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aqueous organic solid formation from formaldehyde via the formose reaction and subsequent reactions is a possible candidate for the origin of complex primitive chondritic insoluble organic matter (iom) and refractory carbon in comets. the rate of formation of organic solids from formaldehyde was studied as a function of temperature and time, with and without ammonia, in order to derive kinetic expressions for polymer yield. the evolution in molecular structure as a function of time and temperature was studied using infrared spectroscopy. using these kinetic expressions, the yield of organic solids is estimated for extended time and temperature ranges. for example, the half-life for organic solid formation is ∼5 days at 373 k, ∼200 days at 323 k, and ∼70 years at 273 k with ammonia, and ∼25 days at 373 k, ∼13 years at 323 k, and ∼2 × 104 years at 273 k without ammonia. these results indicate that organic solids could form during the aqueous alteration in meteorite parent bodies. if liquid water existed early in the interiors of kuiper belt objects (kbos), formaldehyde could convert into organic solids at temperatures close to 273 k, and possibly even below 273 k in the ammonia-water system. | a kinetic study of the formation of organic solids from formaldehyde: implications for the origin of extraterrestrial organic solids in primitive solar system objects |
asteroids that are targets of spacecraft missions are interesting because they present us with an opportunity to validate ground-based spectral observations. one such object is near-earth asteroid (nea) (162173) ryugu, which is the target of the japanese space agency's (jaxa) hayabusa2 sample return mission. we observed ryugu using the 3-m nasa infrared telescope facility on mauna kea, hawaii, on 2016 july 13 to constrain the object's surface composition, meteorite analogues, and link to other asteroids in the main belt and nea populations. we also modelled its photometric properties using archival data. using the lommel-seeliger model we computed the predicted flux for ryugu at a wide range of viewing geometries as well as albedo quantities such as geometric albedo, phase integral, and spherical bond albedo. our computed albedo quantities are consistent with results from ishiguro et al. our spectral analysis has found a near-perfect match between our spectrum of ryugu and those of nea (85275) 1994 ly and mars-crossing asteroid (316720) 1998 be7, suggesting that their surface regoliths have similar composition. we compared ryugu's spectrum with that of main belt asteroid (302) clarissa, the largest asteroid in the clarissa asteroid family, suggested as a possible source of ryugu by campins et al. we found that the spectrum of clarissa shows significant differences with our spectrum of ryugu, but it is similar to the spectrum obtained by moskovitz et al. the best possible meteorite analogues for our spectrum of ryugu are two cm2 carbonaceous chondrites, mighei and alh83100. | ground-based characterization of hayabusa2 mission target asteroid 162173 ryugu: constraining mineralogical composition in preparation for spacecraft operations |
we model a variety of meteoroid streams originating from asteroid 3200 phaethon and follow their dynamical evolution. the modelling is performed for several past perihelion passages of the parent body. the particles in the models are perturbed (i) only by the gravity of planets, and (ii) both by gravity and by the poynting-robertson effect. we confirm that the meteoroid complex of phaethon consists of two filaments: geminids and daytime sextantids. the most of the geminids are found to be younger than about 1000 years old and their physical properties have to correspond to values of the parameter β (giving the strength of the poynting-robertson drag) between ∼0.005 and ∼0.01, the age of the daytime sextantids has to significantly exceed 10 millennia and β ranges from ∼0.0005 to ∼0.001. the discrepancy between the ages and β-values of particles released from the same source can be explained by the dynamical argument that old sextantids with a relatively small β cannot occur in the geminid filament and that young geminids cannot occur in the sextantid filament. | meteor complex of asteroid 3200 phaethon: its features derived from theory and updated meteor data bases |
carbonates record information regarding the timing, nature and conditions of the fluids circulating through asteroid parent bodies during aqueous alteration events. determining carbonate abundances and their relationships with organic matter improves our understanding of the genesis of major carbonaceous components in chondritic materials. in this study, five cm2 carbonaceous chondrites (cm2.2 nogoya, cm2.3 jbilet winselwan, cm2.5 murchison, cm2 santa cruz, and cm2tii wisconsin range 91600) were studied with raman spectroscopy. carbonates were identified in these meteorite samples by the distinctive raman band in the ∼1100 cm-1 region, representing the symmetric stretching vibration mode (ν1) of the (co3)2- anion. carbonates identified in the meteorite samples are all calcite, with the exception of a single dolomite grain in nogoya. the v1 positions of the cm calcites are 2-3 cm-1 higher than in pure calcite, which suggests that they contain significant impurity cations. typical graphitic first-order d and g bands were identified in the meteorite matrix as well as in ∼25% of the analyzed carbonate grains. from the raman results, we postulate that the carbonates might not have formed under equilibrium conditions from a single fluid. the first generation of carbonate is interpreted to have formed from highly oxidized fluids that led to the oxidation of organic matter (om) and produced carbonates that are om-barren. the second generation of carbonate was formed from a more evolved aqueous fluid with the presence of om. the raman parameters of the organics in carbonates clearly deviate from the matrix om which suggests that the carbonate organics contain very different carbonaceous components that are distinct from the typical amorphous om of the cm matrix. the occurrence of different generations of carbonate in close proximity may be partly responsible for the wide range in estimated ages of carbonates in carbonaceous chondrites reported in previous studies. | investigation of organo-carbonate associations in carbonaceous chondrites by raman spectroscopy |
aims: multi-epoch spitzer space telescope 24 μm data is utilized from the mipsgal and taurus legacy surveys to detect asteroids based on their relative motion.methods: infrared detections are matched to known asteroids and average diameters and albedos are derived using the near earth asteroid thermal model (neatm) for 1865 asteroids ranging in size from 0.2 to 169 km. a small subsample of these objects was also detected by iras or msx and the single wavelength albedo and diameter fits derived from these data are within the uncertainties of the iras and/or msx derived albedos and diameters and available occultation diameters, which demonstrates the robustness of our technique.results: the mean geometric albedo of the small main belt asteroids in this sample is pv = 0.134 with a sample standard deviation of 0.106. the albedo distribution of this sample is far more diverse than the iras or msx samples. the cumulative size-frequency distribution of asteroids in the main belt at small diameters is directly derived and a 3σ deviation from the fitted size-frequency distribution slope is found near 8 km. completeness limits of the optical and infrared surveys are discussed. tables 1-3 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/578/a42 | the kilometer-sized main belt asteroid population revealed by spitzer |
outer solar system exploration by a small spacecraft using a solar power sail is investigated. a solar power sail is an extended form of a solar sail that has thin-film solar cells attached over its surface. this concept makes it possible to generate a large amount of power with less weight resources than conventional means. thereby, even a small spacecraft, which has a strong constraint on available resources, can drive high-power ion thrusters to obtain large δv . combining electric propulsion with gravity assists allows the spacecraft to reach the outer solar system using less propellant. the spacecraft can not only survive by means of solar power in the outer solar system, but also drive electric thrusters there to perform challenging missions such as asteroid or comet rendezvous. in this paper, a framework for exploring the outer solar system using a 50-kg-class small spacecraft is presented. the characteristics of solar electric propulsion under the solar power sail model are disclosed, and a design scheme for missions to the outer planets and beyond are addressed. providing the specific design of the 50-kg-class solar power sail-craft, centaur rendezvous mission design is performed as a feasibility study. | solar electric propulsion by a solar power sail for small spacecraft missions to the outer solar system |
vesta, the second most massive asteroid, has long been perceived as anhydrous. recent studies suggesting the presence of hydrated minerals and past subsurface water have challenged this long-standing perception. yet, direct geologic indications of water activity on vesta's surface were unexpected. herein we show evidence that transient water flowed on the surface, in a debris-flow-like process, and left distinctive geomorphologic features. based on detailed analysis of highest-resolution (∼20 m/pixel) images obtained by the dawn spacecraft, we identify a class of locally occurring, interconnected and curvilinear gully networks on the walls of young (< hundreds of ma) impact craters, ending in lobate deposits near the crater floors. as curvilinear systems only occur within impact craters, we propose that they formed by a particulate-dominated flow of transient water that was released from buried ice-bearing deposits by impact-induced heating and melting. this interpretation is in accordance with the occurrence of pitted terrain on lobate deposits and crater floors. pitted terrain is proposed to result from the degassing of volatiles. the proposed buried ice-bearing deposits are likely localized in extent and may be currently extant in vesta's subsurface. together with the discovery of water evaporation on ceres and water activity on several small asteroids, our results support the new paradigm that water is widespread in the asteroid belt. | geomorphological evidence for transient water flow on vesta |
nucleosynthetic isotope anomalies of planetary materials provide insight into their genetic ties, informing our understanding of early solar system isotopic architecture and evolution. isotope anomalies of non‑carbonaceous (nc) and carbonaceous (cc) materials in multi-element space suggests their variability primarily emerged from mixing between several primordial nebular source regions in the nascent protoplanetary disk. in particular, it has been suggested that the elemental and isotopic compositions of cc meteorites reflect admixtures of nc-like, ci-like, and cai-like components. despite the plethora of elements for which isotope anomalies have been characterized, no mixing model has quantitatively reproduced cc meteorite compositions for more than two elements. in this paper, we leverage the recent characterization of fe isotope anomalies in nc and cc materials, as well as cais, to place new constraints on the evolution of the early solar system and the origin of the cc chondrites. we first respond to the recent proposal, based on fe isotope analyses of returned samples from cb-type asteroid ryugu, that ryugu and ci chondrites are genetically distinct from nc and cc bodies, originating from a third "ci reservoir" beyond the location of the cc reservoir. namely, we propose that the appearance of such a trichotomy in meteoritic heritages arises from the current lack of fe isotope data for cc achondrites. we go on to present a self-consistent mixing model that explains the ti, cr, fe, and ca concentrations and isotope anomalies of the cm, cv, co, ck, and cr chondrite groups via admixing of (i) elementally oc-like material, (ii) ci/ryugu-like material, (iii) isotopically cai-like dust, and (iv) cais sensu stricto. we find that the cai-like dust constitutes a major and broadly constant fraction (∼36%) of all cc chondrites, and identify the ci-like component with the bulk composition of the solar system's parent molecular cloud, denoting it bmc for "bulk molecular cloud." we interpret our results in the context of a qualitative model for early solar system isotopic evolution. | the nc-cc dichotomy explained by significant addition of cai-like dust to the bulk molecular cloud (bmc) composition |
asteroid (3200) phaethon is a near-earth apollo asteroid with an unusual orbit that brings it closer to the sun than any other known asteroid. its last close approach to the earth was in 2017 mid-december and the next one will be on 2026 october. previous rotationally time-resolved spectroscopy of phaethon showed that its spectral slope is slightly bluish, in agreement with its b/f taxonomic classification, but at some rotational phases, it changes to slightly reddish. motivated by this result, we performed time-resolved imaging polarimetry of phaethon during its recent close approach to the earth. phaethon has a spin period of 3.604 h, and we found a variation of the linear polarization with rotation. this seems to be a rare case in which such variation is unambiguously found, also a consequence of its fairly large amplitude. combining this new information with the brightness and colour variation as well as previously reported results from arecibo radar observations, we conclude that there is no variation of the mineralogy across the surface of phaeton. however, the observed change in the linear polarization may be related to differences in the thickness of the surface regolith in different areas or local topographic features. | rotational variation of the linear polarization of the asteroid (3200) phaethon as evidence for inhomogeneity in its surface properties |
the unique inner-belt asteroid 311p/panstarrs (formerly p/2013 p5) is notable for its sporadic, comet-like ejection of dust in nine distinct epochs spread over ∼250 days in 2013. this curious behavior has been interpreted as the product of localized, equatorward landsliding from the surface of an asteroid rotating at the brink of instability. we obtained new hubble space telescope observations to directly measure the nucleus and to search for evidence of its rapid rotation. we find a nucleus with mid-light absolute magnitude hv= 19.14 ± 0.02, corresponding to an equal-area circle with radius 190 ± 30 m (assuming geometric albedo pv= 0.29). however, instead of providing photometric evidence for rapid nucleus rotation, our data set a lower limit to the light-curve period, p ≥ 5.4 hr. the dominant feature of the light curve is a v-shaped minimum, ∼0.3 mag deep, which is suggestive of an eclipsing binary. under this interpretation, the time-series data are consistent with a secondary/primary mass ratio, ms /mp∼ 1:6, a ratio of separation/primary radius, r/rp∼ 4 and an orbit period ∼0.8 days. these properties lie within the range of other asteroid binaries that are thought to be formed by rotational breakup. while the light-curve period is long, centripetal dust ejection is still possible if one or both components rotate rapidly (≲2 hr) and have small light-curve variation because of azimuthal symmetry. indeed, radar observations of asteroids in critical rotation reveal “muffin-shaped” morphologies, which are closely azimuthally symmetric and which show minimal light curves. our data are consistent with 311p being a close binary in which one or both components rotates near the centripetal limit. the mass loss in 2013 suggests that breakup occurred recently and could even be on-going. a search for fragments that might have been recently ejected beyond the hill sphere reveals none larger than effective radius re∼ 10 m. | the nucleus of active asteroid 311p/(2013 p5) panstarrs |
several datasets of pm2.5 concentrations over europe during the 1990-2015 period, were used to calculate health impacts from chronic exposure to total particle matter below 2.5 μm (i.e. pm2.5). the datasets used in the analysis include the european topic centre on air pollution and climate change mitigation (etc/acm), the copernicus atmospheric monitoring service (cams), the global burden of disease (gbd), the world health organization (who) as well as the eurodelta-trends (edt) multi-model reanalysis developed specifically for europe. the exposure to ambient pm2.5 concentrations was calculated as population weighted annual average pm2.5 concentrations by country. the calculated exposure to pm2.5 was later used as input in the health impact assessment (hia) alpha-riskpoll (arp) tool to retrieve the total number of premature deaths. our results indicate a substantial reduction in the number of premature deaths from pm2.5 exposure in europe over the 1990-2010 period, between nearly 30 and 50%. putting all the data-sets together, even if they do not cover the whole period, a decrease of even around 60% is observed between 1990 and 2015. for the countries included in this study, the estimated number of premature deaths from pm2.5 in 1990 was found to be around 960 000 (median of all the available datasets), whereas in 2015 it was found to be around 445 000. however, the variability in the estimated premature deaths from the different pm2.5 datasets was found to be large during the early 90s (around a factor of 2). for the latest years of the investigated period (2005 onwards), where a relatively flat trend in the pm2.5 exposure was observed, the differences between the different datasets were smaller. even though our results indicate a reduction in the number of premature deaths from chronic exposure to pm2.5, the numbers remain considerable in 2015, underlining the need to continue improving air quality in the future. | long-term health impact assessment of total pm2.5 in europe during the 1990-2015 period |
the national aeronautics and space administration (nasa) psyche mission will visit the 226-km diameter main belt asteroid (16) psyche, our first opportunity to visit a metal-rich object at close range. the unique and poorly understood nature of psyche offers a challenge to the mission as we have little understanding of the surface morphology and composition. it is commonly accepted that the main evolutionary process for asteroid surfaces is impact cratering. while a considerable body of literature is available on collisions on rocky/icy objects, less work is available for metallic targets with compositions relevant to psyche. here we present a suite of impact experiments performed at the nasa ames vertical gun range facility on several types of iron meteorites and foundry-cast ingots that have similar fe-ni compositions as the iron meteorites. our experiments were designed to better understand crater formation (e.g., size, depth), over a range of impact conditions, including target temperature and composition. we find that the target strength, as inferred from crater sizes, ranges from 700 to 1,300 mpa. target temperature has measurable effects on strength, with cooled targets typically 10-20% stronger. crater morphologies are characterized by sharp, raised rims and deep cavities. further, we derive broad implications for psyche's collisional evolution, in light of available low resolution shape models. we find that the number of large craters (>50 km) is particularly diagnostic for the overall bulk strength of psyche. if confirmed, the number of putative large craters may indicate that psyche's bulk strength is significantly reduced compared to that of intact iron meteorites. | hypervelocity impact experiments in iron-nickel ingots and iron meteorites: implications for the nasa psyche mission |
cellular processes are influenced by liquid phase separation, but its role in dna repair is unclear. here, we show that in saccharomyces cerevisiae, liquid droplets made up of dna repair proteins cooperate with different types of dna damage-inducible intranuclear microtubule filaments (dims) to promote the clustering of dna damage sites and maintain genome stability. rad52 dna repair proteins at different dna damage sites assemble in liquid droplets that fuse into a repair centre droplet via the action of petite dims (pti-dims). this larger droplet concentrates tubulin and projects short aster-like dims (aster-dims), which tether the repair centre to longer dims mediating the mobilization of damaged dna to the nuclear periphery for repair. our findings indicate that cooperation between rad52 liquid droplets and various types of nuclear filaments promotes the assembly and function of the dna repair centre. | dna repair by rad52 liquid droplets |
the chicxulub impact caused a crash in productivity in the world's oceans which contributed to the extinction of ∼75% of marine species. in the immediate aftermath of the extinction, export productivity was locally highly variable, with some sites, including the chicxulub crater, recording elevated export production. the long-term transition back to more stable export productivity regimes has been poorly documented. here, we present elemental abundances, foraminifer and calcareous nannoplankton assemblage counts, total organic carbon, and bulk carbonate carbon isotope data from the chicxulub crater to reconstruct changes in export productivity during the first 3 myr of the paleocene. we show that export production was elevated for the first 320 kyr of the paleocene, declined from 320 kyr to 1.2 myr, and then remained low thereafter. a key interval in this long decline occurred 900 kyr to 1.2 myr post impact, as calcareous nannoplankton assemblages began to diversify. this interval is associated with fluctuations in water column stratification and terrigenous flux, but these variables are uncorrelated to export productivity. instead, we postulate that the turnover in the phytoplankton community from a post-extinction assemblage dominated by picoplankton (which promoted nutrient recycling in the euphotic zone) to a paleocene pelagic community dominated by relatively larger primary producers like calcareous nannoplankton (which more efficiently removed nutrients from surface waters, leading to oligotrophy) is responsible for the decline in export production in the southern gulf of mexico.plain language summarythe end cretaceous mass extinction was caused by the impact of an asteroid in what is now the yucatán peninsula, méxico. the impact ejected aerosols and dust into the air that reduced sunlight transmission, causing a severe decline in photosynthesis and the collapse of marine food webs. however, the change in the amount of organic matter created by photosynthesizing plankton that was delivered to the seafloor (export productivity) was variable across the oceans. at some places, including the chicxulub crater, export productivity was actually high immediately after the impact. we produced a ∼3-million -year record of export productivity in the crater to determine how long it remained elevated and why it eventually declined. export production was very high for the first 320,000 years after the impact, declined from 320,000 to 1,200,000 years after the impact, and then remained low. we found that this production was not related to the input of nutrients nor the degree of stratification of the ocean, but instead was probably driven by the increase in the cell size of phytoplankton. larger phytoplankton removed nutrients from the surface waters as they sank, prompting an increase in species which are better adapted to low-nutrient waters.key points export productivity at chicxulub was elevated for 1.2 myr post k-pg; it was very high for the first 0.32 myr and declined from 0.32-1.2 myr the final decline in export productivity ∼0.9-1.2 myr is associated with the termination of calcareous nannoplankton disaster assemblages export productivity change is not correlated with stratification or terrigenous input and was likely driven by changes in the phytoplankton | early paleocene paleoceanography and export productivity in the chicxulub crater |
in this work we aim to constrain the slope of the size distribution of main-belt asteroids, at their primordial state. to do so we turn out attention to the part of the main asteroid belt between 2.82 and 2.96 au, the so-called "pristine zone", which has a low number density of asteroids and few, well separated asteroid families. exploiting these unique characteristics, and using a modified version of the hierarchical clustering method we are able to remove the majority of asteroid family members from the region. the remaining, background asteroids should be of primordial origin, as the strong 5/2 and 7/3 mean-motion resonances with jupiter inhibit transfer of asteroids to and from the neighboring regions. the size-frequency distribution of asteroids in the size range 17 < d(km) < 70 has a slope q ≃ - 1 . using monte-carlo methods, we are able to simulate, and compensate for the collisional and dynamical evolution of the asteroid population, and get an upper bound for its size distribution slope q = - 1.43 . in addition, applying the same 'family extraction' method to the neighboring regions, i.e. the middle and outer belts, and comparing the size distributions of the respective background populations, we find statistical evidence that no large asteroid families of primordial origin had formed in the middle or pristine zones. | reconstructing the size distribution of the primordial main belt |
the presence of giant planets influences potentially habitable worlds in numerous ways. massive celestial neighbors can facilitate the formation of planetary cores and modify the influx of asteroids and comets toward earth analogs later on. furthermore, giant planets can indirectly change the climate of terrestrial worlds by gravitationally altering their orbits. investigating 147 well-characterized exoplanetary systems known to date that host a main-sequence star and a giant planet, we show that the presence of “giant neighbors” can reduce a terrestrial planet’s chances to remain habitable, even if both planets have stable orbits. in a small fraction of systems, however, giant planets slightly increase the extent of habitable zones provided that the terrestrial world has a high climate inertia. in providing constraints on where giant planets cease to affect the habitable zone size in a detrimental fashion, we identify prime targets in the search for habitable worlds. | giant planets: good neighbors for habitable worlds? |
resonance orbits around a uniformly rotating asteroid are studied from the approach of periodic orbits in this work. three periodic families (denoted as i, ii, and iii in the paper) are fundamental in organizing the resonance families. for the planar case: (1) genealogy and stability of families i, ii and the prograde resonance families are studied. for extremely irregular asteroids, family genealogy close to the asteroid is greatly distorted from that of the two body-problem (2bp), indicating that it is inappropriate to treat the orbital motions as perturbed keplerian orbits. (2) genealogy and stability of family iii are also studied. stability of this family may be destroyed by the secular resonance between the orbital ascending node's precession and the asteroid's rotation. for the spatial case: (1) genealogy of the near circular three-dimensional periodic families are studied. the genealogy may be broken apart by families of eccentric frozen orbits whose argument of perigee is ;frozen; in space. (2) the joint effects between the secular resonance and the orbital resonances may cause instability to three-dimensional orbital motion with orbit inclinations close to the critical values. applying the general methodology to a case study - the asteroid eros and also considering higher order non-spherical terms, some extraordinary orbits are found, such as the ones with orbital plane co-rotating with the asteroid, and the stable frozen orbits with argument of perigee librating around values different from 0°, 90°, 180°, 270°. | genealogy and stability of periodic orbit families around uniformly rotating asteroids |
the ∼20-m sized asteroid that entered the earth's atmosphere at 19 km/s over the chelyabinsk region of russia on february 15, 2013, broke and deposited ∼500 kt of kinetic energy at 45-25 km altitude, causing an airburst strong enough to create widespread glass damage. the shockwave hit a densely populated area. more than a thousand people asked for medical assistance at hospitals. in this paper, we analyze the available information about how many and what type of injuries were sustained. we combine previously collected data from government reports and from phone and internet surveys shortly after the event with newly collected data from local hospitals. as expected, the percentage of injuries was highest near the asteroid trajectory, but surprisingly the type of injury (cuts or bruises) do not show dependence on the distance from the asteroid trajectory. results are compared to asteroid impact risk assessment models. the results provide insight for first responders in future asteroid impacts and help to rеfine these models. | study of injuries from the chelyabinsk airburst event |
in order to obtain the gravitational field of a general finite body inside its brillouin sphere, we developed a new method to compute the field accurately. first, the body is assumed to consist of some layers in a certain spherical polar coordinate system and the volume mass density of each layer is expanded as a maclaurin series of the radial coordinate. second, the line integral with respect to the radial coordinate is analytically evaluated in a closed form. third, the resulting surface integrals are numerically integrated by the split quadrature method using the double exponential rule. finally, the associated gravitational acceleration vector is obtained by numerically differentiating the numerically integrated potential. numerical experiments confirmed that the new method is capable of computing the gravitational field independently of the location of the evaluation point, namely whether inside, on the surface of, or outside the body. it can also provide sufficiently precise field values, say of 14-15 digits for the potential and of 9-10 digits for the acceleration. furthermore, its computational efficiency is better than that of the polyhedron approximation. this is because the computational error of the new method decreases much faster than that of the polyhedron models when the number of required transcendental function calls increases. as an application, we obtained the gravitational field of 433 eros from its shape model expressed as the 24 × 24 spherical harmonic expansion by assuming homogeneity of the object. | precise and fast computation of the gravitational field of a general finite body and its application to the gravitational study of asteroid eros |
the effects of dynamical coupling between the rotational (attitude) and translational (orbital) motion of spacecraft near small solar system bodies is investigated. this coupling arises due to the weak gravity of these bodies, as well as solar radiation pressure. the traditional approach assumes a point-mass spacecraft model to describe the translational motion of the spacecraft, while the attitude motion is considered to be completely decoupled from the translational motion. the model used here to describe the rigid-body spacecraft dynamics includes the non-uniform rotating gravity field of the small body up to second degree and order along with the attitude dependent terms, solar tide, and solar radiation pressure. this model shows that the second degree and order gravity terms due to the small body affect the dynamics of the spacecraft to the same extent as the orbit-attitude coupling due to the primary gravity (zeroth order) term. variational integrators are used to simulate the dynamics of both the rigid spacecraft and the point mass. the small bodies considered here are modeled after near-earth objects (neo) 101955 bennu, and 25143 itokawa, and are assumed to be triaxial ellipsoids with uniform density. differences in the numerically obtained trajectories of a rigid spacecraft and a point mass are then compared, to illustrate the impact of the orbit-attitude coupling on spacecraft dynamics in proximity of small bodies. possible implications on the performance of model-based spacecraft control and on the station-keeping budget, if the orbit-attitude coupling is not accounted for in the model of the dynamics, are also discussed. an almost globally asymptotically stable motion estimation scheme based solely on visual/optical feedback that estimates the relative motion of the asteroid with respect to the spacecraft is also obtained. this estimation scheme does not require a model of the dynamics of the asteroid, which makes it perfectly suited for asteroids whose properties are not well known. | coupled orbit-attitude dynamics and relative state estimation of spacecraft near small solar system bodies |
dark material on vesta may consist of carbonaceous chondrite-like material delivered by impact events. this study uses hypervelocity impact experiments to assess the viability of the impact delivery hypothesis. experiments reveal that impact events deliver significant fractions of the projectile to the target during impacts at average vestan speeds. hence, dark material can plausibly be delivered to vesta by impacts, with the projectile component accumulating in the regolith with time. projectile retention is sensitive to impact angle, ranging from 7% for 30° impacts (measured from horizontal) to 72% for vertical impacts. averaged over the probability distribution of impact angles, 17% of the projectile's mass remains in or near the crater. projectile-contaminated breccias largely remain inside the crater for vertical impacts. in oblique impacts, projectile-contaminated pieces concentrate downrange beyond the crater rim. based on experiments, projectile delivery is expected for typical vestan impact conditions, not only for extraordinary events such as low-probability and very low-speed (e.g., <2 km s-1) impacts. these experiments indicate that other (non-dark) impactors contaminate the vestan regolith. regolith-laden bodies in environments with similar impact speeds also may accrete significant amounts of foreign debris. | delivering a projectile component to the vestan regolith |
the hayabusa 2 mission is targeted to explore the asteroid (162173) 1999 ju3 and return surface as well as sub-surface samples through a novel impactor. upon its return, at the end of 2020, the spacecraft will release the capsule for earth re-entry and drift away from the planet. based on the current mission profile, the spacecraft is expected to retain 30 kg of xenon propellant for trajectory maneuvers after the capsule is released. this remaining fuel can be used to extend the mission and improve its scientific return by exploring a new target. work herein outlines an extension plan for hayabusa 2, detailing the target selection process and its subsequent trajectory design. due to final earth escape trajectory, considering the excess velocity and orbital geometry, the only available extension option is an asteroid flyby. one of the most important trajectory characteristic is to maximize the spacecraft's optical detection capabilities. as a result the asteroid 2001 wr1 is identified as the most promising target candidate. the resulting trajectory uses all the available xenon with 100% duty cycle. furthermore, the extension lasts for 932 days and offers 1.57 days of optical navigation time for a flyby on june 27, 2023. | hayabusa 2 extension plan: asteroid selection and trajectory design |
astrometric positions of moving objects in the solar system have been measured using a variety of star catalogs in the past. previous work has shown that systematic errors in star catalogs can affect the accuracy of astrometric observations. that, in turn, can influence the resulting orbit fits for minor planets. in order to quantify these systematic errors, we compare the positions and proper motion of stellar sources in the most utilized star catalogs to the second release of the gaia star catalog. the accuracy of gaia astrometry allows us to unambiguously identify local biases and derive a scheme that can be used to correct past astrometric observations of solar system objects. here, we provide substantially improved debiasing tables for 26 astrometric catalogs that were extensively used in minor planet astrometry. revised corrections near the galactic center eliminate artifacts that could be traced back to reference catalogs used in previous debiasing schemes. median differences in stellar positions between catalogs now tend to be on the order of several tens of milliarcseconds (mas) but can be as large as 175 mas. median stellar proper motion corrections scatter around 0.3 mas/yr and range from 1to 4 mas/yr for star catalogs with and without proper motion, respectively. the tables presented in this work contain a posteriori corrections meant to improve orbit fits based on optical observations that were measured against astrometric catalogs other than gaia. however, astrometrists are strongly encouraged to make use of the most recent gaia astrometric catalog when submitting new observations. since previous debiasing schemes already reduced systematics in past observations to a large extent, corrections beyond the current work may not be needed in the foreseeable future. | star catalog position and proper motion corrections in asteroid astrometry ii: the gaia era |
we describe zstreak, a semi-real-time pipeline specialized in detecting small, fast-moving, near-earth asteroids (neas), which is currently operating on the data from the newly commissioned zwicky transient facility (ztf) survey. based on a prototype originally developed by waszczak et al. (2017) for the palomar transient factory (ptf), the predecessor of ztf, zstreak features an improved machine-learning model that can cope with the 10× data rate increment between ptf and ztf. since its first discovery on 2018 february 5 (2018 cl), ztf/zstreak has discovered 45 confirmed new neas over a total of 232 observable nights until 2018 december 31. most of the discoveries are small neas, with diameters less than ∼100 m. by analyzing the discovery circumstances, we find that objects having the first to last detection time interval under 2 hr are at risk of being lost. we will further improve real-time follow-up capabilities, and work on suppressing false positives using deep learning. | toward efficient detection of small near-earth asteroids using the zwicky transient facility (ztf) |
it has been suggested that the comet-like activity of main belt comets (mbcs) is due to the sublimation of sub-surface water-ice that has been exposed as a result of their surfaces being impacted by meter-sized bodies. we have examined the viability of this scenario by simulating impacts between meter-sized and kilometer-sized objects using a smooth particle hydrodynamics approach. simulations have been carried out for different values of the impact velocity and impact angle, as well as different target material and water-mass fractions. results indicate that for the range of impact velocities corresponding to those in the asteroid belt, the depth of an impact crater is slightly larger than 10 m, suggesting that if the activation of mbcs is due to the sublimation of sub-surface water-ice, this ice has to exist no deeper than a few meters from the surface. results also show that ice exposure occurs in the bottom and on the interior surface of impact craters, as well as on the surface of the target where some of the ejected icy inclusions are re-accreted. while our results demonstrate that the impact scenario is indeed a viable mechanism to expose ice and trigger the activity of mbcs, they also indicate that the activity of the current mbcs is likely due to ice sublimation from multiple impact sites and/or the water contents of these objects (and other asteroids in the outer asteroid belt) is larger than the 5% that is traditionally considered in models of terrestrial planet formation, providing more ice for sublimation. we present the details of our simulations and discuss their results and implications. | triggering sublimation-driven activity of main belt comets |
near-earth asteroids (neas) in the 1-100 meter size range are estimated to be ∼1,000 times more numerous than the ∼15,000 currently cataloged neas, most of which are in the 0.5-10 kilometer size range. impacts from 10-100 meter size neas are not statistically life-threatening, but may cause significant regional damage, while 1-10 meter size neas with low velocities relative to earth are compelling targets for space missions. we describe the implementation and initial results of a real-time nea-discovery system specialized for the detection of small, high angular rate (visually streaked) neas in palomar transient factory (ptf) images. ptf is a 1.2-m aperture, 7.3 deg2 field of view (fov) optical survey designed primarily for the discovery of extragalactic transients (e.g., supernovae) in 60-second exposures reaching ∼20.5 visual magnitude. our real-time nea discovery pipeline uses a machine-learned classifier to filter a large number of false-positive streak detections, permitting a human scanner to efficiently and remotely identify real asteroid streaks during the night. upon recognition of a streaked nea detection (typically within an hour of the discovery exposure), the scanner triggers follow-up with the same telescope and posts the observations to the minor planet center for worldwide confirmation. we describe our 11 initial confirmed discoveries, all small neas that passed 0.3-15 lunar distances from earth. lastly, we derive useful scaling laws for comparing streaked-nea-detection capabilities of different surveys as a function of their hardware and survey-pattern characteristics. this work most directly informs estimates of the streak-detection capabilities of the zwicky transient facility (ztf, planned to succeed ptf in 2017), which will apply ptf’s current resolution and sensitivity over a 47-deg2 fov. | small near-earth asteroids in the palomar transient factory survey: a real-time streak-detection system |
we observed the episodically active asteroid (6478) gault in 2020 with multiple telescopes in asia and north america and found that it is no longer active after its recent outbursts at the end of 2018 and the start of 2019. the inactivity during this apparition allowed us to measure the absolute magnitude of gault of hr = 14.63 ± 0.02, gr = 0.21 ± 0.02 from our secular phase-curve observations. in addition, we were able to constrain gault's rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 august, september, and october. the photometric lightcurves have a repeating ≲0.05 mag feature suggesting that (6478) gault has a rotation period of ∼2.5 hr and may have a semispherical or top-like shape, much like the near-earth asteroids ryugu and bennu. the rotation period of ∼2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the yarkovsky-o'keefe-radzievskii-paddack effect. | time-series and phase-curve photometry of the episodically active asteroid (6478) gault in a quiescent state using apo, growth, p200, and ztf |
context. the javalambre photometric local universe survey (j-plus) is an observational campaign that aims to obtain photometry in 12 ultraviolet-visible filters (0.3−1 μm) over ∼8500 deg2 of the sky observable from javalambre (teruel, spain). due to its characteristics and observation strategy, this survey will allow a great number of solar system small bodies to be analyzed, and with improved spectrophotometric resolution with respect to previous large-area photometric surveys in optical wavelengths.aims: the main goal of the present work is to present the first catalog of magnitudes and colors of minor bodies of the solar system compiled using the first data release (dr1) of the j-plus observational campaign: the moving objects observed from javalambre (mooja) catalog.methods: using the compiled photometric data we obtained very-low-resolution reflectance (photo)spectra of the asteroids. we first used a σ-clipping algorithm in order to remove outliers and clean the data. we then devised a method to select the optimal solar colors in the j-plus photometric system. these solar colors were computed using two different approaches: on one hand, we used different spectra of the sun convolved with the filter transmissions of the j-plus system, and on the other, we selected a group of solar-type stars in the j-plus dr1 according to their computed stellar parameters. finally, we used the solar colors to obtain the reflectance spectra of the asteroids.results: we present photometric data in the j-plus filters for a total of 3122 minor bodies (3666 before outlier removal), and we discuss the main issues with the data, as well as some guidelines to solve them. mooja catalog of colors and magnitudes are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/655/a47 | j-plus: a first glimpse at the spectrophotometry of asteroids. the mooja catalog |
we calculate the present-day impact flux on mars and its variation over the martian year, using the current data on the orbital distribution of known mars-crossing minor planets. we adapt the öpik-wetherill formulation for calculating collision probabilities, paying careful attention to the non-uniform distribution of the perihelion longitude and the argument of perihelion owed to secular planetary perturbations. we find that, at the current epoch, the mars crossers have an axial distribution of the argument of perihelion, and the mean direction of their eccentricity vectors is nearly aligned with mars' eccentricity vector. these previously neglected angular non-uniformities have the effect of depressing the mean annual impact flux by a factor of about 2 compared to the estimate based on a uniform random distribution of the angular elements of mars-crossers; the amplitude of the seasonal variation of the impact flux is likewise depressed by a factor of about 4-5. we estimate that the flux of large impactors (of absolute magnitude h < 16) within ±30° of mars' aphelion is about three times larger than when the planet is near perihelion. extrapolation of our results to a model population of meter-size mars-crossers shows that if these small impactors have a uniform distribution of their angular elements, then their aphelion-to-perihelion impact flux ratio would be 11-15, but if they track the orbital distribution of the large impactors, including their non-uniform angular elements, then this ratio would be about 3. comparison of our results with the current dataset of fresh impact craters on mars (detected with mars-orbiting spacecraft) appears to rule out the uniform distribution of angular elements. | the current impact flux on mars and its seasonal variation |
classical correlation can be locked via quantum means: quantum data locking. with a short secret key, one can lock an exponentially large amount of information in order to make it inaccessible to unauthorized users without the key. quantum data locking presents a resource-efficient alternative to one-time pad encryption which requires a key no shorter than the message. we report experimental demonstrations of a quantum data locking scheme originally proposed by d. p. divincenzo et al. [phys. rev. lett. 92, 067902 (2004), 10.1103/physrevlett.92.067902] and a loss-tolerant scheme developed by o. fawzi et al. [j. acm 60, 44 (2013), 10.1145/2518131]. we observe that the unlocked amount of information is larger than the key size in both experiments, exhibiting strong violation of the incremental proportionality property of classical information theory. as an application example, we show the successful transmission of a photo over a lossy channel with quantum data (un)locking and error correction. | experimental quantum data locking |
comet 67p/churyumov-gerasimenko (67p) was imaged with the 2 m telescope at mt. wendelstein observatory in the alps. coma and tail monitoring was performed during 51 nights between 2015 august 22 and 2016 may 9. the images through r and i sloan digital sky survey (sdss) filters show the dust distribution around the comet, while images in the sdss g filter also indicate the presence of coma gas in early 2015 september. the dust colour of 67p implies intrinsic reddening of 9 per cent/100 nm. after maximum, shortly after perihelion passage, the dust activity decreased with a heliocentric exponent of 4.1-4.2 from late 2015 september until 2016 may. the opposition surge during early 2016 can be explained by a linear light scattering phase function (β ∼ 0.04) or an asteroid-like hg-type phase function (g ∼ 0.15). the radial brightness profile indicates a 'quasi-steady-state' dust coma from late september to the end of 2015. dust fragmentation during about a month after perihelion may be responsible for radial coma profiles with slopes below unity, while dust accumulation due to very slow dust expansion velocity may result in steeper than unity profiles during 2016. three fan-shape dust structures are characterized in the coma of 67p. a short dust ejection event on 2015 august 22-23 has produced a dust arc-let and jet feature in the coma. in 2015 september, the appearance of cometary dust tail is dominated by the young dust produced around perihelion. the older dust dominates the tail appearance as of 2015 mid-november. | mt. wendelstein imaging of the post-perihelion dust coma of 67p/churyumov-gerasimenko in 2015/2016 |
the quadrantid meteor shower is among the strongest annual meteor showers, and has drawn the attention of scientists for several decades. the stream is unusual, among others, for several reasons: its very short duration around maximum activity (≈12-14 h) as detected by visual, photographic and radar observations, its recent onset (around 1835 ad quetelet, l.a.j. [1839]. catalogue des principles apparitions d'etoiles filantes) and because it had been the only major stream without an obvious parent body until 2003. ever since, there have been debates as to the age of the stream and the nature of its proposed parent body, asteroid 2003 eh1. in this work, we present results on the most probable age and formation mechanism of the narrow portion of the quadrantid meteoroid stream. for the first time we use data on eight high precision photographic quadrantids, equivalent to gram-kilogram size, to constrain the most likely age of the core of the stream. out of eight high-precision photographic quadrantids, five pertain directly to the narrow portion of the stream. in addition, we also use data on five high-precision radar quadrantids, observed within the peak of the shower. we performed backwards numerical integrations of the equations of motion of a large number of 'clones' of both, the eight high-precision photographic and five radar quadrantid meteors, along with the proposed parent body, 2003 eh1. according to our results, from the backward integrations, the most likely age of the narrow structure of the quadrantids is between 200 and 300 years. these presumed ejection epochs, corresponding to 1700-1800 ad, are then used for forward integrations of large numbers of hypothetical meteoroids, ejected from the parent 2003 eh1, until the present epoch. the aim is to constrain whether the core of the quadrantid meteoroid stream is consistent with a previously proposed relatively young age (≈200 years). | on the age and formation mechanism of the core of the quadrantid meteoroid stream |
the x-ray source 1e 161348-5055 in the supernova remnant rcw 103 recently exhibited x-ray activity typical of magnetars, i.e. neutron stars with magnetic fields ≳ 1014-1015 g. however, 1e 161348-5055 has an observed period of 6.67 h, in contrast to magnetars which have a spin period of seconds. here we describe a simple model which can explain the spin evolution of 1e 161348-5055, as well as other magnetars, from an initial period of milliseconds that would be required for dynamo generation of magnetar-strength magnetic fields. we propose that the key difference between 1e 161348-5055 and other magnetars is the persistence of a remnant disc of small total mass. this disc caused 1e 161348-5055 to undergo ejector and propeller phases in its life, during which strong torques caused a rapid increase of its spin period. by matching its observed spin period and ≈1-3 kyr age, we find that 1e 161348-5055 has the (slightly) highest magnetic field of all known magnetars, with b ∼ 5 × 1015 g, and that its disc had a mass of ∼1024 g, comparable to that of the asteroid ceres. | ejector and propeller spin-down: how might a superluminous supernova millisecond magnetar become the 6.67 h pulsar in rcw 103 |
small asteroids intersecting earth's orbit can deliver extraterrestrial rocks to earth, called meteorites. this process is accompanied by a luminous phenomena in the atmosphere called bolides or fireballs. observations of bolides provide pre-atmospheric orbits of meteorites, physical and chemical properties of small asteroids, and the flux (i.e., frequency of impacts) of bodies at earth in the centimeter to decameter size range. in this chapter we explain the processes occurring during the penetration of cosmic bodies through the atmosphere and review the methods of bolide observations. we compile available data on the fireballs associated with 22 instrumentally observed meteorite falls. among them are the heterogeneous falls almahata sitta (2008 tc3) and benešov, which revolutionized our view on the structure and composition of small asteroids; the příbram-neuschwanstein orbital pair, carbonaceous chondrite meteorites with orbits on the asteroid-comet boundary; and the chelyabinsk fall, which produced a damaging blast wave. while most meteoroids disrupt into fragments during atmospheric flight, the carancas meteoroid remained nearly intact and caused a crater-forming explosion on the ground. | small near-earth asteroids as a source of meteorites |
we present an analysis of asteroid (3200) phaethon using coronagraphic observations from 2008 to 2022 by the cor2 cameras onboard the twin solar terrestrial relations observatory spacecraft. although undetected in individual images, phaethon was visible in stacks combined from the same perihelion observations, yet only at small (≲30°) but not large (≳150°) phase angles. the observations are in line with the contribution from a bare nucleus, thereby seriously contradicting the interpretation based on hi-1 observations that attributes the perihelion activity to the ejection of μm-sized dust. we obtained an upper limit to the effective cross section of μm-sized dust to be ≲105 m2, at least three orders of magnitude smaller than earlier estimates based on hi-1 data. on the contrary, the cor2 observations cannot rule out the existence of mm-sized or larger debris around phaethon. however, the fact that no postperihelion debris tail has ever been detected for phaethon suggests the unimportance of such dust in the perihelion activity. we thus conclude that the perihelion activity of phaethon is highly unlikely relevant to the ejection of dust. rather, we deduce that the activity is associated with gas emissions, possibly fe i and/or na d lines. to verify our conjecture and to fully understand the perihelion activity of phaethon, more observations at small heliocentric distances are desired. we compile a list of observing windows ideal for the search of gas emissions of the asteroid from ground telescopes. the best opportunities will be during total solar eclipses. | perihelion activity of (3200) phaethon is not dusty: evidence from stereo/cor2 observations |
we study nodal librations of outer particles in the framework of the elliptical restricted three-body problem including general relativity (gr) effects. from an analytical treatment based on secular interactions up to quadrupole level, we derive equations that define the nodal libration region of an outer test particle, which depends on the physical and orbital parameters of the bodies of the system. from this, we analyse how the gr constrains the semimajor axis of outer test particles that experience nodal librations under the effects of an inner planet around a single stellar component. such an upper limit of the semimajor axis, which is called a2,lim, depends on the mass of the star ms, the mass m1, the semimajor axis a1, and the eccentricity e1 of the inner planet, and the eccentricity e2 of the outer test particle. on the one hand, our results show that the greater m1, a1, and e2 and the smaller ms, the greater the value of a2,lim. on the other hand, for fixed ms, m1, a1, and e2, a2,lim does not strongly depend on e1, except for large values of such an orbital parameter. we remark that n-body experiments of particular scenarios that include gr show results consistent with the analytical criteria derived in this research. moreover, the study of hypothetical small body populations of real systems composed of a single star and an inner planetary-mass companion show that the gr effects can play a very important role in their global dynamics. | constraints to the semimajor axis of outer particles with nodal librations by general relativity effects |
main-belt asteroid (16) psyche is the largest m-type asteroid, a class of object classically thought to be the metal cores of differentiated planetesimals and the parent bodies of the iron meteorites. de kleer, cambioni, and shepard (2021, https://doi.org/10.3847/psj/ac01ec) presented new data from the atacama large millimeter array (alma), from which they derived a global best-fit thermal inertia and dielectric constant for psyche, proxies for regolith particle size, porosity, and/or metal content, and observed thermal anomalies that could not be explained by surface albedo variations only. motivated by this, here we fit a model to the same alma data set that allows dielectric constant and thermal inertia to vary across the surface. we find that psyche has a heterogeneous surface in both dielectric constant and thermal inertia but, intriguingly, we do not observe a direct correlation between these two properties over the surface. we explain the heterogeneity in dielectric constant as being due to variations in the relative abundance of metal and silicates. furthermore, we observe that the lowlands of a large depression in psyche's shape have distinctly lower thermal inertia than the surrounding highlands. we propose that the latter could be explained by a thin mantle of fine regolith, fractured bedrock, and/or implanted silicate-rich materials covering an otherwise metal-rich surface. all these scenarios are indicative of a collisionally evolved world. | the heterogeneous surface of asteroid (16) psyche |
giant planet migration is an important phenomenon in the evolution of planetary systems. recent works have shown that giant planet growth and migration can shape the asteroid belt, but these works have not considered interactions between planetesimals. we have calculated the evolution of planetesimal disks, including planetesimal-planetesimal collisions, during gas giant growth and migration. the numbers, locations, and impact velocities of these collisions depend on the specific growth and migration path. we find that giant planet growth alone has little effect on impact velocities, and most of the planetesimals scattered by growing giants do not undergo collisions. in contrast, we find that giant planet migration induces large numbers of high-velocity collisions between planetesimals. these impacts have sufficient velocities to cause shock-induced vaporization for both water ice and silicate components of planetesimals and to cause disruption of the bodies. new bodies may form from impact debris. collisional evolution reduces the efficiency of planetesimal implantation into the asteroid belt. a small fraction of the largest planetesimals implanted into the asteroid belt would have been processed via collisions. we identify important consequences of planetesimal collisions that have not been considered in planet accretion models. the prevalence of high-velocity collisions during giant planet migration, and their potential links to the properties of meteorites and the formation of chondrules, makes impact vaporization a critically important phenomenon. the consequences of vaporizing planetesimal constituents require further detailed study. new collision outcome models for impacts within the nebula, and models for new planetesimal formation are needed. | colliding in the shadows of giants: planetesimal collisions during the growth and migration of gas giants |
the surface geology of jupiter's trojan asteroids is one of the scientific investigations of the nasa lucy mission. a dedicated geology working group will implement these studies using primarily panchromatic and color imaging data and complement the interpretation of these data with theoretical models, such as collisional evolution models. the lucy science team will also rely on experience and lessons learned from prior space missions, such as nasa's near, dawn, osiris-rex, and new horizons. | surface geology of jupiter's trojan asteroids |
both observations of c-type near-earth asteroids and laboratory investigations of carbonaceous chondritic meteorites provide strong evidence for a high microporosity of c-type asteroids. boulder microporosity values derived from in-situ measurements at the surface of the rubble-pile nea (162173) ryugu are as high as 55 %, which is substantially higher than for water-rich carbonaceous chondrite samples and could indicate distinct evolution paths for the parent body of ryugu and parent bodies of carbonaceous chondrites, despite spectral similarities. in the present study, we calculate the evolution of the temperature and porosity for early solar system's planetesimals in order to constrain the range of parameters that result in microporosities compatible with ryugu's high-porosity material and likely burial depths for the boulders observed at the surface. by varying key properties of the parent body, such as accretion time t0 and radius r that have strong influence on temperature and porosity and by comparing the interior porosity distribution with the measured boulder microporosity, hydration, and partial dehydration of the material, we constrain a field within the (r, t0)-diagram appropriate for bodies that are likely to have produced such material. our calculations indicate a parent body size of only a few km and its early accretion within ≲2 - 3 myr after the formation of ca-al-rich inclusions (cais). a gradual final porosity profile of best-fit bodies indicates production of both low- and high-density boulders from the parent body material. by contrast, parent body properties for ci and cm chondrites obtained by fitting carbonate formation data indicate a radius of ≈20 - 25 km and an accretion time of ≈3.75 myr after cais. these results imply a population of km-sized early accreting highly porous planetesimals as parent bodies of the rubble-pile nea ryugu (and, potentially, other neas) and a population of larger and late accreting less porous planetesimals as parent bodies of water-rich carbonaceous chondrites. | microporosity and parent body of the rubble-pile nea (162173) ryugu |
most close-in planetary satellites are in synchronous rotation, which is usually the stable end-point of tidal despinning. saturn's moon hyperion is a notable exception by having a chaotic rotation. hyperion's dynamical state is a consequence of its high eccentricity and its highly prolate shape. as many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries, and a minority of asteroidal secondaries may be in that state. the question of secondary rotation is also important for the action of the binary yarkovsky-o'keefe-radzievskii-paddack (byorp) effect, which can quickly evolve orbits of synchronous (but not nonsynchronous) secondaries. here we report results of a large set of short numerical simulations which indicate that, apart from synchronous and classic chaotic rotation, close-in irregularly shaped asteroidal secondaries can occupy an additional, intermediate rotational state. in this "barrel instability" the secondary slowly rolls along its long axis, while the longest axis is staying largely aligned with the primary-secondary line. this behavior may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down byorp. we show that the binary's eccentricity, separation measured in secondary's radii and the secondary's shape are all important for determining whether the system settles in synchronous rotation, chaotic tumbling, or barrel instability. we compare our results for synthetic asteroids with known binary pairs to determine which of these behaviors may be present in the near-earth asteroid binary population. | barrel instability in binary asteroids |
little is known about earth quasi-satellites, a class of near-earth small solar system bodies that orbit the sun but remain close to the earth, because they are faint and difficult to observe. here we use the large binocular telescope (lbt) and the lowell discovery telescope (ldt) to conduct a comprehensive physical characterization of quasi-satellite (469219) kamoʻoalewa and assess its affinity with other groups of near-earth objects. we find that (469219) kamoʻoalewa rotates with a period of 28.3 (+1.8/−1.3) minutes and displays a reddened reflectance spectrum from 0.4-2.2 microns. this spectrum is indicative of a silicate-based composition, but with reddening beyond what is typically seen amongst asteroids in the inner solar system. we compare the spectrum to those of several material analogs and conclude that the best match is with lunar-like silicates. this interpretation implies extensive space weathering and raises the prospect that kamo'oalewa could comprise lunar material. | lunar-like silicate material forms the earth quasi-satellite (469219) 2016 ho3 kamoʻoalewa |
we present classical and quantum algorithms for approximating partition functions of classical hamiltonians at a given temperature. our work has two main contributions: first, we modify the classical algorithm of štefankovič, vempala and vigoda (\emph{j.~acm}, 56(3), 2009) to improve its sample complexity; second, we quantize this new algorithm, improving upon the previously fastest quantum algorithm for this problem, due to harrow and wei (soda 2020). the conventional approach to estimating partition functions requires approximating the means of gibbs distributions at a set of inverse temperatures that form the so-called cooling schedule. the length of the cooling schedule directly affects the complexity of the algorithm. combining our improved version of the algorithm of štefankovič, vempala and vigoda with the paired-product estimator of huber (\emph{ann.\ appl.\ probab.}, 25(2),~2015), our new quantum algorithm uses a shorter cooling schedule than previously known. this length matches the optimal length conjectured by štefankovič, vempala and vigoda. the quantum algorithm also achieves a quadratic advantage in the number of required quantum samples compared to the number of random samples drawn by the best classical algorithm, and its computational complexity has quadratically better dependence on the spectral gap of the markov chains used to produce the quantum samples. | simpler (classical) and faster (quantum) algorithms for gibbs partition functions |
the formation of the solar system's giant planets predated the ultimate epoch of massive impacts that concluded the process of terrestrial planet formation. following their formation, the giant planets' orbits evolved through an episode of dynamical instability. several qualities of the solar system have recently been interpreted as evidence of this event transpiring within the first ∼100 myr after the sun's birth; around the same time as the final assembly of the inner planets. in a series of recent papers we argued that such an early instability could resolve several problems revealed in classic numerical studies of terrestrial planet formation; namely the small masses of mars and the asteroid belt. in this paper, we revisit the early instability scenario with a large suite of simulations specifically designed to understand the degree to which earth and mars' formation are sensitive to the specific evolution of jupiter and saturn's orbits. by deriving our initial terrestrial disks directly from recent high-resolution simulations of planetesimal accretion, our results largely confirm our previous findings regarding the instability's efficiency of truncating the terrestrial disk outside of the earth-forming region in simulations that best replicate the outer solar system. moreover, our work validates the primordial 2:1 jupiter-saturn resonance within the early instability framework as a viable evolutionary path for the solar system. while our simulations elucidate the fragility of the terrestrial system during the epoch of giant planet migration, many realizations yield outstanding solar system analogs when scrutinized against a number of observational constraints. finally, we highlight the inability of models to form adequate mercury-analogs and the low eccentricities of earth and venus as the most significant outstanding problems for future numerical studies to resolve. | the early instability scenario: mars' mass explained by jupiter's orbit |
context. after the discovery of rings around the largest known centaur object, (10199) chariklo, we carried out observation campaigns of stellar occultations produced by the second-largest known centaur object, (2060) chiron, to better characterize its physical properties and presence of material on its surroundings.aims: we aim to provide constraints on (2060) chiron's shape for the first time using stellar occultations. we investigate the detectability of material previously observed in its vicinity using the 2018 occultation data obtained from south africa astronomical observatory (saao).methods: we predicted and successfully observed two stellar occultations by chiron. these observations were used to constrain its size and shape by fitting elliptical limbs with equivalent surface radii in agreement with radiometric measurements. we also obtained the properties of the material observed in 2011 with the same technique used to derive chariklo's ring properties in our previous works, used to obtain limits on the detection of secondary events in our 2018 observation.results: constraints on the (2060) chiron shape are reported for the first time. assuming an equivalent radius of requiv = 105−7+6 km, we obtained a semi-major axis of a = 126 ± 22 km. considering chiron's true rotational light curve amplitude and assuming it has a jacobi equilibrium shape, we were able to derive a 3d shape with a semi-axis of a = 126 ± 22 km, b = 109 ± 19 km, and c = 68 ± 13 km, implying in a volume-equivalent radius of rvol= 98 ± 17 km. we determined the physical properties of the 2011 secondary events around chiron, which may then be directly compared with those of chariklo rings, as the same method was used. data obtained from saao in 2018 do not show unambiguous evidence of the proposed rings, mainly due to the large sampling time. meanwhile, we discarded the possible presence of a permanent ring similar to (10199) chariklo's c1r in optical depth and extension.conclusions: using the first multi-chord stellar occultation by (2060) chiron and considering it to have a jacobi equilibrium shape, we derived its 3d shape, implying a density of 1119 ± 4 kg m−3. new observations of a stellar occultation by (2060) chiron are needed to further investigate the material's properties around chiron, such as the occultation predicted for september 10, 2023. | constraints on (2060) chiron's size, shape, and surrounding material from the november 2018 and september 2019 stellar occultations |
we present recent updates and improvements of the graphical processing unit (gpu) n-body code genga. modern state-of-the-art simulations of planet formation require the use of a very high number of particles to accurately resolve planetary growth and to quantify the effect of dynamical friction. at present the practical upper limit is in the range of 30,000-60,000 fully interactive particles; possibly a little more on the latest gpu devices. while the original hybrid symplectic integration method has difficulties to scale up to these numbers, we have improved the integration method by (i) introducing higher level changeover functions and (ii) code improvements to better use the most recent gpu hardware efficiently for such large simulations. we added treatments of non-newtonian forces such as general relativity, tidal interaction, rotational deformation, the yarkovsky effect, and poynting-robertson drag, as well as a new model to treat virtual collisions of small bodies in the solar system. we added new tools to genga, such as semi-active test particles that feel more massive bodies but not each other, a more accurate collision handling and a real-time opengl visualization. we present example simulations, including a 1.5 billion year terrestrial planet formation simulation that initially started with 65,536 particles, a 3.5 billion year simulation without gas giants starting with 32,768 particles, the evolution of asteroid fragments in the solar system, and the planetesimal accretion of a growing jupiter simulation. genga runs on modern nvidia and amd gpus. | genga. ii. gpu planetary n-body simulations with non-newtonian forces and high number of particles |
we present new thermophysical model fits of 1847 asteroids, deriving thermal inertia, diameter, and bond and visible geometric albedo. we use thermal flux measurements obtained by the wide-field infrared survey explorer (wise) during its fully cryogenic phase, when both the 12 μm (w3) and 22 μm (w4) bands were available. we take shape models and spin information from the database of asteroid models from inversion techniques (damit) and derive new shape models through lightcurve inversion and combining wise photometry with existing damit lightcurves. when we limit our sample to the asteroids with the most reliable shape models and thermal flux measurements, we find broadly consistent thermal inertia relations with recent studies. we apply fits to the diameters d (km) and thermal inertia γ (j m-2 s-0.5 k-1) normalized to 1 au with a linear relation of the form $\mathrm{log}[{\rm{\gamma }}]=\alpha +\beta \mathrm{log}[d]$ , where we find α = 2.667 ± 0.059 and β = -0.467 ± 0.044 for our sample alone and α = 2.509 ± 0.017 and β = -0.352 ± 0.012 when combined with other literature estimates. we find little evidence of any correlation between rotation period and thermal inertia, owing to the small number of slow rotators to consider in our sample. while the large uncertainties on the majority of our derived thermal inertia only allow us to identify broad trends between thermal inertia and other physical parameters, we can expect a significant increase in high-quality thermal flux measurements and asteroid shape models with upcoming infrared and wide-field surveys, enabling even more thermophysical modeling of higher precision in the future. | thermal properties of 1847 wise-observed asteroids |
we combined the ground-based and gaia data release 3 (dr3) asteroid observations to determine the masses of 20 asteroids with asteroid-asteroid close encounters. in order to take full advantage of the high-precision observations from gaia, we use the fisher information to select appropriate model parameters and the modified encke's equation of motion to construct a dynamical model complete at the level of observation precision. with diameters from literature, bulk densities of 20 asteroids are derived. the results indicate that the utilization of gaia dr3 provides substantial benefits in terms of improving mass precision. among the 20 asteroids analyzed in our study, we find that 10 asteroids achieved a mass precision better than 5%, and 15 asteroids better than 10%. | dynamical masses of 20 asteroids determined with gaia dr3 asteroid observations |
we report observations of four asteroid-crossing events in transiting exoplanet survey satellite light curves masquerading as self-lensing pulses from binary systems containing main-sequence stars and black hole or neutron-star companions. the observed changes in flux and the durations of the events appear to be consistent with self-lensing pulses provided that (a) the compact-object mass is greater than 2 solar masses, and (b) the transit is not a perfect alignment, i.e., the center of the lens is not passing directly in front of the center of the source. we examine the relationship between the physical characteristics of these asteroid crossings and the derived parameters of our self-lensing model fits to the data sets. as the search for new self-lensing systems continues, we caution observers about such false-positive signals imitating real self-lensing pulses. | false-positive self-lensing events: tess observing asteroid-crossing events in disguise |
asteroids belonging to the ch spectral taxonomic class are defined by the presence of an absorption near 0.7 μm, which is interpreted as due to fe-bearing phyllosilicates. phyllosilicates also cause strong absorptions in the 3 μm region, as do other hydrated and hydroxylated minerals and h2o ice. over the past decade, spectral observations have revealed different 3 μm band shapes in the asteroid population. although a formal taxonomy is yet to be fully established, the “pallas-type” spectral group is most consistent with the presence of phyllosilicates. if ch class and pallas type are both indicative of phyllosilicates, then all ch-class asteroids should also be pallas-type. in order to test this hypothesis, we obtained 42 observations of 36 ch-class asteroids in the 2 to 4 μm spectral region. we found that 88% of the spectra have 3 μm band shapes most consistent with the pallas-type group. this is the first asteroid class for which such a strong correlation has been found. because the ch class is defined by the presence of an absorption near 0.7 μm, this demonstrates that the 0.7 μm band serves not only as a proxy for the presence of a band in the 3 μm region, but specifically for the presence of pallas-type bands. there is some evidence for a correlation between band depth at 2.95 μm and absolute magnitude and/or albedo. however, we find only weak correlations between 2.95 μm band depth and semimajor axis. the connection between band depths in the 0.7 and 3 μm regions is complex and in need of further investigation. | the ch-class asteroids: connecting a visible taxonomic class to a 3 μm band shape |
there is a correlation between the components of the yorp effect of most asteroids, which drives the obliquity and spin rate of the affected bodies in a consistent pattern. this allows for a clear and unambiguous picture for how the spin rates and poles of asteroids affected by yorp will evolve and simplifies the overall picture for how populations will migrate on average. the yorp effect can also lead to a previously unexplored equilibrium state for affected bodies. this equilibrium state is a function of the usual normal yorp effect (which arises due to the global shape asymmetry of the asteroid) and the tangential yorp effect (which arises due the transport of thermal energy through rocky surface features). estimates from current shape models show that 10%-20% of asteroids have the proper condition to be captured in this equilibrium state, indicating that the occurrence of this state may be significant. the existence of this attractor for the asteroid population means that objects affected by yorp may leave their usual yorp cycles and maintain a constant spin rate over long time periods—this has significant implications for our interpretation of asteroid spin rate evolution and related theories for their physical evolution. | systematic structure and sinks in the yorp effect |
previous missions have revealed that small solar system bodies are topographically diverse, which raises an immense challenge to a lander that aims to perform scientific measurements at different locations on the surface of the target. in recent years, hopping mechanism has attracted considerable attention due to its adaptability to the granular regolith and the low-gravity environment. however, the hopping dynamics related to granular materials remains to be explored, which will contribute not only to future space missions but also to the understanding of the dynamical behaviour of granular systems under low gravity. in this paper, we studied the hopping locomotion of a cuboid lander on the regolith surface of an asteroid. numerical simulations are performed based on the soft-sphere discrete element method. we systematically explored the effects of the controlled parameter and physical properties of the regolith particles. the results show that the hopping outcomes (velocity, angle, and morphology of the cavity left in the regolith) are strongly dependent on these parameters. the high resistance improves the robustness of granular force networks, therefore the lander hops farther in gravel-like media than less frictional media. when the cohesion between regolith particles is included, the cavity left after the hop becomes a mild indentation, differing from the non-cohesive cases, that give distinct crater-like cavities. | numerical simulations of the controlled motion of a hopping asteroid lander on the regolith surface |
the earth trojans are coorbitals librating around the lagrange points l 4 or l 5 of the sun-earth system. although many numerical studies suggest that they can maintain their dynamical status and be stable on timescales up to a few tens of thousands of years or even longer, they remain an elusive population. thus far only one transient member (2010 tk7) has been discovered serendipitously. here, we present a dynamical study of asteroid 2020 xl5. with our meticulous follow-up astrometric observations of the object, we confirmed that it is a new earth trojan. however, its eccentric orbit brings it close encounters with venus on a frequent basis. based on our n-body integration, we found that the asteroid was captured into the current earth trojan status in the fifteenth century, and then it has a likelihood of 99.5% to leave the l 4 region within the next ~10 kyr. therefore, it is most likely that 2020 xl5 is dynamically unstable over this timescale. | the second earth trojan 2020 xl5 |
the asteroid belt is the remnant of the original planetesimal population in the inner solar system. however, the asteroids currently have orbits with all possible values of eccentricities and inclinations compatible with long-term dynamical stability, whereas the initial planetesimal orbits should have been quasicircular and almost coplanar. the total mass now contained in the asteroid population is a small fraction of that existing primordially. also, asteroids with different chemical/mineralogical properties are not ranked in an orderly manner with mean heliocentric distance (orbital semimajor axis) as one might expect from the existence of a radial gradient of the temperature in the protoplanetary disk, but they are partially mixed. these properties show that the asteroid belt has been severely sculpted by one or a series of processes during its lifetime. this paper reviews the processes that have been proposed so far, discussing the properties that they explain and the problems with which they are confronted. emphasis is paid to the interplay between the dynamical and the collisional evolution of the asteroid population, which allows the use of the size distribution or crater densities observed in the asteroid belt to constrain the dynamical models. we divide the asteroid belt evolution into three phases. the first phase started during the lifetime of the gaseous protoplanetary disk, when the giant planets formed and presumably experienced large-scale migrations, and continued after the removal of the gas, during the buildup of the terrestrial planets. the second phase occurred after the removal of the gaseous protoplanetary disk, and it became particularly lively for the asteroid belt when the giant planets suddenly changed their orbits as a result of a mutual dynamical instability and the interaction with the transneptunian planetesimal disk. the third phase covers the aftermath of the giant-planet instability through the present day. | the dynamical evolution of the asteroid belt |
unistellar has created the enhanced vision telescope (evscope), a compact telescope that amplifies light so users can see hundreds of nebulae and galaxies directly through its electronics eyepiece. it can also pinpoint and identify objects in the sky, making amateur astronomy fun and more accessible to the public. thanks to its sensitivity and accuracy, the evscope is a powerful tool able to generate data that can be used by scientists to search for transient events like supernovae, near-earth asteroids, and comets. this constellation of small, & smart telescopes could also enhance and supplement data generated by the small number of large telescopes operating today. unistellar initiated a partnership with the seti institute to identify and implement scientific applications for a network of evscopes. we summarize in this article the technology behind the evscope and its real-time data processing (enhanced vision, automatic field detection), then show several applications accessible to future users, including asteroid occultations, the detection of the atmosphere of pluto and observations of near-earth asteroids. the unistellar network has the potential to make citizen astronomy a popular reality by offering all users (new or experienced) a tool to explore the night sky with a powerful and reliable instrument while they contribute to scientific investigations. | unistellar evscopes: smart, portable, and easy-to-use telescopes for exploration, interactive learning, and citizen astronomy |
a seminal result of håstad [j. acm, 48(4):798--859, 2001] shows that it is np-hard to find an assignment that satisfies $\frac{1}{|g|}+\varepsilon$ fraction of the constraints of a given $k$-lin instance over an abelian group, even if there is an assignment that satisfies $(1-\varepsilon)$ fraction of the constraints, for any constant $\varepsilon>0$. engebretsen et al. [theoretical computer science, 312(1):17--45, 2004] later showed that the same hardness result holds for $k$-lin instances over any finite non-abelian group. unlike the abelian case, where we can efficiently find a solution if the instance is satisfiable, in the non-abelian case, it is np-complete to decide if a given system of linear equations is satisfiable or not, as shown by goldmann and russell [information and computation, 178(1):253--262. 2002]. surprisingly, for certain non-abelian groups $g$, given a satisfiable $k$-lin instance over $g$, one can in fact do better than just outputting a random assignment using a simple but clever algorithm. the approximation factor achieved by this algorithm varies with the underlying group. in this paper, we show that this algorithm is {\em optimal} by proving a tight hardness of approximation of satisfiable $k$-lin instance over {\em any} non-abelian $g$, assuming $p \neq np$. as a corollary, we also get $3$-query probabilistically checkable proofs with perfect completeness over large alphabets with improved soundness. | optimal inapproximability of satisfiable $k$-lin over non-abelian groups |
nearly every star known to host planets will become a white dwarf, and nearly 100 planet-hosts are now known to be accompanied by binary stellar companions. here, we determine how a binary companion triggers instability in otherwise unconditionally stable single-star two-planet systems during the giant branch and white dwarf phases of the planet host. we perform about 700 full-lifetime (14 gyr) simulations with a0 and f0 primary stars and secondary k2 companions, and identify the critical binary distance within which instability is triggered at any point during stellar evolution. we estimate this distance to be about seven times the outer planet separation for circular binaries. our results help characterize the fates of planetary systems, and in particular which ones might yield architectures which are conducive to generating observable metal pollution in white dwarf atmospheres. | binary star influence on post-main-sequence multi-planet stability |
in this era of spatially resolved observations of planet-forming disks with atacama large millimeter array (alma) and large ground-based telescopes such as the very large telescope (vlt), keck, and subaru, we still lack statistically relevant information on the quantity and composition of the material that is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. space infrared telescope for cosmology and astrophysics (spica) is an infrared space mission concept developed jointly by japan aerospace exploration agency (jaxa) and european space agency (esa) to address these questions. the key unique capabilities of spica that enable this research are (1) the wide spectral coverage $10{-}220 μm$ , (2) the high line detection sensitivity of $(1{-}2) × 10^{-19} w m^{-2}$ with $r ∼ 2 000{-}5 000$ in the far-ir (safari), and $10^{-20} w m^{-2}$ with $r ∼ 29 000$ in the mid-ir (spica mid-infrared instrument (smi), spectrally resolving line profiles), (3) the high far-ir continuum sensitivity of 0.45 mjy (safari), and (4) the observing efficiency for point source surveys. this paper details how mid- to far-ir infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet-forming period. these observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. the high spectral resolution mid-ir is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. infrared spectroscopy (mid- to far-ir) of key solid-state bands is crucial for assessing whether extensive radial mixing, which is part of our solar system history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our solar system comets/asteroids. we demonstrate that the spica mission concept would allow us to achieve the above ambitious science goals through large surveys of several hundred disks within $∼\!2.5$ months of observing time. | the formation of planetary systems with spica |
we report petrologic studies and oxygen isotope analyses of normal and anomalous eucrites, termed eucrite-type achondrites. petrologically anomalous eucrite-type achondrites can have normal oxygen isotope compositions, and vice versa. two basaltic eucrites with normal oxygen isotope compositions contain pyroxenes with anomalous fe/mn engendered by parent body processes acting on normal eucrites: solid-state reduction by s gas in eet 87542, and reduction during crystallization by magmatic s in que 94484. cataclastic basaltic breccias pca 82502 and pca 91007 are paired (petrology, anomalous oxygen). although isotopically like pasamonte, they are petrologically distinct. we confirm the petrological and isotopic anomalies of cumulate gabbro eet 92023; likely formed by impact melting of mixed cumulate and basaltic materials. many main group eucrites include plagioclases that retain near-liquidus compositions despite metamorphic overprinting. stannern group eucrites contain more sodic plagioclase, which is consistent with the melt hybridization hypothesis for stannern group magma formation. the lack of more calcic plagioclase suggests reactive exchange of the anorthite component of the primary melt with the albitic component of the crust. asteroids that are modestly different in composition can produce virtually indistinguishable basalts, providing a ready explanation for the eucrite-type achondrite suite. small stochastic variations in petrologic evolution can cause substantial differences in rocks produced on an asteroid. | eucrite-type achondrites: petrology and oxygen isotope compositions |
rising ocean temperatures are threatening marine species and populations worldwide, and ectothermic taxa are particularly vulnerable. echinoderms are an ecologically important phylum of marine ectotherms and shifts in their population dynamics can have profound impacts on the marine environment. the effects of warming on echinoderms are highly variable across controlled laboratory‑based studies. accordingly, synthesis of these studies will facilitate the better understanding of broad patterns in responses of echinoderms to ocean warming. herein, a meta‑analysis incorporating the results of 85 studies (710 individual responses) is presented, exploring the effects of warming on various performance predictors. the mean responses of echinoderms to all magnitudes of warming were compared across multiple biological responses, ontogenetic life stages, taxonomic classes, and regions, facilitated by multivariate linear mixed effects models. further models were conducted, which only incorporated responses to warming greater than the projected end‑of‑century mean annual temperatures at the collection sites. this meta‑analysis provides evidence that ocean warming will generally accelerate metabolic rate (+32%) and reduce survival (−35%) in echinoderms, and echinoderms from subtropical (−9%) and tropical (−8%) regions will be the most vulnerable. the relatively high vulnerability of echinoderm larvae to warming (−20%) indicates that this life stage may be a significant developmental bottleneck in the near‑future, likely reducing successful recruitment into populations. furthermore, asteroids appear to be the class of echinoderms that are most negatively affected by elevated temperature (−30%). when considering only responses to magnitudes of warming representative of end‑of‑century climate change projections, the negative impacts on asteroids, tropical species and juveniles were exacerbated (−51%, −34% and −40% respectively). the results of these analyses enable better predictions of how keystone and invasive echinoderm species may perform in a warmer ocean, and the possible consequences for populations, communities and ecosystems. | impacts of ocean warming on echinoderms: a meta‑analysis |
ten benthic fauna taxa in a polluted marine area adjacent to mcmurdo station, antarctica were deemed to be potential biomonitors because pcbs, ddts, pahs, copper, lead and/or zinc in their tissues were significantly higher than in tissues of taxa living in reference areas (p < 0.05). concentrations of pcbs and ddt were highest in trematomus (fish). total pah concentrations were highest in alcyonium antarcticum (soft coral), isotealia antarctica (anemone) and l. elliptica. copper and lead concentrations were highest in laternula elliptica (bivalve) and flabegraviera mundata (polychaete), and lowest in trematomus and parbolasia corrugatus (nemertean). however, copper concentrations were even higher in the asteroids perknaster fuscus antarcticus, odontaster validus and psilaster charcoti. bioaccumulation factors for different species were highest for pcbs and ddt, and lowest for lead. bioaccumulation of some contaminants are likely prevalent in benthic taxa at mcmurdo station, but concentrations are usually low relative to human consumption standards. | using epibenthic fauna as biomonitors of local marine contamination adjacent to mcmurdo station, antarctica |
the dynamics of lofted dust on airless bodies have been the subject of much study since the 1960s, when the lunar horizon glow was first observed. lofted dust dynamics have important implications for the evolution of an airless body's surface properties. to date, most of these studies have had to rely on assumptions of initial conditions of the lofted dust grains due to a lack of experimental results. in this paper, we present a study of lofted dust grains, making use of initial conditions obtained from recent laboratory results. additionally, we distinguish between photoemission rates from isolated dust grains and from the bulk regolith. we explore dust lofting dynamics across a large size range of dust grains (0.1 to 10 μm) and the surface gravity of their parent bodies (0.0001 to 1 lunar g). charging and lofting results reveal a complex interplay between the grain size, gravity, initial charge, and the various charging currents. it is shown that the sheath electric field becomes increasingly significant in the lofted dust dynamics as the gravitational field decreases. due to the initial negative charge of dust grains lofted from a positively charged regolith surface, their lofting heights are found to be generally reduced compared to uncharged grains with similar initial speeds. we show that micron-sized dust grains can be lofted to high altitudes and even escape from smaller bodies, leading to the loss of fine-grained materials from the surface. | dynamics of electrostatically lofted dust on airless planetary bodies |
the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) spacecraft collected a sample from the asteroid bennu in 2020. this achievement leveraged an autonomous optical navigation approach called natural feature tracking (nft). nft provided spacecraft state updates by correlating asteroid surface features rendered from previously acquired terrain data with images taken by the onboard navigation camera. the success of nft was the culmination of years of preparation and collaboration to ensure that feature data would meet navigation requirements. this paper presents the findings from ground testing performed prior to the spacecraft's arrival at bennu, in which synthetic data were used to develop and validate the technical approach for building nft features. correlation sensitivity testing using synthetic models of bennu enabled the team to characterize the terrain properties that worked well for feature correlation, the challenges posed by smoother terrain, and the impact of imaging conditions on correlation performance. the team found that models constructed from image data by means of stereophotoclinometry (spc) worked better than those constructed from laser altimetry data, except when test image pixel sizes were more than a factor of 2 smaller than those of the images used for spc, and when topography was underrepresented and resulted in incorrect shadows in rendered features. degradation of laser altimetry data related to noise and spatial sampling also led to poor correlation performance. albedo variation was found to be a key contributor to correlation performance; topographic data alone were insufficient for nft. | ground testing of digital terrain models to prepare for osiris-rex autonomous vision navigation using natural feature tracking |
context. the calern asteroid polarimetric survey (caps), a collaboration between the inaf astrophysical observatory of torino (italy) and the observatoire de la côte d'azur (nice, france), has produced new asteroid polarimetric data for a number of years, and is one of the most important, currently active projects of asteroid polarimetry.aims: the purpose of this paper is to make public the caps data collected thus far, to explain the adopted techniques of data reduction and computation of phase-polarisation curves for the measured objects, and explain, by means of some examples, the importance of the caps database.methods: the pipeline of data reduction has been recently updated and made as automatic as possible, using numerical algorithms developed specifically for the purposes of caps. the derivation of phase-polarisation curves for the observed asteroids is done using established criteria and algorithms that have recently been slightly improved, and are also summarised in this paper.results: the caps catalogue is a steadily growing source of information which can be exploited for different purposes, including, but not limited to, an updated calibration of the relations existing between different polarimetric parameters and the geometric albedo of the objects, and a study of classes of objects that can be most easily identified by means of their polarimetric properties. these subjects will be more specifically discussed in separate papers.conclusions: asteroid polarimetry data nicely complement the results of other more commonly used techniques, including visible and ir photometry and spectroscopy. caps contains a lot of much-desired information about physical properties, which can hardly be inferred by means of other techniques. full tables a.1 and a.2 are available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/665/a66 | the calern asteroid polarisation survey. an updated catalogue of asteroid polarimetric data |
context. shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark c/x asteroid population.aims: the exact pressure-temperature conditions of the shock-induced darkening are not well constrained. thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure.methods: a spherical shock experiment with chelyabinsk ll5 was performed in order to study the changes in its optical properties. the spherical shock experiment geometry allows for a gradual increase of shock pressure from ~15 gpa at a rim toward hundreds of gigapascals in the center.results: four distinct zones were observed with an increasing shock load. the optical changes are minimal up to ~50 gpa. in the region of ~50-60 gpa, shock darkening occurs due to the troilite melt infusion into silicates. this process abruptly ceases at pressures of ~60 gpa due to an onset of silicate melting. at pressures higher than ~150 gpa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. the shock darkening affects the ultraviolet, visible, and near-infrared region while changes to the mir spectrum are minimal.conclusions: shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. this implies a reduced amount of shock-darkened material produced during the asteroid collisions. all measured data as well as full resolution images can be found at https://dx.doi.org/10.5281/zenodo.3584942 | experimental constraints on the ordinary chondrite shock darkening caused by asteroid collisions |
the velocity scaling method of ma et al., as an extension of nacozy's manifold correction scheme, can frequently take the solution of a numerical integration back to a surface determined by an integral of the equations of motion. an elliptic restricted three-body hamiltonian of the sun, major and minor planets in a rotating frame is explicitly dependent on time and, therefore, is not a conserved quantity. in this case, there is no jacobi conservative integral available but there is a jacobi non-conservative integral. this seems to be an obstacle to applying the velocity scaling correction method. here are two points about an effective way to overcome this obstacle. first, because of the hamiltonian having momentum- and coordinate-dependent terms associated with the contributions from the non-inertial frame, a scaling correction factor should be used to act on the velocities in the jacobi non-conservative integral although the momenta are integration variables. secondly, at each integration step, the value of the hamiltonian obtained from an integral invariant relation is referred to as a more accurate reference value; the scaling factor versus the velocities is given by constraining the numerical solution to remain on the jacobi non-conservative integral along this reference value. numerical experiments show that a lower-order non-symplectic algorithm plus the velocity scaling scheme demonstrates good numerical performance in suppressing the rapid growth of integration errors, compared to the lower-order uncorrected algorithm. the correction scheme is powerful for eliminating spurious non-physical chaos due to integration errors. it is found that a larger eccentricity of the giant planet will increase the possibility of chaos or escape of the asteroid. | implementation of the velocity scaling method for elliptic restricted three-body problems |
micromega, a miniaturized near-infrared hyperspectral microscope, has been selected to characterize in the laboratory the samples returned from ryugu by the hayabusa2 mission. micromega has been delivered to the extraterrestrial samples curation center of the japanese aerospace exploration agency at the institute of space and astronautical science in july 2020 and then mounted and calibrated to be ready for the analyses of the samples returned to earth on december 6, 2020. micromega was designed to analyze the returned samples within a field of view of 5 × 5 mm2 and a spatial sampling of 22.5 µm. it acquires 3d near-infrared hyperspectral image-cubes by imaging the sample with monochromatic images sequentially covering the 0.99-3.65 µm spectral range, with a typical spectral sampling of 20 cm-1. this paper reports the calibration processes performed to extract scientific data from these micromega image-cubes. the determination of the instrumental response and the spectral calibration is detailed. we meet or exceed the goals of achieving an accuracy of ~20% for the absolute reflectance level, 1% for the relative wavelength-to-wavelength reflectance, and <5 nm for the peak position of the detected absorption features. for the nominal measurements of ryugu samples with micromega/curation, the instrument performance also reaches a signal-to-noise ratio of >100 over the entire spectral range. by characterizing the entire collection of the returned samples at the microscopic scale, micromega/curation offers the potential to provide unprecedented insights into the composition and history of their asteroid parent body. | calibration and performances of the micromega instrument for the characterization of asteroid ryugu returned samples |
large clasts are common on extraterrestrial bodies, and these are traditionally termed "blocks" and "boulders". these two terms can easily raise confusion, however, because they are used in a sense that differs from geological definitions. several classifications of large clasts are currently in use in the earth sciences, and they differ only in detail. they restrict the size of boulders to 1-4 m; larger particles are called "megaclasts". the analysis of the published information on large clasts on planet satellites, asteroids, and comets imply that the particles often described as "boulders" actually are megaclasts; boulders, as the term is used in the earth sciences, are too small to be detected given the limited resolution of most images obtained. it were therefore scientifically preferable if the established geological literature were applied in the modern planetary and space research. it appears sensible to distinguish boulders from megaclasts; the latter comprise bodies that might be subdivided granulometrically into blocks, megablocks, and superblocks. it is also shown that the abundance of megaclasts on extraterrestrial bodies may itself be beneficial for our understanding of such particles, which are rare on earth. | something more than boulders: a geological comment on the nomenclature of megaclasts on extraterrestrial bodies |
an intercomparison of different aerosol chemical characterization techniques has been performed as part of a chamber study of biogenic secondary organic aerosol (bsoa) formation and aging at the atmosphere simulation chamber saphir (simulation of atmospheric photochemistry in a large reaction chamber). three different aerosol sampling techniques - the aerosol collection module (acm), the chemical analysis of aerosol online (charon) and the collection thermal-desorption unit (td) were connected to proton transfer reaction time-of-flight mass spectrometers (ptr-tof-mss) to provide chemical characterization of the soa. the techniques were compared among each other and to results from an aerosol mass spectrometer (ams) and a scanning mobility particle sizer (smps). the experiments investigated soa formation from the ozonolysis of β-pinene, limonene, a β-pinene-limonene mix and real plant emissions from pinus sylvestris l. (scots pine). the soa was subsequently aged by photo-oxidation, except for limonene soa, which was aged by no3 oxidation.despite significant differences in the aerosol collection and desorption methods of the ptr-based techniques, the determined chemical composition, i.e. the same major contributing signals, was found by all instruments for the different chemical systems studied. these signals could be attributed to known products expected from the oxidation of the examined monoterpenes. the sampling and desorption method of acm and td provided additional information on the volatility of individual compounds and showed relatively good agreement.averaged over all experiments, the total aerosol mass recovery compared to an smps varied within 80 ± 10, 51 ± 5 and 27 ± 3 % for charon, acm and td, respectively. comparison to the oxygen-to-carbon ratios (o : c) obtained by ams showed that all ptr-based techniques observed lower o : c ratios, indicating a loss of molecular oxygen either during aerosol sampling or detection. the differences in total mass recovery and o : c between the three instruments resulted predominantly from differences in the field strength (e/n) in the drift tube reaction ionization chambers of the ptr-tof-ms instruments and from dissimilarities in the collection/desorption of aerosols. laboratory case studies showed that ptr-tof-ms e/n conditions influenced fragmentation which resulted in water and further neutral fragment losses of the detected molecules. since acm and td were operated in higher e/n than charon, this resulted in higher fragmentation, thus affecting primarily the detected oxygen and carbon content and therefore also the mass recovery. overall, these techniques have been shown to provide valuable insight on the chemical characteristics of bsoa and can address unknown thermodynamic properties such as partitioning coefficient values and volatility patterns down to a compound-specific level. | comparison of three aerosol chemical characterization techniques utilizing ptr-tof-ms: a study on freshly formed and aged biogenic soa |
after its release and a descent and bouncing phase, the hayabusa2 lander mascot came to a final rest and mascot's camera mascam acquired a set of images of the surface of ryugu. with mascam's instantaneous field of view of about 1 mrad, the images provide pixel scales from 0.2 to 0.5 mm pixel-1 in the foreground and up to 1 cm pixel-1 for surface parts in the background. using a stereo-photogrammetric analysis of the mascam images taken from slightly different positions due to commanded and unintentional movements of the mascot lander, we were able to determine the orientation for the different measurement positions. furthermore, we derived a 3d surface model of mascot's vicinity. although the conditions for 3d stereo processing were poor due to very small stereo angles, the derived 3d model has about 0.5 cm accuracy in the foreground at 20 cm distance and about 1.5 cm at a distance of 40-50 cm. | the hayabusa2 lander mascot on the surface of asteroid (162173) ryugu - stereo-photogrammetric analysis of mascam image data |
a phase-resolved wave model is derived from an ocean circulation model for the purpose of studying wave-current effects in nearshore zones. one challenge is to adapt the circulation model to the specificities of wave physics. this mainly concerns the consideration of non-hydrostatic effects and the parametrization of wave breaking. the non-hydrostatic pressure is calculated using the artificial compressibility method (acm). the acm-induced errors on wave dispersion properties are examined in detail in the context of the linear theory using idealized test cases. the possible compromise between the precision achieved on non-hydrostatic physics and the adjustable cpu cost of the acm method is looked at in detail. the modification of the wave characteristics by the bathymetric slope and the breaking of waves are then examined from a linear slope beach laboratory experiment. finally the model is evaluated on the issue of rip currents and their feedback on the wave field using a laboratory experiment of a beach with a bar intersected by channels. | 3d phase-resolved wave modelling with a non-hydrostatic ocean circulation model |
surface and subsurface materials of c-type near-earth asteroid 162173 ryugu were collected and successfully returned to the earth in the hayabusa2 mission. fourier transform infrared spectroscopy (ftir) has been conducted to characterize these returned samples as one of the initial descriptions in a non-destructive manner under a purified nitrogen condition without terrestrial contamination. we selected the individual grains and aggregate samples that were not severely influenced by the reflection of incident beam at the sapphire dish and analyzed their reflectance spectra using the primary component analysis (pca). the result indicates that ryugu returned samples are highly homogeneous with only a little heterogeneity. the average spectrum of the main pca group is represented by four absorption bands at 2.7, 3.05, 3.4, and 3.95 μm. the spectral feature is consistent with that obtained from bulk ftir measurements, indicating potential presence of hydroxyl, organics, and carbonates. rarely observed types of grains with unique spectra are categorized into three groups: significantly high reflectance, carbonates, and hydroxyl compounds with broad oh absorption. | homogeneity and heterogeneity in near-infrared ftir spectra of ryugu returned samples |
singhbhum craton in eastern india is one of the oldest and perhaps geologically and geophysically most complex geological terrains on the surface of the earth, containing a number of intra-cratonic archean volcanic suites. in the present study, we investigate mesoarchean volcanic rocks of the simlipal complex, a tiger reserve in the mayurbhanj district of odisha (india). our results provide a new understanding of the regional geodynamic scenario of the eoarchean singhbhum craton, including the nature of plume-lithosphere interaction based on the detailed analysis of geological, geochemical and geophysical data. whole-rock geochemical studies exhibit large variation in sio2 (39.30-60.57 wt%), tio2 (0.20-1.55 wt%), al2o3 (4.45-15.63 wt%), mgo (5.25-37.00 wt%) and cao (3.46-11.26 wt%) with low to moderately high cr (50-1503 ppm) and ni (36-550 ppm) contents. these rocks are cumulates to porphyritic and petrographically and geochemically, can be classified as ultramafic (lherzolite, pyroxenite), picrite, basalt, basaltic andesite, andesite and boninite. their trace elements and hfse/ree patterns indicate that they belong to the same parental magma. rare earth elements and trace element patterns exhibit moderate fractionation with a coherent pattern of (la/yb)n: 1.38-8.50, (gd/yb)n: 0.92-2.59 and (la/sm)n: 1.11-4.40, consistent with polybaric melting. the present study suggests that these rocks were generated by decompressive melting of a mantle plume head at a depth of garnet to spinel lherzolite field together with fractional crystallization and crustal contamination in the subcontinental lithospheric mantle (sclm), which is corroborated by the highly uplifted nature of this terrain, associated with positive gravity anomalies. this plume had a mantle potential temperature between 1400 and 1700 °c and pressure reaching 4.4 gpa. massive upwarping of the lower crust to an extremely shallow depth of about 4 km from the surface, 21 km thick magmatic underplating above the moho and the lithosphere asthenosphere boundary at 81 km, would support plume-induced active crust-mantle thermal interaction and extremely warm and deformed nature of the lithosphere beneath the simlipal volcanic complex. based on the findings of millerite (nis), quench/spinifex texture and shock metamorphic features in these volcanic rocks, we infer that there could be a possibility that the suggested mantle plume in the study area may have been triggered by an asteroidal impact. | mineral chemistry, geochemistry and geophysical investigations of simlipal volcanics from eoarchean singhbhum craton (eastern india): geodynamic implications of pervasive plume-lithosphere interaction |
distant retrograde orbits (dros) gained a novel wave of fame in space mission design because of their numerous advantages within the framework of the us plans for bringing a large asteroid sample in the vicinity of the earth as the next target for human exploration. dros are stable solutions of the three-body problem that can be used whenever an object, whether of natural or artificial nature, is required to remain in the neighborhood of a celestial body without being gravitationally captured by it. as such, they represent an alternative option to halo orbits around the collinear lagrangian points l1 and l2. also known under other names ( e.g., quasi-satellite orbits, cis-lunar orbits, family- f orbits) these orbital configurations found interesting applications in several mission profiles, like that of a spacecraft orbiting around the small irregularly shaped satellite of mars phobos or the large jovian moon europa. in this paper a basic explanation of the dro dynamics is presented in order to clarify some geometrical properties that characterize them. their accessibility is then discussed from the point of view of mission analysis under different assumptions. finally, their relevance within the framework of the present asteroid hazard protection programs is shown, stressing the significant increase in warning time they would provide in the prediction of impactors coming from the direction of the sun. | distant retrograde orbits and the asteroid hazard |
recognition of the main morphostructural features of the western edge of the huila plateau (sw angola) can be done by using remote sensing techniques associated with field work. a digital elevation model (dem) of the area was built for this purpose. this model is based on altimeter data acquired from the aster sensor, on which image processing techniques such as enhancement techniques, contrast change and filtering were applied. other techniques, such as rgb colour composition, were also tested. the processed satellite images were interpreted by visual process and the results were then compared with available geological maps (scale 1: 1 000 000). to facilitate both analysis and interpretation, the edge of the plateau was divided into three sectors: northern (or chongoroi edge), central (or humpata edge) and southern (or oncocua edge). for each sector, the main morphological aspects and main lineament systems were identified and characterized. in the specific case of the central sector, these parameters were also confirmed by field work. this study shows that the morphology of the western edge of the plateau is dominated by n50°w-n60°w, n60°e and n-s trending main tectonic systems. these results have important implications in terms of geological mapping and regional tectonics as well as in land-use planning and other areas, such as hydrogeology or geotechnics. | morphostructural characterization of the western edge of the huila plateau (sw angola), based on remote sensing techniques |
compound-specific carbon isotope analysis (δ13c) of meteoritic organic compounds can be used to elucidate the abiotic chemical reactions involved in their synthesis. the soluble organic content of the murchison carbonaceous chondrite has been extensively investigated over the years, with a focus on the origins of amino acids and the potential role of strecker-cyanohydrin synthesis in the early solar system. previous δ13c investigations have targeted α-amino acid and α-hydroxy acid strecker products and reactant hcn; however, δ13c values for meteoritic aldehydes and ketones (strecker precursors) have not yet been reported. as such, the distribution of aldehydes and ketones in the cosmos and their role in prebiotic reactions have not been fully investigated. here, we have applied an optimized o-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (pfbha) derivatization procedure to the extraction, identification, and δ13c analysis of carbonyl compounds in the murchison meteorite. a suite of aldehydes and ketones, dominated by acetaldehyde, propionaldehyde, and acetone, were detected in the sample. δ13c values, ranging from -10.0‰ to +66.4‰, were more 13c-depleted than would be expected for aldehydes and ketones derived from the interstellar medium, based on interstellar 12c/13c ratios. these relatively 13c-depleted values suggest that chemical processes taking place in asteroid parent bodies (e.g., oxidation of the iom) may provide a secondary source of aldehydes and ketones in the solar system. comparisons between δ13c compositions of meteoritic aldehydes and ketones and other organic compound classes were used to evaluate potential structural relationships and associated reactions, including strecker synthesis and alteration-driven chemical pathways. | compound-specific carbon isotope compositions of aldehydes and ketones in the murchison meteorite |
the dart (double asteroid redirection test) mission will impact a spacecraft on the secondary (dimorphos) of the binary asteroid system didymos in 2022 september, with the goal of altering the orbital period of dimorphos about didymos sufficiently to be observed from ground-based observations. numerical impact modeling is a crucial component in understanding the outcome of the dart experiment, and while many have investigated the effects of target properties, such as material strength and porosity (which remain unknown), an often overlooked factor is the importance of accurately representing the spacecraft itself in such models. most impact modeling to date has considered simple impactor geometries such as a solid uniform sphere, but in reality the spacecraft is a complex shape full of different components, open spaces, and thin walled structures. at a minimum, a simple solid representation underestimates the surface area of the impact: for a small body such as dimorphos (approximately 160 m in diameter), the difference between a spacecraft spanning 20 m (including solar arrays) impacting and a sub-1 m idealized shape may be important. in this paper, we compare models impacting high-fidelity models of the spacecraft based on the cad geometry with various simplified impactors, in order to assess the potential importance of this effect. we find that the difference between the simplest impactor geometries (such as a uniform sphere) and the real spacecraft is measurable, and has an interesting dependence on the material properties of the asteroid itself. | spacecraft geometry effects on kinetic impactor missions |
asteroid families are the remnants of the catastrophic collision, and their fundamental physical properties provide us the information of their parent bodies and evolutions. especially, the orbit and spin characteristics can reflect the influences of the yarkovsky effect and the yarkovsky-o'keefe-radzievskii-paddack (yorp) effect on the evolution of the asteroid family, respectively. based on the asteroid lightcurve database (lcdb), the spin rate distribution of the flora asteroid family is studied, and a tendency that the spin rates of the small flora family asteroids assemble primarily in the range of 3-5 d^{-1} is found; by analysis on the spin states of the flora family asteroids, a phenomenon can be also found that the most majority of this asteroid family members lie in the prograde rotating state. however, for some flora family asteroids which locate in the semi-major axis less than 2.2 au, the ratio between the number of prograde rotating bodies and that of retrograde ones is similar to that of the near-earth asteroids which have the corresponding ratio of 1:3. furthermore, for those prograde rotating flora family asteroids whose semi-major axis is more than 2.2 au, a portion of the members assemble in a special range reflecting a certain relationship between the semi-axis and the absolute magnitude, in which nine members show the similar feature of the slivan state. | study on the spin characteristics of the flora asteroid family |
we have recently shown that spiral density waves propagating in accretion disks can undergo a parametric instability by resonantly coupling with and transferring energy into pairs of inertial waves (or inertial-gravity waves when buoyancy is important). in this paper, we perform inviscid three-dimensional global hydrodynamic simulations to examine the growth and consequence of this instability operating on the spiral waves driven by a jupiter-mass planet in a protoplanetary disk. we find that the spiral waves are destabilized via the spiral wave instability (swi), generating hydrodynamic turbulence and sustained radially alternating vertical flows that appear to be associated with long wavelength inertial modes. in the interval 0.3 {r}{{p}}≤slant r≤slant 0.7{r}{{p}}, where r p denotes the semimajor axis of the planetary orbit (assumed to be 5 au), the estimated vertical diffusion rate associated with the turbulence is characterized by {α }{diff}∼ (0.2{--}1.2)× {10}-2. for the disk model considered here, the diffusion rate is such that particles with sizes up to several centimeters are vertically mixed within the first pressure scale height. this suggests that the instability of spiral waves launched by a giant planet can significantly disperse solid particles and trace chemical species from the midplane. in planet formation models where the continuous local production of chondrules/pebbles occurs over myr timescales to provide a feedstock for pebble accretion onto these bodies, this stirring of solid particles may add a time constraint: planetary embryos and large asteroids have to form before a gas giant forms in the outer disk, otherwise the swi will significantly decrease the chondrule/pebble accretion efficiency. | the spiral wave instability induced by a giant planet. i. particle stirring in the inner regions of protoplanetary disks |
to date, reflectance spectra of jupiter trojan asteroids have revealed no distinctive absorption features. for this reason, the surface composition of these objects remains a subject of speculation. spectra have revealed, however, that the jupiter trojan asteroids consist of two distinct sub-populations that differ in the optical to near-infrared colors. the origins and compositional differences between the two sub-populations remain unclear. here, we report the results from a 2.2-3.8 μm spectral survey of a collection of 16 jupiter trojan asteroids, divided equally between the two sub-populations. we find clear spectral absorption features centered around 3.1 μm in the less-red population. additional absorption consistent with that expected from organic materials might also be present. no such features are see in the red population. a strong correlation exists between the strength of the 3.1 μm absorption feature and the optical to near-infrared color of the objects. while, traditionally, absorptions such as these in dark asteroids are modeled as being due to fine-grain water frost, we find it physically implausible that the special circumstances required to create such fine-grained frost would exist on a substantial fraction of the jupiter trojan asteroids. we suggest, instead, that the 3.1 μm absorption on trojans and other dark asteroids could be due to n-h stretch features. additionally, we point out that reflectivities derived from wise observations show a strong absorption beyond 4 μm for both populations. the continuum of 3.1 μm features and the common absorption beyond 4 μm might suggest that both sub-populations of jupiter trojan asteroids formed in the same general region of the early solar system. | the 3-4 μm spectra of jupiter trojan asteroids |
asteroids in mean motion resonances with giant planets are common in the solar system, but it was not until recently that several asteroids in retrograde mean motion resonances with jupiter and saturn were discovered. a retrograde co-orbital asteroid of jupiter, 2015 bz509 is confirmed to be in a long-term stable retrograde 1:1 mean motion resonance with jupiter, which gives rise to our interests in its unique resonant dynamics. in this paper, we investigate the phase-space structure of the retrograde 1:1 resonance in detail within the framework of the circular restricted three-body problem. we construct a simple integrable approximation for the planar retrograde resonance using canonical contact transformation and numerically employ the averaging procedure in closed form. the phase portrait of the retrograde 1:1 resonance is depicted with the level curves of the averaged hamiltonian. we thoroughly analyze all possible librations in the co-orbital region and uncover a new apocentric libration for the retrograde 1:1 resonance inside the planet’s orbit. we also observe the significant jumps in orbital elements for outer and inner apocentric librations, which are caused by close encounters with the perturber. | dynamic portrait of the retrograde 1:1 mean motion resonance |
we present the k2 light curves of a large sample of untargeted main-belt asteroids (mbas) detected with the kepler space telescope. the asteroids were observed within the uranus superstamp, a relatively large, continuous field with a low stellar background designed to cover the planet uranus and its moons during campaign 8 of the k2 mission. the superstamp offered the possibility of obtaining precise, uninterrupted light curves of a large number of mbas and thus determining unambiguous rotation rates for them. we obtained photometry for 608 mbas, and were able to determine or estimate rotation rates for 90 targets, of which 86 had no known values before. in an additional 16 targets we detected incomplete cycles and/or eclipse-like events. we found the median rotation rate to be significantly longer than that of the ground-based observations, indicating that the latter are biased toward shorter rotation rates. our study highlights the need and benefits of further continuous photometry of asteroids. | main-belt asteroids in the k2 uranus field |
near-earth asteroid (3200) phaethon is notable for its association with a strong annual meteor shower, the geminids, indicative of one or more episodes of mass ejection in the past. the mechanism of phaethon’s past activity is not yet understood. here, we present a hubble space telescope (hst) search of meter-sized fragments in the vicinity of phaethon, carried out during phaethon’s historic approach to earth in mid-december of 2017. numerical simulations conducted to guide hst’s pointing also show that the dynamical evolution of phaethon-originated particles is quick, as ejected materials take no longer than ∼250 years to spread to the entire orbit of phaethon. our search was completed down to a 4 m class limit (assuming phaethon-like albedo) and was expected to detect 0.035% of particles ejected by phaethon in the past several decades. the negative result of our search capped the total mass loss of phaethon over the past few dozen orbits to be 1012 kg at the 3σ level, taking the best estimates of size power-law from meteor observations and spacecraft data. our result also implies a millimeter-sized dust flux of < {10}-12 {{{m}}}-2 {{{s}}}-1 within 0.1 au of phaethon, suggesting that any phaethon-bound mission is unlikely to encounter dense dust clouds. | in search of recent disruption of (3200) phaethon: model implication and hubble space telescopesearch |
the development of an immersion-and invariance-based adaptive state variable feedback control law for the closed orbit and hovering control of spacecraft in the vicinity of asteroids is the subject of this paper. the celestial body is assumed to be rotating with constant angular velocity about a fixed axis. also, it is assumed that the mass and moments of inertia matrix of the asteroid, and the mass of the spacecraft are not known. the objective is to control the orbit of the spacecraft despite uncertainties in the system parameters. based on the immersion and invariance theory, a noncertainty-equivalence adaptive control system is designed for steering the spacecraft along prescribe closed orbits or to fixed points for hovering control. the control system has a modular structure - consisting of an stabilizing control module and an parameter identifier. the control law is synthesized using filtered signals so as to circumvent the complexity of the immersion and immersion methodology. unlike certainty-equivalence systems, the parameter estimates include judiciously selected nonlinear state-dependent algebraic functions and partial estimates derived from an integral update law. by the lyapunov analysis, it is shown that the trajectory tracking error asymptotically converges to zero and all the signals in the closed-loop system are bounded. for illustration, numerical results are presented for control around 433 eros and ida asteroids. these results show that, despite uncertainties in the relative spacecraft dynamics, the adaptive law accomplishes closed orbit as well as hovering control. | immersion-and invariance-based adaptive control of asteroid-orbiting and - hovering spacecraft |
the two clearwater lake impact structures (québec, canada) are generally interpreted as a crater doublet formed by the impact of a binary asteroid. here, arguments are presented that raise important questions about the proposed double impact scenario. new 40ar/39ar dating of two virtually fresh impact melt rock samples from the ⩾36 km west clearwater lake impact structure yielded two statistically robust early permian plateau ages with a weighted mean of 286.2 ± 2.2 (2.6) ma (2σ; mswd = 0.33; p = 0.57). in contrast, 40ar/39ar results for two chloritized melt rocks from the ∼26 km east clearwater lake impact structure produced disturbed age spectra suggestive of a distinct extraneous argon component. although individually weakly robust, age spectra corrected for the trapped argon component and inverse isochron plots for the east clearwater melt rocks consistently yielded apparent ages around ∼460-470 ma. no permian signal was found in either of these melt aliquots. our new 40ar/39ar results reproduce earlier 40ar/39ar plateau ages (∼283 ma and ∼465 ma, respectively) for the two impact structures by bottomley et al. (1990) and are in conflict with a previous, statistically non-robust rb-sr age of 287 [293] ± 26 ma for east clearwater. the combined cluster of apparent ages of ∼460-470 ma, derived from four different samples across the impact melt sheet, is very unlikely to represent a 'false age effect' due to the incorporation of extraneous argon into the melt; instead, it strongly favors a middle ordovician age for the east clearwater impact and impact-induced hydrothermal chloritization. moreover, the clearwater impact structures are characterized by different natural remanent magnetizations testifying to separate geologic histories, an effect unexpected in the case of a permian double impact. whereas the west clearwater impact affected ordovician carbonates incorporated into the impact breccia, drill core reports from the 1960s concluded that clasts of ordovician sedimentary rocks are seemingly absent in the impact breccia lens of the east clearwater lake impact structure, which is overlain by >100 m of post-impact sandstones, shales and carbonates. no resolvable impactor contamination has so far been detected in the west clearwater impact melt rocks, whereas east clearwater carries a distinct ordinary (possibly l-) chondritic impactor signature in its melt rocks. east clearwater lake might thus represent one among a long list of ordovician impact structures in north america and northern europe that were presumably formed in response to the l-chondrite asteroid breakup event ∼470 ma ago. paleogeographic reconstructions show that the ordovician east clearwater impact probably occurred in a near-coastal to shallow marine setting, while the permian west clearwater impact hit continental pangaea. along with the new 40ar/39ar data, the paleomagnetic, sedimentologic, and geochemical findings suggest that the close spatial arrangement of the two clearwater lakes is most likely pure coincidence. the two impact structures seem to represent a 'false doublet' struck by impacts separated by ∼180 million years in time. the new results for the clearwater lake impact structures have major implications for the reliable identification of doublet impact craters and the rate of binary asteroid impacts on earth and on other planetary bodies in the inner solar system. | new 40ar/39ar dating of the clearwater lake impact structures (québec, canada) - not the binary asteroid impact it seems? |
the close-proximity exploration of small celestial bodies of our solar system is the current frontier of space exploration. trajectory design and exploitation of the natural dynamics around such bodies represents a very challenging astrodynamics problem, due to their weak and highly chaotic gravitational environment. the paper discusses design solutions for the ballistic landing of a small and passive probe, released to land on the smaller of a binary asteroid couple. the work is focused on the asteroid impact mission (aim) case study, although the methods and analyses presented are general and applicable to any binary asteroid scenario. the binary system is modeled using a shape-based three-body problem and three-body solutions are investigated within the didymos binary system. manifold dynamics near libration points associated to the asteroid three-body system are exploited to find low-energy and high-success landing trajectories. the validity of implemented approach and solutions found are discussed and results in terms of success rate and landing dispersion are shown. | ballistic landing design on binary asteroids: the aim case study |
the mascot radiometer mara on board the hayabusa2 mission will measure surface brightness temperatures on the surface of asteroid (162173) ryugu in six wavelength bands. here we present a method to constrain surface thermophysical properties from mara measurements. moreover, uncertainties when determining surface thermal inertia as well as emissivity are estimated. using data from all filters and assuming constant emissivity, thermal inertia of a homogeneous surface can be determined with an uncertainty range of 250 ±16 jm-2k-1s - 1 / 2 , while the emissivity uncertainty is below 6%. similar results are obtained if emissivity is allowed to vary as a function of wavelength and if the mara channels with the best signal-to-noise ratio are used to constrain thermal inertia. if the observed surface is heterogeneous and two morphologically different units are present in the instrument's field of view, thermal inertia of the subunits can be retrieved independently if their contrast in terms of thermophysical properties is large enough. if, for example, the surface is covered by equal area fractions of fine-grained and coarse-grained material, then thermal inertia is found to be retrievable with uncertainties of 658 ±78 and 54 ±22 jm-2k-1s - 1 / 2 for the coarse-grained and fine-grained fraction, respectively. | a method to derive surface thermophysical properties of asteroid (162173) ryugu (1999ju3) from in-situ surface brightness temperature measurements |
the first known asteroid with the orbit inside that of venus is 2020 av2. this may be the largest member of a new population of small bodies with the aphelion smaller than 0.718 au, called vatiras. the surface of 2020 av2 is being constantly modified by the high temperature, by the strong solar wind irradiation that characterizes the innermost region of the solar system, and by high-energy micrometeorite impacts. the study of its physical properties represents an extreme test-case for the science of near-earth asteroids. here, we report spectroscopic observations of 2020 av2 in the 0.5-1.5-μm wavelength interval. these were performed with the nordic optical telescope and the william herschel telescope. based on the obtained spectra, we classify 2020 av2 as a sa-type asteroid. we estimate the diameter of this vatira to be $1.50_{-0.65}^{+1.10}$ km by considering the average albedo of a-type and s-complex asteroids ( $p_v=0.23_{-0.08}^{+0.11}$ ), and the absolute magnitude (h = 16.40 ± 0.78 mag). the wide spectral band around 1 μm shows the signature of an olivine-rich composition. the estimated band centre bic = 1.08 ± 0.02 μm corresponds to a ferroan olivine mineralogy similar to that of brachinite meteorites. | physical characterization of 2020 av2, the first known asteroid orbiting inside venus orbit |
the satellite of (225088) 2007 or10 was discovered on archival hubble space telescope images and along with new observations with the wfc3 camera in late 2017 we have been able to determine the orbit. the orbit's notable eccentricity, e ≈ 0.3, may be a consequence of an intrinsically eccentric orbit and slow tidal evolution, but may also be caused by the kozai mechanism. dynamical considerations also suggest that the moon is small, deff < 100 km. based on the newly determined system mass of 1.75 ·1021 kg, 2007 or10 is the fifth most massive dwarf planet after eris, pluto, haumea and makemake. the newly determined orbit has also been considered as an additional option in our radiometric analysis, provided that the moon orbits in the equatorial plane of the primary. assuming a spherical shape for the primary this approach provides a size of 1230 ± 50 km, with a slight dependence on the satellite orbit orientation and primary rotation rate chosen, and a bulk density of 1.75 ± 0.07 g cm-3 for the primary. a previous size estimate that assumed an equator-on configuration (1535-225+75 km) would provide a density of 0.92-0.14+0.46 g cm-3, unexpectedly low for a 1000 km-sized dwarf planet. | the mass and density of the dwarf planet (225088) 2007 or10 |
gravitational features are a fundamental source of information to learn more about the interior structure and composition of planets, moons, asteroids, and comets. gravitational field modeling typically approximates the target body with a sphere, leading to a representation in spherical harmonics. however, small celestial bodies are often irregular in shape and hence poorly approximated by a sphere. a much better suited geometrical fit is achieved by a triaxial ellipsoid. this is also mirrored in the fact that the associated harmonic expansion (ellipsoidal harmonics) shows a significantly better convergence behavior as opposed to spherical harmonics. unfortunately, complex mathematics and numerical problems (arithmetic overflow) so far severely limited the applicability of ellipsoidal harmonics. in this paper, we present a method that allows expanding ellipsoidal harmonics to a considerably higher degree compared to existing techniques. we apply this novel approach to model the gravitational field of comet 67p, the final target of the rosetta mission. the comparison of results based on the ellipsoidal parameterization with those based on the spheroidal and spherical approximations reveals that the latter is clearly inferior; the spheroidal solution, on the other hand, is virtually just as accurate as the ellipsoidal one. finally, in order to generalize our findings, we assess the gravitational field modeling performance for some 400 small bodies in the solar system. from this investigation we generally conclude that the spheroidal representation is an attractive alternative to the complex ellipsoidal parameterization, on the one hand, and the inadequate spherical representation, on the other hand. | spheroidal and ellipsoidal harmonic expansions of the gravitational potential of small solar system bodies. case study: comet 67p/churyumov-gerasimenko |
we present thermal infrared observations of the active asteroid (and geminid meteoroid stream parent) 3200 phaethon using the very large telescope. the images, at 10.7 μm wavelength, were taken with phaethon at its closest approach to earth (separation of 0.07 au) in 2017 december, at a linear resolution of about 14 km. we probe the hill sphere (of radius ∼66 km) for trapped dust and macroscopic bodies, finding neither, and we set limits to the presence of unbound dust. the derived limits to the optical depth of dust near phaethon depend somewhat on the assumed geometry, but are of an order of 10-5. the upper limit to the rate of loss of mass in dust is ≲14 kg s-1. this is ∼50 times smaller than the rate needed to sustain the geminid meteoroid stream in steady state. the observations thus show that the production of the geminids does not proceed in a steady state. | high-resolution thermal infrared imaging of 3200 phaethon |
we have carried out simulations to predict the performance of a new space-based telescopic survey operating at thermal infrared wavelengths that seeks to discover and characterize a large fraction of the potentially hazardous near-earth asteroid (nea) population. two potential architectures for the survey were considered: one located at the earth-sun l1 lagrange point, and one in a venus-trailing orbit. a sample cadence was formulated and tested, allowing for the self-follow-up necessary for objects discovered in the daytime sky on earth. synthetic populations of neas with sizes as small as 140 m in effective spherical diameter were simulated using recent determinations of their physical and orbital properties. estimates of the instrumental sensitivity, integration times, and slew speeds were included for both architectures assuming the properties of newly developed large-format 10 μm hgcdte detector arrays capable of operating at ∼35 k. our simulation included the creation of a preliminary version of a moving object processing pipeline suitable for operating on the trial cadence. we tested this pipeline on a simulated sky populated with astrophysical sources such as stars and galaxies extrapolated from spitzer space telescope and wide-field infrared explorer data, the catalog of known minor planets (including main belt asteroids, comets, jovian trojans, planets, etc.), and the synthetic nea model. trial orbits were computed for simulated position-time pairs extracted from the synthetic surveys to verify that the tested cadence would result in orbits suitable for recovering objects at a later time. our results indicate that the earth-sun l1 and venus-trailing surveys achieve similar levels of integral completeness for potentially hazardous asteroids larger than 140 m; placing the telescope in an interior orbit does not yield an improvement in discovery rates. this work serves as a necessary first step for the detailed planning of a next-generation nea survey. | survey simulations of a new near-earth asteroid detection system |
observations in 2013 and 2014 of the centaur 10199 chariklo and its ring system consistently indicated that the radial width of the inner, more massive ring varies with longitude. that strongly suggests that this ring has a finite eccentricity despite the fast differential precession that chariklo’s large quadrupole moment should induce. if the inferred apse alignment is maintained by the ring’s self-gravity, as it is for the uranian rings, we estimate a ring mass of a few times 1016 g and a typical particle size of a few meters. these values imply a collisional spreading time of ∼105 years, which is somewhat shorter than the typical centaur dynamical lifetime of a few million years and much shorter than the age of the solar system. in light of this time constraint, we evaluate previously suggested ring formation pathways including collisional ejection and satellite disruption. we also investigate in detail a contrasting formation mechanism, the lofting of dust particles off chariklo’s surface into orbit via outflows of sublimating co and/or n2 triggered after chariklo was scattered inward by giant planets. this alternate scenario predicts that rings should be common among 100 km class centaurs but rare among kuiper belt objects and smaller centaurs. it also predicts that centaurs should show seasonal variations in cometary activity with activity maxima occurring shortly after equinox. | on the mass and origin of chariklo’s rings |
1i/`oumuamua is the first interstellar object observed passing through the solar system. understanding the nature of these objects will provide crucial information about the formation and evolution of planetary systems, and the chemodynamical evolution of the galaxy as a whole. we obtained the galactic orbital parameters of this object, considering eight different models for the galaxy, and compared it to those of stars of different ages from the geneva-copenhagen survey (gcs). assuming that the galactic orbital evolution of this object is similar to that of stars, we applied a bayesian analysis and used the distribution of stellar velocities, as a function of age, to obtain a probability density function for the age of `oumuamua. we considered two models for the age-velocity dispersion relation (avr): the traditional power law, fitted using data from the gcs, and a model that implements a second power law for younger ages, which we fitted using a sample of 153 open clusters (ocs). we find that the slope of the avr is smaller for ocs than it is for field stars. using these avrs, we constrained an age range of 0.01-1.87 gyr for `oumuamua and characterized a most likely age ranging between 0.20 and 0.45gyr, depending on the model used for the avr. we also estimated the intrinsic uncertainties of the method due to not knowing the exact value of the solar motion and the particularities of 1i/`oumuamua's ejection. | a kinematical age for the interstellar object 1i/`oumuamua |
we present multiepoch infrared photometry and spectroscopy obtained with warm spitzer, subaru, and the stratospheric observatory for infrared astronomy to assess variability for the young (∼20 myr) and dusty debris systems around hd 172555 and hd 113766a. no variations (within 0.5%) were found for the former at either 3.6 or 4.5 μm, while significant nonperiodic variations (peak to peak of ∼10%-15% relative to the primary star) were detected for the latter. relative to the spitzer infrared spectrograph spectra taken in 2004, multiepoch mid-infrared spectra reveal no change in either the shape of the prominent 10 μm solid-state features or the overall flux levels (no more than 20%) for both systems, corroborating the fact that the population of submicron-size grains that produce the pronounced solid-state features is stable over a decadal timescale. we suggest that these submicron-size grains were initially generated in an optically thick clump of debris of millimeter-size vapor condensates resulting from a recent violent impact between large asteroidal or planetary bodies. because of the shielding from the stellar photons provided by this clump, intense collisions led to an overproduction of fine grains that would otherwise be ejected from the system by radiation pressure. as the clump is sheared by its orbital motion and becomes optically thin, a population of very fine grains could remain in stable orbits until poynting-robertson drag slowly spirals them into the star. we further suggest that the 3-5 μm disk variation around hd 113766a is consistent with a clump/arc of such fine grains on a modestly eccentric orbit in its terrestrial zone. | mid-infrared studies of hd 113766 and hd 172555: assessing variability in the terrestrial zone of young exoplanetary systems |
biologically relevant abiotic extraterrestrial soluble organic matter (som) has been widely investigated to study the origin of life and the chemical evolution of protoplanetary disks. synthesis of biologically relevant organics, in particular, seems to require aqueous environments in the early solar system. however, som in primitive meteorites includes numerous chemical species besides the biologically relevant ones, and the reaction mechanisms that comprehensively explain the complex nature of som are unknown. besides, the initial reactants, which formed before asteroid accretion, were uncharacterized. we examined the mass distribution of som extracted from three distinct tagish lake meteorite fragments, which exhibit different degrees of aqueous alteration though they originated from a single asteroid. we report that mass distributions of som in the primordial fragments are well fit by the schulz-zimm (sz) model for the molecular weight distribution patterns found in chain-growth polymerization experiments. also, the distribution patterns diverge further from sz with increasing degrees of aqueous alteration. these observations imply that the complex nature of the primordial som (1) was established before severe alteration on the asteroid, (2) possibly existed before parent-body accretion, and (3) later became simplified on the asteroid. therefore, aqueous reactions on asteroids are not required conditions for cultivating complex som. furthermore, we found that overall h/c ratios of som decrease with increasing aqueous alteration, and the estimate of h loss from the som is 10%-30%. organics seem to be a significant h2 source that may have caused subsequent chemical reactions in the tagish lake meteorite parent body. | aqueous alteration on asteroids simplifies soluble organic matter mixtures |
the zodiacal dust complex, a population of dust and small particles that pervades the solar system, provides important insight into the formation and dynamics of planets, comets, asteroids, and other bodies. we present a new set of data obtained from direct measurements of momentum transfer to a spacecraft from individual particle impacts. this technique is made possible by the extreme precision of the instruments flown on the lisa pathfinder spacecraft, a technology demonstrator for a future space-based gravitational wave observatory. pathfinder employed a technique known as drag-free control that achieved rejection of external disturbances, including particle impacts, using a micropropulsion system. using a simple model of the impacts and knowledge of the control system, we show that it is possible to detect impacts and measure properties such as the transferred momentum, direction of travel, and location of impact on the spacecraft. in this paper, we present the results of a systematic search for impacts during 4348 hr of pathfinder data. we report a total of 54 candidates with transferred momenta ranging from 0.2 to 230 μns. we furthermore make a comparison of these candidates with models of micrometeoroid populations in the inner solar system, including those resulting from jupiter-family comets (jfcs), oort cloud comets, halley-type comets, and asteroids. we find that our measured population is consistent with a population dominated by jfcs, with some evidence for a smaller contribution from halley-type comets, in agreement with consensus models of the zodiacal dust complex in the momentum range sampled by lisa pathfinder. | micrometeoroid events in lisa pathfinder |
through their delivery of water and organics, near-earth objects (neos) played an important role in the emergence of life on our planet. however, they also pose a hazard to the earth, as asteroid impacts could significantly affect our civilization. potentially hazardous asteroids (phas) are those that, in principle, could possibly impact the earth within the next century, producing major damage. about 1600 phas are currently known, from an estimated population of 4700 ± 1450. however, a comprehensive characterization of the pha physical properties is still missing. here we present spectroscopic observations of 14 phas, which we have used to derive their taxonomy, meteorite analogs, and mineralogy. combining our results with the literature, we investigated how phas are distributed as a function of their dynamical and physical properties. in general, the “carbonaceous” phas seem to be particularly threatening, because of their high porosity (limiting the effectiveness of the main deflection techniques that could be used in space) and low inclination and minimum orbit intersection distance (moid) with the earth (favoring more frequent close approaches). v-type phas also present low moid values, which can produce frequent close approaches (as confirmed by the recent discovery of a limited space weathering on their surfaces). we also identified those specific objects that deserve particular attention because of their extreme rotational properties, internal strength, or possible cometary nature. for phas and neos in general, we identified a possible anti-correlation between the elongation and the rotational period, in the range of prot ≈ 5-80 hr. this would be compatible with the behavior of gravity-dominated aggregates in rotational equilibrium. for periods ≳80-90 hr, such a trend stops, possibly under the influence of the yorp effect and collisions. however, the statistics is very low, and further observational and theoretical work is required to characterize such slow rotators. | grasping the nature of potentially hazardous asteroids |
we apply our novel markov chain monte carlo (mcmc)-based algorithm for asteroid mass estimation to asteroid (16) psyche, the target of nasa's eponymous psyche mission, based on close encounters with 10 different asteroids, and obtain a mass of (1.117 ± 0.039) × 10-11 m⊙. we ensure that our method works as expected by applying it to asteroids (1) ceres and (4) vesta, and find that the results are in agreement with the very accurate mass estimates for these bodies obtained by the dawn mission. we then combine our mass estimate for psyche with the most recent volume estimate to compute the corresponding bulk density as (3.88 ± 0.25) g cm-3. the estimated bulk density rules out the possibility of psyche being an exposed, solid iron core of a protoplanet, but is fully consistent with the recent hypothesis that ferrovolcanism would have occurred on psyche. | mass and density of asteroid (16) psyche |
context. spectrophotometry data of asteroids obtained in the 1980s showed that there are large variations in their near-ultraviolet (nuv) reflectance spectra. reflectance spectra at nuv wavelengths are important because they help detect the presence of hydrated minerals and organics on the asteroid surfaces. however, the nuv wavelength region has not been fully investigated yet using spectroscopic data.aims: the aim of our study is to obtain the near-ultraviolet to visible (nuv-vis, 0.35-0.95 μm) reflectance spectra of primitive asteroids with a focus on members of the themis and polana-eulalia complex families. this characterization allows us to discuss the origin of two recent sample return mission target asteroids, (162173) ryugu and (101955) bennu.methods: we obtain low-resolution visible spectra of target asteroids down to 0.35 μm using the telescopes located at the roque de los muchachos observatory (la palma, spain) and revisit spectroscopic data that have already been published. using new spectroscopic and already published spectrophotometric and spectroscopic data, we study the characteristics of the nuv-vis reflectance spectra of primitive asteroids, focusing on data of the themis family and the polana-eulalia family complex. finally, we compare the nuv characteristics of these families with (162173) ryugu and (101955) bennu. in this work, we also study systematic effects due to the use of the five commonly used stars in landolt's catalog as solar analogs to obtain the asteroid reflectance in the nuv wavelength range. we compare the spectra of five g-stars in landolt's catalog with the spectrum of the well-studied solar analog hyades 64, also observed on the same nights.results: we find that many widely used landolt's g-type stars are not solar analogs in the nuv wavelength spectral region and thus are not suitable for obtaining the reflectance spectra of asteroids. we also find that, even though the themis family and the polanaeulalia family complex show a similar blueness at visible wavelengths, the nuv absorption of the themis family is much deeper than that of the polana-eulalia family complex. we did not find significant differences between the new polana and eulalia families in terms of the nuv-vis slope. (162173) ryugu's and (101955) bennu's spectral characteristics in the nuv-vis overlaps with those of the polana-eulalia family complex which implies that it is the most likely origin of these two near-earth asteroids. | near-ultraviolet to visible spectroscopy of the themis and polana-eulalia complex families |
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