’s geometric albedo between 3.1% (sphere) and 4.9% (ellipsoid), while the ring i/f reflectivity is less constrained between 0.6% (jacobi) and 8.9% (sphere). the ellipsoid model explains both the optical light curve and the long-term photometry variation of the system, giving a plausible value for the geometric albedo of the ring particles of 10%-15%. the derived mass of chariklo of 6-8 × 1018 kg places the rings close to 3:1 resonance between the ring mean motion and chariklo’s rotation period. based on observations obtained at the southern astrophysical research (soar) telescope, which is a joint project of the ministério da ciência, tecnologia, e inovação (mcti) da república federativa do brasil, the u.s. national optical astronomy observatory (noao), the university of north carolina at chapel hill (unc), and michigan state university (msu). | size and shape of chariklo from multi-epoch stellar occultations |
we were able to accurately predict the shadow path and successfully observe an occultation of a bright star by chiron on december 15, 2022. the kottamia astronomical observatory in egypt did not detect the occultation by the solid body, but we found three extinction features in the light curve that had symmetrical counterparts with respect to the central time of the occultation. one of the features is broad and shallow, whereas the other two features are sharper, with a maximum extinction of ∼25% at the achieved spatial resolution of 19 km per data point. from the wise observatory in israel, we detected the occultation caused by the main body and several extinction features surrounding the body. when all the secondary features are plotted in the sky plane, we find that they can be caused by a broad ∼580 km disk with concentrations at radii of 325 ± 16 km and 423 ± 11 km surrounding chiron. at least one of these structures appears to be outside the roche limit. the ecliptic coordinates of the pole of the disk are λ = 151° ±8° and β = 18° ±11°, in agreement with previous results. we also reveal our long-term photometry results, indicating that chiron had suffered a brightness outburst of at least 0.6 mag between march and september 2021 and that chiron was still somewhat brighter at the occultation date than at its nominal pre-outburst phase. the outermost extinction features might be consistent with a bound or temporarily bound structure associated with the brightness increase. however, the nature of the brightness outburst is unclear, and it is also unclear whether the dust or ice released in the outburst could be feeding a putative ring structure or whether it is emanating from it. | changing material around (2060) chiron revealed by an occultation on december 15, 2022 |
planet formation begins with collisional growth of small planetesimals accumulating into larger ones. such growth occurs while planetesimals are embedded in a gaseous protoplanetary disc. however, small planetesimals experience collisions and gas drag that lead to their destruction on short time-scales, not allowing, or requiring fine-tuned conditions for the efficient growth of ∼metre-sized objects. here we show that ∼104 interstellar objects such as the recently detected 1i/2017-u1 (`oumuamua) could have been captured, and become part of the young solar system, together with up to hundreds of ∼km-sized ones. the capture rates are robust even for conservative assumptions on the protoplanetary disc structure, local stellar environment, and planetesimal interstellar medium density. `seeding' of such planetesimals then catalyses further planetary growth into planetary embryos, and potentially alleviates the main challenges with the metre-sized growth barrier. the capture model is in synergy with the current leading planet formation theories, providing the missing link to the first planetesimals. moreover, planetesimal capture provides a far more efficient route for lithopanspermia than previously thought. | planet seeding through gas-assisted capture of interstellar objects |
context. a large fraction of transneptunian objects are found in binary pairs, ~30% in the cold classical population between ahel ~ 39 and ~48 au. observationally, these binaries generally have components of similar size and colour. previous work has shown that gravitational collapse of a pebble cloud is an efficient mechanism for producing such systems. since the bi-lobate nature of 2014 mu69 (arrokoth) was discovered, interest in gravitational collapse as a pathway for forming contact binaries has also grown.aims: we investigate the formation of binary systems through gravitational collapse by considering a wider range of binary masses than previous studies. we analysed in detail the properties of the bound systems that are formed and compared them to observations.methods: we performed n-body simulations of gravitational collapse of a pebble cloud using the rebound package, with an integrator designed for rotating reference frames and robust collision detection. we conducted a deep search for gravitationally bound particles at the end of the gravitational collapse phase and tested their stability. for all systems produced, not just for the most massive binaries, we investigated the population characteristics of their mass and orbital parameters.results: we found that gravitational collapse is an efficient producer of bound planetesimal systems. on average, about 1.5 bound systems were produced per cloud in the mass range studied here. in addition to large equal-sized binaries, we found that gravitational collapse produces massive bodies with small satellites and low-mass binaries with a high mass ratio. our results disfavour the collapse of high-mass clouds, in line with reported upper mass limits of clouds formed by the streaming instability. gravitational collapse can create binary systems analogous to arrokoth, and collisions in a collapsing cloud should be gentle enough to preserve a bi-lobed structure. | investigating gravitational collapse of a pebble cloud to form transneptunian binaries |
we investigate the possible origins of real high-inclination centaurs and trans-neptunian objects using a high-resolution statistical search for stable orbits that simulates their evolution back in time to the epoch when planet formation ended 4.5 billion years in the past. the simulation is a precise orbit determination method that does not involve ad hoc initial conditions or assumptions such as those found in planetesimal disc relaxation models upon which their conclusions depend. it can therefore be used to independently test origin theories based on relaxation models by examining the past orbits of specific real objects. here, we examined 17 multiple-opposition high-inclination centaurs and the two polar trans-neptunian objects 2008 kv42 and (471325) 2011 kt19. the statistical distributions show that their orbits were nearly polar 4.5 gyr in the past, and were located in the scattered disc and inner oort cloud regions. early polar inclinations cannot be accounted for by current solar system formation theory as the early planetesimal system must have been nearly flat in order to explain the low-inclination asteroid and kuiper belts. furthermore, the early scattered disc and inner oort cloud regions are believed to have been devoid of solar system material as the planetesimal disc could not have extended far beyond neptune's current orbit in order to halt the planet's outward migration. the nearly polar orbits of high-inclination centaurs 4.5 gyr in the past therefore indicate their probable early capture from the interstellar medium. | an interstellar origin for high-inclination centaurs |
we report on our detailed characterization of earth's second known temporary natural satellite, or minimoon, asteroid 2020 cd3. an artificial origin can be ruled out based on its area-to-mass ratio and broadband photometry, which suggest that it is a silicate asteroid belonging to the s or v complex in asteroid taxonomy. the discovery of 2020 cd3 allows for the first time a comparison between known minimoons and theoretical models of their expected physical and dynamical properties. the estimated diameter of ${1.2}_{-0.2}^{+0.4}$ m and geocentric capture approximately a decade after the first known minimoon, 2006 rh120, are in agreement with theoretical predictions. the capture duration of 2020 cd3 of at least 2.7 yr is unexpectedly long compared to the simulation average, but it is in agreement with simulated minimoons that have close lunar encounters, providing additional support for the orbital models. 2020 cd3's atypical rotation period, significantly longer than theoretical predictions, suggests that our understanding of meter-scale asteroids needs revision. more discoveries and a detailed characterization of the population can be expected with the forthcoming vera c. rubin observatory legacy survey of space and time. | establishing earth's minimoon population through characterization of asteroid 2020 cd3 |
in this work, we model the collisional evolution of the jupiter trojans and determine under which conditions the eurybates-queta system survives. we show that the collisional strength of the jupiter trojans and the age of the eurybates family and by extension queta are correlated. the collisional grinding of the jupiter trojan population over 4.5 gy results in a size-frequency distribution (sfd) that remains largely unaltered at large sizes (>10 km) but is depleted at small sizes (10 m to 1 km). this results in a turnover in the sfd, the location of which depends on the collisional strength of the material. it is to be expected that the trojan sfd bends between 1 and 10 km. based on the sfd of the eurybates family, we find that the family was likely the result of a catastrophic impact onto a 100 km rubble pile target. this corresponds to objects with a rather low collisional strength (10 times weaker than that of basaltic material studied in benz & asphaug). assuming this weak strength, and an initial cumulative slope of the size-frequency distribution of 2.1 between diameters of 2 m and 100 km when the trojans were captured, the existence of queta, the satellite of eurybates, implies an upper limit for the family age of 3.7 gy. alternatively, we demonstrate that an unconventional collisional strength with a minimum at 20 m is a plausible candidate to ensure the survival of queta over the age of the solar system. finally, we show how different collisional histories change the expected number of craters on the targets of the lucy mission and that lucy will be able to differentiate between them. | implications for the collisional strength of jupiter trojans from the eurybates family |
with the successful impact of the nasa double asteroid redirection test (dart) spacecraft in the didymos-dimorphos binary asteroid system, we provide an initial analysis of the post-impact perturbed binary asteroid dynamics. to compare our simulation results with observations, we introduce a set of "observable elements" calculated using only the physical separation of the binary asteroid, rather than traditional keplerian elements. using numerical methods that treat the fully spin-orbit-coupled dynamics, we estimate the system's mass and the impact-induced changes in orbital velocity, semimajor axis, and eccentricity. we find that the changes to the mutual orbit depend strongly on the separation distance between didymos and dimorphos at the time of impact. if dimorphos enters a tumbling state after the impact, this may be observable through changes in the system's eccentricity and orbit period. we also find that any dart-induced reshaping of dimorphos would generally reduce the required change in orbital velocity to achieve the measured post-impact orbit period, and will be assessed by the esa hera mission in 2027. | the perturbed full two-body problem: application to post-dart didymos |
collected by mars rovers and orbital modules data allowed the researchers to reconstruct the possible stages of development of mars: the first geological era - phyllocian (4,5 - 4,0-3,8)×109 years ago, the second era - theiikian (4,0-3, - 3,5-3,3)×109 years ago, and about (3,5 - 3,3)×109 years ago the third era began - siderikan. in the first era, mars was like on the ancient earth: had the thick atmosphere, and there was much warmer than it is now. that is, the planet had once been a much more suited for the existence of life there than it is today. in those years, there was a simple life on earth, and it is possible that it could have arisen on mars. falling of fragments of cometary nuclei on the surface of the planet can bring embryos of possible life (panspermia). later, impact craters - have preserved the resultant life, sprinkled some signs of life by soil emissions. a catastrophic collision with a large asteroid has led to the formation of enormous astrobleme hellas. it is located near the southern polar region. now, it is a plan, with a diameter of more than 4000 km, which is narrowed at the bottom to 1500 km and is surrounded by rocks emissions. its depth reaches 9 km. emissions of millions of tons of soil on thousands of kilometers - have covered a significant part of the surface of mars. on such a surface could be the possible samples of just started to arise life | is there life on mars and where necessary to search for its traces |
chondrites are fragments of unmelted asteroids that formed due to gravitational instabilities in turbulent regions of the solar protoplanetary disk. hydrated chondrites are common among meteorites, indicating that a substantial fraction of the rocky bodies that formed early in the solar system accreted water ice grains that subsequently melted due to heat released by the radioactive decay of 26al. however, the thermal histories of asteroids are still largely unknown; increased knowledge would provide fundamental information on their timing of accretion and their physical characteristics. here we show that hydrated meteorites (cm chondrites) contain previously uncharacterized calcium carbonates with peculiar oxygen isotopic compositions (δ17o ≈ -2.5‰), which artificially produce the mass-independent trend previously reported for carbonates. based on these isotopic data, we propose a new model to quantitatively estimate the precipitation temperatures of secondary phases (carbonates and serpentine). it reveals that chondritic secondary phases recorded a gradual increase in temperature during the extent of aqueous alteration, from -10°c to a maximum of 250°c. we also show that the thermal path of c-type asteroids is independent of the initial oxygen isotopic composition of the primordial water ice grains that they accreted. our estimated temperatures for hydrated asteroids remain lower than those experienced by other carbonaceous chondrites, providing strong constraints for modeling the formation conditions and size distribution of water-rich asteroids, especially in anticipation of the return of samples of water-rich asteroids to earth by the osiris-rex and hayabusa2 missions. | thermal evolution of hydrated asteroids inferred from oxygen isotopes |
nasa's double asteroid redirection test (dart) mission is the first full-scale planetary defense mission. the target is the binary asteroid (65803) didymos, in which the smaller component dimorphos (~164 m equivalent diameter) orbits the larger component didymos (~780 m equivalent diameter). the dart spacecraft will impact dimorphos, changing the system's mutual orbit by an amount that correlates with dart's kinetic deflection capability. the spacecraft collision with dimorphos creates an impact crater, which reshapes the body. also, some particles ejected from the dart impact site on dimorphos eventually reach didymos. because didymos's rapid spin period (2.26 hr) may be close to its stability limit for structural failure, the ejecta reaching didymos may induce surface disturbance on didymos. while large uncertainties exist, nonnegligible reshaping scenarios on didymos and dimorphos are possible if certain conditions are met. our analysis shows that given a surface slope uncertainty on dimorphos of 45°, with no other information about its local topography, and if the dart-like impactor is treated as spherical, the ejecta cone crosses didymos with speeds ≳14 m s-1 in 13% of simulations. additional work is necessary to determine the amount of mass delivered to didymos from the dart impact and whether the amount of kinetic energy delivered is sufficient to overcome cohesive forces in those cases. if nonnegligible (but small) reshaping occurs for either of these asteroids, the resulting orbit perturbation and reshaping are measurable by earth-based observations. | double asteroid redirection test (dart): structural and dynamic interactions between asteroidal elements of binary asteroid (65803) didymos |
different discretization and trust-region methods are compared for the low-thrust fuel-optimal trajectory optimization problem using successive convex programming. in particular, the differential and integral formulations of the adaptive pseudospectral legendre-gauss-radau method, an arbitrary-order legendre-gauss-lobatto technique based on hermite interpolation, and a first-order-hold discretization are considered. the number of discretization points and segments is varied. moreover, two hard-trust-region methods and a soft-trust-region strategy are compared. it is briefly discussed whether these methods, if implemented on relevant hardware, would fulfill the general requirements for onboard guidance. a perturbed cubic interpolation and the propagation of the nonlinear dynamics are used to generate initial guesses of varying quality. interplanetary transfers to a near-earth asteroid, venus, and asteroid dionysus are chosen to assess the overall performance. | performance assessment of convex low-thrust trajectory optimization methods |
the five libration points of a sun-planet system are stable or unstable fixed positions at which satellites or asteroids can remain fixed relative to the two orbiting bodies. a moon orbiting around the planet causes a time-dependent perturbation on the system. here, we address the sense in which invariant structure remains. we employ a transition state theory developed previously for periodically driven systems with a rank-1 saddle in the context of chemical reactions. we find that a satellite can be parked on a so-called time-periodic transition state trajectory - which is an orbit restricted to the vicinity of the libration point l2 for infinitely long time - and investigate the stability properties of that orbit. | on the stability of satellites at unstable libration points of sun-planet-moon systems |
worldwide tsunamis driven by atmospheric waves-or planetary meteotsunami waves-are extremely rare events. they mostly occur during supervolcano explosions or asteroid impacts capable to generate atmospheric acoustic-gravity waves including the lamb waves that can circle the globe multiple times. recently, such ocean waves have been globally recorded after the hunga tonga-hunga ha'apai volcano eruption on 15 january 2022, but did not pose any serious danger to the coastal communities. however, this study highlights that the mostly ignored destructive potential of planetary meteotsunami waves can be compared to the well-studied tsunami hazards. in practice, several process-oriented numerical experiments are designed to force a global ocean model with the realistic atmospheric response to the hunga tonga-hunga ha'apai event rescaled in speed and amplitude. these simulations demonstrate that the meteotsunami surges can be higher than 1 m (and up to 10 m) along more than 7% of the world coastlines. planetary meteotsunami waves thus have the potential to cause serious coastal damages and even human casualties during volcanic explosions or asteroid impacts either releasing intense acoustic energy or producing internal atmospheric gravity waves triggering the deep-ocean proudman resonance at a speed of ∼212 m s−1. based on records of catastrophic events in earth's history, both scenarios are found to be realistic, and consequently, the global meteotsunami hazards should now be properly assessed to prepare for the next big volcanic eruption or asteroid impact even occurring inland. | destructive potential of planetary meteotsunami waves beyond the hunga tonga-hunga ha`apai volcano eruption |
understanding the origin and evolution of near-earth asteroids (neas) is an issue of scientific interest and practical importance because neas are potentially hazardous to the earth. however, when and how neas formed and their evolutionary history remain enigmas. here, we report the u-pb systematics of itokawa particles for the first time. ion microprobe analyses of seven phosphate grains from a single particle provide an isochron age of 4.64 ± 0.18 billion years (1σ). this ancient phosphate age is thought to represent the thermal metamorphism of itokawa's parent body, which is identical to that of typical ll chondrites. in addition, the incorporation of other particles suggests that a significant shock event might have occurred 1.51 ± 0.85 billion years ago (1σ), which is significantly different from the shock ages of 4.2 billion years of the majority of shocked ll chondrites and similar to that of the chelyabinsk meteorite. combining these data with recent ar-ar studies on particles from a different landing site, we conclude that a globally intense impact, possibly a catastrophic event, occurred ca. 1.4 ga ago. this conclusion enables us to establish constraints on the timescale of asteroid disruption frequency, the validity of the crater chronology and the mean lifetime of small neas. | thermal and impact histories of 25143 itokawa recorded in hayabusa particles |
early stage smoke detection using image and video analysis is an important area of research due to its enormous applications in mitigating fire hazards and ensuring environmental safety. numerous solutions have been proposed for real-time smoke detection using conventional image processing, machine learning, and deep learning techniques. smoke pattern, motion analysis, color and texture are important characteristics that help identify it in the outdoor environment. vision-based smoke detection algorithms can be broadly classified into three categories: smoke classification, segmentation, and bounding box estimation. this paper presents a comprehensive survey of existing techniques on smoke detection in the outdoor environment using image and video analysis. to perform the survey, initially 271 articles were collected from different sources like google scholar, science direct, ieee xplore, springerlink, wiley and acm digital library using the keyword search. based on their focus on the vision-based solutions for the outdoor environment, 126 articles were identified as relevant to the present survey. starting from the initial ip approaches that are frequently referred in the literature, machine learning and deep learning approaches have also been reviewed for each type of smoke detection. performance of algorithms, datasets used in the research, evaluation metrics, challenges and future directions of research are also discussed. | a survey on vision-based outdoor smoke detection techniques for environmental safety |
we report evidence of comet-like activity on asteroid 2009 dq118, a quasi-hilda object near the 3:2 interior mean-motion resonance with jupiter. this discovery was made by volunteers as part of the active asteroids citizen science project, a nasa partner hosted on the zooniverse platform. follow-up archival searches yielded over 20 images of 2009 dq118 exhibiting a comet-like tail on ut 2016 march 8 and 9 acquired with the dark energy camera on the blanco 4 m telescope at the cerro tololo inter-american observatory, chile. these images were taken when 2009 dq118 was near its 2016 perihelion passage. 2009 dq118 will next reach perihelion on ut 2023 april 22; hence, the next several months are an excellent time to observe 2009 dq118 to search for a second epoch of activity for this object. | comet-like activity discovered on quasi-hilda asteroid 2009 dq118 |
acapulcoites-lodranites, ureilites, brachinites, brachinite-like achondrites and winonaites are the main groups of primitive achondrites. they are variably depleted in incompatible lithophile elements (al, na, k and rare earth elements) and siderophile/chalcophile elements relative to chondrites and are interpreted as the residual mantle of planetesimals from which silicate melts and sulfide/metal melts were extracted. we use a series of melting experiments conducted with various chondritic compositions (cv, cm, ci, h and ll) to constrain the oxygen fugacity (fo2), the temperature, extent of melting and the initial bulk composition of the parent bodies of primitive achondrites. they melted at different and variable fo2: δiw -0.5/-1.0 for brachinites, δiw -1.3/-2.5 for ureilites, δiw -1.6/-2.7 for acapulcoites/lodranites and δiw -2.5/-3.0 for winonaites (with δiw = log fo2 - (log fo2)iw; iw being the iron-wustite buffer). those main groups of primitive achondrites, which have nucleosynthetic anomalies characteristic of the "non-carbonaceous" reservoir and the inner solar system, were not initially depleted in na2o and k2o relative to the sun's photosphere. this suggests, in accordance with the enrichment in the heavy isotopes of zn, rb and k in eucrites, that the depletion of moderately volatile elements in planetesimals that melted to a larger extent (e.g. vesta, the angrite parent body) resulted from evaporative losses during partial melting. the depletion of moderately volatile elements in terrestrial planets is likely inherited from partial melting and differentiation of small planetary bodies rather than from the incomplete condensation of the solar nebula. | formation of primitive achondrites by partial melting of alkali-undepleted planetesimals in the inner solar system |
measuring the strengths of asteroidal materials is important for developing mitigation strategies for potential earth impactors and for understanding properties of in situ materials on asteroids during human and robotic exploration. studies of asteroid disruption and fragmentation have typically used the strengths determined from terrestrial analog materials, although questions have been raised regarding the suitability of these materials. the few published measurements of meteorite strength are typically significantly greater than those estimated from the stratospheric breakup of meter-sized meteoroids. given the paucity of relevant strength data, the scale-varying strength properties of meteoritic and asteroidal materials are poorly constrained. based on our uniaxial failure studies of centimeter-sized cubes of a carbonaceous and ordinary chondrite, we develop the first weibull failure distribution analysis of meteorites. this weibull distribution projected to meter scales, overlaps the strengths determined from asteroidal airbursts and can be used to predict properties of to the 100 m scale. in addition, our analysis shows that meter-scale boulders on asteroids are significantly weaker than small pieces of meteorites, while large meteorites surviving on earth are selected by attrition. further, the common use of terrestrial analog materials to predict scale-dependent strength properties significantly overestimates the strength of meter-sized asteroidal materials and therefore is unlikely well suited for the modeling of asteroid disruption and fragmentation. given the strength scale-dependence determined for carbonaceous and ordinary chondrite meteorites, our results suggest that boulders of similar composition on asteroids will have compressive strengths significantly less than typical terrestrial rocks. | scale-dependent measurements of meteorite strength: implications for asteroid fragmentation |
alteration of iron sulfides on the lunar surface by space weathering is poorly understood. we examined space weathering features of iron sulfides in lunar mature soil grains using scanning electron microscopy (sem) and transmission electron microscopy (tem). sem observations reveal that iron sulfides have vesicular textures and iron whiskers on their surfaces. iron sulfides observed using tem are troilite and nc-pyrrhotite. the space-weathered rim on the iron sulfides is characterized by crystallographic misorientations and the disappearance of superstructure reflections of troilite in electron diffraction patterns. these crystallographic modifications are probably produced by solar wind irradiation. the rim contains opened vesicles that are aligned along the c-plane of the sulfides, as well as numerous tiny vesicles. the fe/s ratio at the surface of the rim is higher than in non-altered regions, indicating selective sulfur loss from the surface. iron whiskers protrude from the space weathered rim and consist of polycrystalline metallic iron. the sulfide rims and the iron whiskers are both coated with vapor-deposited materials rich in o and si. the combined processes driven by the solar wind irradiation, heating during impact events, solar uv radiation, and the thermal cycling may cause vesicular textures, selective sulfur escape from the iron sulfides, and the formation of the iron whiskers. the rim textures support the notion that the enrichment of heavy sulfur isotopes in mature lunar soils is caused by space weathering of iron sulfides. the space weathered rims on lunar iron sulfides are similar to those observed in regolith samples from asteroid itokawa. therefore, alterations of sulfide surface might be common among airless bodies in the solar system. | space weathering of iron sulfides in the lunar surface environment |
we performed h+ and he+ irradiation experiments on slabs of the murchison cm2 meteorite to simulate solar wind irradiation of carbonaceous asteroids. two separate 6 mm × 6 mm regions were irradiated with 1 kev h+ and 4 kev he+, respectively, to fluences of 8.1 × 1017 ions/cm2 for h+ and 1 × 1018 ions/cm2 for he+. unirradiated and irradiated surfaces were analyzed using x-ray photoelectron spectroscopy (xps), visible to near-infrared spectroscopy (vnir; 0.35-2.5 μm), and microprobe two-step laser-desorption mass spectrometry (μl2ms). we also performed analytical field-emission scanning transmission electron microscopy (fe-stem) on focused ion beam (fib) cross-sections extracted from olivine grains and matrix material within the h+- and he+-irradiated regions. in situ xps analyses suggest that ion irradiation results in the removal of most surface carbon and the partial reduction of surface iron to lower oxidation states. in response to he+-irradiation, we observe brightening (longward of ~0.75 μm) and reddening of reflectance spectra, which is a departure from typical lunar-style space weathering. additionally, h+- and he+-irradiation have opposing effects on organic carbon content: h+-irradiation increases the abundance of some low-molecular-weight free organic species by breaking down macromolecular material while he+-irradiation causes a decrease in overall organic content by cleaving bonds and sputtering constituent atoms. this suggests that solar wind h+-irradiation and solar wind he+-irradiation change the organic functional group chemistry of asteroidal regolith in different ways. in contrast to some previous experimental space weathering studies, we observe an increase in h2o and oh- abundances in our sample in response to both types of ion irradiation. fe-stem and energy dispersive x-ray spectroscopy (edx) analyses show complete amorphization of matrix phyllosilicates in ion-affected rims, partial amorphization of olivine, and changes in si and mg concentrations at and/or near the surface. we discuss the implications of these results for understanding the complex nature of space weathering on primitive, carbon-rich asteroids and for analyzing future returned samples from carbonaceous asteroids bennu and ryugu. | characterizing the spectral, microstructural, and chemical effects of solar wind irradiation on the murchison carbonaceous chondrite through coordinated analyses |
micrometeorites (mms) recovered from surface snow near the dome fuji station, antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. we carried out a comprehensive study on seven porous and fluffy mms [four chondritic porous (cp) mms and three fluffy fine-grained (fluffy fg) mms] and one fine-grained type 1 (fg c1) mm for comparison with scanning electron microscope, transmission electron microscope, x-ray absorption near-edge structure analysis, and secondary ion mass spectrometer. they show a variety of early aqueous activities. four out of the seven cp mms contain glass with embedded metal and sulfide (gems) and enstatite whiskers/platelets and do not have hydrated minerals. despite the same mineralogy, organic chemistry of the cp mms shows diversity. two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (ctbnd n) and/or nitrogen heterocyclic groups with d and 15n enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. another two cp mms are poorer in organic materials than the above-mentioned mms. organic material in one of them is richer in aromatic c than the cp mms mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. in addition, bulk chemical compositions of gems in the latter organic poor cp mms are more homogeneous and have higher fe/(si + mg + fe) ratios than those of gems in the former organic-rich cp mms. functional group of the organic materials and amorphous silicate in gems in the organic-poor cp mms may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals. three fluffy fg mms contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. phyllosilicates in thee mms are richer in fe than those in hydrated idps, typical fine-grained hydrated (fg c1) mms, and hydrated carbonaceous chondrites. one of the fluffy fg mms contains amorphous silicate, which is richer in fe than gems and contains little or no nanophase fe metal but contains fe sulfide. because the chemical compositions of the amorphous silicate are within the compositional field of gems in cp idps, the amorphous silicate may be alteration products of gems. the entire compositional field of gems in the cp mms and the amorphous silicate in the fluffy fg mm matches that of the previously reported total compositional range of gems in idps. one fluffy fg mm contains mg-rich phyllosilicate along with fe-rich phyllosilicate and mg-fe carbonate. mg-rich phyllosilicate and mg-fe carbonate may have been formed through the reaction of fe-rich phyllosilicate, mg-rich olivine and pyroxene, and water with c-bearing chemical species. these data indicate that cp mms and fluffy fg mms recovered from antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. because mineralogy and isotopic and structural features of organic materials in d10ib009 are comparable with isotopically primitive idps, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). by contrast, organic-poor cp mms may have experienced the earliest stage of aqueous alteration and fluffy fg mms experienced weak aqueous alteration. the precursor materials of the parent bodies of fluffy fg mms probably contained abundant gems or gems-like materials like cp idps, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as cr3s. however, highly porous nature of organic-poor cp mms and fluffy fg mms suggests that parent bodies of these mms must have been much more porous than the parent bodies of primitive carbonaceous chondrites. given no phyllosilicate among the returned samples of 81p/wild 2 comet, the mms may have been derived from porous icy asteroids such as active asteroids as well as p- and d-type asteroids rather than comets. | variation of mineralogy and organic material during the early stages of aqueous activity recorded in antarctic micrometeorites |
chondritic meteorites are fragments of asteroids, the building blocks of planets, that retain a record of primordial processes. important in their early evolution was impact-driven lithification, where a porous mixture of millimetre-scale chondrule inclusions and sub-micrometre dust was compacted into rock. in this article, the shock compression of analogue precursor chondrite material was probed using state of the art dynamic x-ray radiography. spatially-resolved shock and particle velocities, and shock front thicknesses were extracted directly from the radiographs, representing a greatly enhanced scope of data than could be measured in surface-based studies. a statistical interpretation of the measured velocities showed that mean values were in good agreement with those predicted using continuum-level modelling and mixture theory. however, the distribution and evolution of wave velocities and wavefront thicknesses were observed to be intimately linked to the mesoscopic structure of the sample. this article provides the first detailed experimental insight into the distribution of extreme states within a shocked powder mixture, and represents the first mesoscopic validation of leading theories concerning the variation in extreme pressure-temperature states during the formation of primordial planetary bodies. | probing the early stages of shock-induced chondritic meteorite formation at the mesoscale |
this paper presents an improved algorithm for the 2d and 3d fourier forward modeling of gravity fields caused by polyhedral bodies with constant and exponential density distributions. three modifications have been made to the fourier forward algorithm introduced in a previous paper. first, vertex-based fourier-domain expressions are used instead of the original face-based fourier-domain expressions, which simplify the computation of the anomaly spectrum considerably, especially in 3d modeling problems. second, instead of using a pure gauss-fft sampling of the anomaly spectrum, we apply an improved sampling strategy by combining a nonuniform spherical sampling with a low-order gauss-fft sampling. in this way, the number of samplings required in the fourier domain reduces to about 1/3 and 1/7 of those required in a pure gauss-fft algorithm for 2d and 3d modeling problems, respectively. a significant acceleration over the original algorithm is achieved. third, we incorporate all three types of nonuniform fast fourier transform algorithms to transform directly a uniform or nonuniform anomaly spectrum to gravity fields either on a regular grid, or at a set of arbitrary positions. extra interpolation operations are no longer needed. synthetic numerical tests show that for gravity vector components, the new algorithm runs about 3 times faster in 2d modeling and 7 times faster in 3d modeling than the original ones, while maintaining the same level of accuracy. for the gravity potential, the new algorithm is significantly superior to the pure gauss-fft solution both in numerical accuracy and in efficiency. we apply this novel approach to compute the gravitational fields of asteroid 101955 bennu and comet 67p/churyumov-gerasimenko. the 2d algorithm works very efficiently for the computation of gravity fields on horizontal planes. the 3d algorithm is valid both outside, on, and inside the source's bounding surface, with relative errors less than 0.1% for the gravity potential and less than 2% for the gravity vector. by comparing to modeling results of analytical and spherical harmonic-based solutions, we generally conclude that the fourier-based algorithm introduced here is an attractive alternative to these conventional solutions, especially for nonspherical, irregularly shaped bodies with complex geometries. | improved fourier modeling of gravity fields caused by polyhedral bodies: with applications to asteroid bennu and comet 67p/churyumov-gerasimenko |
we estimate the capture rate of interstellar objects by means of three-body gravitational interactions. we apply this model to the sun-jupiter system and the alpha centauri a&b binary system, and find that the radius of the largest captured object is a few tens of km and earth-sized, respectively. we explore the implications of our model for the transfer of life by means of rocky material. the interstellar comets captured by the “fishing net” of the solar system can be potentially distinguished by their differing orbital trajectories and ratios of oxygen isotopes through high-resolution spectroscopy of water vapor in their tails. | implications of captured interstellar objects for panspermia and extraterrestrial life |
in ordinary chondrites (ocs), phosphates and feldspar are secondary minerals known to be the products of parent-body metamorphism. both minerals provide evidence that metasomatic fluids played a role during metamorphism. we studied the petrology and chemistry of phosphates and feldspar in petrologic type 4-6 l chondrites, to examine the role of metasomatic fluids, and to compare metamorphic conditions across all three oc groups. apatite in l chondrites is cl-rich, similar to h chondrites, whereas apatite in ll chondrites has lower cl/f ratios. merrillite has similar compositions among the three chondrite groups. feldspar in l chondrites shows a similar equilibration trend to ll chondrites, from a wide range of plagioclase compositions in petrologic type 4 to a homogeneous albitic composition in type 6. this contrasts with h chondrites which have homogeneous albitic plagioclase in petrologic types 4-6. alkali- and halogen-rich and likely hydrous metasomatic fluids acted during prograde metamorphism on oc parent bodies, resulting in albitization reactions and development of phosphate minerals. fluid compositions transitioned to a more anhydrous, cl-rich composition after the asteroid began to cool. differences in secondary minerals between h and l, ll chondrites can be explained by differences in fluid abundance, duration, or timing of fluid release. phosphate minerals in the regolith breccia, kendleton, show lithology-dependent apatite compositions. bulk cl/f ratios for ocs inferred from apatite compositions are higher than measured bulk chondrite values, suggesting that bulk f abundances are overestimated and that bulk cl/f ratios in ocs are similar to ci. | phosphate and feldspar mineralogy of equilibrated l chondrites: the record of metasomatism during metamorphism in ordinary chondrite parent bodies |
to understand oxygen isotope ratios and redox conditions of the chondrule formation environments of the outer rigions of the asteroid belt, we analyzed major element concentrations and oxygen isotope ratios of olivine grains in chondrules, isolated forsterite, and isolated olivine from the wis 91600 and met 00432 carbonaceous chondrites, which are thought to have originated from d-type asteroids located in the outer asteroid belt. the oxygen isotope ratios of individual chondrules and isolated grains show a wide variation in δ18o from -9.9‰ to +9.1‰ along the carbonaceous chondrite anhydrous mineral (ccam) and primitive chondrule mineral (pcm) lines. the δ17o (= δ17o - 0.52 × δ18o) values of the measured objects increase with decreasing mg#; i.e., feo-poor objects (mg# > 90; type i chondrules and isolated forsterites) mainly have δ17o values of ca. -6‰, and feo-rich objects (mg# < 90; type ii chondrules and isolated olivines) have δ17o values ranging from -3‰ to +2‰. similar trends are observed for ferromagnesian silicate particles from comet wild2 and cr chondrite chondrules, particularly in terms of feo-rich objects with δ17o values ranging from -3‰ to +2‰. it is suggested that feo-rich objects formed in the outer regions of the asteroid belt and were transported to the outer solar nebular regions where comet wild2 formed. | oxygen isotope reservoirs in the outer asteroid belt inferred from oxygen isotope systematics of chondrule olivines and isolated forsterite and olivine grains in tagish lake-type carbonaceous chondrites, wis 91600 and met 00432 |
context. cm-like asteroids (ch and cgh classes) are a major population within the broader c-complex, encompassing about 10% of the mass of the main asteroid belt. their internal structure has been predicted to be homogeneous, based on their compositional similarity as inferred from spectroscopy and numerical modeling of their early thermal evolution.aims: here we aim to test this hypothesis by deriving the density of the cm-like asteroid (41) daphne from detailed modeling of its shape and the orbit of its small satellite.methods: we observed daphne and its satellite within our imaging survey with the very large telescope extreme adaptive-optics sphere/zimpol camera and complemented this data set with earlier keck/nirc2 and vlt/naco observations. we analyzed the dynamics of the satellite with our genoid meta-heuristic algorithm. combining our high-angular resolution images with optical lightcurves and stellar occultations, we determine the spin period, orientation, and 3d shape, using our adam shape modeling algorithm.results: the satellite orbits daphne on an equatorial, quasi-circular, prograde orbit, like the satellites of many other large main-belt asteroids. the shape model of daphne reveals several large flat areas that could be large impact craters. the mass determined from this orbit combined with the volume computed from the shape model implies a density for daphne of 1.77 ± 0.26 g cm-3 (3 σ). this densityis consistent with a primordial cm-like homogeneous internal structure with some level of macroporosity (≈ 17%).conclusions: based on our analysis of the density of daphne and 75 other ch/cgh-type asteroids gathered from the literature, we conclude that the primordial internal structure of the cm parent bodies was homogeneous. based on observations made with (1) eso telescopes at the la silla paranal observatory under programs http://281.c-5011 (pi dumas), http://099.d-0098 (sphere gto), and http://199.c-0074(a) (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.the reduced and deconvolved ao images and the 3d shape model are publicly available at http://observations.lam.fr/astero/ and at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/623/a132 | homogeneous internal structure of cm-like asteroid (41) daphne |
the asteroid belt is characterized by the radial mixing of bodies with different physical properties, a very low mass compared to minimum mass solar nebula expectations and has an excited orbital distribution, with eccentricities and inclinations covering the entire range of values allowed by the constraints of dynamical stability. models of the evolution of the asteroid belt show that the origin of its structure is strongly linked to the process of terrestrial planet formation. the grand tack model presents a possible solution to the conundrum of reconciling the small mass of mars with the properties of the asteroid belt, including the mass depletion, radial mixing and orbital excitation. however, while the inclination distribution produced in the grand tack model is in good agreement with the one observed, the eccentricity distribution is skewed towards values larger than those found today. here, we evaluate the evolution of the orbital properties of the asteroid belt from the end of the grand tack model (at the end of the gas nebula phase when planets emerge from the dispersing gas disk), throughout the subsequent evolution of the solar system including an instability of the giant planets approximately 400 myr later. before the instability, the terrestrial planets were modeled on dynamically cold orbits with jupiter and saturn locked in a 3:2 mean motion resonance. the model continues for an additional 4.1 gyr after the giant planet instability. our results show that the eccentricity distribution obtained in the grand tack model evolves towards one very similar to that currently observed, and the semimajor axis distribution does the same. the inclination distribution remains nearly unchanged with a slight preference for depletion at low inclination; this leads to the conclusion that the inclination distribution at the end of the grand tack is a bit over-excited. also, we constrain the primordial eccentricities of jupiter and saturn, which have a major influence on the dynamical evolution of the asteroid belt and its final orbital structure. | is the grand tack model compatible with the orbital distribution of main belt asteroids? |
we present a method to identify distant solar system objects in long-term wide-field asteroid survey data, and conduct a search for them in the pan-starrs1 (ps1) image data acquired from 2010 to mid-2015. we demonstrate that our method is able to find multi-opposition orbital links, and we present the resulting orbital distributions which consist of 154 centaurs, 255 classical trans-neptunian objects (tnos), 121 resonant tnos, 89 scattered disc objects (sdos) and 10 comets. our results show more than half of these are new discoveries, including a newly discovered 19th magnitude tno. our identified objects do not show clustering in their argument of perihelia, which if present, might support the existence of a large unknown planetary-sized object in the outer solar system. | distant solar system objects identified in the pan-starrs1 survey |
we present a new extensive analysis of the old problem of finding a satisfactory calibration of the relation between the geometric albedo and some measurable polarization properties of the asteroids. to achieve our goals, we use all polarimetric data at our disposal. for the purposes of calibration, we use a limited sample of objects for which we can be confident to know the albedo with good accuracy, according to previous investigations of other authors. we find a new set of updated calibration coefficients for the classical slope-albedo relation, but we generalize our analysis and we consider also alternative possibilities, including the use of other polarimetric parameters, one being proposed here for the first time, and the possibility to exclude from best-fitting analyses the asteroids having low albedos. we also consider a possible parabolic fit of the whole set of data. | on the calibration of the relation between geometric albedo and polarimetric properties for the asteroids |
we present deepstreaks, a convolutional-neural-network, deep-learning system designed to efficiently identify streaking fast-moving near-earth objects that are detected in the data of the zwicky transient facility (ztf), a wide-field, time-domain survey using a dedicated 47 deg2 camera attached to the samuel oschin 48-inch telescope at the palomar observatory in california, united states. the system demonstrates a 96-98 per cent true positive rate, depending on the night, while keeping the false positive rate below 1 per cent. the sensitivity of deepstreaks is quantified by the performance on the test data sets as well as using known near-earth objects observed by ztf. the system is deployed and adapted for usage within the ztf solar system framework and has significantly reduced human involvement in the streak identification process, from several hours to typically under 10 min per day. | deepstreaks: identifying fast-moving objects in the zwicky transient facility data with deep learning |
asteroid material is detected in white dwarfs (wds) as atmospheric pollution by metals, in the form of gas/dust discs, or in photometric transits. within the current paradigm, minor bodies need to be scattered, most likely by planets, into highly eccentric orbits where the material gets disrupted by tidal forces and then accreted on to the star. this can occur through a planet-planet scattering process triggered by the stellar mass-loss during the post main-sequence (ms) evolution of planetary systems. so far, studies of the n-body dynamics of this process have used artificial planetary system architectures built ad hoc. in this work, we attempt to go a step further and study the dynamical instability provided by more restrictive systems that, at the same time, allow us an exploration of a wider parameter space: the hundreds of multiple planetary systems found around ms stars. we find that most of our simulated systems remain stable during the ms, red, and asymptotic giant branch and for several gyr into the wd phases of the host star. overall, only ≈2.3 ${{\ \rm per\ cent}}$ of the simulated systems lose a planet on the wd as a result of dynamical instability. if the instabilities take place during the wd phase most of them result in planet ejections with just five planetary configurations ending as a collision of a planet with the wd. finally 3.2 ${{\ \rm per\ cent}}$ of the simulated systems experience some form of orbital scattering or orbit crossing that could contribute to the pollution at a sustained rate if planetesimals are present in the same system. | dynamical evolution of two-planet systems and its connection with white dwarf atmospheric pollution |
self-replicating probes are spacecraft with the capacity to create copies of themselves. self-replication would potentially allow for an exponential increase in the number of probes and thereby drastically improve the efficiency of space exploration. despite this potential, an integrated assessment of self-replicating space probes has not been presented since the 1980s, and it is still unclear how far they are feasible. in this paper, we propose a concept for a partially self-replicating probe for space exploration based on current and near-term technologies, with a focus on small spacecraft. the purpose is to chart a path towards self-replication with near-term benefits, rather than attempting full self-replication. for this reason, components such as microchips and other microelectronic components are brought with the initial probe and are not replicated. we estimate that such a probe would be capable of replicating 70% of its mass. to further increase this percentage, we identify technology gaps which may be usefully addressed. we conclude that small-scale, partially self-replicating probes are feasible near-term. their benefits would become significant in exploration missions requiring in the order of a dozen of probes. | near-term self-replicating probes - a concept design |
this paper describes the architecture and demonstrates the capabilities of a newly developed, physically-based imaging simulator environment called sispo, developed for small solar system body fly-by and terrestrial planet surface mission simulations. the image simulator utilises the open-source 3-d visualisation system blender and its cycles rendering engine, which supports physically based rendering capabilities and procedural micropolygon displacement texture generation. the simulator concentrates on realistic surface rendering and has supplementary models to produce realistic dust- and gas-environment optical models for comets and active asteroids. the framework also includes tools to simulate the most common image aberrations, such as tangential and sagittal astigmatism, internal and external comatic aberration, and simple geometric distortions. the model framework's primary objective is to support small-body space mission design by allowing better simulations for characterisation of imaging instrument performance, assisting mission planning, and developing computer-vision algorithms. sispo allows the simulation of trajectories, light parameters and camera's intrinsic parameters. | sispo: space imaging simulator for proximity operations |
recently, the inner main belt asteroid (152830) dinkinesh was identified as an additional fly- by target for the lucy mission. the heliocentric orbit and approximate absolute magnitude of dinkinesh are known, but little additional information was available prior to its selection as a target. in particular, the lack of color spectrophotometry or spectra made it impossible to assign a spectral type to dinkinesh from which its albedo could be estimated. we set out to remedy this knowledge gap by obtaining visible wavelength spectra with the keck telescope on 2022 november 23 and with gemini-south on 2022 december 27. the spectra measured with the keck i/low resolution imaging spectrometer (lris) and the gemini south/gemini multi-object spectrograph south (gmos-s) are most similar to the average spectrum of s- and sq-type asteroids. the most diagnostic feature is the ≈15 ± 1% silicate absorption feature at ≈0.9-1.0 μm. small s- and sq-type asteroids have moderately high albedos ranging from 0.17 to 0.35. using this albedo range for dinkinesh in combination with measured absolute magnitude, it is possible to derive an effective diameter and surface brightness for this body. the albedo, size and surface brightness are important inputs required for planning a successful encounter by the lucy spacecraft. | keck and gemini spectral characterization of lucy mission fly-by target (152830) dinkinesh |
in the framework of the visible neas observations survey (vinos) that uses several telescopes at the canary islands observatories since 2018, we observed two superfast rotator neas, 2021 ny1 and 2022 ab. we obtained photometry and spectrophotometry of both targets and visible spectroscopy of 2022 ab. light curves of 2021 ny1 obtained in four different nights between 2021 september 30 and 2021 october 16 return a rotation period p = 13.3449 ± 0.0013 minutes and a light curve amplitude a = 1.00 mag. we found that 2021 ny1 is a very elongated superfast rotator with an axis ratio a/b ≥ 3.6. we also report colours (g - r) = 0.664 ± 0.013, (r - i) = 0.186 ± 0.013, and (i - zs) = -0.117 ± 0.012 mag. these are compatible with an s-type asteroid. the light curves of 2022 ab obtained on 2021 january 5 and 2021 january 8 show a rotation period p = 3.0304 ± 0.0008 min, with amplitudes a = 0.52 and a = 0.54 mag. 2022 ab is also an elongated object with axis ratio a/b ≥ 1.6. the obtained colours are (g - r) = 0.400 ± 0.017, (r - i) = 0.133 ± 0.017, and (i - zs) = 0.093 ± 0.016. these colours are similar to those of the x-types, but with an unusually high (g - r) value. spectra obtained on 2022 january 12 and 2022 january 14 are consistent with the reported colours. the spectral upturn over the 0.4 - 0.6 $\mu \mathrm{m}$ region of 2022 ab does not fit with any known asteroid taxonomical class or meteorite spectrum, confirming its unusual surface properties. | observations of two superfast rotator neas: 2021 ny1 and 2022 ab |
we have carried out a systematic study involving sem, epma, and tem analyses to determine the textures and compositions of sulfides and sulfide-metal assemblages in a suite of minimally to weakly altered cm and cr carbonaceous chondrites. we have attempted to constrain the distribution and origin of primary sulfides that formed in the solar nebula, rather than by secondary asteroidal alteration processes. our study focused primarily on sulfide assemblages associated with chondrules, but also examined some occurrences of sulfides within the matrices of these meteorites. although sulfides are a minor phase in carbonaceous chondrites, we have determined that primary sulfide grains are actually a major proportion of the sulfide grains in weakly altered cm chondrites and have survived aqueous alteration relatively unscathed. in minimally altered cr chondrites, we have determined that essentially all of the sulfides are of primary origin, confirming the observations of schrader et al. (<link href="#maps13108-bib-0054"/>). the pyrrhotite-pentlandite intergrowth (ppi) grains formed from crystallization of monosulfide solid solution (mss) melts, while sulfide-rimmed metal (srm) grains formed from sulfidization of fe,ni metal. micron-sized metal inclusions in some ppi grains may have formed by co-crystallization of metal and sulfide from a sulfide melt that experienced s volatilization during the chondrule formation event, or alternatively, may be a remnant of sulfidization of fe,ni metal that also occurred during chondrule formation. sulfur fugacity for srm grains ranged from -18 to -10 (log units) largely in agreement with predicted solar nebular values. our observations show that understanding the formation mechanisms of primary sulfide grains provides clues to solar nebular conditions, such as the sulfur fugacity during chondrule formation. | primary iron sulfides in cm and cr carbonaceous chondrites: insights into nebular processes |
the moon is an archive of impact cratering in the solar system throughout the past 4.5 billion years. it preserves this record better than larger, more complex planets like the earth, mars and venus, which have largely lost their ancient crusts through geological reprocessing and hydrospheric/atmospheric weathering. identifying the parent bodies of impactors (i.e. asteroid bodies, comets from the kuiper belt or the oort cloud) provides geochemical and chronological constraints for models of solar system dynamics, helping to better inform our wider understanding of the evolution of the solar system and the transfer of small bodies between planets. in this review article, we discuss the evidence for populations of impactors delivered to the moon at different times in the past. we also propose approaches to the identification and characterisation of meteoritic material on the moon in the context of future lunar exploration efforts. | the moon: an archive of small body migration in the solar system |
the 26al-26mg short-lived chronometer has been widely used for dating ancient objects in studying the early solar system. here, we use this chronometer to investigate and refine the geological history of the asteroid 4-vesta. ten meteorites widely believed to come from vesta (4 basaltic eucrites, 3 cumulate eucrites and 3 diogenites) and the unique achondrite asuka 881394 were selected for this study. all samples were analyzed for their δ26mg∗ and 27al/24mg ratios, in order to construct both whole rock and model whole rock isochrons. mineral separation was performed on 8 of the hed's in order to obtain internal isochrons. while whole rock al-mg analyses of hed's plot on a regression that could be interpreted as a vestan planetary isochron, internal mineral isochrons indicate a more complex history. crystallization ages obtained from internal 26al-26mg systematic in basaltic eucrites show that vesta's upper crust was formed during a short period of magmatic activity at 2.66-0.58+1.39 million years (ma) after calcium-aluminum inclusions (after cai). we also suggest that impact metamorphism and subsequent age resetting could have taken place at the surface of vesta while 26al was still extant. cumulate eucrites crystallized progressively from 5.48-0.60+1.56 to >7.25 ma after cai. model ages obtained for both basaltic and cumulate eucrites are similar and suggest that the timing of differentiation of a common eucrite source from a chondritic body can be modeled at 2.88-0.12+0.14 ma after cai, i.e. contemporaneously from the onset of the basaltic eucritic crust. based on their cumulate texture, we suggest cumulate eucrites were likely formed deeper in the crust of vesta. diogenites have a more complicated history and their 26al-26mg systematics show that they likely formed after the complete decay of 26al and thus are younger than eucrites. this refined chronology for eucrites and diogenites is consistent with a short magma ocean stage on 4-vesta from which the basaltic eucrites rapidly crystallized. in order to explain the younger age and the complex history of diogenites, we postulate that a second episode of magmatism was possibly triggered by a mantle overturn. we bring a refined chronology of the geological history of vesta that shows that the asteroid has known a more-complex differentiation than previously thought. | differentiation and magmatic activity in vesta evidenced by 26al-26mg dating in eucrites and diogenites |
we report u-pb, 87rb-87sr, 40ar-39ar, and 238u/235u isotopic data for paired ungrouped achondrites nwa 6704 and nwa 6693 that were derived from a highly oxidised parent body with broadly chondritic composition (warren et al., 2013; hibiya et al., 2019). pb-isotopic ages derived from isochrons for multiple acid-leached pyroxene fractions are 4562.76 + 0.22/-0.30 ma for nwa 6704 and 4562.63 + 0.29/-0.21 ma for nwa 6693, calculated using 238u/235u ratio of 137.7784 ± 0.0097 measured in nwa 6704. the rb-sr mineral isochron age of 4543 ± 46 ma (initial 87sr/86sr = 0.699013 ± 0.000055) is consistent with the pb-isotopic age. together with 187re-187os isochron age of 4576 ± 250 ma for nwa 6704 (hibiya et al., 2019), and 26al-26mg and 53mn-53cr ages calculated using the rapidly crystallized angrite d'orbigny as a time anchor are also consistent with the pb-isotopic age (sanborn et al., 2019), these data indicate that the parent rocks of nwa 6693 and nwa 6704 remained closed to migration of both lithophile and siderophile elements since crystallisation and initial cooling. the whole rock 40ar-39ar age of 4199 ± 32 ma suggests a complete resetting of the k-ar system approximately 360 ma after crystallisation. a later event at ≤2.12 ga partially reset the k-ar system as shown by the low temperature heating steps. both meteorites have high 87rb/86sr ratios (up to 7.0 in nwa 6693 pyroxene) and very radiogenic 87sr/86sr up to 1.15. together with the absence of secondary disturbance in the rb-sr and u-pb systems, this makes them suitable for cross-calibration of the isotopic chronometers. these meteorites are also promising candidates to serve as age reference samples for the early solar system chronology, as an alternative or complement to angrites of the early generation (d'orbigny, sahara 99555) that are currently used for this purpose. plagioclase in nwa 6704 has a sufficiently low rb/sr ratio to define precise initial 87sr/86sr of 0.698997 ± 0.000027, which corresponds to the time of separation of the parent body precursor material from the solar nebula of 1.5 ± 2.1 ma. this value suggests that the parent asteroid accreted within 3.6 ma after cai formation, or before 4563.7 ma using the cai age of 4567.3 ma (connelly et al., 2012). | u-pb, rb-sr and ar-ar systematics of the ungrouped achondrites northwest africa 6704 and northwest africa 6693 |
evaluating the molecular distribution of organic compounds in pristine extraterrestrial materials is cornerstone to understanding the abiotic synthesis of organics and allows us to better understand the molecular diversity available during the formation of our solar system and before the origins of life on earth. in this work, we identify multiple organic compounds in solvent extracts of asteroid ryugu samples a0106 and c0107 and the orgueil meteorite using two-dimensional gas chromatography and time-of-flight high resolution mass spectrometry (gc×gc-hrms). our analyses found similarities between the molecular distribution of organic compounds in ryugu and the ci carbonaceous chondrite orgueil. specifically, several pahs and organosulfides were found in ryugu and orgueil suggesting an interstellar and parent body origin for these compounds. we also evaluated the common relationship between ryugu, orgueil, and comets, such as wild-2; however, until comprehensive compound-specific isotopic analyses for these organic species are undertaken, and until the effects of parent body processes and earth's weathering processes on meteoritic organics are better understood, their parent-daughter relationships will remain unanswered. finally, the study of organic compounds in ryugu samples and the curation practices for the future preservation of these unvaluable materials are also of special interest for future sample return missions, including nasa's osiris-rex asteroid sample return mission. | pahs, hydrocarbons, and dimethylsulfides in asteroid ryugu samples a0106 and c0107 and the orgueil (ci1) meteorite |
we used long duration observations from the transient exoplanet survey satellite (tess) to investigate the behavior of comet c/2014 un271 bernardinelli-bernstein at large heliocentric distances. by combining data from sector 03 (976 30 minute exposures from 2018), and sectors 29 and 30 (3585 and 3410 10 minute exposures, respectively, from 2020), we produced deep coadded images of the comet. a comparison of these results with similarly processed images of inactive kuiper belt objects and asteroids reveals that the comet was already exhibiting coma at heliocentric distances 23.8 and 21.2 au, making this one of the most distant comets for which preperihelion activity has been directly detected. a simple syndyne analysis of asymmetries in the coma suggests that activity probably started several years prior to these observations, and likely arose from emission in roughly the sunward direction. the images were used to produce photometric lightcurves, though no rotational variability was detected. we used neowise observations from 2020 november 26-28 to place an upper limit of 2 × 1028 molecules s-1 (3σ) on the co production rate. | early activity in comet c/2014 un271 bernardinelli-bernstein as observed by tess |
we report a nanosims search for presolar grains in the cm chondrites asuka (a) 12169 and a12236. we found 90 presolar o rich grains and 25 sic grains in a12169, giving matrix normalized abundances of 275 (+55/−50, 1σ) ppm or, excluding an unusually large grain, 236 (+37/−34) ppm for o rich grains and 62 (+15/−12) ppm for sic grains. for a12236, 18 presolar silicates and 6 sics indicate abundances of 58 (+18/−12) and 20 (+12/−8) ppm, respectively. the sic abundances are in the typical range of primitive chondrites. the abundance of presolar o rich grains in a12169 is essentially identical to that in co3.0 dominion range 08006, higher than in any other chondrites, while in a12236, it is higher than found in other cms. these abundances provide further strong support that a12169 and a12236 are the least altered cms as indicated by petrographic investigations. the similar abundances, isotopic distributions, silicate/oxide ratios, and grain sizes of the presolar o rich grains found here to those of presolar grains in highly primitive co, cr, and ungrouped carbonaceous chondrites (ccs) indicate that the cm parent body(ies) accreted a similar population of presolar oxides and silicates in their matrices to those accreted by the parent bodies of the other cc groups. the lower abundances and larger grain sizes seen in some other cms are thus most likely a result of parent body alteration and not heterogeneity in nebular precursors. presolar silicates are unlikely to be present in high abundances in returned samples from asteroids ryugu and bennu since remote sensing data indicate that they have experienced substantial aqueous alteration. | presolar stardust in highly pristine cm chondrites asuka 12169 and asuka 12236 |
the miniaturised asteroid remote geophysical observer (m-argo) mission is designed to be esa's first stand-alone cubesat to independently travel in deep space with its own electric propulsion and direct-to-earth communication systems in order to rendezvous with a near-earth asteroid. deep-space cubesats are appealing owing to the scaled mission costs. however, the operational costs are comparable to those of traditional missions if ground-based orbit determination is employed. thus, autonomous navigation methods are required to favour an overall scaling of the mission cost for deep-space cubesats. m-argo is assumed to perform an autonomous navigation experiment during the deep-space cruise phase. this paper elaborates on the deep-space navigation experiment exploiting the line-of-sight directions to visible beacons in the solar system. the aim is to assess the experiment feasibility and to quantify the performances of the method. results indicate feasibility of the autonomous navigation for m-argo with a 3σ accuracy in the order of 1000 km for the position components and 1 m/s for the velocity components in good observation conditions, utilising miniaturized optical sensors. | deep-space optical navigation for m-argo mission |
this paper investigates the equatorial cavities found on asteroids 2008 ev5 and 2000 dp107 alpha. as the likelihood of these cavities being impact craters is demonstrated to be low, the paper presents a fission mechanism that explains their existence as a scar of past fission events. the dynamical environment of "top-shaped" asteroids is such that, at high spin rates, an identifiable equatorial region enters into tension before the rest of the body. we propose hypothetical past shapes for 2008 ev5 and 2000 dp107, with mass added within the cavity to recreate a smoother equatorial ridge. the dynamical environment of these hypothetical parent bodies reveal that this modified region is indeed set in tension when spin is increased. the fission process requires tensile strength at the interface between the ejecta and the remaining body, at the moment of fission, between 0 and 2 pa for 2008 ev5 and between 0 and 15 pa for 2000 dp107, depending on the precise fission scenario considered. going back to the spin-up deformation phase of the asteroids, the paper examines how kinetic sieving can form predominantly rocky equators, whose tensile strength could be much lower than that of the rest of the body. this process could explain the low cohesion values implied for this fission mechanism. | equatorial cavities on asteroids, an evidence of fission events |
small bodies are among the best tracers of our solar system's history. a large number of space missions to small bodies (past and future) offer a unique opportunity to use these bodies as a natural laboratory to study the different processes, mechanical structures, and responses that drive the origin and evolution of small bodies, which are connected to the origin, evolution, and current architecture of the solar system. images of small bodies sent by spacecraft have revealed unexpectedly rich and complex geological worlds. in addition to very diverse compositions, small bodies in the solar system have highly diverse shapes and structures, which reflect both different evolutionary paths and material properties. furthermore, each individual body has diverse geological features on its surface, which include craters of various sizes and depths, boulders of different sizes and morphologies, lineaments, fractures, pits, signatures of landslides, terraces, and ridges. such a geological richness could not be detected via ground-based observations, and we are still at the beginning of understanding their significance on the low-gravity surfaces on which they manifest. the combination of space mission data and numerical modeling allows us to enrich our understanding of the origin, evolution, and physical properties of these fascinating bodies. for instance, starting from the shape models, bulk densities, and spin rates determined from space mission data, we can investigate the formation mechanisms that lead to the observed properties of small bodies. we can also infer the interior and mechanical properties (e.g., friction and cohesion) that allow a small body to be structurally stable, as well as its further potential evolution under processes such as a spin rate increase or an impact. then, considering the various processes that these bodies experience during their evolution, we can investigate how these processes modify their properties and, in turn, how those properties influence the outcome of these processes. this paper reviews our current knowledge of small-body shapes and structures and discusses the various processes that are responsible for their formation and evolution, which can modify the characteristics of the bodies. we separately consider each population of small bodies, although in some cases, such as active asteroids and comets, the distinction between two populations solely in terms of physical properties is not clear. we then summarize the main findings regarding the physical properties of small bodies that have been the target of rendezvous or sample return missions. | shapes, structures, and evolution of small bodies |
during solar system condensation, the early earth formed through planetesimal accretion, including collision of a mars-sized asteroid. these processes rapidly increased the overall thermal budget and partial fusion of the planet. aided by heat supplied by radioactivity and infall of the fe-ni core, devolatilization and chemical-density stratification attended planetary growth. after the thermal maximum at ∼4.4 ga, terrestrial temperatures gradually declined as an early hadean magma ocean solidified. by ∼4.3-4.2 ga, h2o oceans + a dense co2-rich atmosphere blanketed the terrestrial surface. near-surface temperatures had fallen well below the low-p solidi of dry peridotite, basalt, and granite, ∼1300, ∼1120, and ∼950 °c, respectively. at less than half their melting t, rocky materials existed as thin lithospheric platelets in the surficial hadean earth. upper mantle stagnant-lid convection may have operated locally, but was rapidly overwhelmed by heat build-up-induced asthenospheric circulation, rifting and subduction, because massive heat transfer required vigorous mantle overturn in the early, hot planet. bottom-up mantle overturn, involving abundant plume ascent, brought deep-seated heat to the surface. it decreased over time as cooling, plate enlargement, and top-down plate descent increased. thickening, lateral extension, and contraction typified the post-hadean lithosphere. geologic evolutionary stages included: (a) ∼4.5-4.4 ga, the magma ocean solidified, generating ephemeral, ductile platelets; (b) ∼4.4-2.7 ga, small oceanic and continental plates were produced, then were destroyed by mantle return flow before ∼4.0 ga; eventually, continental material began to accumulate as largely subsea, sialic crust-capped lithospheric collages; (c) ∼2.7-1.0 ga, progressive suturing of old shields and younger orogenic belts led to cratonal plates typified by emerging continental freeboard, intense sedimentary differentiation, and episodic glaciation during transpolar plate drift; temporally limited stagnant-lid mantle convection occurred beneath growing supercontinents; (d) ∼1.0 ga-present, laminar-flowing mantle cells are capped by giant, stately moving plates. near-restriction of komatiitic lavas to the archean, and formation of multicycle sediments, ophiolite complexes ± alkaline igneous rocks, and high-pressure/ultrahigh-pressure (hp/uhp) metamorphic belts in youngest proterozoic and phanerozoic orogens reflect increasing density of cool oceanic plates, but decreasing subductability of enlarging, more buoyant continental plates. attending assembly of supercontinents, negative buoyancy of thickening oceanic lithosphere began to control the overturn of suboceanic mantle as cold, top-down convection. the scales and dynamics of hot asthenospheric upwelling versus plate foundering and mantle return flow (bottom-up plume ascent versus top-down plate subduction) evolved gradually, due to planetary cooling. after accretion of the earth, heat transfer through mantle convection has resulted in the existence of surficial rocky plates or platelets, and vigorous, lithosphere-coupled mantle overturn since ∼4.4 ga. thus plate-tectonic processes have typified the earth's thermal history since hadean time. | earth's thermal evolution, mantle convection, and hadean onset of plate tectonics |
satellite remote sensing has been used as an effective tool to monitor and manage seagrass beds, but this tool is not appropriate to use in highly turbid waters along the coast of korea. in this study, satellite data were used to identify the method for detecting seagrass beds in turbid bay waters and describing temporal changes over the past 24 years. moreover, we found the cause of seagrass die-off phenomenon by observing the long-term satellite images and evaluating the impact of the typhoon on seagrass beds. all seagrass spectra from different sensors (landsat tm/etm+, aster, spot-4, and kompsat-2) have low reflectance in green and high in nir regions, whereas unvegetated seawater has the opposite spectrum features. a training area in the green band and mahalanobis distance classification algorithm was adopted for classification and mapping of seagrass beds. the error matrix using the in situ reference data for kompsat-2 image classification was 72.9% accurate. the average area of seagrass beds was 4.6 km2 from may 1990 to january 2012, and it was consistently >4.0 km2. a die-off of seagrass beds was observed in september 2012 after typhoon bolaven, tembin, and sanba consecutively passed the study site. when typhoon sanba passed the study site, it had sustained maximum wind speed (147.6 km h-1) during low tide, unlike the other typhoons. we found that the water column buffer did not have any effect on resistance of seagrass bed to disturbance, which led to greater damage. additionally, the three sequential typhoons that passed through during the short time probably produced a cumulative effect. these results allow an understanding of past changes, and reveal the sudden and influential changes in seagrass distribution. as seagrass removal might have negative effect on other associated communities, comprehensive monitoring is required to ensure that disturbed seagrass habitats is recovered naturally. | observation of typhoon-induced seagrass die-off using remote sensing |
primordial black holes formed in an early postinflation matter-dominated epoch during preheating provide a novel pathway for a source of the dark matter that utilizes known physics in combination with plausible speculations about the role of quantum gravity. two cases are considered here: survival of planck-scale relics and an early universe accretion scenario for the formation of primordial black holes of asteroid-scale masses. | primordial rotating black holes |
in 2022 september, the dart spacecraft (nasa's contribution to the asteroid impact & deflection assessment (aida) collaboration) will impact the asteroid dimorphos, the secondary in the didymos system. the crater formation and material ejection will affect the orbital period. in 2027, hera (esa's contribution to aida) will investigate the system, observe the crater caused by dart, and characterize dimorphos. before hera's arrival, the target properties will not be well-constrained. the relationships between observed orbital change and specific target properties are not unique, but hera's observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. in this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well-defined target materials. in contrast to previous studies, care is taken to use consistent crushing behavior (e.g., distension as a function of pressure) for a given porosity for all codes. first, we validate the codes against impact experiments into a regolith simulant. second, we benchmark the codes at the dart impact scale for a range of target material parameters (10%-50% porosity, 1.4-100 kpa cohesion). aligning the crushing behavior improves the consistency of the derived momentum enhancement between the three codes to within +/-5% for most materials used. based on the derived mass-velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain. | momentum enhancement during kinetic impacts in the low-intermediate-strength regime: benchmarking and validation of impact shock physics codes |
the trojan asteroids of jupiter and neptune are likely to have been captured from original heliocentric orbits in the dynamically excited (“hot”) population of the kuiper belt. however, it has long been known that the optical color distributions of the jovian trojans and the hot population are not alike. this difference has been reconciled with the capture hypothesis by assuming that the trojans were resurfaced (for example, by sublimation of near-surface volatiles) upon inward migration from the kuiper belt (where blackbody temperatures are ∼40 k) to jupiter’s orbit (∼125 k). here, we examine the optical color distribution of the neptunian trojans using a combination of new optical photometry and published data. we find a color distribution that is statistically indistinguishable from that of the jovian trojans but unlike any sub-population in the kuiper belt. this result is puzzling, because the neptunian trojans are very cold (blackbody temperature ∼50 k) and a thermal process acting to modify the surface colors at neptune’s distance would also affect the kuiper belt objects beyond, where the temperatures are nearly identical. the distinctive color distributions of the jovian and neptunian trojans thus present us with a conundrum: they are very similar to each other, suggesting either capture from a common source or surface modification by a common process. however, the color distributions differ from any plausible common source population, and there is no known modifying process that could operate equally at both jupiter and neptune. | the trojan color conundrum |
the jupiter trojans constitute an important asteroidal population both in number and also in relation to their dynamical and physical properties. they are asteroids located around l4 and l5 lagrangian points on relatively stable orbits, in 1: 1 mean motion resonance with jupiter. however, not all of them lie in orbits that remain stable over the age of the solar system. unstable zones allow some trojans to escape in time scales shorter than the solar system age. this may contribute to populate other small body populations. in this paper, we study this process by performing long-term numerical simulations of the observed trojans, focusing on the trajectories of those that leave the resonance. the orbits of current trojan asteroids are taken as initial conditions and their evolution is followed under the gravitational action of the sun and the planets. we built "occupancy maps" that represent the zones in the solar system where escaped trojans should be found. we find the rate of escape of trojans from l5, ∼ 1.1 times greater than from l4. the majority of escaped trojans have encounters with jupiter although they have encounters with the other planets too. the median lifetime of escaped trojans in the solar system is ∼ 264, 000 years for l4 and ∼ 249, 000 years for l5. almost all escaped trojans reach the comet zone, ∼ 90% cross the centaur zone and only l4 trojans reach the transneptunian zone. considering the real asymmetry between l4 and l5, we show that 18 l4 trojans and 14 l5 trojans with diameter d > 1 km are ejected from the resonance every myr. the contribution of the escaped trojans to other minor body populations would be negligible, being the contribution from l4 and l5 to jupiter-family comets (jfcs) and no-jfcs almost the same, and the l4 contribution to centaurs and tnos, orders of magnitude greater than that of l5. considering the collisional removal, besides the dynamical one, and assuming that trojans that escape due to collisions follow the same dynamical behavior that the ones removed by dynamics, we would have a minor contribution of trojans to comets and centaurs. however, there would be some specific regions were escaped trojans could be important such as asteroids in cometary orbits (acos), encke-type comets, shoemaker-levy 9-type impacts on jupiter and near-earth objects (neos). | the dynamical evolution of escaped jupiter trojan asteroids, link to other minor body populations |
we present an analysis of survey observations targeting the leading l4 jupiter trojan cloud near opposition using the wide-field suprime-cam ccd camera on the 8.2 m subaru telescope. the survey covered about 38 deg2 of sky and imaged 147 fields spread across a wide region of the l4 cloud. each field was imaged in both the g‧ and the i‧ band, allowing for the measurement of g - i color. we detected 557 trojans in the observed fields, ranging in absolute magnitude from h = 10.0 to h = 20.3. we fit the total magnitude distribution to a broken power law and show that the power-law slope rolls over from 0.45 ± 0.05 to {0.36}-0.09+0.05 at a break magnitude of {h}b={14.93}-0.88+0.73. combining the best-fit magnitude distribution of faint objects from our survey with an analysis of the magnitude distribution of bright objects listed in the minor planet center catalog, we obtain the absolute magnitude distribution of trojans over the entire range from h = 7.2 to h = 16.4. we show that the g - i color of trojans decreases with increasing magnitude. in the context of the less-red and red color populations, as classified in wong et al. using photometric and spectroscopic data, we demonstrate that the observed trend in color for the faint trojans is consistent with the expected trend derived from extrapolation of the best-fit color population magnitude distributions for bright cataloged trojans. this indicates a steady increase in the relative number of less-red objects with decreasing size. finally, we interpret our results using collisional modeling and propose several hypotheses for the color evolution of the jupiter trojan population. based on data collected at subaru telescope, which is operated by the national astronomical observatory of japan. | the color-magnitude distribution of small jupiter trojans |
the am cvn systems are a class of he-rich, post-period minimum, semidetached, ultracompact binaries. their long-term light curves have been poorly understood due to the few systems known and the long (hundreds of days) recurrence times between outbursts. we present combined photometric light curves from the lincoln near earth asteroid research, catalina real-time transient survey, and palomar transient factory synoptic surveys to study the photometric variability of these systems over an almost 10 yr period. these light curves provide a much clearer picture of the outburst phenomena that these systems undergo. we characterize the photometric behaviour of most known outbursting am cvn systems and establish a relation between their outburst properties and the systems' orbital periods. we also explore why some systems have only shown a single outburst so far and expand the previously accepted phenomenological states of am cvn systems. we conclude that the outbursts of these systems show evolution with respect to the orbital period, which can likely be attributed to the decreasing mass transfer rate with increasing period. finally, we consider the number of am cvn systems that should be present in modelled synoptic surveys. | long-term photometric behaviour of outbursting am cvn systems |
we present the first self-consistent simulations of the coupled spin-shape evolution of small gravitational aggregates under the influence of the yorp effect. because of yorp’s sensitivity to surface topography, even small centrifugally driven reconfigurations of aggregates can alter the yorp torque dramatically, resulting in spin evolution that can differ qualitatively from the rigid-body prediction. one-third of our simulations follow a simple evolution described as a modified yorp cycle. two-thirds exhibit one or more of three distinct behaviors—stochastic yorp, self-governed yorp, and stagnating yorp—which together result in yorp self-limitation. self-limitation confines rotation rates of evolving aggregates to far narrower ranges than those expected in the classical yorp cycle, greatly prolonging the times over which objects can preserve their sense of rotation. simulated objects are initially randomly packed, disordered aggregates of identical spheres in rotating equilibrium, with low internal angles of friction. their shape evolution is characterized by rearrangement of the entire body, including the deep interior. they do not evolve to axisymmetric top shapes with equatorial ridges. mass loss occurs in one-third of the simulations, typically in small amounts from the ends of a prolate-triaxial body. we conjecture that yorp self-limitation may inhibit formation of top-shapes, binaries, or both, by restricting the amount of angular momentum that can be imparted to a deformable body. stochastic yorp, in particular, will affect the evolution of collisional families whose orbits drift apart under the influence of yarkovsky forces, in observable ways. | coupled spin and shape evolution of small rubble-pile asteroids: self-limitation of the yorp effect |
bennu is an ~500-m-diameter rubble-pile asteroid that is the target of detailed study by the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission. here we use data from the osiris-rex laser altimeter to assess depth-to-diameter ratios (d/d) of 108 impact craters larger than 10 m in diameter. the d/d of craters on bennu ranges from 0.02 to 0.19. the mean is 0.10 ± 0.03. the smallest craters show the broadest range in d/d, consistent with d/d measurements on other asteroids. a few craters have central mounds, which is interpreted as evidence that a more competent substrate lies a few meters beneath them. the range of d/d narrows as crater size increases, with craters larger than 80 m tending toward smaller d/d. at large scales, increases in target strength with depth, combined with target curvature, may affect crater morphometry. | the morphometry of impact craters on bennu |
white dwarfs containing orbiting planetesimals or their debris represent crucial benchmarks by which theoretical investigations of post-main-sequence planetary systems may be calibrated. the photometric transit signatures of likely planetary debris in the ztf j0139+5245 white dwarf system have an orbital period of about 110 d. an asteroid which breaks up to produce this debris may spin itself to destruction through repeated close encounters with the star without entering its roche radius and without influence from the white dwarf's luminosity. here, we place coupled constraints on the orbital pericentre (q) and the ratio (β) of the middle to longest semiaxes of a triaxial asteroid which disrupts outside of this white dwarf's roche radius (rroche) soon after attaining its 110-d orbit. we find that disruption within tens of years is likely when β ≲ 0.6 and q ≈ 1.0-2.0rroche, and when β ≲ 0.2 out to q ≈ 2.5rroche. analysing the longer time-scale disruption of triaxial asteroids around ztf j0139+5245 is desirable but may require either an analytical approach relying on ergodic theory or novel numerical techniques. | constraining the origin of the planetary debris surrounding ztf j0139+5245 through rotational fission of a triaxial asteroid |
the only discovery of earth trojan 2010 tk7 and the subsequent launch of osiris-rex have motived us to investigate the stability around the triangular lagrange points of the earth, l4 and l5. in this paper we present detailed dynamical maps on the (a0, i0) plane with the spectral number (sn) indicating the stability. two main stability regions, separated by a chaotic region arising from the ν3 and ν4 secular resonances, are found at low (i0 ≤ 15°) and moderate (24 ° ≤i0 ≤ 37°) inclinations, respectively. the most stable orbits reside below i0 = 10° and they can survive the age of the solar system. the nodal secular resonance ν13 could vary the inclinations from 0° to ∼10° according to their initial values, while ν14 could pump up the inclinations to ∼20° and upwards. the fine structures in the dynamical maps are related to higher degree secular resonances, of which different types dominate different areas. the dynamical behaviour of the tadpole and horseshoe orbits, reflected in their secular precession, show great differences in the frequency space. the secular resonances involving the tadpole orbits are more sensitive to the frequency drift of the inner planets, thus the instabilities could sweep across the phase space, leading to the clearance of tadpole orbits. we are more likely to find terrestrial companions on horseshoe orbits. the yarkovsky effect could destabilize earth trojans in varying degrees. we numerically obtain the formula describing the stabilities affected by the yarkovsky effect and find the asymmetry between the prograde and retrograde rotating earth trojans. the existence of small primordial earth trojans that avoid being detected but survive the yarkovsky effect for 4.5 gyr is substantially ruled out. | orbital stability of earth trojans |
asteroids are primitive solar system bodies that evolve both collisionally and through disruptions arising from rapid rotation. these processes can lead to the formation of binary asteroids and to the release of dust, both directly and, in some cases, through uncovering frozen volatiles. in a subset of the asteroids called main-belt comets, the sublimation of excavated volatiles causes transient comet-like activity. torques exerted by sublimation measurably influence the spin rates of active comets and might lead to the splitting of bilobate comet nuclei. the kilometre-sized main-belt asteroid 288p (300163) showed activity for several months around its perihelion 2011 (ref. 11), suspected to be sustained by the sublimation of water ice and supported by rapid rotation, while at least one component rotates slowly with a period of 16 hours (ref. 14). the object 288p is part of a young family of at least 11 asteroids that formed from a precursor about 10 kilometres in diameter during a shattering collision 7.5 million years ago. here we report that 288p is a binary main-belt comet. it is different from the known asteroid binaries in its combination of wide separation, near-equal component size, high eccentricity and comet-like activity. the observations also provide strong support for sublimation as the driver of activity in 288p and show that sublimation torques may play an important part in binary orbit evolution. | a binary main-belt comet |
the near-earth asteroid (469219) kamo'oalewa (aka 2016 ho3) is an earth coorbital and a potential space mission target. its short-term dynamics are characterized by a periodic switching between quasisatellite and horseshoe configurations. due to its small diameter of only about 36 m, the yarkovsky effect may play a significant role in the long-term dynamics. in this work, we addressed this issue by studying the changes in the long-term motion of kamo'oalewa caused by the yarkovsky effect. we used an estimation of the magnitude of the yarkovsky effect assuming different surface compositions and introduced the semimajor axis drift by propagating orbits of test particles representing the clones of the nominal orbit. our simulations showed that the yarkovsky effect may cause kamo'oalewa to exit from the earth coorbital region a bit faster when compared to a purely gravitational model. nevertheless, it still could remain an earth companion for at least 0.5 my in the future. our results imply that kamo'oalewa is the most stable earth's coorbital object known so far, not only from a short-term perspective but also on long timescales. | the role of the yarkovsky effect in the long-term dynamics of asteroid (469219) kamo'oalewa |
vatira-class near-earth objects (neos) have orbits entirely interior to the orbit of venus with aphelia 0.307 < q < 0.718 au. recently discovered asteroid 2020 av2 by the zwicky transient facility on 4 january 2020 is the first known object on a vatira orbit. numerical integrations of 2020 av2's nominal orbit show it remaining in the vatira region for the next few hundred kyr before coupling to venus and evolving onto an atira orbit (neos entirely interior to earth's orbit with 0.718 < q < 0.983 au) and eventually scattering out to earth-crossing. the numerical integrations of 9900 clones within 2020 av2's orbital uncertainty region show examples of vatira orbits trapped in the 3:2 mean-motion resonance with venus at semimajor axis a ≈ 0.552 au that can survive on the order of a few myr. possible 2020 av2 orbits also include those on vatira orbits between mercury and venus that only rarely cross that of a planet. together the 3:2 resonance and these rarely-planet-crossing orbits provide a meta-stable region of phase space that are stable on timescales of several myr. if 2020 av2 is currently in this meta-stable region (or was in the past), that may explain its discovery as the first vatira and may be where more are discovered. | orbital dynamics of 2020 av2: the first vatira asteroid |
of the 21 known gaseous debris discs around white dwarfs, a large fraction of them display observational features that are well described by an eccentric distribution of gas. in the absence of embedded objects or additional forces, these discs should not remain eccentric for long time-scales, and should instead circularize due to viscous spreading. the metal pollution and infrared excess we observe from these stars is consistent with the presence of tidally disrupted sub-stellar bodies. we demonstrate, using smoothed particle hydrodynamics, that a sublimating or partially disrupting planet on an eccentric orbit around a white dwarf will form and maintain a gas disc with an eccentricity within 0.1 of, and lower than, that of the orbiting body. we also demonstrate that the eccentric gas disc observed around the white dwarf sdss j1228 + 1040 can be explained by the same hypothesis. | formation of eccentric gas discs from sublimating or partially disrupted asteroids orbiting white dwarfs |
context. the esa rosetta spacecraft, currently orbiting around comet 67p/churyumov-gerasimenko, has already provided in situ measurements of the dust grain properties from several instruments,particularly osiris and giada. we propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution.aims: to constrain the dust grain properties, we take rosetta osiris and giada results into account, and combine osiris data during the approach phase (from late april to early june 2014) with a large data set of ground-based images that were acquired with the eso very large telescope (vlt) from february to november 2014.methods: a monte carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. key properties of the grains (density, velocity, and size distribution) were obtained from rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. in this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately.results: the dust parameters derived from the inner coma measurements by osiris and giada and from distant imaging using vlt data are consistent, except for the power index of the size-distribution function, which is α = -3, instead of α = -2, for grains smaller than 1 mm. this is possibly linked to the presence of fluffy aggregates in the coma. the onset of cometary activity occurs at approximately 4.3 au, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 au. this implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the miro experiment. | the dust environment of comet 67p/churyumov-gerasimenko from rosetta osiris and vlt observations in the 4.5 to 2.9 au heliocentric distance range inbound |
the search for signs of life through the detection of exoplanet atmosphere biosignature gases is gaining momentum. yet, only a handful of rocky exoplanet atmospheres are suitable for observation with planned next-generation telescopes. to broaden prospects, we describe the possibilities for an aerial, liquid water cloud-based biosphere in the atmospheres of sub neptune-sized temperate exoplanets, those receiving earth-like irradiation from their host stars. one such planet is known (k2-18b) and other candidates are being followed up. sub neptunes are common and easier to study observationally than rocky exoplanets because of their larger sizes, lower densities, and extended atmospheres or envelopes. yet, sub neptunes lack any solid surface as we know it, so it is worthwhile considering whether their atmospheres can support an aerial biosphere. we review, synthesize, and build upon existing research. passive microbial-like life particles must persist aloft in a region with liquid water clouds for long enough to metabolize, reproduce, and spread before downward transport to lower altitudes that may be too hot for life of any kind to survive. dynamical studies are needed to flesh out quantitative details of life particle residence times. a sub neptune would need to be a part of a planetary system with an unstable asteroid belt in order for meteoritic material to provide nutrients, though life would also need to efficiently reuse and recycle metals. the origin of life may be the most severe limiting challenge. regardless of the uncertainties, we can keep an open mind to the search for biosignature gases as a part of general observational studies of sub neptune exoplanets. | possibilities for an aerial biosphere in temperate sub neptune-sized exoplanet atmospheres |
fumaroles are the surface manifestation of hydrothermal circulation and can be influenced by magmatic, hydrothermal, hydrological and tectonic processes. this study investigates the temporal changes in fumarole temperatures and spatial extent on aluto, a restless volcano in the main ethiopian rift (mer), in order to better understand the controls on fluid circulation and the interaction between the magmatic and hydrothermal systems. thermal infrared (tir) satellite images, acquired by the advanced spaceborne thermal emission and reflection radiometer (aster) over the period of 2004 to 2016, are used to generate time series of the fumarole temperatures and areas. the thermal anomalies identified in the aster images coincide with known fumaroles with temperatures > 80 °c and are located on or close to fault structures, which provide a pathway for the rising fluids. most of the fumaroles, including those along the major zone of hydrothermal upwelling, the artu jawe fault zone, have pixel-integrated temperature variations of only 2 ± 1.5 °c. the exception are the bobesa fumaroles located on a hypothesised caldera ring fault which show pixel-integrated temperature changes of up to 9 °c consistent with a delayed response of the hydrothermal system to precipitation. we conclude that fumaroles along major faults are strongly coupled to the magmatic-hydrothermal system and are relatively stable with time, whereas those along shallower structures close to the rift flank are more strongly influenced by seasonal variations in groundwater flow. the use of remote sensing data to monitor the thermal activity of aluto provides an important contribution towards understanding the behaviour of this actively deforming volcano. this method could be used at other volcanoes around the world for monitoring and geothermal exploration. | satellite observations of fumarole activity at aluto volcano, ethiopia: implications for geothermal monitoring and volcanic hazard |
high-resolution 3d information on lunar and planetary surfaces is crucial for planetary exploration missions and science. photogrammetry is a state-of-the-art technology for generating 3d topographic models of surfaces such as digital elevation models (dems). the performance of the photogrammetry and the resulting dems is affected by image matching. however, most matching algorithms fail when the images have large differences in illumination and subtle textures. this problem can be addressed by integrating photoclinometry into the photogrammetric process. this paper presents an integrated photogrammetric and photoclinometric approach that is able to generate pixel-resolution dems of the lunar surface and is illumination invariant. the incorporation of photoclinometry into photogrammetry involves two main steps. first, a photoclinometry assisted image matching (pam) approach is developed by integrating photometric stereo analysis in the image matching to create pixel-wise matches, even for images with large illumination differences. second, the dem derived from photogrammetry using the matching results is further refined to pixel-wise resolution using photoclinometry with a shadow constraint. the proposed approach has been used for high-resolution topographic mapping at the chang'e-4 and chang'e-5 landing sites using lunar reconnaissance orbiter camera (lroc) narrow angle camera (nac) images acquired under different illumination conditions. the results indicate that the proposed approach is robust to severe inconsistencies in illumination and subtle textures in cases where the conventional approaches fail. the approach is able to achieve geometric accuracies comparable to photogrammetry but more small-scale topographic details. the proposed approach can also be used for high-resolution topographic mapping of other planetary bodies such as mercury or asteroids, and provides a useful reference for similar topographic mapping on earth. | an integrated photogrammetric and photoclinometric approach for illumination-invariant pixel-resolution 3d mapping of the lunar surface |
the japanese hayabusa2 mission has revealed in detail the physical characteristics of the c-type asteroid 162173 ryugu, in particular, its spinning top-shaped rubble-pile structure and potentially high organic content. a widely accepted formation scenario for ryugu is catastrophic collision between larger asteroids and the subsequent slow gravitational accumulation of collisional debris. an alternative scenario is that ryugu is an extinct comet that lost its icy components. here, we numerically simulated the sublimation of water ice from a porous cometary nucleus until the refractory components, such as silicate rocks and organic matter, were left behind as evaporative residues. such a process represents the transformation from a comet to an asteroid. the spin-up related to the shrinking nucleus, associated with water ice sublimation, was also calculated. the result of the calculation indicates that the cometary origin scenario can account for all the features of ryugu discussed above. we conclude that organic-rich spinning top-shaped rubble-pile asteroids, such as ryugu, are comet-asteroid transition objects or extinct comets. | the asteroid 162173 ryugu: a cometary origin |
building upon the recent development of solar sailing primer vector theory and its successful applications, we propose a new formulation for indirect solar-sail trajectory optimization, which minimizes solar angle (cone angle between the sail normal and sunlight vectors) over a trajectory. the minimum solar-angle objective is introduced to address a typical demand in mission design: having the ability to design trajectories with fixed time-of-flight, which is especially crucial when the mission involves time-sensitive events, such as scientific observations with specific lighting conditions, gravity assists at specific epochs, to name a few. we derive an analytical optimal control law for minimum solar-angle sail transfers by applying pontryagin's optimality principle. our theoretical results illuminate that a quantity termed solar sailing primer vector characterizes the optimal solar-sail control law for both minimum-time and minimum solar-angle transfers, as is the case in lawden's primer vector theory for conventional low-thrust transfers. we numerically demonstrate these theoretical results by applying them to asteroid rendezvous transfers for nasa's nea scout mission. the numerical examples also reveal the numerical advantage of using the minimum solar-angle objective over the minimum-time one for solar-sail trajectory design because of the smoother optimal control profile. solar sailing primer vector theory provides a tool to characterize the optimal control law independent of particular state representations or solution methods, enabling mission designers to combine it with a wealth of techniques developed for low-thrust trajectory optimization. | indirect trajectory optimization via solar sailing primer vector theory: minimum solar-angle transfers |
nasa's osiris-rex mission to asteroid (101955) bennu relied on the production of real-time shape models for both spacecraft navigation and scientific analysis. the primary method of constructing shape models during the early phases of the mission was image-based stereophotoclinometry (spc). the spc shape models were used for operational planning, navigation, sample site selection, and initial scientific investigations. to this end, detailed analyses of the quality of each shape model and a thorough documentation of all sources of error were vital to ensure proper considerations of the limitations of each model. in this paper, we present methods used during the osiris-rex mission to validate the spc shape models and construct the associated quality reports. although developed for the osiris-rex mission, these validation techniques can be applied to spc-derived shape models of other planetary bodies. | validation of stereophotoclinometric shape models of asteroid (101955) bennu during the osiris-rex mission |
the solar system's terrestrial planets are thought to have accreted over millions of years out of a sea of smaller embryos and planetesimals. because it is impossible to know the surface density profile for solids and size frequency distribution in the primordial solar nebula, distinguishing between the various proposed evolutionary schemes has historically been difficult. nearly all previous simulations of terrestrial planet formation assume that moon- to mars-massed embryos formed throughout the inner solar system during the primordial gas-disk phase. however, validating this assumption through models of embryo accretion is computationally challenging because of the large number of bodies required. here, we reevaluate this problem with gpu-accelerated, direct n-body simulations of embryo growth starting from r ∼ 100 km planetesimals. we find that embryos emerging from the primordial gas phase at a given radial distance already have masses similar to the largest objects at the same semimajor axis in the modern solar system. thus, earth and venus attain ∼50% of their modern mass, mars-massed embryos form in the mars region, and ceres-massed objects are prevalent throughout asteroid belt. consistent with other recent work, our new initial conditions for terrestrial accretion models produce markedly improved solar system analogs when evolved through the giant impact phase of planet formation. however, we still conclude that an additional dynamical mechanism such as giant planet migration is required to prevent earth-massed mars analogs from growing. | embryo formation with gpu acceleration: reevaluating the initial conditions for terrestrial accretion |
results from a meteor head echo shower survey using the quasi continuous meteor observations of the high power large aperture radar maarsy, located in northern norway (69.30°n, 16.04°e) are presented. the data set comprises 760 000 head echoes detected during two and half years sensitive to an effective limiting masses below 10-8 kg. using a wavelet shower search algorithm, we identified 33 meteor showers in the data set all of which are found in the iau meteor shower catalog. we find ∼ 1% of all measured head echoes at these masses are associated with meteor showers. comparison of shower radiants from this survey with the observation of the canadian meteor orbit radar (cmor) transverse scattering radar system shows generally good agreement, although there are large differences in the measured durations of some meteor showers. differential mass indices (s) of ∼ 1.5-1.6 are measured for the perseids (per), geminids (gem) and quadrantids (qua) showers. the orionids (ori) show a much steeper mass index of 2.0, in agreement with other observations at small particle sizes, suggesting the halleyid showers, in particular, are rich in very small meteoroids. | a meteoroid stream survey using meteor head echo observations from the middle atmosphere alomar radar system (maarsy) |
ion-scale magnetospheres have been observed around comets, weakly magnetized asteroids, and localized regions on the moon and provide a unique environment to study kinetic-scale plasma physics, in particular in the collision-less regime. in this work, we present the results of particle-in-cell simulations that replicate recent experiments on the large plasma device at the university of california, los angeles. using high-repetition rate lasers, ion-scale magnetospheres were created to drive a plasma flow into a dipolar magnetic field embedded in a uniform background magnetic field. the simulations are employed to evolve idealized 2d configurations of the experiments, study highly resolved, volumetric datasets, and determine the magnetospheric structure, magnetopause location, and kinetic-scale structures of the plasma current distribution. we show the formation of a magnetic cavity and a magnetic compression in the magnetospheric region, and two main current structures in the dayside of the magnetic obstacle: the diamagnetic current, supported by the driver plasma flow, and the current associated with the magnetopause, supported by both the background and driver plasmas with some time-dependence. from multiple parameter scans, we show a reflection of the magnetic compression, bounded by the length of the driver plasma, and a higher separation of the main current structures for lower dipolar magnetic moments. | laser-driven, ion-scale magnetospheres in laboratory plasmas. ii. particle-in-cell simulations |
returned samples from cb-type asteroid (162173) ryugu exhibit very dark spectra in visible and near-infrared ranges, generally consistent with the hayabusa2 observations. a critical difference is that a structural water absorption of hydrous silicates is around twice as deep in the returned samples compared with those of ryugu's surface, suggesting ryugu surface is more dehydrated. here we use laboratory experiments data to indicate the spectral differences between returned samples and asteroid surface are best explained if ryugu surface has (1) higher porosity, (2) larger particle size, and (3) more space-weathered condition, with the last being the most effective. on ryugu, space weathering by micrometeoroid bombardments promoting dehydration seem to be more effective than that by solar-wind implantation. extremely homogeneous spectra of the ryugu's global surface is in contrast with the heterogeneous s-type asteroid (25143) itokawa's spectra, which suggests space weathering has proceeded more rapidly on cb-type asteroids than s-type asteroids. | space weathering acts strongly on the uppermost surface of ryugu |
hayabusa2 is an asteroid sample return mission carried out by the japan aerospace exploration agency. the spacecraft was launched in 2014 and arrived at the target asteroid ryugu on june 27, 2018. during the 1.5-year proximity phase, several critical operations (including two landing/sampling operations) were successfully performed. they were based on autonomous image-based descent and landing techniques. this paper describes an imagebased autonomous navigation scheme of the hayabusa2 mission using artificial landmarks named target markers (tms). its basic algorithm, and the in-flight results of the first touchdown and its rehearsal, are shown. | image-based autonomous navigation of hayabusa2 using artificial landmarks: the design and brief in-flight results of the first landing on asteroid ryugu |
developing highly efficient, sustainable carbon cathodes is essential for emerging zn-ion hybrid supercapacitors (zics). herein, lignin's novel chemical modification (amination) has been developed to produce high quantity pyrrolic-n moieties as active sites. furthermore, chemically modified amine moieties in lignin are vital as a natural self-activating template to generate hierarchical porosity in the 2d (graphene-like) architecture with exceedingly high surface area (2926.4 m2g-1). the rationally introduced dominated pyrrolic-n moieties boost the zn-ion storage capacity and reaction kinetics due to the dual energy storage mechanism and efficient charge transfer between pyrrolic-n and zn+2 ions. furthermore, the pyrrolic-n species are energetically favorable for the adsorption of zn+2 ions by the formation of n-zn+2 chemical bonds. besides, the nitrogen oxides reduce the intrinsic resistance and induce a more polarized surface, resulting in high wettability and efficient transfer of electrolytes into the pores of hydrophobic carbon materials. subsequently, the chemically modified lignin-derived activated carbon material (chem-acm) as a cathode in zics delivers a high capacity of 161.2 ma h g-1 at 1 a g-1 with the admirable energy density of 106.7 w h kg-1 at 897 w kg-1 and excellent retention capacity (94%) after 10,000 cycles. mainly, the assembled quasi solid-state zics using chem-acm retains the remarkable storage capacity (202 ma h g-1 at 0.2 ag-1) even at a high bending angle. notably, the chem-acm has been further employed in symmetric supercapacitors as an electrode, and it displays exceptional specific capacitance of 354 fg-1 at 0.5 ag-1 with tremendous energy (43.5 w h kg-1) and the power density (0.53 kw kg-1). additionally, the charge storage capability of chem-acm is positively dependent on high nitrogen contents, and it is extrapolated that pyrrolic-n moieties are dominant active sites. hence, the designed amination-assisted biocarbon synthesis provides a new way to prepare high nitrogen-containing biocarbon for zics and further understand pyrrolic-n species' impact on zn-ion storage. | rational design of pyrrolic-n dominated carbon material derived from aminated lignin for zn-ion supercapacitors |
we provide the spherical harmonic solutions to evaluate the external gravitational field of a general polyhedral body with arbitrary polynomial density contrast, including the gravitational potential and its arbitrary-order derivatives. the linear recursive algorithm for computation of the spherical harmonic coefficients of the potential is derived by using the gauss divergence theorem and the stokes theorem, and the computations are performed on the basis of the division of general polygonal pyramid of the polyhedron instead of the division of tetrahedron. the algorithm of this paper can handle the density contrast in both horizontal and vertical directions and the polynomial function of the density at arbitrary degree. both the conversion relations of the density function and the arbitrary-order derivatives of the spherical harmonic potential between the initial and rotated reference frames are given in tensor product forms, which assist the calculations. the space-domain method for evaluating the gravity field of the polyhedral body may leads to numerical problems at a remote observation point. however, the spherical harmonic method is numerically stable at arbitrary observation points outside the smallest enclosed sphere. the numerical experiments for three actual and synthetic polyhedral models including a right rectangular prism with cubic density varying with depth, the asteroid 433 eros with cubic polynomial density and a right rectangular prism with quartic polynomial density, are implemented to test the accuracy, convergence, and numerical stability of the spherical harmonic algorithm. | spherical harmonic expansions for the gravitational field of a polyhedral body with polynomial density contrast |
using new data and recent models this paper derives a total combined flux model of the mass reaching earth as interplanetary material. for the small sizes the interplanetary flux model by grün et al. (1985) was used which describes the mass flux at 1 au for meteoroids in the mass range 10-21 kg to about 10-1 kg. for the large objects the flux models by brown et al. (2002) were used which were derived for bodies greater than 1 m and are based on sensor data of fireballs that entered the earth atmosphere. for the intermediate size range interpolations and alternative models based on meteor and fireball data were used. all flux models were converted to an altitude of 100 km above the earth surface to make them comparable. the total combined flux model covers more than 34 orders of magnitude in mass. using recent measurements and alternative flux models the uncertainties of the obtained model were estimated. recent measurements include in-situ impact data on retrieved space hardware and optical meteor and fireball data. depending on the models and interpolation used the interplanetary material that enters the earth atmosphere per day is in the range of 30-180 t with a best guess value of 54 t per day for an upper cut-off size of 1 km. if the upper size limit is placed at 0.5 m which is the largest size where statistically a daily impact is expected, the expected mass influx is slightly more than 32 t per day. the combined models with interpolations suggest deviations from a simple power law. the flux in the diameter range of 0.01-0.1 m appears not as large as suggested by a simple power law interpolation. | mass accumulation of earth from interplanetary dust, meteoroids, asteroids and comets |
nasa's dart spacecraft is planned to reach and impact asteroid dimorphos, the small moon of binary asteroid (65803) didymos, at a velocity of 6 km s-1 in late 2022 september. dart will be the first mission to test the "kinetic impactor" technique, aimed at deflecting the orbital path of a potentially hazardous asteroid. the success and effectiveness of this technique resides in the efficiency of momentum exchange between the spacecraft and the impacted target. this depends on many factors, including the cratering process, the formation of ejecta, and their fate, as they remain in the system or escape from it, carrying momentum away. here we provide an overview of the cratering process, including ejecta formation and their subsequent dynamical evolution. we use different methodologies to model the physics of the problem, including smoothed particle hydrodynamics to model the cratering and ejecta formation process after the hypervelocity impact, n-body granular simulations to model early collisional processes between ejecta fragments right after cratering, and high-fidelity planetary propagation to model the dynamical evolution of ejecta during their purely ballistic phase. we highlight the key features of each phase and their role in defining the dynamical fate of ejecta. we investigate the effect of surface cohesion in the impacted target and identify the qualitative behavior of ejecta particles as a function of the key parameters of the problem. we provide quantitative estimates for the specific case study related to the dart-dimorphos scenario and a selected range of target properties. | ejecta formation, early collisional processes, and dynamical evolution after the dart impact on dimorphos |
the jovian trojans are two swarms of objects located around the l4 and l5 lagrange points. the population is thought to have been captured by jupiter during the solar system's youth. within the swarms, six collisional families have been identified in previous work, with four in the l4 swarm, and two in the l5. our aim is to investigate the stability of the two trojan swarms, with a particular focus on these collisional families. we find that the members of trojan swarms escape the population at a linear rate, with the primordial l4 (23.35 per cent escape) and l5 (24.89 per cent escape) population sizes likely 1.31 and 1.35 times larger than today. given that the escape rates were approximately equal between the two trojan swarms, our results do not explain the observed asymmetry between the two groups, suggesting that the numerical differences are primordial in nature, supporting previous studies. upon leaving the trojan population, the escaped objects move on to orbits that resemble those of the centaur and short-period comet populations. within the trojan collisional families, the 1996 rj and 2001 uv209 families are found to be dynamically stable over the lifetime of the solar system, whilst the hektor, arkesilos and ennomos families exhibit various degrees of instability. the larger eurybates family shows 18.81 per cent of simulated members escaping the trojan population. unlike the l4 swarm, the escape rate from the eurybates family is found to increase as a function of time, allowing an age estimation of approximately 1.045 ± 0.364 × 109 yr. | stability of jovian trojans and their collisional families |
low-albedo, hydrated objects dominate the list of the largest asteroids. these objects have varied spectral shapes in the 3-μm region, where diagnostic absorptions due to volatile species are found. dawn's visit to ceres has extended the view shaped by ground-based observing and shown that world to be a complex one, potentially still experiencing geological activity. we present 33 observations from 2.2 to 4.0 μm of eight large (d > 200 km) asteroids from the c spectral complex, with spectra inconsistent with the hydrated minerals we see in meteorites. we characterize their absorption band characteristics via polynomial and gaussian fits to test their spectral similarity to ceres, the asteroid 24 themis (thought to be covered in ice frost), and the asteroid 51 nemausa (spectrally similar to the cm meteorites). we confirm most of the observations are inconsistent with what is seen in meteorites and require additional absorbers. we find clusters in band centers that correspond to ceres- and themis-like spectra, but no hiatus in the distribution suitable for use to simply distinguish between them. we also find a range of band centers in the spectra that approaches what is seen on comet 67p. finally, variation is seen between observations for some objects, with the variation on 324 bamberga consistent with hemispheric-level difference in composition. given the ubiquity of objects with 3-μm spectra unlike what we see in meteorites, and the similarity of those spectra to the published spectra of ceres and themis, these objects appear much more to be archetypes than outliers. | infrared spectroscopy of large, low-albedo asteroids: are ceres and themis archetypes or outliers? |
the goal of project gauss (genesis of asteroids and evolution of the solar system) is to return samples from the dwarf planet ceres. ceres is the most accessible candidate of ocean worlds and the largest reservoir of water in the inner solar system. it shows active volcanism and hydrothermal activities in recent history. recent evidence for the existence of a subsurface ocean on ceres and the complex geochemistry suggest past habitability and even the potential for ongoing habitability. gauss will return samples from ceres with the aim of answering the following top-level scientific questions: what is the origin of ceres and what does this imply for the origin of water and other volatiles in the inner solar system? | gauss - genesis of asteroids and evolution of the solar system |
the double asteroid redirection test (dart) is the first planetary defense mission to demonstrate the kinetic deflection technique. the dart spacecraft will collide with the asteroid dimorphos, the smaller component of the binary asteroid system (65803) didymos. the dart impact will excavate surface/subsurface materials of dimorphos, leading to the formation of a crater and/or some magnitude of reshaping (i.e., shape change without significant mass loss). the ejecta may eventually hit didymos's surface. if the kinetic energy delivered to the surface is high enough, reshaping may also occur in didymos, given its near-critical spin rate. reshaping on either body will modify the mutual gravitational field, leading to a reshaping-induced orbital period change, in addition to the impact-induced orbital period change. if left unaccounted for, this could lead to an erroneous interpretation of the effect of the kinetic deflection technique. here we report the results of full two-body problem simulations that explore how reshaping influences the mutual dynamics. in general, we find that the orbital period becomes shorter linearly with increasing reshaping magnitude. if didymos's shortest axis shrinks by ~0.7 m, or dimorphos's intermediate axis shrinks by ~2 m, the orbital period change would be comparable to the earth-based observation accuracy, ~7.3 s. constraining the reshaping magnitude will decouple the reshaping- and impact-induced orbital period changes; didymos's reshaping may be constrained by observing its spin period change, while dimorphos's reshaping will likely be difficult to constrain but will be investigated by the esa's hera mission that will visit didymos in late 2026. | nasa's double asteroid redirection test (dart): mutual orbital period change due to reshaping in the near-earth binary asteroid system (65803) didymos |
formed from a catastrophic collision of a parent body larger than 150 km in diameter, the flora family is located in the innermost part of the main belt near the {ν }6 secular resonance. objects in this region, when pushed onto planet-crossing orbits, tend to have relatively high probabilities of striking the earth. these factors suggest that flora may be a primary source of present-day ll chondrite-like neos and earth/moon impactors. to investigate this possibility, we used collisional and dynamical models to track the evolution of flora family members. we created an initial flora family and followed test asteroids 1 and 3 km in diameter using a numerical code that accounted for both planetary perturbations and nongravitational effects. our flora family members reproduce the observed semimajor axis, eccentricity, and inclination distributions of the real family after ≃ 1 to 1.4 gyr. a consistency with the surface age inferred from crater spatial densities found on (951) gaspra may favor the latter age. our combined collisional and dynamical runs indicate that the family has lost nearly 90% of its initial kilometer-sized members. at its peak, 100{--}300 {myr} after the family-forming event, flora family members filled neo space with nearly 1000 d≥slant 1 {km} size bodies before fading to its present contribution of 35-50 such neos. therefore, it is not currently a major source of large neos. we also find 700-950 and 35-47 kilometer-sized asteroids struck the earth and moon, respectively, most within the first 300 myr after family formation. these results imply that flora played a major role in providing impacts to the mid-proterozoic earth. | forming the flora family: implications for the near-earth asteroid population and large terrestrial planet impactors |
the gap between two component debris discs is often taken to be carved by intervening planets scattering away the remnant planetesimals. we employ n-body simulations to determine how the time needed to clear the gap depends on the location of the gap and the mass of the planets. we invert this relation, and provide an equation for the minimum planet mass, and another for the expected number of such planets, that must be present to produce an observed gap for a star of a given age. we show how this can be combined with upper limits on the planetary system from direct imaging non-detections (such as with gpi or sphere) to produce approximate knowledge of the planetary system. | the unseen planets of double belt debris disc systems |
we present the discovery of activity originating from quasi-hilda object 2018 cz16, a finding stemming from the citizen science project active asteroids. for 2018 cz16 we identified a broad (~60°) but short (~5″) tail in archival blanco 4 m data from cerro tololo inter-american observatory, chile, (ctio) dark energy camera images from ut 2018 may 15, 17 and 18. activity occurred 2 months prior to perihelion, consistent with sublimation-driven activity. | cometary activity on quasi-hilda object 2018 cz16 |
the regolith transport near the surface of an asteroid is inherently sensitive to the local topography. in this paper, conditions of surface mass shedding and the subsequent evolution of the shedding material are studied for the primary of 65803 didymos, serving as a representative for a large group of top-shaped asteroids that rotate near their critical spin limits. we considered the influences of an asymmetric shape and a non-spherical gravity, and demonstrate that these asymmetries play a significant role in the shedding process as well as in the subsequent orbital motion. the mass shedding conditions are given as a function of the geological coordinates, and show a clear-cut dependency on the local topographic features. we find that at different stages of the yarkovsky-o’keefe-radzievskii-paddack spin-up, the bulged areas exhibit a uniform superior advantage of enabling mass shedding over the depressed areas. “dead zones” free from mass shedding are found around the polar sites. numerical simulations show that the orbital motion of the shedding material experiences a drastic change as the spin rate is approaching the critical limit. the “mass leaking” effect is reinforced as the spin rate increases; the lower spin rates correspond to a higher capability of trapping the lofted particles in the vicinity of the asteroid, which statistically improves the probability of collisional growth in orbit. we also find that the topological transition of the equilibrium point can in practice lead to rapid clearance of the shedding material and transport of their orbits to larger distances from the surface. | the dynamical complexity of surface mass shedding from a top-shaped asteroid near the critical spin limit |
entry and breakup models predict that airburst in the earth's atmosphere is likely for non-metallic asteroids with diameters up to approximately 200 meters. (collins, 2005; collins, 2017; wheeler, 2017). objects of this size can deposit over 250 megatons of energy into the atmosphere. fast-running ground damage prediction codes for such events rely heavily upon methods developed from nuclear weapons research to estimate the damage potential for an airburst at altitude (collins, 2005; mathias, 2017; rumpf, 2017; rumpf, 2016; hills, 1993). in particular, these tools rely upon the powerful yield scaling laws developed for point-source blasts that are used in conjunction with a height of burst (hob) map to predict ground damage for an airburst of a specific energy at a given altitude. while this approach works extremely well for yields as large as tens of megatons, it becomes less accurate as asteroid size and effective yields increase to the hundreds of megatons potentially released in larger airburst events. accordingly, this study revisits the assumptions underlying this approach and shows how atmospheric buoyancy becomes important as yield increases beyond a few megatons. we then use large-scale three-dimensional simulations to construct numerically generated height of burst maps that are appropriate at the higher energy levels associated with the entry of asteroids with diameters of hundreds of meters. these numerically generated hob maps can then be incorporated into engineering methods for damage prediction, significantly improving their accuracy for asteroids with diameters greater than 80-100 m. | simulation-based height of burst map for asteroid airburst damage prediction |
observed planetary debris in white dwarf atmospheres predominately originate from the destruction of small bodies on highly eccentric (>0.99) orbits. despite their importance, these minor planets have coupled physical and orbital evolution, which has remained largely unexplored. here, we present a novel approach for estimating the influence of fast chaotic rotation on the orbital evolution of high-eccentricity triaxial asteroids, and formally characterize the propagation of their angular rotation velocities and orbital elements as random time processes. by employing the impulse approximation, we demonstrate that the violent gravitational interactions during periastron passages transfer energy between the orbit and asteroid’s rotation. if the distribution of spin impulses were symmetric around zero, then the net result would be a secular decrease of the semimajor axis and a further increase of the eccentricity. we find evidence, however, that the chaotic rotation may be self regulated in such a manner that these effects are reduced or nullified. we discover that asteroids on highly eccentric orbits can break themselves apart—in a type of yorp-less (yarkovsky-o’keefe-radzievskii-paddack) rotational fission—without actually entering the roche radius, with potentially significant consequences for the distribution of debris and energy requirements for gravitational scattering in metal-polluted white dwarf planetary systems. this mechanism provides a steady stream of material impacting a white dwarf without rapidly depleting the number of small bodies in the stellar system. | chaotic rotation and evolution of asteroids and small planets in high-eccentricity orbits around white dwarfs |
strassen's asymptotic rank conjecture [progr. math. 120 (1994)] claims a strong submultiplicative upper bound on the rank of a three-tensor obtained as an iterated kronecker product of a constant-size base tensor. the conjecture, if true, most notably would put square matrix multiplication in quadratic time. we note here that some more-or-less unexpected algorithmic results in the area of exponential-time algorithms would also follow. specifically, we study the so-called set cover conjecture, which states that for any $\epsilon>0$ there exists a positive integer constant $k$ such that no algorithm solves the $k$-set cover problem in worst-case time $\mathcal{o}((2-\epsilon)^n|\mathcal f|\operatorname{poly}(n))$. the $k$-set cover problem asks, given as input an $n$-element universe $u$, a family $\mathcal f$ of size-at-most-$k$ subsets of $u$, and a positive integer $t$, whether there is a subfamily of at most $t$ sets in $\mathcal f$ whose union is $u$. the conjecture was formulated by cygan et al. in the monograph parameterized algorithms [springer, 2015] but was implicit as a hypothesis already in cygan et al. [ccc 2012, acm trans. algorithms 2016], there conjectured to follow from the strong exponential time hypothesis. we prove that if the asymptotic rank conjecture is true, then the set cover conjecture is false. using a reduction by krauthgamer and trabelsi [stacs 2019], in this scenario we would also get a $\mathcal{o}((2-\delta)^n)$-time randomized algorithm for some constant $\delta>0$ for another well-studied problem for which no such algorithm is known, namely that of deciding whether a given $n$-vertex directed graph has a hamiltonian cycle. | the asymptotic rank conjecture and the set cover conjecture are not both true |
in this paper, we demonstrate gap amplification for reconfiguration problems. in particular, we prove an explicit factor of pspace-hardness of approximation for three popular reconfiguration problems only assuming the reconfiguration inapproximability hypothesis (rih) due to ohsaka (stacs 2023). our main result is that under rih, maxmin binary csp reconfiguration is pspace-hard to approximate within a factor of $0.9942$. moreover, the same result holds even if the constraint graph is restricted to $(d,\lambda)$-expander for arbitrarily small $\frac{\lambda}{d}$. the crux of its proof is an alteration of the gap amplification technique due to dinur (j. acm, 2007), which amplifies the $1$ vs. $1-\epsilon$ gap for arbitrarily small $\epsilon > 0$ up to the $1$ vs. $1-0.0058$ gap. as an application of the main result, we demonstrate that minmax set cover reconfiguration and minmax dominating set reconfiguratio} are pspace-hard to approximate within a factor of $1.0029$ under rih. our proof is based on a gap-preserving reduction from label cover to set cover due to lund and yannakakis (j. acm, 1994). however, unlike lund--yannakakis' reduction, the expander mixing lemma is essential to use. we highlight that all results hold unconditionally as long as "pspace-hard" is replaced by "np-hard," and are the first explicit inapproximability results for reconfiguration problems without resorting to the parallel repetition theorem. we finally complement the main result by showing that it is np-hard to approximate maxmin binary csp reconfiguration within a factor better than $\frac{3}{4}$. | gap amplification for reconfiguration problems |
debris discs are typically revealed through the presence of excess emission at infrared wavelengths. most discs exhibit excess at mid- and far-infrared wavelengths, analogous to the solar system’s asteroid and edgeworth-kuiper belts. recently, stars with strong (∼1%) excess at near-infrared wavelengths were identified through interferometric measurements. using the high precision polarimetric instrument, we examined a sub-sample of these hot dust stars (and appropriate controls) at parts-per-million sensitivity in sdss g‧ (green) and r‧ (red) filters for evidence of scattered light. no detection of strongly polarized emission from the hot dust stars is seen. we, therefore, rule out scattered light from a normal debris disk as the origin of this emission. a wavelength-dependent contribution from multiple dust components for hot dust stars is inferred from the dispersion (the difference in polarization angle in red and green) of southern stars. contributions of 17 ppm (green) and 30 ppm (red) are calculated, with strict 3-σ upper limits of 76 and 68 ppm, respectively. this suggests weak hot dust excesses consistent with thermal emission, although we cannot rule out contrived scenarios, e.g., dust in a spherical shell or face-on discs. we also report on the nature of the local interstellar medium (ism), obtained as a byproduct of the control measurements. highlights include the first measurements of the polarimetric color of the local ism and the discovery of a southern sky region with a polarization per distance thrice the previous maximum. the data suggest that λ max, the wavelength of maximum polarization, is bluer than typical. | polarization measurements of hot dust stars and the local interstellar medium |
recently, there has been a worldwide proliferation of instruments and networks dedicated to observing meteors, including airborne and future space-based monitoring systems . there has been a corresponding rapid rise in high quality data accumulating annually. in this paper, we present a method embodied in the open-source software program "meteor toolkit", which can effectively and accurately process these data in an automated mode and discover the pre-impact orbit and possibly the origin or parent body of a meteoroid or asteroid. the required input parameters are the topocentric pre-atmospheric velocity vector and the coordinates of the atmospheric entry point of the meteoroid, i.e. the beginning point of visual path of a meteor, in an earth centered-earth fixed coordinate system, the international terrestrial reference frame (itrf). our method is based on strict coordinate transformation from the itrf to an inertial reference frame and on numerical integration of the equations of motion for a perturbed two-body problem. basic accelerations perturbing a meteoroid's orbit and their influence on the orbital elements are also studied and demonstrated. our method is then compared with several published studies that utilized variations of a traditional analytical technique, the zenith attraction method, which corrects for the direction of the meteor's trajectory and its apparent velocity due to earth's gravity. we then demonstrate the proposed technique on new observational data obtained from the finnish fireball network (ffn) as well as on simulated data. in addition, we propose a method of analysis of error propagation, based on general rule of covariance transformation. | orbit determination based on meteor observations using numerical integration of equations of motion |
since the release of llm-based tools such as github copilot and chatgpt the media and popular scientific literature, but also journals such as the communications of the acm, have been flooded with opinions how these tools will change programming. the opinions range from ``machines will program themselves'', to ``ai does not help programmers''. of course, these statements are meant to to stir up a discussion, and should be taken with a grain of salt, but we argue that such unfounded statements are potentially harmful. instead, we propose to investigate which skills are required to develop software using llm-based tools. in this paper we report on an experiment in which we explore if computational thinking (ct) skills predict the ability to develop software using llm-based tools. our results show that the ability to develop software using llm-based tools can indeed be predicted by the score on a ct assessment. there are many limitations to our experiment, and this paper is also a call to discuss how to approach, preferably experimentally, the question of which skills are required to develop software using llm-based tools. we propose to rephrase this question to include by what kind of people/programmers, to develop what kind of software using what kind of llm-based tools. | what skills do you need when developing software using chatgpt? (discussion paper) |
hera represents the european space agency's inaugural planetary defence space mission, and plays a pivotal role in the asteroid impact and deflection assessment international collaboration with nasa dart mission that performed the first asteroid deflection experiment using the kinetic impactor techniques. with the primary objective of conducting a detailed post-impact survey of the didymos binary asteroid following the dart impact on its small moon called dimorphos, hera aims to comprehensively assess and characterize the feasibility of the kinetic impactor technique in asteroid deflection while conducting in-depth investigation of the asteroid binary, including its physical and compositional properties as well as the effect of the impact on the surface and/or shape of dimorphos. in this work we describe the hera radio science experiment, which will allow us to precisely estimate key parameters, including the mass, which is required to determine the momentum enhancement resulting from the dart impact, mass distribution, rotational states, relative orbits, and dynamics of the asteroids didymos and dimorphos. through a multi-arc covariance analysis we present the achievable accuracy for these parameters, which consider the full expected asteroid phase and are based on ground radiometric, hera optical images, and hera to cubesats intersatellite link radiometric measurements. the expected formal uncertainties for didymos and dimorphos gm are better than 0.01% and 0.1%, respectively, while their j2 formal uncertainties are better than 0.1% and 10%, respectively. regarding their rotational state, the absolute spin pole orientations of the bodies can be recovered to better than 1 degree, and dimorphos spin rate to better than 10^-3%. dimorphos reconstructed relative orbit can be estimated at the sub-m level [...] | the hera radio science experiment at didymos |
we introduce the fundamental ideas and challenges of predictable ai, a nascent research area that explores the ways in which we can anticipate key indicators of present and future ai ecosystems. we argue that achieving predictability is crucial for fostering trust, liability, control, alignment and safety of ai ecosystems, and thus should be prioritised over performance. while distinctive from other areas of technical and non-technical ai research, the questions, hypotheses and challenges relevant to predictable ai were yet to be clearly described. this paper aims to elucidate them, calls for identifying paths towards ai predictability and outlines the potential impact of this emergent field. | predictable artificial intelligence |
the near-earth object surveyor (neo surveyor) mission has a requirement to find two-thirds of the potentially hazardous asteroids larger than 140 m in size. in order to determine the mission's expected progress toward this goal during design and testing, as well as the actual progress during the survey, a simulation tool has been developed to act as a consistent and quantifiable yardstick. we test that the survey simulation software is correctly predicting on-sky positions and thermal infrared fluxes by using it to reproduce the published measurements of asteroids from the neowise mission. we then extended this work to find previously unreported detections of known near-earth asteroids in the neowise data archive, a search that resulted in 21,661 recovery detections, including 1166 objects that had no previously reported neowise observations. these efforts demonstrate the reliability of the neo surveyor survey simulator tool and the perennial value of searchable image and source catalog archives for extending our knowledge of the small bodies of the solar system. | validation of the survey simulator tool for the neo surveyor mission using neowise data |
being the first of its kind, the white dwarf wd 1145+017 exhibits a complex system of disintegrating debris which offers a unique opportunity to study its disruption process in real time. even with plenty of transit observations there are no clear constraints on the masses or eccentricities of such debris. using n-body simulations, we show that masses greater than ≃1020 kg (a tenth of the mass of ceres) or orbits that are not nearly circular (eccentricity > 10-3) dramatically increase the chances of the system becoming unstable within 2 yr, which would contrast with the observational data over this timespan. we also provide a direct comparison between transit phase shifts detected in the observations and by our numerical simulations. | mass and eccentricity constraints on the planetary debris orbiting the white dwarf wd 1145+017 |
exploration of asteroid (101955) bennu by the osiris-rex mission has provided an in-depth look at this rubble-pile near-earth asteroid. in particular, the measured gravity field and the detailed shape model of bennu indicate significant heterogeneities in its interior structure, compatible with a lower density at its center. here we combine gravity inversion methods with a statistical rubble-pile model to determine the density and size-frequency distribution (sfd) index of the rubble that constitutes bennu. the best-fitting models indicate that the sfd of the interior is consistent with that observed on the surface, with a cumulative sfd index of approximately - 2 . 9 . the rubble bulk density is approximately 1.35 g/cm3, corresponding to a 12% macro-porosity. we find the largest rubble particle to be approximately 145 m, whereas the largest void is approximately 10 m. | internal rubble properties of asteroid (101955) bennu |
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