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the distribution of the short-lived radionuclide 26al in the early solar system remains a major topic of investigation in planetary science. thousands of analyses are now available but grossite-bearing ca-, al-rich inclusions (cais) are underrepresented in the database. recently found grossite-bearing inclusions in co3 chondrites provide an opportunity to address this matter. we determined the oxygen and magnesium isotopic compositions of individual phases of 10 grossite-bearing cais in the dominion range (dom) 08006 (co3.0) and dom 08004 (co3.1) chondrites. all minerals in dom 08006 cais as well as hibonite, spinel, and pyroxene in dom 08004 are uniformly 16o-rich (δ17o = -25 to -20‰) but grossite and melilite in dom 08004 cais are not; δ17o of grossite and melilite range from -11 to 0‰ and from -23 up to 0‰, respectively. even within this small suite, in the two chondrites a bimodal distribution of the inferred initial 26al/27al ratios (26al/27al)0 is seen, with four having (26al/27al)0 ≤1.1 × 10-5 and six having (26al/27al)0 ≥3.7 × 10-5. five of the 26al-rich cais have (26al/27al)0 within error of 4.5 × 10-5; these values can probably be considered indistinguishable from the "canonical" value of 5.2 × 10-5 given the uncertainty in the relative sensitivity factor for grossite measured by secondary ion mass spectrometry. we infer that the 26al-poor cais probably formed before the radionuclide was fully mixed into the solar nebula. all minerals in the dom 08006 cais, as well as spinel, hibonite, and al-diopside in the dom 08004 cais retained their initial oxygen isotopic compositions, indicating homogeneity of oxygen isotopic compositions in the nebular region where the co grossite-bearing cais originated. oxygen isotopic heterogeneity in cais from dom 08004 resulted from exchange between the initially 16o-rich (δ17o -24‰) melilite and grossite and 16o-poor (δ17o 0‰) fluid during hydrothermal alteration on the co chondrite parent body; hibonite, spinel, and al-diopside avoided oxygen isotopic exchange during the alteration. grossite and melilite that underwent oxygen isotopic exchange avoided redistribution of radiogenic 26mg and preserved undisturbed internal al-mg isochrons. the δ17o of the fluid can be inferred from o-isotopic compositions of aqueously formed fayalite and magnetite that precipitated from the fluid on the co parent asteroid. this and previous studies suggest that o-isotope exchange during fluid-rock interaction affected most cais in co ≥3.1 chondrites. | oxygen and al-mg isotopic compositions of grossite-bearing refractory inclusions from co3 chondrites |
the almahata sitta strewn field is dominated by ureilites, but contains a large fraction of chondritic fragments of various types. we analyzed stable isotopes of he, ne, ar, kr, and xe, and the cosmogenic radionuclides 10be, 26al, and 36cl in six chondritic almahata sitta fragments (el6 breccia, el6, el3-5, cb, ll4/5, r-like). the cosmic-ray exposure (cre) ages of five of the six samples have an average of 19.2 ± 3.3 ma, close to the average of 19.5 ± 2.5 ma for four ureilites. the cosmogenic radionuclide concentrations in the chondrites indicate a preatmospheric size consistent with almahata sitta. this corroborates that almahata sitta chondrite samples were part of the same asteroid as the ureilites. however, ms-179 has a lower cre age of 11.0 ± 1.4 ma. further analysis of short-lived radionuclides in fragment ms-179 showed that it fell around the same time, and from an object of similar size as almahata sitta, making it almost certain that ms-179 is an almahata sitta fragment. instead, its low cre age could be due to gas loss, chemical heterogeneity that may have led to an erroneous 21ne production-rate, or, perhaps most likely, ms-179 could represent the true 4π exposure age of almahata sitta (or an upper limit thereof), while all other samples analyzed so far experienced exposure on the parent body of similar lengths. finally, ms-179 had an extraordinarily high activity of neutron-capture 36cl, 600 dpm kg-1, the highest activity observed in any meteorite to date, related to a high abundance of the cl-bearing mineral lawrencite. | cosmic-ray exposure ages of six chondritic almahata sitta fragments |
the asteroid impact & deflection assessment (aida) mission is planning to visit the didymos binary system in 2022 in order to perform the first demonstration ever of the kinetic impact technique. binary asteroids are an ideal target for this since the deflection of the secondary body can be accurately measured by a satellite orbiting in the system. however, these binaries offer an extremely rich dynamical environment whose accurate investigation through analytical approaches is challenging at best and requires a significant number of restrictive assumptions. for this reason, a numerical investigation of the dynamical environment in the vicinity of the didymos system is offered in this paper. after computing various families of periodic orbits, their robustness is assessed in a high-fidelity environment consisting of the perturbed restricted full three-body problem. the results of this study suggest that several nominally stable trajectories, including the triangular libration points, should not be considered as safe as a state vector perturbation may cause the spacecraft to drift from the nominal orbit and possibly impact one of the primary bodies within a few days. nonetheless, there exist two safe solutions, namely terminator and interior retrograde orbits. the first one is adequate for observation purposes of the entire system and for communications. the second one is more suitable to perform close investigations of the primary body. | numerical investigation of the dynamical environment of 65803 didymos |
granvik et al. reported an absence of asteroids on orbits with perihelia near the sun that they attribute to the "supercatastrophic disruption" of these bodies. here we investigate whether there is evidence for this process among other bodies with similarly low perihelia: near-earth asteroids, solar and heliospheric observatory (soho) comets, and meter- and millimeter-sized meteoroids. we determine that no known near-earth asteroids have past (last 104 yr) histories residing significantly inside the granvik et al. limit, indirectly supporting the disruption hypothesis. the exception is asteroid (467372) 2004 lg, which spent 2500 yr within this limit and thus presents a challenge to that theory. phaethon has a perihelion distance hovering just above the limit and may be undergoing slow disruption, which may be the source of its dust complex. we find that the rate at which ungrouped soho comets are observed is consistent with expected rates for the injection of small (25 m) class asteroids into the near-sun region and suggest that this fraction of the soho-observed comet population may in fact be asteroidal in origin. we also find that there is an absence of meter-sized bodies with near-sun perihelia but an excess of millimeter-sized meteoroids. this implies that if near-sun asteroids disrupt, they do not simply fragment into meter-sized chunks but ultimately disintegrate into millimeter-sized particles. we propose that the disruption of near-sun asteroids, as well as the anomalous brightening and destruction processes that affect soho comets, occur through meteoroid erosion, that is, the removal of material through impacts by high-speed near-sun meteoroids. | supercatastrophic disruption of asteroids in the context of soho comet, fireball, and meteor observations |
the strategy of detecting physiological signals and body movements using fabric-based pressure sensors offers the opportunity to unobtrusively collect multimodal health metrics using loose-fitting, familiar garments in natural environments. (a. kiaghadi, s. z. homayounfar, j. gummeson, t. andrew, and d. ganesan, proc. acm interact. mob. wearable ubiquitous technol., 3, 1-29 (2019)). however, many sensing scenarios, such as sleep and posture monitoring, involve an added static pressure from exerted body weight, which overpowers weaker pressure signals originating from heartbeats, respiration and pulse and phonation. here, we introduce an all-fabric piezoionic pressure sensor (pression) that, on account of its ionic conductivity, functions over a wide range of static and dynamic applied pressures (from subtle ballistic heartbeats and pulse waveforms, to larger-scale body movements). this piezoionic sensor also maintains its pressure responsivity in the presence of an added background pressure and upon integration into loose-fitting garments. the broad ability of pression to record a wide variety of physiological signals in realistic environments was confirmed by acquiring heartbeat, pulse, joint motion, phonation and step data from different body locations. pression's sensitivity, along with its low-cost fabrication process, qualifies it as a uniquely useful sensing element in wearable health monitoring systems. | pression: an all-fabric piezoionic pressure sensor for extracting physiological metrics in both static and dynamic contexts |
impact-induced seismic waves are supposed to cause movements of regolith particles, resulting in modifications of asteroidal surfaces. the imparted seismic energy is thus a key parameter to determining the scale and magnitude of this seismic shaking process. it is important to study the propagation velocity, attenuation rate, and vibration period of the impact-induced seismic wave to estimate the seismic energy. hence, we conducted impact cratering experiments at kobe university using a 200-μm glass beads target to simulate a regolith layer, and measured the impact-induced seismic wave using three accelerometers set on the target surface at differences ranging from 3.2 to 12.7 cm. the target was impacted with three kinds of projectiles at ∼100 m s-1 using a one-stage gas gun. the propagation velocity of the seismic wave in the beads target was 108.9 m s-1, and the maximum acceleration, gmax, in the unit of m s-2, measured by each accelerometer showed good correlation with the distance from the impact point normalized by the crater radius, x/r, irrespective of projectile type. they also were fitted by one power-law equation, gmax = 102.19 (x/r)-2.21. the half period of the first peak of the measured seismic waves was ∼0.72 ms, and this duration was almost consistent with the penetration time of each projectile into the target. according to these measurements, we estimated the impact seismic efficiency factor, that is, the ratio of seismic energy to kinetic energy of the projectile, to be almost constant, 5.7 × 10-4 inside the crater rim, while it exponentially decreased with distance from the impact point outside the crater rim. at a distance quadruple of the crater radius, the efficiency factors were 4.4 × 10-5 for polycarbonate projectile and 9.5 × 10-5 for alumina and stainless steel projectiles. | experimental study on impact-induced seismic wave propagation through granular materials |
laboratory impact experiments have found that impact fragments tend to be elongated. their shapes, as defined by axes a, b and c, these being the maximum dimensions of the fragment in three mutually orthogonal planes (a ⩾ b ⩾ c), are distributed around mean values of the axial ratios b/a ∼ 0.7 and c/a ∼ 0.5. this corresponds to a:b:c in the simple proportion 2:√2:1. the shape distributions of some boulders on asteroid eros, the small- and fast-rotating asteroids (diameter <200 m and rotation period <1 h), and asteroids in young families, are similar to those of laboratory fragments created in catastrophic disruptions. catastrophic disruption is, however, a process that is different from impact cratering. in order to systematically investigate the shapes of fragments in the range from impact cratering to catastrophic disruption, impact experiments for basalt targets 5-15 cm in size were performed. a total of 28 impact experiments were carried out by firing a spherical nylon projectile (diameter 7.14 mm) perpendicularly into the target surface at velocities of 1.60-7.13 km/s. more than 12,700 fragments with b ⩾ 4 mm generated in the impact experiments were measured. we found that the mean value of c/a in each impact decreases with decreasing impact energy per unit target mass. for instance, the mean value of c/a in an impact cratering event is nearly 0.2, which is considerably smaller than c/a in a catastrophic disruption (∼0.5). the data presented here can provide important evidence to interpret the shapes of asteroids and boulders on asteroid surfaces, and can constrain current interpretations of asteroid formation. as an example, by applying our experimental results to the boulder shapes on asteroid itokawa's surface, we can infer that itokawa's parent body must have experienced a catastrophic disruption. | fragment shapes in impact experiments ranging from cratering to catastrophic disruption |
the recently discovered first interstellar object 1i/2017 u1 (`oumuamua) has brightness that varies by a factor of 10, a range greater than that of any solar system asteroid, a spectrum characteristic of type d asteroids, and no evidence of evaporating volatiles, contrary to expectation for exo-oort clouds. `oumuamua is possibly the first example of the proposed `jurads', objects depleted in volatiles and ejected from planetary systems during the post-main sequence evolution of their parent stars. i suggest that heating by the star's giant stage fluidized a precursor object as well as driving off any volatiles, causing it to assume the jacobi ellipsoidal shape of a self-gravitating incompressible liquid. the collision that produced the inferred tumbling motion may have occurred thousands of years after the formation of 1i/2017 u1 `oumuamua. jacobi ellipsoids have a unique relation among rotation rate, density and axial ratio. the inferred axial ratio ⪆5 suggests a lower bound on the density of 1.6 g cm-3, apparently excluding an icy interior unless it is almost entirely frozen co2. `oumuamua may be related to accreting objects that pollute white dwarf atmospheres and that may make soft gamma repeaters. | why is interstellar object 1i/2017 u1 (`oumuamua) rocky, tumbling and possibly very prolate? |
escalating observations of exo-minor planets and their destroyed remnants both passing through the solar system and within white dwarf planetary systems motivate an understanding of the orbital history and fate of exo-kuiper belts and planetesimal discs. here, we explore how the structure of a 40-1000 au annulus of planetesimals orbiting inside of a solar system analogue that is itself initially embedded within a stellar cluster environment varies as the star evolves through all of its stellar phases. we attempt this computationally challenging link in four parts: (1) by performing stellar cluster simulations lasting 100 myr, (2) by making assumptions about the subsequent quiescent 11 gyr main-sequence evolution, (3) by performing simulations throughout the giant branch phases of evolution, and (4) by making assumptions about the belt's evolution during the white dwarf phase. throughout these stages, we estimate the planetesimals' gravitational responses to analogues of the four solar system giant planets, as well as to collisional grinding, galactic tides, stellar flybys, and stellar radiation. we find that the imprint of stellar cluster dynamics on the architecture of ≳100 km-sized exo-kuiper belt planetesimals is retained throughout all phases of stellar evolution unless violent gravitational instabilities are triggered either (1) amongst the giant planets, or (2) due to a close (≪103 au) stellar flyby. in the absence of these instabilities, these minor planets simply double their semimajor axis while retaining their primordial post-cluster eccentricity and inclination distributions, with implications for the free-floating planetesimal population and metal-polluted white dwarfs. | linking the formation and fate of exo-kuiper belts within solar system analogues |
recent advances in cubesats technology are leading the transition from purely education tools to actual scientific missions. the small volumes and masses, the versatile purpose, as well as the fast development time associated with a potential high return-to-cost ratio are at the origin of the increasing number of new mission proposals, also beyond low earth orbit (leo). the purpose of this study is to assess the cubesats ability to complement an interplanetary scientific mission. the proposed aida (asteroid impact and deflection assessment) mission, an esa/nasa joint effort to demonstrate the kinetic impact technique to change the motion of an asteroid in space, has been selected as case study, having a mission context particularly suitable in showing cubesats supporting capabilities. the feasibility study of a mission involving the use of cubesats as secondaries for technology demonstration and science purposes was performed. mission objectives and requirements were defined, followed by the development of concepts of operations and mission architectures proposals. eventually, multiple trade-off tools were adopted to define the proposed mission baseline, which involves the deployment of two 3u cubesats performing a detachment to achieve the final configuration of one 2u and four 1u cubesats. the scientific campaign conducted by the cubesats includes gravitational and magnetic field mapping, on-surface chemical-physical measurements via multiple wide chip-size-sensor nets deployed from orbit, on-surface seismic measurements via landing of the 2u cubesat, direct observation of the impact from multiple viewpoints and evaluation of the asteroid's orbit deflection due to the impact. the mission proposed involves also some important technological demonstrators. the s-ieps (scalable-ion electrospray propulsion system) has been considered as propulsion system, while a potential landing system has been proposed to achieve the soft touchdown of the 2u cubesat. finally, an inter-satellite communication link via laser has been included as main communication system. the proposed mission baseline has shown that cubesats can be successfully integrated as multi-platform systems to provide useful support to interplanetary missions. this solution may enable the capability to acquire more detailed information with the possibility to combine them to obtain better results with respect to single-platform systems. the proposed mission concept represents a valuable low-cost piggyback solution adaptable to several mission contexts, with a potential high return and a remarkable attitude for the implementation and testing of new technologies and operations. in this context, this study provides a useful framework for the design and development of interplanetary cubesats missions. | interplanetary cubesats for asteroid exploration: mission analysis and design |
we present evidence, via a large survey of 191 new spectra along with previously published spectra, of a divide in the 3 μm spectral properties of the low-albedo asteroid population. one group ("sharp types," or sts, with band centers <3 μm) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group ("not sharp types," or nsts, with bands centered >3 μm) is not represented in the meteorite literature but is as abundant as the sts among large objects. both groups are present in most low-albedo asteroid taxonomic classes, and, except in limited cases, taxonomic classifications based on 0.5-2.5 μm data alone cannot predict whether an asteroid is an st or nst. statistical tests show that the sts and nsts differ in average band depth, semimajor axis, and perihelion at confidence levels ≥98% while not showing significant differences in albedo. we also show that many nsts have a 3 μm absorption band shape like comet 67p and likely represent an important small-body composition throughout the solar system. a simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the nst group accreting h2o and nh3 and the st group only accreting h2o, with subsequent thermal and chemical evolution resulting in the minerals seen today. such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of d-class asteroids found today. | the nature of low-albedo small bodies from 3 μm spectroscopy: one group that formed within the ammonia snow line and one that formed beyond it |
in recent years, several small basaltic v-type asteroids have been identified all around the main belt. most of them are members of the vesta dynamical family, but an increasingly large number appear to have no link with it. the question that arises is whether all these basaltic objects do indeed come from vesta. to find the answer to the above questioning, we decided to perform a statistical analysis of the spectroscopic and mineralogical properties of a large sample of v-types, with the objective to highlight similarities and differences among them, and shed light on their unique, or not, origin. the analysis was performed using 190 visible and near-infrared spectra from the literature for 117 v-type asteroids. the asteroids were grouped according to their dynamical properties and their computed spectral parameters compared. comparison was also performed with spectral parameters of a sample of hed meteorites and data of the surface of vesta taken by the vir instrument on board of the dawn spacecraft. our analysis shows that although most of the v-type asteroids in the inner main belt do have a surface composition compatible with an origin from vesta, this seem not to be the case for v-types in the middle and outer main belt. | spectral characterization of v-type asteroids - ii. a statistical analysis |
comet p/2019 ld2 has orbital elements currently resembling those of a jupiter trojan, and therefore superficially appears to represent a unique opportunity to study the volatile content and active behavior of a member of this population for the first time. however, numerical integrations show that it was previously a centaur before reaching its current jupiter trojan-like orbit in 2018 july, and is expected to return to being a centaur in 2028 february, before eventually becoming a jupiter-family comet in 2063 february. the case of p/2019 ld2 highlights the need for mechanisms to quickly and reliably dynamically classify small solar system bodies discovered in current and upcoming wide-field surveys. | the transient jupiter trojan-like orbit of p/2019 ld2 (atlas) |
returning humans to the moon presents an unprecedented opportunity to determine the origin of volatiles stored in the permanently shaded regions (psrs), which trace the history of lunar volcanic activity, solar wind surface chemistry, and volatile delivery to the earth and moon through impacts of comets, asteroids, and micrometeoroids. so far, the source of the volatiles sampled by the lunar crater observation and sensing satellite (lcross) plume has remained undetermined. we show here that the source could not be volcanic outgassing and the composition is best explained by cometary impacts. ruling out a volcanic source means that volatiles in the top 1-3 meters of the cabeus psr regolith may be younger than the latest volcanic outgassing event (~1 billion years ago; gya). | exogenic origin for the volatiles sampled by the lunar crater observation and sensing satellite impact |
the deflection of potentially dangerous asteroids has been treated with great intensity and has gained more and more attention in scientific research. different techniques are developed over the years. among these techniques, we found the kinetic impact deflection technique to be the most viable at the moment. in this work we address the kinetic impact deflection technique, but in a scenario where we have a short time to deflect an asteroid that will collide with earth. for this, we also use a maneuver similar to a powered gravity-assisted maneuver with earth in a previous passage to change the trajectory of the asteroid to avoid the collision. we apply this technique in three scenarios: (i) impulse before the close encounter, (ii) impulse during the close encounter, and (iii) impulse after the close encounter. we observe that some trajectories are symmetric with respect to the line sun–earth, and others are asymmetric. we show that, using this technique, it is possible to change the trajectory of the asteroid, even in a short period, to avoid the collision without using a large variation of velocity in the orbit of the asteroid. | deflecting an asteroid on a collision course with earth using a powered swing-by maneuver |
this study explores the possibility of improving the impact of the advanced himawari imager (ahi) clear-sky radiance data assimilation (da), focusing on cloud detection. first, the performance of the "clear-channel" detection scheme of the minimum residual (mr) method embedded in the gridpoint statistical interpolation (gsi) da system is compared with the performances of the clouds from advanced very high resolution radiometer extended (clavr-x) cloud processing system and the moderate resolution imaging spectroradiometer (modis) cloud-product-generating algorithm. the mr scheme does not reliably identify optically thin clouds along cloud edges. the mr-estimated cloud-top pressures are often too high for upper-level clouds, rendering some cloud-contaminated channels falsely clear. an infrared-only ahi cloud mask (acm) algorithm is added to the mr scheme to perform a so-called double cloud detection (dcd). the dcd scheme adds nine acm tests for selecting clear pixels and two thin cloud tests for rejecting pixels affected by upper-level clouds. for a 1-month period, we show the positive impacts of assimilating ahi infrared channels on short-term forecasts of temperature and humidity using the dcd scheme rather than the mr scheme. improvements in the dcd experiment extend more vertically, horizontally, and temporally than those in the mr experiment during the 48-hr forecasting time. in terms of daily variations in forecasting performance, the dcd experiment consistently improves while the mr experiment fluctuates between improvement and degradation. such improvements come from an elimination of those data having negative observation-minus-background values of large magnitudes due to cloud contamination, which causes positive biases in humidity analyses. | improved himawari-8/ahi radiance data assimilation with a double cloud detection scheme |
an electric solar wind sail uses the natural solar wind stream to produce low but continuous thrust by interacting with a number of long thin charged tethers. it allows a spacecraft to generate a thrust without consuming any reaction mass. the aim of this paper is to investigate the use of a spacecraft with such a propulsion system to deflect an asteroid with a high relative velocity away from an earth collision trajectory. to this end, we formulate a simulation model for the electric solar wind sail. by summing thrust vectors exerted on each tether, a dynamic model which gives the relation between the thrust and sail attitude is proposed. orbital maneuvering by fixing the sail's attitude and changing tether voltage is considered. a detailed study of the deflection of fictional asteroids, which are assumed to be identified 15 years before earth impact, is also presented. assuming a spacecraft characteristic acceleration of 0.5 mm/s 2, and a projectile mass of 1,000 kg, we show that the trajectory of asteroids with one million tons can be changed enough to avoid a collision with the earth. finally, the effectiveness of using this method of propulsion in an asteroid deflection mission is evaluated in comparison with using flat photonic solar sails. | electric solar wind sail kinetic energy impactor for asteroid deflection missions |
space weathering is one of the most common surface process occurring on atmosphere-free bodies such as asteroids and the moon. it is caused mainly by solar wind irradiation and the impact of micrometeoroids. in order to simulate space weathering effects, in particular those produced by hypervelocity impacts, we produced microcraters via ultra-short (∼100 fs) laser irradiation of crystallographically oriented slices of forsterite-rich (fo94.7) olivine. the main advantages of the application of a femtosecond laser radiation to reproduce the space weathering effects are (1) the high peak irradiance (1015 w cm-2), which generates the propagation of the shock wave at the nanosecond timescale (i.e., timescale of the micrometeoroid impacts); (2) the rapid transfer of energy to the target material, which avoids the interaction of laser light with the developing vapor plume; (3) a small laser beam, which allows the effects of a single impact to be simulated. the results of our spectroscopic and electron microscopic investigation validate this approach: the samples show strong darkening and reddening of the reflectance spectra and structural damages similar to the natural microcraters found on regolith grains of the moon and asteroid 25143 itokawa. detailed investigations of several microcrater cross-sections by transmission electron microscopy allowed the detection of shock-induced defect microstructures. from the top to the bottom of the grain, the shock wave causes evaporation, melting, solid-state recrystallization, misorientation, fracturing, and the propagation of dislocations with burgers vectors parallel to [001]. the formation of a short-lived vapor plume causes the kinetic fractionation of the gas and the preferential loss of lighter elements, mostly magnesium and oxygen. the high temperatures within the melt layer and the kinetic loss of oxygen promote the thermal reduction of iron and nickel, which leads to the formation of metallic nanoparticles (npfe0). the final stage of the microcrater formation is the cooling of the melt layer that results in its partial crystallization and the formation of olivine crystals with a palisade-like texture. | femtosecond laser irradiation of olivine single crystals: experimental simulation of space weathering |
the discovery of olivine on vesta's surface by the vir imaging spectrometer onboard the dawn space mission has forced us to reconsider our views of vestan petrogenetic models. olivines were expected to be present in the interior of vesta: in the mantle of a vertically layered body as invoked by the magma ocean models, or at the base (or within) the mantle-crust boundary as proposed by fractionation models. olivines have been detected by vir-dawn in two wide areas near arruntia and bellicia, regions located in the northern hemisphere. interestingly, these olivine-rich terrains are far from the rheasilvia and the more ancient veneneia basins, which are expected to have excavated the crust down to reach the mantle. in this work we present our attempts to identify other undetected olivine rich areas on vesta by using spectral parameters sensitive to olivine such as the band area ratio (bar) and other specific parameters created for the detection of olivines on mars (forsterite, fayalite and a generic olivine index). as a preliminary step we calibrated these parameters by means of vis-ir spectra of different hed meteorite samples: behaviors versus sample grain size and albedo were analyzed and discussed. we selected the bar and the forsterite index as the best parameters that can be used on vesta. a cross-correlation analysis has been applied in order to detect olivine signature on the vir hyperspectral cubes. these detections have then been confirmed by an anti-correlation analysis between the bar and one of the olivine parameters, independent of the first method applied. in agreement with the recent discovery, arruntia and bellicia were found to be as the most olivine-rich areas, i.e. where the parameter values are strongest. in addition we detected 6 new regions, all but one located in the vesta north hemisphere. this result confirms again that the old petrogenetic models cannot be straightforwardly applied to vesta and should be reshaped in the view of these new detections. an alternative and very recent option can be represented by the model according to which surface "eruption" of material from the mantle, including olivine can reach the surface of vesta. | detection of new olivine-rich locations on vesta |
evidence of marine target impacts, binary impact craters, or impact clusters are rare on earth. seismic reflection data from the guinea plateau, west africa, reveal a ≥8.5-km-wide structure buried below ~300 to 400 m of paleogene sediment with characteristics consistent with a complex impact crater. these include an elevated rim above a terraced crater floor, a pronounced central uplift, and extensive subsurface deformation. numerical simulations of crater formation indicate a marine target (~800-m water depth) impact of a ≥400-m asteroid, resulting in a train of large tsunami waves and the potential release of substantial quantities of greenhouse gases from shallow buried black shale deposits. our stratigraphic framework suggests that the crater formed at or near the cretaceous-paleogene boundary (~66 million years ago), approximately the same age as the chicxulub impact crater. we hypothesize that this formed as part of a closely timed impact cluster or by breakup of a common parent asteroid. seismic data reveal a candidate impact crater offshore west africa that formed close in time to the k-pg extinction event. | the nadir crater offshore west africa: a candidate cretaceous-paleogene impact structure |
the conventional least-squares asteroid mass determination algorithm allows us to solve for the mass of a large subject asteroid that is perturbing the trajectory of a smaller test asteroid. however, this algorithm is necessarily a first approximation, ignoring the possibility that the subject asteroid may itself be perturbed by the test asteroid, or that the encounter’s precise geometry may be entangled with encounters involving other asteroids. after reviewing the conventional algorithm, we use it to calculate the masses of 30 main-belt asteroids. compared to our previous results, we find new mass estimates for eight asteroids (11 parthenope, 27 euterpe, 51 neimausa, 76 freia, 121 hermione, 324 bamberga, 476 hedwig, and 532 herculina) and significantly more precise estimates for six others (2 pallas, 3 juno, 4 vesta, 9 metis, 16 psyche, and 88 thisbe). however, we also find that the conventional algorithm yields questionable results in several gravitationally coupled cases. to address such cases, we describe a new algorithm that allows the epoch state vectors of the subject asteroids to be included as solve-for parameters, allowing for the simultaneous solution of the masses and epoch state vectors of multiple subject and test asteroids. we then apply this algorithm to the same 30 main-belt asteroids and conclude that mass determinations resulting from current and future high-precision astrometric sources (such as gaia) should conduct a thorough search for possible gravitational couplings and account for their effects. | simultaneous mass determination for gravitationally coupled asteroids |
a consequence of the assumptions of the infinitesimal model, one of the most important theoretical foundations of quantitative genetics, is that phenotypic traits are predicted to be most often normally distributed (so‑called gaussian traits). but phenotypic traits, especially those interesting for evolutionary biology, might be shaped according to very diverse distributions. here, i show how quantitative genetics tools have been extended to account for a wider diversity of phenotypic traits using first the threshold model and then more recently using generalized linear mixed models. i explore the assumptions behind these models and how they can be used to study the genetics of non‑gaussian complex traits. i also comment on three recent methodological advances in quantitative genetics that widen our ability to study new kinds of traits: the use of "modular" hierarchical modeling (e.g., to study survival in the context of capture–recapture approaches for wild populations); the use of aster models to study a set of traits with conditional relationships (e.g., life‑history traits); and, finally, the study of high‑dimensional traits, such as gene expression. | quantitative genetic methods depending on the nature of the phenotypic trait |
space weathering effects on the rocky s-class asteroids are well understood. however, on the low-albedo c-complex asteroids, such as spacecraft targets bennu and ryugu, the situation is more complicated, especially due to a lack of spectral features throughout the visible-near infrared spectral region. here we show, through a combination of observational data and laboratory data of carbonaceous chondrites, phyllosilicates, and mixtures, that the uv-visible spectral region is a diagnostic regime for studying space weathering effects on c-complex asteroids. we show that space-weathering-produced opaque constituents, such as graphitized carbons, darken mixtures with phyllosilicates and produce a bluing the uv-visible spectrum, consistent with what is seen on the asteroids compared with carbonaceous chondrites. furthermore, we demonstrate that the uv upturns in the spectra of bennu and ryugu are consistent with the presence of graphitized carbon on those surfaces, the result of surface processing. | c-complex asteroids: uv-visible spectral characteristics and implications for space weathering effects |
the phase function of the dust coma of comet 67p has been determined from rosetta/osiris images. this function shows a deep minimum at phase angles near 100°, and a strong backscattering enhancement. these two properties cannot be reproduced by regular models of cometary dust, most of them based on wavelength-sized and randomly oriented aggregate particles. we show, however, that an ensemble of oriented elongated particles of a wide variety of aspect ratios, with radii r ≳ 10 μm, and whose long axes are perpendicular to the direction of the solar radiation, are capable of reproducing the observed phase function. these particles must be absorbing, with an imaginary part of the refractive index of about 0.1 to match the expected geometric albedo, and with porosity in the 60%-70% range. | models of rosetta/osiris 67p dust coma phase function |
the dusty regolith covering the surfaces of asteroids and planetary satellites differs in size, shape, and composition from terrestrial soil particles and is subject to environmental conditions very different from those found on earth. this regolith evolves in a low ambient pressure and low-gravity environment. its response to low-velocity impacts, such as those that may accompany human and robotic exploration activities, may be completely different than what is encountered on earth. experimental studies of the response of planetary regolith in the relevant environmental conditions are thus necessary to facilitate future solar system exploration activities.we combined the results and provided new data analysis elements for a series of impact experiments into simulated planetary regolith in low-gravity conditions using two experimental setups and a range of microgravity platforms. the physics of regolith impacts in microgravity experiment (prime) flew on several parabolic aircraft flights, enabling the recording of impacts into granular materials at speeds of ∼ 4-230 cm/s. the collisions into dust experiment (collide) is conceptually close to the prime setup. it flew on the space shuttle in 1998 and 2001 and more recently on the blue origin new shepard rocket, recording impacts into simulated regolith at speeds between 1 and 120 cm/s.results of these experimental campaigns found that there is a significant change in the regolith behavior with the gravity environment. in a 10 -2 g environment (with g being the gravity acceleration at the surface of the earth), only embedding of the impactor was observed and ejecta production was produced for most impacts at > 20 cm/s. once at microgravity levels (<10-4 g), the lowest impact energies also produced impactor rebound. in these microgravity conditions, ejecta started to be produced for impacts at > 10 cm/s. the measured ejecta speeds were somewhat lower than the ones measured at reduced-gravity levels, but the ejected masses were higher. in general, the mean ejecta velocity shows a power-law dependence on the impact energy with an index of ∼ 0.5. when projectile rebound occurred, we observed that its coefficients of restitution on the bed of regolith simulant decrease by a factor of 10 with increasing impact speeds from ∼ 5 up to 100 cm/s. we could also observe an increased cohesion between the jsc-1 grains compared to the quartz sand targets. | regolith behavior under asteroid-level gravity conditions: low-velocity impact experiments |
we report on a kepler spacecraft survey during the k2 mission to characterize the rotational properties of 56 trojan asteroids in the l4 cloud. more than one rotational period was observed for 51 of these targets, allowing for well constrained lightcurve rotation periods and amplitudes, five of which are found to be in conflict with previously published values. we find ∼10% of objects have rotational periods longer than 100 hr, an excess of slow rotators 10 times larger than suggested from the literature. investigation of the rotational frequencies of our kepler sample when combined with high-quality lightcurves in the literature reveals the distribution of rotational frequencies is non-maxwellian even when consideration is given to size-dependent variations in rotational rate. from investigation of lightcurve shapes and amplitudes, we estimate the binary fraction within the trojan population to be ∼6%-36% depending on the methodology utilized to identify binary candidates. | trojan asteroids in the kepler campaign 6 field |
we propose a lsst solar system near-sun survey, to be implemented during twilight hours, that extends the seasonal reach of lsst to its maximum as fresh sky is uncovered at about 50 square degrees per night (1500 sq. deg. per lunation) in the morning eastern sky, and surveyable sky is lost at the same rate to the western evening sky due to the earth's synodic motion. by establishing near-horizon fence post picket lines to the far west and far east we address solar system science use cases (including near earth objects, interior earth objects, potentially hazardous asteroids, earth trojans, near-sun asteroids, sun-grazing comets, and dormant comets) as well as provide the first look and last look that lsst will have at the transient and variable objects within each survey field. this proposed near-sun survey will also maximize the overlap with the field of regard of the proposed neocam spacecraft that will be stationed at the earth's l1 lagrange point and survey near quadrature with the sun. this will allow lsst to incidently follow-up neocam targets and vice-versa (as well as targets from missions such as euclid), and will roughly correspond to the earth's l4 and l5 regions. | a near-sun solar system twilight survey with lsst |
this study focuses on the secular dynamics of orbital motion around asteroids with joint effects of c20 term and solar radiation pressure (srp). with their combined influences, two specific orbits are firstly studied, namely the solar terminator orbit (sto) and the heliotropic orbit. then, the global orbital motion other than the two specific ones is investigated. finally, the influence of the asteroid's orbital eccentricity around the sun on the secular dynamics is discussed. | secular dynamics around small bodies with solar radiation pressure |
extrasolar debris disks are the dust disks found around nearby main sequence stars arising from the breakup of asteroids and comets orbiting the stars. far-ir surveys (e.g., with herschel) showed that ∼20% of stars host detectable dust levels. while dust temperatures suggest a location at 10s of au comparable with our kuiper belt, orders of magnitude more dust is required implying a planetesimal population more comparable with the primordial kuiper belt. high-resolution imaging (e.g., with alma) has mapped the nearest and brightest disks, providing evidence for structures shaped by an underlying planetary system. some of these are analogous to structures in our own kuiper belt (e.g., the hot and cold classical, resonant, scattered disk, and cometary populations), while others have no solar system counterpart. co gas is seen in some debris disks and inferred to originate in the destruction of planetesimals with a similar volatile-rich composition to solar system comets. this chapter reviews our understanding of extrasolar kuiper belts and of how our own kuiper belt compares with those of neighboring stars. | extrasolar kuiper belts |
debris discs around main-sequence stars are belts of planetesimals - asteroids and comets - formed in the protoplanetary discs around young stars. planetesimals comprise both the building blocks of planets around young stars and the source of dusty debris around older stars. imaging observations of dust continuum emission and scattered light reveal the location of these planetesimal belts around their host stars. analysis of debris discs observed at millimetre wavelengths revealed a trend between the discs' radii and the host star luminosities. this trend was tentatively linked to the preferential formation of dust-producing planetesimals near snow lines (specifically co) in the protoplanetary discs around the host stars. here, we perform a homogeneous analysis of 95 debris discs observed at far-infrared wavelengths by the herschel space observatory and fit the obtained distribution of radii and widths as a function of stellar luminosity with a power-law relation. we identify a trend in disc radius as a function of stellar luminosity similar to that identified at millimetre wavelengths, but cannot convincingly recover it from the available data set due to the large uncertainties on disc radius and width inherent in the marginally spatially resolved data, and the bias of smaller discs around more distant stars (which are also the more luminous) being omitted from our analysis. we see a trend in disc temperature as a function of stellar luminosity, consistent with previous findings from similar analyses. | a search for trends in spatially resolved debris discs at far-infrared wavelengths |
we have developed a method for simulating the mesoscale compaction of early solar system solids in low-velocity impact events using the isale shock physics code. chondrules are represented by non-porous disks, placed within a porous matrix. by simulating impacts into bimodal mixtures over a wide range of parameter space (including the chondrule-to-matrix ratio, the matrix porosity and composition, and the impact velocity), we have shown how each of these parameters influences the shock processing of heterogeneous materials. the temperature after shock processing shows a strong dichotomy: matrix temperatures are elevated much higher than the chondrules, which remain largely cold. chondrules can protect some matrix from shock compaction, with shadow regions in the lee side of chondrules exhibiting higher porosity that elsewhere in the matrix. using the results from this mesoscale modeling, we show how the ɛ - α porous-compaction model parameters depend on initial bulk porosity. we also show that the timescale for the temperature dichotomy to equilibrate is highly dependent on the porosity of the matrix after the shock, and will be on the order of seconds for matrix porosities of less than 0.1, and on the order of tens to hundreds of seconds for matrix porosities of ∼0.3-0.5. finally, we have shown that the composition of the post-shock material is able to match the bulk porosity and chondrule-to-matrix ratios of meteorite groups such as carbonaceous chondrites and unequilibrated ordinary chondrites. | mesoscale modeling of impact compaction of primitive solar system solids |
minor bodies trapped in 1:1 co-orbital resonances with a host planet could be relevant to explain the origin of captured satellites. among the giant planets, uranus has one of the smallest known populations of co-orbitals, three objects, and all of them are short-lived. asteroid 2015 db216 has an orbital period that matches well that of uranus, and here we investigate its dynamical state. direct n-body calculations are used to assess the current status of this object, reconstruct its immediate dynamical past, and explore its future orbital evolution. a covariance matrix-based monte carlo scheme is presented and applied to study its short-term stability. we find that 2015 db216 is trapped in a temporary co-orbital resonance with uranus, the fourth known minor body to do so. a detailed analysis of its dynamical evolution shows that it is an unstable but recurring co-orbital companion to uranus. it currently follows an asymmetric horseshoe trajectory that will last for at least 10 kyr, but it may remain inside uranus' co-orbital zone for millions of years. as in the case of other transient uranian co-orbitals, complex multibody ephemeral mean motion resonances trigger the switching between the various resonant co-orbital states. the new uranian co-orbital exhibits a secular behaviour markedly different from that of the other known uranian co-orbitals because of its higher inclination, nearly 38°. given its rather unusual discovery circumstances, the presence of 2015 db216 hints at the existence of a relatively large population of objects moving in similar orbits. | asteroid 2015 db216: a recurring co-orbital companion to uranus |
deriving thermophysical properties such as thermal inertia from thermal infrared observations provides useful insights into the structure of the surface material on planetary bodies. the estimation of these properties is usually done by fitting temperature variations calculated by thermophysical models to infrared observations. for multiple free model parameters, traditional methods such as least-squares fitting or markov chain monte carlo methods become computationally too expensive. consequently, the simultaneous estimation of several thermophysical parameters, together with their corresponding uncertainties and correlations, is often not computationally feasible and the analysis is usually reduced to fitting one or two parameters. data assimilation (da) methods have been shown to be robust while sufficiently accurate and computationally affordable even for a large number of parameters. this paper will introduce a standard sequential da method, the ensemble square root filter, for thermophysical modelling of asteroid surfaces. this method is used to re-analyse infrared observations of the mara instrument, which measured the diurnal temperature variation of a single boulder on the surface of near-earth asteroid (162173) ryugu. the thermal inertia is estimated to be 295 ± 18 $\mathrm{j\, m^{-2}\, k^{-1}\, s^{-1/2}}$ , while all five free parameters of the initial analysis are varied and estimated simultaneously. based on this thermal inertia estimate the thermal conductivity of the boulder is estimated to be between 0.07 and 0.12, $\mathrm{w\, m^{-1}\, k^{-1}}$ and the porosity to be between 0.30 and 0.52. for the first time in thermophysical parameter derivation, correlations and uncertainties of all free model parameters are incorporated in the estimation procedure that is more than 5000 times more efficient than a comparable parameter sweep. | thermophysical modelling and parameter estimation of small solar system bodies via data assimilation |
context. with an estimated diameter in the 320-350 km range, (704) interamnia is the fifth largest main belt asteroid and one of the few bodies that fills the gap in size between the four largest bodies with d > 400 km (ceres, vesta, pallas and hygiea) and the numerous smaller bodies with diameter ≤200 km. however, despite its large size, little is known about the shape and spin state of interamnia and, therefore, about its bulk composition and past collisional evolution.aims: we aimed to test at what size and mass the shape of a small body departs from a nearly ellipsoidal equilibrium shape (as observed in the case of the four largest asteroids) to an irregular shape as routinely observed in the case of smaller (d ≤ 200 km) bodies.methods: we observed interamnia as part of our eso vlt/sphere large program (id: 199.c-0074) at thirteen different epochs. in addition, several new optical lightcurves were recorded. these data, along with stellar occultation data from the literature, were fed to the all-data asteroid modeling algorithm to reconstruct the 3d-shape model of interamnia and to determine its spin state.results: interamnia's volume-equivalent diameter of 332 ± 6 km implies a bulk density of ρ = 1.98 ± 0.68 g cm-3, which suggests that interamnia - like ceres and hygiea - contains a high fraction of water ice, consistent with the paucity of apparent craters. our observations reveal a shape that can be well approximated by an ellipsoid, and that is compatible with a fluid hydrostatic equilibrium at the 2σ level.conclusions: the rather regular shape of interamnia implies that the size and mass limit, under which the shapes of minor bodies with a high amount of water ice in the subsurface become irregular, has to be searched among smaller (d ≤ 300 km) less massive (m ≤ 3 × 1019 kg) bodies. the reduced images are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/633/a65 based on observations made with eso telescopes at the la silla paranal observatory under program 199.c-0074 (pi: vernazza). | (704) interamnia: a transitional object between a dwarf planet and a typical irregular-shaped minor body |
we introduce a new computational technique for searching for faint moving sources in astronomical images. starting from a maximum-likelihood estimate for the probability of the detection of a source within a series of images, we develop a massively parallel algorithm for searching through candidate asteroid trajectories that utilizes graphics processing units (gpu). this technique can search over 1010 possible asteroid trajectories in stacks of the order of 10-15 4k × 4k images in under a minute using a single consumer grade gpu. we apply this algorithm to data from the 2015 campaign of the high cadence transient survey (hits) obtained with the dark energy camera (decam). we find 39 previously unknown kuiper belt objects (kbos) in the 150 square degrees of the survey. comparing these asteroids to an existing model for the inclination distribution of the kuiper belt we demonstrate that we recover a kbo population above our detection limit consistent with previous studies. software used in this analysis is made available as an open source package. | fast algorithms for slow moving asteroids: constraints on the distribution of kuiper belt objects |
a set of 50,000 artificial earth impacting asteroids was used to obtain, for the first time, information about the dominance of individual impact effects such as wind blast, overpressure shock, thermal radiation, cratering, seismic shaking, ejecta deposition, and tsunami for the loss of human life during an impact event for impactor sizes between 15 and 400 m and how the dominance of impact effects changes over size. information about the dominance of each impact effect can enable disaster managers to plan for the most relevant effects in the event of an asteroid impact. furthermore, the analysis of average casualty numbers per impactor shows that there is a significant difference in expected loss for airburst and surface impacts and that the average impact over land is an order of magnitude more dangerous than one over water. | asteroid impact effects and their immediate hazards for human populations |
we present shape models and volume estimates of twenty asteroids based on relative photometry and adaptive optics images. we discuss error estimation and the effects of myopic deconvolution on shape solutions. for further analysis of the information capacities of data sources, we also present and discuss ambiguity and uniqueness results for the reconstruction of nonconvex shapes from photometry. | adaptive optics and lightcurve data of asteroids: twenty shape models and information content analysis |
fireball networks establish the trajectories of meteoritic material passing through earth's atmosphere, from which they can derive pre-entry orbits. triangulated atmospheric trajectory data require different orbit determination methods to those applied to observational data beyond the earth's sphere of influence, such as telescopic observations of asteroids. currently, the vast majority of fireball networks determine and publish orbital data using an analytical approach, with little flexibility to include orbital perturbations. here, we present a novel numerical technique for determining meteoroid orbits from fireball network data and compare it to previously established methods. the re-entry of the hayabusa spacecraft, with its known pre-earth orbit, provides a unique opportunity to perform this comparison as it was observed by fireball network cameras. as initial sightings of the hayabusa spacecraft and capsule were made at different altitudes, we are able to quantify the atmosphere's influence on the determined pre-earth orbit. considering these trajectories independently, we found the orbits determined by the novel numerical approach to align closer to jaxa's telemetry in both cases. using simulations, we determine the atmospheric perturbation to become significant at 90 km—higher than the first observations of typical meteorite dropping events. using further simulations, we find the most substantial differences between techniques to occur at both low entry velocities and moon passing trajectories. these regions of comparative divergence demonstrate the need for perturbation inclusion within the chosen orbit determination algorithm. | comparing analytical and numerical approaches to meteoroid orbit determination using hayabusa telemetry |
we report a comprehensive analysis of the global spectrophotometric properties of ceres using the images collected by the dawn framing camera through seven color filters from april to june 2015 during the rc3 (rotational characterization 3) and survey mission phases. we derived the hapke model parameters for all color filters. the single-scattering albedo of ceres at 555 nm wavelength is 0.14 ± 0.04, the geometric albedo is 0.096 ± 0.006, and the bolometric bond albedo is 0.037 ± 0.002. the asymmetry factors calculated from the best-fit two-term henyey-greenstein (hg) single-particle phase functions (sppfs) show a weak wavelength dependence from -0.04 at 438 nm increasing to 0.002 at >900 nm, suggesting that the phase reddening of ceres is dominated by single-particle scattering rather than multiple scattering or small-scale surface roughness. the hapke roughness parameter of ceres is derived to be 20° ± 6°, with no wavelength dependence. the phase function of ceres presents appreciably strong scattering around 90° phase angle that cannot be fitted with a single-term hg sppf, suggesting possible stronger forward scattering component than other asteroids previously analyzed with spacecraft data. we speculate that such a scattering characteristic of ceres might be related to its ubiquitous distribution of phyllosilicates and high abundance of carbonates on the surface. we further grouped the reflectance data into a 1° latitude-longitude grid over the surface of ceres, and fitted each grid independently with both empirical models and the hapke model to study the spatial variations of photometric properties. our derived albedo maps and color maps are consistent with previous studies [nathues, a., et al., 2016, planet. space sci. 134, 122-127; schröder, s.e., et al., 2017, icarus 288, 201-225]. the sppf over the surface of ceres shows an overall correlation with albedo distribution, where lower albedo is mostly associated with stronger backscattering and vice versa, consistent with the general trend among asteroids. on the other hand, the hapke roughness parameter does not vary much across the surface of ceres, except for the ancient vendimia planitia region that is associated with a slightly higher roughness. furthermore, the spatial distributions of the sppf and the hapke roughness do not depend on wavelength. based on the wavelength dependence of the sppf of ceres, we hypothesize that the regolith grains on ceres either contain a considerable fraction of μm-sized or smaller particles, or are strongly affected by internal scatterers of this size. | spectrophotometric modeling and mapping of ceres |
context. hot exozodiacal dust has been shown to be present in the innermost regions of an increasing number of main sequence stars over the past 15 yr. however, the origin of hot exozodiacal dust and its connection with outer dust reservoirs remains unclear.aims: we aim to explore the possible connection between hot exozodiacal dust and warm dust reservoirs (≥100 k) in asteroid belts.methods: we use precision near-infrared interferometry with vlti/pionier to search for resolved emission at h-band around a selected sample of 62 nearby stars that show possible signs of warm dust populations.results: our observations reveal the presence of resolved near-infrared emission around 17 out of 52 stars with sufficient data quality. for four of these, the emission is shown to be due to a previously unknown stellar companion. the 13 other h-band excesses are thought to originate from the thermal emission of hot dust grains, close to their sublimation temperature. taking into account earlier pionier observations, where some stars with warm dust were also observed, and after re-evaluating the warm dust content of all our pionier targets through spectral energy distribution modeling, we find a detection rate of 17.1−4.6+8.1% for h-band excess around main sequence stars hosting warm dust belts, which is statistically compatible with the occurrence rate of 14.6−2.8+4.3% found around stars showing no signs of warm dust. after correcting for the sensitivity loss due to partly unresolved hot disks, under the assumption that they are arranged in a thin ring around their sublimation radius, we find tentative evidence at the 3σ level that h-band excesses around stars with outer dust reservoirs (warm or cold) could be statistically larger than h-band excesses around stars with no detectable outer dust.conclusions: our observations do not suggest a direct connection between warm and hot dust populations at the sensitivity level of the considered instruments, although they bring to light a possible correlation between the level of h-band excess and the presence of outer dust reservoirs in general. based on observations made with eso telescopes at the la silla paranal observatory under program ids 093.c-0712 and 094.c-0325. | a near-infrared interferometric survey of debris-disk stars. vii. the hot-to-warm dust connection |
volatile-rich asteroids are crucial to understanding the transport of water and organics to the terrestrial planet forming region in the early solar system. observations of two such asteroids by hayabusa2 and origins, spectral interpretation, resource identification, security, regolith explorer (osiris-rex) suggest a relationship between these bodies and ci, cm, and cy chondrites. to confirm this, meteorite spectra need to be collected under appropriate conditions for comparison with asteroid observations. we report midinfrared (mir) emissivity spectra (5.5-50 μm) obtained under ambient and simulated asteroid environment conditions and near-infrared (nir) reflectance spectra (2-5 μm) of cm and cy chondrite fine-particulate (<35 μm) powders for which bulk mineralogy was determined using x-ray diffraction. reflectance spectra show a 3 μm feature associated with -oh/h2o that shifts from shorter (∼2.72 μm) to longer (∼2.90 μm) wavelengths and develops a rounder shape and reduced band area with increasing thermal metamorphism. in the mir, the transparency feature (tf) and features in the si-o bending region (>15 μm) can be used to infer the relative degree of aqueous alteration, and to resolve the effects of aqueous and thermal alteration, when combined with nir spectral parameters. the mir spectra of metamorphosed cy chondrites are distinct from cm chondrite spectra, including a plateau around the christiansen feature (∼8.00-12.50 μm) and features at longer wavelengths in the si-o bending region (e.g., ∼25.50 μm compared to ∼24.30 μm in the cm spectra). we additionally report potential implications of the spectra and parameters determined in this study for the results from hayabusa2 and osiris-rex. | a spectral investigation of aqueously and thermally altered cm, cm-an, and cy chondrites under simulated asteroid conditions for comparison with osiris-rex and hayabusa2 observations |
we estimate the total population of near-earth objects (neos) in the solar system using an extensive, "solar-system-to-pixels" fake-asteroid simulation to debias detections of real neos by the atlas survey. down to absolute magnitudes h = 25 and 27.6 (diameters of ∼34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 ± 0.49) × 105 and (1.59 ± 0.45) × 107 neos, respectively. most of the plausible sources of error tend toward underestimation, so the true populations are likely larger. we find the distribution of h magnitudes steepens for neos fainter than h ∼ 22.5, making small asteroids more common than extrapolation from brighter h mags would predict. our simulation indicates a strong bias against detecting small but dangerous asteroids that encounter earth with high relative velocities—i.e., asteroids in highly inclined and/or eccentric orbits. worldwide neo discovery statistics indicate this bias affects global neo detection capability to the point that an observational census of small asteroids in such orbits is probably not currently feasible. prompt and aggressive followup of neo candidates, combined with closer collaborations between segments of the global neo community, can increase detection rates for these dangerous objects. | neo population, velocity bias, and impact risk from an atlas analysis |
we report on the characterization of the dust activity and dynamical evolution of two faint active asteroids, p/2019 a4, and p/2021 a5, observed with the 10.4 m gtc using both imaging and spectroscopy. asteroid p/2019 a4 activity is found to be linked to an impulsive event occurring some ±10 d around perihelion, probably due to a collision or a rotational disruption. its orbit is stable over 100 myr time-scales. dust tail models reveal a short-term burst producing (2.0 ± 0.7) × 106 kg of dust for maximum particle radius rmax = 1 cm. the spectrum of p/2019 a4 is featureless, and slightly redder than the sun. p/2021 a5 was active ~50 d after perihelion, lasting ~5 to ~60 d, and ejecting (8 ± 2) × 106 kg of dust for rmax = 1 cm. the orbital simulations show that a few percent of dynamical clones of p/2021 a5 are unstable on 20-50 myr time-scales. thus, p/2021 a5 might be an implanted object from the jfc region or beyond. these facts point to water-ice sublimation as the activation mechanism. this object also displays a featureless spectrum, but slightly bluer than the sun. nuclei sizes are estimated in the few hundred meters range for both asteroids. particle ejection speeds (≈0.2 m s-1) are consistent with escape speeds from those small-sized objects. | dust environment of active asteroids p/2019 a4 (panstarrs) and p/2021 a5 (panstarrs) |
primordial black holes (pbhs) in the mass range $\sim 10^{17}- 10^{22}$g are currently unconstrained, and can constitute the full dark matter (dm) density of the universe. motivated by this, in the current work, we aim to relate the existence of pbhs in the said mass range to the production of observable gravitational waves (gws) in the upcoming gw detectors. we follow a relatively model-independent approach assuming that the pbhs took birth in a radiation dominated era from enhanced primordial curvature perturbation at small scales produced by inflation. we show that the constraints from cmb and bao data allow for the possibility of pbhs being the whole of dm density of the universe. finally, we derive the gw spectrum induced by the enhanced curvature perturbations and show that they are detectable in the future gw detectors like elisa, bbo and decigo. | gravitation wave signal from asteroid mass primordial black hole dark matter |
recent estimates of the characteristics of planet nine have suggested that it could be closer than originally assumed. such a planet nine would also be brighter than originally assumed, suggesting the possibility that it has already been observed in wide-field moderate-depth surveys. we search for planet nine in the zwicky transient facility public archive and find no candidates. using known asteroids to calculate the magnitude limit of the survey, we find that we should have detected planet nine throughout most of the northern portion of its predicted orbit-including within the galactic plane-to a 95% detection efficiency of approximately v = 20.5. to aid in understanding detection limits for this and future analyses, we present a full-sky synthetic planet nine population drawn from a statistical sampling of predicted planet nine orbits. we use this reference population to estimate that this survey rules out 56% of predicted planet nine phase space, and we demonstrate how future analyses can use the same synthetic population to continue to constrain the amount of parameter space effectively searched for planet nine. | a search for planet nine using the zwicky transient facility public archive |
there are currently over 20,000 known near-earth asteroids (neas) and more are being discovered on a daily basis. near earth asteroids are the small bodies whose orbits bring them to within 1.3 au of the sun, which makes each one a useful opportunity for science and commercial missions. here we design and generate a trajectory database for mining mission planning by using a high-performance computing system. the database contains 6373 accessible nea missions with maximum mission durations of 6 years in the 2030-2065 timeframe. the accessible asteroids' statistical results show that about 55% of accessible neas can provide stay-time of over 4 years in a 6-year mission. a general mining mission architecture is then proposed, and missions are constructed by using the architecture and the database. the taxonomy results for accessible asteroids from major taxonomy systems are summarized, and the available resources on these asteroids are analysed based on the taxonomy information. for the first time, the entire nea population is assessed realistically from the perspective of asteroid mining and retrievable mass from each asteroid is quantified. suitable targets for mining water, pgms and other resources (e.g. silicates) in the 2030-2065 timeframe are identified. for the asteroids without taxonomy information, we did two analyses: assuming i) they are all c-type and ii) all non-c-type. based on these assumptions, most suitable targets for water and non-water resource mining are identified. these results can be used as guidance for future asteroid mission target selection. | target evaluation for near earth asteroid long-term mining missions |
ultraviolet and optical spectra of the hydrogen-dominated atmosphere white dwarf star g238-44 obtained with fuse, keck/hires, hst/cos, and hst/stis reveal 10 elements heavier than helium: c, n, o, mg, al, si, p, s, ca, and fe. g238-44 is only the third white dwarf with nitrogen detected in its atmosphere from polluting planetary system material. keck/hires data taken on 11 nights over 24 yr show no evidence for variation in the equivalent width of measured absorption lines, suggesting stable and continuous accretion from a circumstellar reservoir. from measured abundances and limits on other elements, we find an anomalous abundance pattern and evidence for the presence of metallic iron. if the pollution is from a single parent body, then it would have no known counterpart within the solar system. if we allow for two distinct parent bodies, then we can reproduce the observed abundances with a mix of iron-rich mercury-like material and an analog of an icy kuiper belt object with a respective mass ratio of 1.7:1. such compositionally disparate objects would provide chemical evidence for both rocky and icy bodies in an exoplanetary system and would be indicative of a planetary system so strongly perturbed that g238-44 is able to capture both asteroid and kuiper belt-analog bodies near-simultaneously within its <100 myr cooling age. | unusual abundances from planetary system material polluting the white dwarf g238-44 |
on june 19, 2020 at 20:05:07 utc, a fireball lasting 5.5 s was observed above western australia by three desert fireball network observatories. the meteoroid entered the atmosphere with a speed of 14.00±0.17 km s-1 and followed a 58° slope trajectory from a height of 75 km down to 18.6 km. despite the poor angle of triangulated planes between observatories (29°) and the large distance from the observatories, a well-constrained kilo-size main mass was predicted to have fallen just south of madura in western australia. however, the search area was predicted to be large due to the trajectory uncertainties. fortunately, the rock was rapidly recovered along the access track during a reconnaissance trip. the 1.072 kg meteorite called madura cave was classified as an l5 ordinary chondrite. the calculated orbit is of aten type (mostly contained within the earth's orbit), only the second time a meteorite was observed on such an orbit, after bunburra rockhole. dynamical modeling shows that madura cave has been in near-earth space for a very long time. the dynamical lifetime in near-earth space for the progenitor meteoroid is predicted to be ~87 myr. this peculiar orbit also points to a delivery from the main asteroid belt via the ν6 resonance, and therefore an origin in the inner belt. this result contributes to drawing a picture for the existence of a present-day l chondrite parent body in the inner belt. | trajectory, recovery, and orbital history of the madura cave meteorite |
we propose to design and build an algorithm that will use a convolutional neural network (cnn) and observations from the unistellar network to reliably detect asteroid occultations. the unistellar network is made of more than 10,000 digital telescopes owned by citizen scientists, and is regularly used to record asteroid occultations. in order to process the increasing amount of observational produced by this network, we need a quick and reliable way to analyze occultations. in an effort to solve this problem, we trained a cnn with artificial images of stars with 20 different types of photometric signals. inputs to the network consist of two stacks of snippet images of stars, one around the star that is supposed to be occulted and a reference star used for comparison. we need the reference star to distinguish between a true occultation and artifacts introduced by a poor atmospheric condition. our occultation detection neural network can analyze three sequences of stars per second with 91% precision and 87% recall. the algorithm is sufficiently fast and robust so we can envision incorporating it on board the evscopes to deliver real-time results. we conclude that citizen science represents an important opportunity for the future studies and discoveries in the occultations, and that application of artificial intelligence will permit us to to take better advantage of the ever-growing quantity of data to categorize asteroids. | odnet: a convolutional neural network for asteroid occultation detection |
codification of free-text clinical narratives have long been recognised to be beneficial for secondary uses such as funding, insurance claim processing and research. the current scenario of assigning codes is a manual process which is very expensive, time-consuming and error prone. in recent years, many researchers have studied the use of natural language processing (nlp), related machine learning (ml) and deep learning (dl) methods and techniques to resolve the problem of manual coding of clinical narratives and to assist human coders to assign clinical codes more accurately and efficiently. this systematic literature review provides a comprehensive overview of automated clinical coding systems that utilises appropriate nlp, ml and dl methods and techniques to assign icd codes to discharge summaries. we have followed the preferred reporting items for systematic reviews and meta-analyses(prisma) guidelines and conducted a comprehensive search of publications from january, 2010 to december 2020 in four academic databases- pubmed, sciencedirect, association for computing machinery(acm) digital library, and the association for computational linguistics(acl) anthology. we reviewed 7,556 publications; 38 met the inclusion criteria. this review identified: datasets having discharge summaries; nlp techniques along with some other data extraction processes, different feature extraction and embedding techniques. to measure the performance of classification methods, different evaluation metrics are used. lastly, future research directions are provided to scholars who are interested in automated icd code assignment. efforts are still required to improve icd code prediction accuracy, availability of large-scale de-identified clinical corpora with the latest version of the classification system. this can be a platform to guide and share knowledge with the less experienced coders and researchers. | a systematic literature review of automated icd coding and classification systems using discharge summaries |
aims: from light curve and radar data we know the spin axis of only 43 near-earth asteroids. in this paper we attempt to constrain the spin axis obliquity distribution of near-earth asteroids by leveraging the yarkovsky effect and its dependence on an asteroid's obliquity.methods: by modeling the physical parameters driving the yarkovsky effect, we solve an inverse problem where we test different simple parametric obliquity distributions. each distribution results in a predicted yarkovsky effect distribution that we compare with a χ2 test to a dataset of 125 yarkovsky estimates.results: we find different obliquity distributions that are statistically satisfactory. in particular, among the considered models, the best-fit solution is a quadratic function, which only depends on two parameters, favors extreme obliquities consistent with the expected outcomes from the yorp effect, has a 2:1 ratio between retrograde and direct rotators, which is in agreement with theoretical predictions, and is statistically consistent with the distribution of known spin axes of near-earth asteroids. | constraints on the near-earth asteroid obliquity distribution from the yarkovsky effect |
we specify the range to which perturbations penetrate a planetesimal system. such perturbations can originate from massive planets or from encounters with other stars. the latter can have an origin in the star cluster in which the planetary system was born, or from random encounters once the planetary system has escaped its parental cluster. the probability of a random encounter, either in a star cluster or in the galactic field depends on the local stellar density, the velocity dispersion and the time spend in that environment. by adopting order of magnitude estimates, we argue that the majority of planetary systems born in open clusters will have a parking zone, in which planetesimals are affected by encounters in their parental star cluster but remain unperturbed after the star has left the cluster. objects found in this range of semimajor axis and eccentricity preserve the memory of the encounter that last affected their orbits, and they can therefore be used to reconstruct this encounter. planetary systems born in a denser environment, such as in a globular cluster are unlikely to have a parking zone. we further argue that some planetary systems may have a frozen zone, in which orbits are not affected either by the more inner massive planets or by external influences. objects discovered in this zone will have preserved information about their formation in their orbital parameters. | the fragility of planetary systems |
in recent years, a paradigm shift has occurred in exoplanet science, wherein low-mass stars are increasingly viewed as a foundational pillar of the search for potentially habitable worlds in the solar neighborhood. however, the formation processes of this rapidly accumulating sample of planet systems are still poorly understood. moreover, it is unclear whether tenuous primordial atmospheres around these earth analogs could have survived the intense epoch of heightened stellar activity that is typical for low-mass stars. we present new simulations of in situ planet formation across the m-dwarf mass spectrum, and derive leftover debris populations of small bodies that might source delayed volatile delivery. we then follow the evolution of this debris with high-resolution models of real systems of habitable zone planets around low-mass stars such as trappist-1, proxima centauri, and toi-700. while debris in the radial vicinity of the habitable zone planets is removed rapidly, thus making delayed volatile delivery highly unlikely, we find that material ubiquitously scattered into an exo-asteroid belt region during the planet-formation process represents a potentially lucrative reservoir of icy small bodies. thus, the presence of external approximately neptune-saturn mass planets capable of dynamically perturbing these asteroids would be a sign that habitable zone worlds around low-mass stars might have avoided complete desiccation. however, we also find that such giant planets significantly limit the efficiency of asteroidal implantation during the planet-formation process. in the coming decade, long-baseline radial velocity studies and roman space telescope microlensing observations will undoubtedly further constrain this process. | habitable planet formation around low-mass stars: rapid accretion, rapid debris removal, and the essential contribution of external giants |
we have conducted high-pressure, high-temperature isotope exchange experiments between molten silicate and molten fe-si-c-alloys to constrain the effect of si on equilibrium fe isotope fractionation during planetary core formation. the values of δ57femetal-silicate at 1850 °c and 1 gpa determined by high-resolution mc-icp-ms in this study range from - 0.013 ± 0.054 ‰ (2se) to 0.072 ± 0.085‰ with 1.34-8.14 atom % si in the alloy, respectively. these results, although not definitive on their own, are consistent with previous experimental results from our group and a model in which elements that substitute for fe atoms in the alloy structure (i.e., ni, s, and si) induce a fractionation of fe isotopes between molten silicate and molten fe-alloys during planetary differentiation. using in situ synchrotron x-ray diffraction data for molten fe-rich alloys from the literature, we propose a model to explain this fractionation behavior in which impurity elements in fe-alloys cause the nearest neighbor atomic distances to shorten, thereby stiffening metallic bonds and increasing the preference of the alloy for heavy fe isotopes relative to the silicate melt. this fractionation results in the bulk silicate mantles of the smaller terrestrial planets and asteroids becoming isotopically light relative to chondrites, with an enrichment of heavy fe isotopes in their cores, consistent with magmatic iron meteorite compositions. our model predicts a bulk silicate mantle δ57fe ranging from -0.01‰ to -0.12‰ for the moon, -0.06‰ to -0.33‰ for mars, and -0.08‰ to -0.33‰ for vesta. independent estimates of the δ57fe of primitive mantle source regions that account for fe isotope fractionation during partial melting agree well with these ranges for all three planetary bodies and suggest that mars and vesta have cores with impurity (i.e., ni, s, si) abundances near the low end of published ranges. therefore, we favor a model in which core formation results in isotopically light bulk silicate mantles for the moon, mars, and vesta. the processes of magma ocean crystallization, mantle partial melting, and fractional crystallization of mantle-derived melts are all likely to result in heavy fe isotope enrichment in the melt phase, which can explain why basaltic samples from these planetary bodies have variable δ57fe values consistently heavier than our bulk mantle estimates. additionally, we find no clear evidence that fe isotopes were fractionated to a detectable level by volatile depletion processes during or after planetary accretion, although it cannot be ruled out. | the effect of core composition on iron isotope fractionation between planetary cores and mantles |
enstatite chondrites are a small clan of meteorites, only ~ 1% out of all meteorite collection. however, they are the most reduced meteorites and have almost identical isotopic compositions to those of the earth, suggestive of significant contributions to the latter and other terrestrial planets. enstatite chondrites contain a unique mineral inventory of sulfides of typical lithophile elements, si-bearing metal, silicide and phosphide, which record the nebular processes and the thermal metamorphism in asteroidal bodies under extremely reducing environments. eh group is mainly characteristic of the higher si content of metallic fe-ni and the higher mns contents of sulfides than el group, indicative of a more reducing condition than the latter. however, the fugacity ph2s could be the same in both eh and el regions, because it was buffered by kamacite and troilite. the majority of sulfides condensed from the nebula, partially enclosing schreibersite micron-spherules formed probably by early melting. another part of troilite, sphalerite and djerfisherite, intergrown with perryite, were produced via sulfidation of metallic fe-ni. minor exotic components were also found in enstatite chondrites, including ca-, al-rich inclusions and feo-rich silicate clasts. the ca-, al-rich inclusions are identical to those in carbonaceous chondrites except for the alteration under reducing environments, and the feo-rich silicate clasts show reduction reactions, both suggestive of migration of dust in the protoplanetary disk. the highly reducing conditions (as c/o ratios) might be established via repeating evaporation and condensation of water ice and organic matter across the snow line along the protoplanetary disk, but need to find evidence. another issue is the preservation of submicron-to-micron-sized presolar grains during high-temperature condensation of the major constituent minerals. after accretion, the parent bodies of eh and el chondrites probably experienced distinct thermal histories, indicated by their distinct petrologic-type distributions and different correlations with the closure temperatures determined by the fes contents of sulfides in contact with troilite. | enstatite chondrites: condensation and metamorphism under extremely reducing conditions and contributions to the earth |
in 2006, vega was discovered to display excess near-infrared (nir) emission. surveys now detect this phenomenon for one fifth of main-sequence stars, across various spectral types and ages. the excesses are interpreted as populations of small, hot dust grains very close to their stars, which must originate from comets or asteroids. however, the presence of such grains in copious amounts is mysterious, since they should rapidly sublimate or be blown out of the system. here, we investigate a potential mechanism to generate excesses: dust migrating inwards under radiation forces sublimates near the star, releasing modest quantities of gas that then traps subsequent grains. this mechanism requires neither specialized system architectures nor high dust supply rates, and could operate across diverse stellar types and ages. the model naturally reproduces many features of inferred dust populations, in particular their location, preference for small grains, steep size distribution, and dust location scaling with stellar luminosity. for sun-like stars, the mechanism can produce ${2.2 \; \mu {\rm m}}$ excesses that are an order of magnitude larger than those at ${8.5 \; \mu {\rm m}}$ , as required by observations. however, for a-type stars the simulated nir excesses were only twice those in the mid-infrared; grains would have to be 5-10 times smaller than those trapped in our model to be able to explain observed nir excesses around a stars. further progress with any hot dust explanation for a stars requires a means for grains to become very hot without either rapidly sublimating or being blown out of the system. | gas trapping of hot dust around main-sequence stars |
operation of a small cubesat in the deep-space microgravity environment brings additional challenging factors including the increased radiation environment, the significant contribution of non-gravitational forces to the satellite orbit, or the limited communication opportunities. these factors need to be taken into account in the form of modifications to the classic cubesat architecture. increased radiation resistance, the semi-autonomous satellite operation, navigation, and the active orbit correction are required. such a modified cubesat platform can potentially deliver a high performance to mass and cost ratios. the asteroid spectral imaging mission (aspect) is a three unit (3u) cubesat mission built on these principles. it is part of the aida (asteroid impact & deflection assessment) project to the binary asteroid didymos. aspect is equipped with a visible to near-infrared hyperspectral imager and will deliver both technological knowledge as well as scientific data about the origin and evolution of solar system small bodies. | feasibility of asteroid exploration using cubesats-aspect case study |
the dwarf planet ceres shows spatially well-defined regions, which exhibit a negative (blue) spectral slope between 0.5 and 2.5 µm. comparisons with planetary bodies known to exhibit a blue slope and spectral properties of materials identified on ceres's surface based on infrared wavelength signatures indicate that the spectral changes could be related to physical properties of the surface material rather than variations in its composition. the close association of bluish surface regions to fresh impact craters implies a possible relationship to an impact-triggered alteration and/or space weathering processes. the bluish regions could be linked with blankets of ultrafine grains and partly amorphous phyllosilicates, which form larger agglomerates due to the sticky behavior of impact-induced phyllosilicate dust and/or the amorphization of the ejecta material during the impact process. space weathering processes (micrometeoritic impacts, temperature changes) cause a reversal of the agglutination process and a recrystallization of the surface material with time resulting in a reddening of the spectral slope. | an investigation of the bluish material on ceres |
chondritic meteorites have been traditionally thought to be samples of undifferentiated bodies that never experienced large-scale melting. this view has been challenged by the existence of post-accretional, unidirectional natural remanent magnetization (nrm) in cv carbonaceous chondrites. the relatively young inferred nrm age [∼10 million years (my) after solar system formation] and long duration of nrm acquisition (1-106 y) have been interpreted as evidence that the magnetizing field was that of a core dynamo within the cv parent body. this would imply that cv chondrites represent the primitive crust of a partially differentiated body. however, an alternative hypothesis is that the nrm was imparted by the early solar wind. here we demonstrate that the solar wind scenario is unlikely due to three main factors: 1) the magnitude of the early solar wind magnetic field is estimated to be <0.1 μt in the terrestrial planet-forming region, 2) the resistivity of chondritic bodies limits field amplification due to pile-up of the solar wind to less than a factor of 3.5 times that of the instantaneous solar wind field, and 3) the solar wind field likely changed over timescales orders of magnitude shorter than the timescale of nrm acquisition. using analytical arguments, numerical simulations and astronomical observations of the present-day solar wind and magnetic fields of young stars, we show that the maximum mean field the ancient solar wind could have imparted on an undifferentiated cv parent body is <3.5 nt, which is 3-4 and 3 orders of magnitude weaker than the paleointensities recorded by the cv chondrites allende and kaba, respectively. therefore, the solar wind is highly unlikely to be the source of the nrm in cv chondrites. nevertheless, future high sensitivity paleomagnetic studies of rapidly-cooled meteorites with high magnetic recording fidelity could potentially trace the evolution of the solar wind field in time. | were chondrites magnetized by the early solar wind? |
we report radar observations (2380-mhz, 13-cm) by the arecibo observatory and optical light curves observed from eight different observatories and collected at the ondřejov observatory of the triple near-earth asteroid system (153591) 2001 sn263. the radar observations were obtained over the course of ten nights spanning february 12-26, 2008 and the light curve observations were made throughout january 12 - march 31, 2008. both data sets include observations during the object's close approach of 0.06558 au on february 20th, 2008. the delay-doppler images revealed the asteroid to be comprised of three components, making it the first known triple near-earth asteroid. only one other object, (136617) 1994 cc is a confirmed triple near-earth asteroid. we present physical models of the three components of the asteroid system. we constrain the primary's pole direction to an ecliptic longitude and latitude of (309 °, - 80 °) ± 15 ° . we find that the primary rotates with a period 3.4256 ± 0.0002 h and that the larger satellite has a rotation period of 13.43 ± 0.01 h , considerably shorter than its orbital period of approximately 6 days. we find that the rotation period of the smaller satellite is consistent with a tidally locked state and therefore rotates with a period of 0.686 ± 0.002 days (fang et al. [2011]. astron. j. 141, 154-168). the primary, the larger satellite, and the smaller satellite have equivalent diameters of 2.5 ± 0.3 km , 0.77 ± 0.12 km , 0.43 ± 0.14 km and densities of 1.1 ± 0.2 g /cm3, 1.0 ± 0.4 g /cm3, 2.3 ± 1.3 g /cm3 , respectively. | physical modeling of triple near-earth asteroid (153591) 2001 sn263 from radar and optical light curve observations |
we developed universal sample holders [the kochi grid, kochi clamp, and okazaki cell) and a transfer vessel (facility-to-facility transfer container (fftc)] to analyze sensitive and fragile samples, such as extremely small extraterrestrial materials. the holders and container prevent degradation, contamination due to the terrestrial atmosphere (water vapor and oxygen gas) and small particles, as well as mechanical sample damage. the fftc can isolate the samples from the effects of the atmosphere for more than a week. the kochi grid and clamp were made for a coordinated micro/nano-analysis that utilizes a focused-ion beam apparatus, transmission electron microscope, and nanoscale secondary ion mass spectrometry. the okazaki cell was developed as an additional attachment for a scanning transmission x-ray microscope that uses near-edge x-ray absorption fine structure (nexafs). these new apparatuses help to minimize possible alterations from the exposure of the samples to air. the coordinated analysis involving these holders was successfully carried out without any sample damage or loss, thereby enabling us to obtain sufficient analytical datasets of textures, crystallography, elemental/isotopic abundances, and molecular functional groups for µm-sized minerals and organics in both the antarctic micrometeorite and a carbonaceous chondrite. we will apply the coordinated analysis to acquire the complex characteristics in samples obtained by the future spacecraft sample return mission.<fig id="figa" position="anchor">[graphic not available: see fulltext] | the universal sample holders of microanalytical instruments of fib, tem, nanosims, and stxm-nexafs for the coordinated analysis of extraterrestrial materials |
as evidenced by the chelyabinsk and tunguska airburst events in russia, decameter-scale near-earth objects (neos) can pose a hazard to human life and infrastructure from the energy they deposit in the atmosphere as they break up. to understand the potential damage these small neos can cause on earth's surface, it is imperative to be able to model their atmospheric entry quickly and accurately. here we compare three semi-analytical models of asteroid airbursts that differ in their descriptions of fragment separation and spreading. each model can be calibrated to produce a good fit to the energy deposition curve inferred from chelyabinsk observations, but in each case the implied initial meteoroid strength is different and when the calibrated models are upscaled to tunguska, the results diverge. this introduces an inter-model uncertainty that compounds the large range of uncertain physical and model parameters that influence probabilistic hazard assessment. uncertainty quantification of airburst energy deposition was performed for a theoretical impacting object with h-magnitude 27, assuming no prior knowledge of any other impactor or model parameter. each of the three models produces a different distribution of airburst outcomes, however, the variation attributable to physical parameter uncertainty is far larger than the inter-model differences. to constrain the initial conditions of the tunguska event, the same uncertainty quantification was performed for an h-magnitude 24 event. among the scenarios consistent with tunguska observations (5-10 km burst altitude, 10-60° trajectory angle, 3-50 mt tnt total energy release) the most likely range of impact conditions was: radius of 25-75 m, mass of 1× 108- 2.5× 109 kg, initial velocity of 11.5-33 km/s, and angle of 25-60°. | uncertainty quantification in continuous fragmentation airburst models |
in the pandemic time, the monitoring of the progression of some diseases is affected and rehabilitation is more complicated. remote monitoring may help solve this problem using mobile devices that embed low-cost sensors, which can help measure different physical parameters. many tests can be applied remotely, one of which is the six-minute walk test (6mwt). the 6mwt is a sub-maximal exercise test that assesses aerobic capacity and endurance, allowing early detection of emerging medical conditions with changes. this paper presents a systematic review of the use of sensors to measure the different physical parameters during the performance of 6mwt, focusing on various diseases, sensors, and implemented methodologies. it was performed with the prisma methodology, where the search was conducted in different databases, including ieee xplore, acm digital library, sciencedirect, and pubmed central. after filtering the papers related to 6mwt and sensors, we selected 31 papers that were analyzed in more detail. our analysis discovered that the measurements of 6mwt are primarily performed with inertial and magnetic sensors. likewise, most research studies related to this test focus on multiple sclerosis and pulmonary diseases. | development technologies for the monitoring of six-minute walk test: a systematic review |
comet nuclei and d-type asteroids have several similarities at optical and near-ir wavelengths, including near-featureless red reflectance spectra, and low albedos. mineral identifications based on these characteristics are fraught with degeneracies, although some general trends can be identified. in contrast, spectral emissivity features in the mid-infrared provide important compositional information that might not otherwise be achievable. jovian trojan d-type asteroids have emissivity features strikingly similar to comet comae, suggesting that they have the same compositions and that the surfaces of the trojans are highly porous. however, a direct comparison between a comet and asteroid surface has not been possible due to the paucity of spectra of comet nuclei at mid-infrared wavelengths. we present 5-35 μm thermal emission spectra of comets 10p/tempel 2, and 49p/arend-rigaux observed with the infrared spectrograph on the spitzer space telescope. our analysis reveals no evidence for a coma or tail at the time of observation, suggesting the spectra are dominated by the comet nucleus. we fit each spectrum with the near-earth asteroid thermal model (neatm) and find sizes in agreement with previous values. however, the neatm beaming parameters of the nuclei, 0.74-0.83, are systematically lower than the jupiter-family comet population mean of 1.03 ± 0.11, derived from 16- and 22-μm photometry. we suggest this may be either an artifact of the spectral reduction, or the consequence of an emissivity low near 16 μm. when the spectra are normalized by the neatm model, a weak 10-μm silicate plateau is evident, with a shape similar to those seen in mid-infrared spectra of d-type asteroids. a silicate plateau is also evident in previously published spitzer spectra of the nucleus of comet 9p/tempel 1. we compare, in detail, these comet nucleus emission features to those seen in spectra of the jovian trojan d-types (624) hektor, (911) agamemnon, and (1172) aneas, as well as those seen in the spectra of seven comet comae. the comet comae present silicate features with two distinct shapes, either trapezoidal, or more rounded, the latter apparently due to enhanced emission near 8 to 8.5 μm. the surfaces of tempel 2, arend-rigaux, and hektor best agree with the comae that present trapezoidal features, furthering the hypothesis that the surfaces of these targets must have high porosities in order to exhibit a spectrum similar to a comet coma. an emissivity minimum at 15 μm, present in the spectra of tempel 2, arend-rigaux, hektor, and agamemnon, is also described, the origin of which remains unidentified. the compositional similarity between d-type asteroids and comets is discussed, and our data supports the hypothesis that they have similar origins in the early solar system. | mid-infrared spectra of comet nuclei |
ordinary chondrites (ocs) are variably thermally metamorphosed meteorites thought to originate from at least three different parent bodies (h, l, and ll) in the main belt of asteroids. the thermal evolutions of oc parent bodies are frequently explained by the onion shell model; however, a competing hypothesis is the fragmentation-reassembly model. the onion shell model proposes undisrupted, internally heated parent bodies with concentrically stratified thermal structure, and posits that oc petrologic types (i.e., 3-6) develop with increasing temperature and burial depth. in this model, petrologic types are inversely correlated with cooling rate in the parent body. the alternative fragmentation-reassembly model invokes catastrophic collisional disruption of parent bodies that initially possessed onion shell structures, followed by rapid reaccretion of hot fragments, forming rubble pile bodies. fragmentation would result in fast cooling (quenching) of collisional fragments from the temperature experienced by the parent body at the time of collision. discrimination between these two models may be possible via investigation of the thermal histories of ocs by application of geothermometry and geospeedometry, which are used to constrain the temperatures and rates through which igneous and metamorphic rock samples cool. most published cooling rate data for oc parent bodies are based on methods that record rates through low closure temperatures (∼500-200 °c) rather than from peak metamorphic temperatures. recently, a rare earth element (ree)-in-two-pyroxene thermometer has been shown to establish peak or magmatic temperatures (tree; liang et al. [2013]) for rocks that cooled at moderate to fast geologic rates. we applied the ree-in-two-pyroxene method to determine peak temperatures for 18 oc samples (mostly type 6), in conjunction with conventional two-pyroxene thermometry (tbkn; brey and köhler [1990]) and ca-in-olivine thermometry (tca-ol; köhler and brey [1990]), to determine closure temperatures and estimate cooling rates for oc parent bodies. inconsistent with slow cooling rates expected within an onion shell structure, we obtain fast cooling at rates ≳0.3 °c/y from peak temperatures of ∼900 °c. corroborating the tree and tbkn measurements, tca-ol suggests that the ocs cooled through tca-ol closure temperatures (∼700 to 800 °c) at ∼10-2 to 10-1 °c/y. these cooling rates are three to six orders of magnitude faster than rates determined using methods sensitive to low temperature (≤500 °c) cooling (e.g., metallography, 40ar-39ar ages, 244pu fission track). we developed a novel numerical thermal model that incorporates fragmentation of an initial onion shell body and reassembly into a rubble pile body that reproduces both the fast cooling from high temperatures and the slow cooling through low temperatures observed in chondritic meteorites. we hypothesize that oc parent bodies initially possessed onion shell thermal structures, but later experienced collisional breakup, then reaccreted rapidly to form thermally stable rubble-pile asteroids. | evidence for early fragmentation-reassembly of ordinary chondrite (h, l, and ll) parent bodies from ree-in-two-pyroxene thermometry |
we conducted a petrologic study of apatite within eight unbrecciated, non-cumulate eucrites and two monomict, non-cumulate eucrites. these data were combined with previously published data to quantify the abundances of f, cl, and h2o in the bulk silicate portion of asteroid 4 vesta (bsv). using a combination of apatite-based melt hygrometry/chlorometry and appropriately paired volatile/refractory element ratios, we determined that bsv has 3.0-7.2 ppm f, 0.39-1.8 ppm cl, and 3.6-22 ppm h2o. the abundances of f and h2o are depleted in bsv relative to ci chondrites to a similar degree as f and h2o in the bulk silicate portion of the moon. this degree of volatile depletion in bsv is similar to what has been determined previously for many moderately volatile elements in 4 vesta (e.g., na, k, zn, rb, cs, and pb). in contrast, cl is depleted in 4 vesta by a greater degree than what is recorded in samples from earth or the moon. based on the cl-isotopic compositions of eucrites and the bulk rock cl/f ratios determined in this study, the eucrites likely formed through serial magmatism of a mantle with heterogeneous δ37cl and cl/f, not as extracts from a partially crystallized global magma ocean. furthermore, the volatile depletion and cl-isotopic heterogeneity recorded in eucrites is likely inherited, at least in part, from the precursor materials that accreted to form 4 vesta and is unlikely to have resulted solely from degassing of a global magma ocean, magmatic degassing of eucrite melts, and/or volatile loss during thermal metamorphism. although our results can be reconciled with the past presence of wide-scale melting on 4 vesta (i.e., a partial magma ocean), any future models for eucrite petrogenesis involving a global magma ocean would need to account for the preservation of a heterogeneous eucrite source with respect to cl/f ratios and cl isotopes. | the abundances of f, cl, and h2o in eucrites: implications for the origin of volatile depletion in the asteroid 4 vesta |
a photometric survey of near-earth asteroids (neas) was conducted from 2012 through 2014 at lulin observatory, taiwan. the measurements of the color indices, b-v, v-r, and v-i allow the classification of 92 neas into seven taxonomic types. of these samples, 39 of them are new classifications. the fractional abundances of these taxonomic complexes are: a ∼3%, c∼6.5%, d∼8%, q∼26%, s∼37%, v∼6.5%, and x∼13%. this result is similar to that of thomas et al. (2011) even though the populations of the d- and x-complex with low albedos are under-represented. the ratio of the c-cluster to the total population of s + c clusters are 0.22 ± 0.06 for h ≤ 17.0 and 0.31 ± 0.06 for h > 17.0, indicating a slightly higher fraction of dark-object population with sizes smaller than 1 km. | photometric survey and taxonomic identifications of 92 near-earth asteroids |
a number of different classifications have been proposed for the cr chondrites; this study aims at reconciling these different schemes. mineralogy-based classification has proved particularly challenging for weakly to moderately altered crs because incipient mineral replacement and elemental mobilization arising from aqueous alteration only affected the most susceptible primary phases, which are generally located in the matrix. secondary matrix phases are extremely fine-grained (generally sub-micron) and heterogeneously mixed with primary nebular materials. compositional and isotopic classification parameters are fraught with confounding factors, such as terrestrial weathering, impact processes, and variable abundance of clasts from different regions of the cr parent body or from altogether different planetary bodies. here, detailed tem observations from eighteen fib sections retrieved from the matrices of nine antarctic cr chondrites (eet 96259, gra 95229, gro 95577, gro 03116, lap 02342, lap 04516, lap 04720, mil 07525, and mil 090001) are presented, representing a range of petrologic types. amorphous fe-mg silicates are found to be the dominant phase in all but the most altered cr chondrite matrices, which still retain significant amounts of these amorphous materials. amorphous fe-mg silicates are mixed with phyllosilicates at the nanometer scale. the ratio of amorphous fe-mg silicates to phyllosilicates decreases as: (1) the size of phyllosilicates, (2) abundance of magnetite, and (3) replacement of fe-ni sulfides increase. carbonates are only abundant in the most altered cr chondrite, gro 95577. nanophase fe-ni metal and tochilinite are present small abundances in most cr matrices. based on the presence, abundance and size of phyllosilicates with respect to amorphous fe-mg silicates, the sub-micron features of cr chondrites have been linked to existing classification sequences, and possible reasons for inconsistencies among classification schemes are discussed. | why is it so difficult to classify renazzo-type (cr) carbonaceous chondrites? - implications from tem observations of matrices for the sequences of aqueous alteration |
the first confirmed interstellar interloper in our solar system, 1i/`oumuamua, is likely to be a minor body ejected from another star, but its brief flyby and faintness made it difficult to study. two remarkable properties are its large (up to 2.5 mag) rotational variability and its motion relative to the sun before encounter. the former suggests an extremely elongated shape (aspect ratio ≥ 10) and the latter an origin from the protoplanetary disc of a young star in a nearby association. against expectations, it is also not comet-like. 1i/`oumuamua's variability can also be explained if it is a contact binary composed of near-equilibrium ellipsoidal components and heterogeneous surfaces, i.e. brighter, dust-mantled inner-facing hemispheres and darker, dust-free outer-facing poles. such shapes are a plausible outcome of radiation, tides, and collisions in systems where planets are clearing planetesimal discs. the probability that 1i/`oumuamua has the same motion as a young (≲100 myr) stellar association by coincidence is <1 per cent. if it is young, its detection versus more numerous, older counterparts could be explained as a selection effect due to darkening of surfaces by galactic cosmic rays and loss of dust. 1i/`oumuamua's apparent lack of ices can be explained if ejected rocky planetesimals are characteristically smaller and thus far more numerous than their icy counterparts: the solar system may currently host several such objects captured by the combined gravity of jupiter and the sun. | what and whence 1i/`oumuamua: a contact binary from the debris of a young planetary system? |
for the first time, spectral signs of subtle coma activity were observed for four main-belt primitive asteroids (145) adeona, (704) interamnia, (779) nina, and (1474) beira around their perihelion distances in september 2012, which were interpreted as manifestations of the sublimation of h2o ice in/under the surface matter (busarev et al., 2015a, 2015b). we confirm the phenomenon for nina when it approached perihelion in september 2016. at the same time, based on results of spectral observations of near-earth asteroid (162,173) ryugu (vilas, 2008) being a target of japan's hayabusa 2 space mission, we suspected a periodic similar transient activity on the cg-type asteroid. however, unlike the main-belt primitive asteroids demonstrating sublimation of ices close to their perihelion distances, the effect on ryugu was apparently registered near aphelion. to explain the difference, we calculated the subsolar temperature depending on heliocentric distance of the asteroids, considered qualitative models of internal structure of main-belt and near-earth primitive asteroids including ice and performed some analytical estimations. presumed temporal sublimation/degassing activity of ryugu is a sign of a residual frozen core in its interior. this could be an indication of a relatively recent transition of the asteroid from the main asteroid belt to the near-earth area. | new candidates for active asteroids: main-belt (145) adeona, (704) interamnia, (779) nina, (1474) beira, and near-earth (162,173) ryugu |
the population of large 100+ km asteroids is thought to be primordial. as such, they are the most direct witnesses of the early history of our solar system available. those among them with satellites allow study of the mass, and hence density and internal structure. we study here the dynamical, physical, and spectral properties of the triple asteroid (107) camilla from lightcurves, stellar occultations, optical spectroscopy, and high-contrast and high-angular-resolution images and spectro-images. using 80 positions measured over 15 years, we determine the orbit of its larger satellite, s/2001 (107) 1, to be circular, equatorial, and prograde, with root-mean-square residuals of 7.8 mas, corresponding to a sub-pixel accuracy. from 11 positions spread over three epochs only, in 2015 and 2016, we determine a preliminary orbit for the second satellite s/2016 (107) 1. we find the orbit to be somewhat eccentric and slightly inclined to the primary's equatorial plane, reminiscent of the properties of inner satellites of other asteroid triple systems. comparison of the near-infrared spectrum of the larger satellite reveals no significant difference with camilla. hence, both dynamical and surface properties argue for a formation of the satellites by excavation from impact and re-accumulation of ejecta in orbit. we determine the spin and 3-d shape of camilla. the model fits well each data set: lightcurves, adaptive-optics images, and stellar occultations. we determine camilla to be larger than reported from modeling of mid-infrared photometry, with a spherical-volume-equivalent diameter of 254 ± 36 km (3σuncertainty), in agreement with recent results from shape modeling (hanus et al., 2017, a&a 601). combining the mass of (1.12 ± 0.01) × 1019 kg (3σuncertainty) determined from the dynamics of the satellites and the volume from the 3-d shape model, we determine a density of 1,280 ± 130 kg · m-3 (3 σ uncertainty). from this density, and considering camilla's spectral similarities with (24) themis and (65) cybele (for which water ice coating on surface grains was reported), we infer a silicate-to-ice mass ratio of 1-6, with a 10-30% macroporosity. | physical, spectral, and dynamical properties of asteroid (107) camilla and its satellites |
castaway is a mission concept to explore our solar system's main asteroid belt. asteroids and comets provide a window into the formation and evolution of our solar system and the composition of these objects can be inferred from space-based remote sensing using spectroscopic techniques. variations in composition across the asteroid populations provide a tracer for the dynamical evolution of the solar system. the mission combines a long-range (point source) telescopic survey of over 10,000 objects, targeted close encounters with 10-20 asteroids and serendipitous searches to constrain the distribution of smaller (e.g. 10 m) size objects into a single concept. with a carefully targeted trajectory that loops through the asteroid belt, castaway would provide a comprehensive survey of the main belt at multiple scales. the scientific payload comprises a 50 cm diameter telescope that includes an integrated low-resolution (r = 30-100) spectrometer and visible context imager, a thermal (e.g. 6-16 μm) imager for use during the flybys, and modified star tracker cameras to detect small (∼10 m) asteroids. the castaway spacecraft and payload have high levels of technology readiness and are designed to fit within the programmatic and cost caps for a european space agency medium class mission, while delivering a significant increase in knowledge of our solar system. | castaway: an asteroid main belt tour and survey |
the airburst events at chelyabinsk and tunguska in russia are the best-documented asteroid impacts of recent times. models that assess the potential danger from such events rely on an accurate picture of their aftermath. here, we re-examine the most critical eyewitness accounts of the tunguska airburst, namely those that describe injuries and casualties, and those that paint a picture of what events were responsible. not all relevant information has survived in the written record and there are contradictions that create some ambiguity. we find that inside and near the tree-fall area were at least 30 people. many lost consciousness and at least 3 passed away (immediately or later) as a direct consequence of the tunguska event. the airburst created a butterfly-shaped pattern of glass damage extending 4-5 times wider than that seen at chelyabinsk. at these larger distances, any injuries from falls, shattering glass cuts, or from uv radiation exposure were not reported. | tunguska eyewitness accounts, injuries, and casualties |
dust and ice mantles on dust grains play an important role in various processes in protoplanetary disks (ppds) around a young star, including planetesimal formation, surface chemistry, and being the reservoir of water in habitable zones. in this paper, we perform two-dimensional modeling of rotational disruption of dust grains and ice mantles due to centrifugal force within suprathermally rotating grains spun-up by radiative torques for disks around t-tauri and herbig ae/be stars. we first study rotational disruption of large composite grains and find that large aggregates could be disrupted into individual nanoparticles via the radiative torque disruption (ratd) mechanism. we then study rotational desorption of ice mantles and ro-thermal desorption of molecules from the ice mantle. we find that ice mantles in the disk's warm surface layer and above can be disrupted into small icy fragments, followed by rapid evaporation of molecules. we suggest that the rotational disruption mechanism can replenish the ubiquitous presence of polycyclic aromatic hydrocarbons/nanoparticles in the hot surface layers of ppds as observed in mid-ir emission, which are presumably destroyed by extreme ultraviolet (uv) stellar photons. we find that the water snowline is more extended in the presence of rotational desorption, which would decrease the number of comets but increase the number of asteroids formed in the solar nebula. finally, we suggest that ratd breaking up carbonaceous grains more efficiently than it does silicates might resolve the carbon deficit problem measured on the earth and rocky bodies. | rotational disruption of dust and ice by radiative torques in protoplanetary disks and the implications for observations |
the aim of this chapter is to describe available evidence for the existence of relict ocean worlds. the focus is on ceres as a clear example of such a world as indicated by the results from the dawn mission. the sections of this chapter will also reflect the differences and commonalities with other recognized ocean worlds. we focus on ceres as an example of relict ocean world and the implications it holds for the broader solar system. the presence of a large amount of water in the outer solar system, the presence of low eutectic salts, and the similar pressure and temperature regimes at depth in icy moons and other dwarf planets suggest that many of these large icy worlds harbor or harbored deep oceans. ceres is an example of relict ocean world. | relict ocean worlds: ceres |
context. because the second reaction wheel failed, a new mission was conceived for the otherwise healthy kepler space telescope. in the course of the k2 mission, the telescope is staring at the plane of the ecliptic. thousands of solar system bodies therefore cross the k2 fields and usually cause additional noise in the highly accurate photometric data.aims: we here follow the principle that some person's noise is another person's signal and investigate the possibility of deriving continuous asteroid light curves. this is the first such endeavor. in general, we are interested in the photometric precision that the k2 mission can deliver on moving solar system bodies. in particular, we investigate space photometric optical light curves of main-belt asteroids.methods: we studied the k2 superstamps that cover the fields of m35, and neptune together with nereid, which were observed in the long-cadence mode (29.4 min sampling). asteroid light curves were generated by applying elongated apertures. we used the lomb-scargle method to determine periodicities that are due to rotation.results: we derived k2 light curves of 924 main-belt asteroids in the m35 field and 96 in the path of neptune and nereid. the light curves are quasi-continuous and several days long. k2 observations are sensitive to longer rotational periods than typical ground-based surveys. rotational periods are derived for 26 main-belt asteroids for the first time. the asteroid sample is dominated by faint objects (>20 mag). owing to the faintness of the asteroids and the high density of stars in the m35 field, only 4.0% of the asteroids with at least 12 data points show clear periodicities or trends that signal a long rotational period, as opposed to 15.9% in the less crowded neptune field. we found that the duty cycle of the observations had to reach 60% to successfully recover rotational periods. full tables 1-4 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/596/a40 | uninterrupted optical light curves of main-belt asteroids from the k2 mission |
volatile-rich and typically oxidized carbonaceous chondrites, such as cv and cm chondrites, potentially respond to impacts differently than do other chondritic materials. understanding impact melting of carbonaceous chondrites has been hampered by the dearth of recognized impact melt samples. in this study we identify five carbonaceous chondrite impact melt clasts in three host meteorites: a cv3red chondrite, a cv3oxa chondrite, and a regolithic howardite. the impact melt clasts in these meteorites respectively formed from cv3red chondrite, cv3oxa chondrite, and cm chondrite protoliths. we identified these impact melt clasts and interpreted their precursors based on their texture, mineral chemistry, silicate bulk elemental composition, and in the case of the cm chondrite impact melt clast, in situ measurement of oxygen three-isotope signatures in olivine. these impact melts typically contain euhedral-subhedral olivine microphenocrysts, sometimes with relict cores, in glassy groundmasses. based on petrography and raman spectroscopy, four of the impact melt clasts exhibit evidence for volatile loss: these melt clasts either contain vesicles or are depleted in h2o relative to their precursors. volatile loss (i.e., h2o) may have reduced the redox state of the cm chondrite impact melt clast. the clasts that formed from the more oxidized precursors (cv3oxa and cm chondrites) exhibit phase and bulk silicate elemental compositions consistent with higher intrinsic oxygen fugacities relative to the clast that formed from a more reduced precursor (cv3red chondrite). the mineral chemistries and assemblages of the cv and cm chondrite impact melt clasts identified here provide a template for recognizing carbonaceous chondrite impact melts on the surfaces of asteroids. | cv and cm chondrite impact melts |
the bulk composition of earth is dramatically carbon-poor compared to that of the interstellar medium, and this phenomenon extends to the asteroid belt. to interpret this carbon deficit problem, the carbonaceous component in grains must have been converted into the gas phase in the inner regions of protoplanetary disks (ppds) prior to planetary formation. we examine the effect of carbon grain destruction on the chemical structure of disks by calculating the molecular abundances and distributions using a comprehensive chemical reaction network. when carbon grains are destroyed and the elemental abundance of the gas becomes carbon-rich, the abundances of carbon-bearing molecules, such as hcn and carbon-chain molecules, increase dramatically near the midplane, while oxygen-bearing molecules, such as {{{h}}}2{{o}} and {co}}2, are depleted. we compare the results of these model calculations with the solid carbon-to-silicon fraction in the solar system. although we find a carbon depletion gradient, there are some quantitative discrepancies: the model shows a higher value at the position of the asteroid belt and a lower value at the location of earth. in addition, using the obtained molecular abundance distributions, coupled with line radiative transfer calculations, we make predictions for alma to potentially observe the effect of carbon grain destruction in nearby ppds. the results indicate that hcn, {{{h}}}13{cn}, and c-{{{c}}}3{{{h}}}2 may be good tracers. | the effect of carbon grain destruction on the chemical structure of protoplanetary disks |
we describe epic 205718330 and epic 235240266, two systems identified in the k2 data whose light curves contain episodic drops in brightness with shapes and durations similar to those of the young `dipper' stars, yet shallower by ∼1-2 orders of magnitude. these `little dippers' have diverse profile shapes with durations of ≃0.5-1.0 d and depths of ≃0.1-1.0 per cent in flux; however, unlike most of the young dipper stars, these do not exhibit any detectable infrared excess indicative of protoplanetary discs, and our ground-based follow-up spectra lack any signatures of youth while indicating that these objects are kinematically old. after ruling out instrumental and/or data processing artefacts as sources of the dimming events, we investigate possible astrophysical mechanisms based on the light curve and stellar properties. we argue that the little dippers are consistent with transits of star-grazing exocomets, and speculate that they are signposts of massive non-transiting exoplanets driving the close-approach orbits. | the little dippers: transits of star-grazing exocomets? |
models of terrestrial planet formation predict that the final stages of planetary assembly—lasting tens of millions of years beyond the dispersal of young protoplanetary disks—are dominated by planetary collisions. it is through these giant impacts that planets like the young earth grow to their final mass and achieve long-term stable orbital configurations1. a key prediction is that these impacts produce debris. so far, the most compelling observational evidence for post-impact debris comes from the planetary system around the nearby 23-million-year-old a-type star hd 172555. this system shows large amounts of fine dust with an unusually steep size distribution and atypical dust composition, previously attributed to either a hypervelocity impact2,3 or a massive asteroid belt4. here we report the spectrally resolved detection of a carbon monoxide gas ring co-orbiting with dusty debris around hd 172555 between about six and nine astronomical units—a region analogous to the outer terrestrial planet region of our solar system. taken together, the dust and carbon monoxide detections favour a giant impact between large, volatile-rich bodies. this suggests that planetary-scale collisions, analogous to the moon-forming impact, can release large amounts of gas as well as debris, and that this gas is observable, providing a window into the composition of young planets. | carbon monoxide gas produced by a giant impact in the inner region of a young system |
context. asteroids with a diameter of up to a few dozen meters may spin very fast and complete an entire rotation within a few minutes. these small and fast-rotating bodies are thought to be monolithic objects because the gravitational force due to their small size is not strong enough to counteract the strong centripetal force caused by the fast rotation. this argument means that the rubble-pile structure is not feasible for these objects. additionally, it is not clear whether the fast spin prevents dust and small particles (regolith) from being kept on their surface.aims: we develop a model for constraining the thermal conductivity of the surface of the small, fast-rotating near-earth asteroids. this model may suggest whether regolith is likely present on these objects.methods: our approach is based on the comparison of the measured yarkovsky drift and a predicted value using a theoretical model that depends on the orbital, physical and thermal parameters of the object. the necessary parameters are either deduced from statistical distribution derived for near-earth asteroids population or determined from observations with associated uncertainty. with this information, we performed monte carlo simulations and produced a probability density distribution for the thermal conductivity.results: applying our model to the superfast rotator asteroid (499998) 2011 pt, we find that the measured yarkovsky drift can only be achieved when the thermal conductivity k of the surface is low. the resulting probability density function for the conductivity is bimodal, with two most likely values being around 0.0001 and 0.005 w m-1 k-1. based on this, we find that the probability that k is lower than 0.1 w m-1 k-1 is at least 95%. this low thermal conductivity might indicate that the surface of 2011 pt is covered with a thermal insulating layer, composed of a regolith-like material similar to lunar dust. | low thermal conductivity of the superfast rotator (499998) 2011 pt |
using the multiband imager mapcam on board the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) spacecraft, we identified 77 instances of proposed exogenic materials distributed globally on the surface of the b-type asteroid (101955) bennu. we identified materials as exogenic on the basis of an absorption near 1 $\mu$m that is indicative of anhydrous silicates. the exogenic materials are spatially resolved by the telescopic camera polycam. all such materials are brighter than their surroundings, and they are expressed in a variety of morphologies: homogeneous, breccia-like, inclusion-like, and others. inclusion-like features are the most common. visible spectrophotometry was obtained for 46 of the 77 locations from mapcam images. principal component analysis indicates at least two trends: (i) mixing of bennu's average spectrum with a strong 1-$\mu$m band absorption, possibly from pyroxene-rich material, and (ii) mixing with a weak 1-$\mu$m band absorption. the end member with a strong 1-$\mu$m feature is consistent with howardite-eucrite-diogenite (hed) meteorites, whereas the one showing a weak 1-$\mu$m feature may be consistent with heds, ordinary chondrites, or carbonaceous chondrites. the variation in the few available near-infrared reflectance spectra strongly suggests varying compositions among the exogenic materials. thus, bennu might record the remnants of multiple impacts with different compositions to its parent body, which could have happened in the very early history of the solar system. moreover, at least one of the exogenic objects is compositionally different from the exogenic materials found on the similar asteroid (162173) ryugu, and they suggest different impact tracks. | widely distributed exogenic materials of varying compositions and morphologies on asteroid (101955) bennu |
individual particles from comet 81p/wild 2 collected by nasa's stardust mission vary in size from small sub-μm fragments found in the walls of the aerogel tracks, to large fragments up to tens of μm in size found towards the termini of tracks. the comet, in an orbit beyond neptune since its formation, retains an intact a record of early-solar-system processes that was compromised in asteroidal samples by heating and aqueous alteration. we measured the o isotopic composition of seven stardust fragments larger than ∼2 μm extracted from five different stardust aerogel tracks, and 63 particles smaller than ∼2 μm from the wall of a stardust track. the larger particles show a relatively narrow range of o isotopic compositions that is consistent with 16o-poor phases commonly seen in meteorites. many of the larger stardust fragments studied so far have chondrule-like mineralogy which is consistent with formation in the inner solar system. the fine-grained material shows a very broad range of o isotopic compositions (-70‰ < δ17o < +60‰) suggesting that wild 2 fines are either primitive outer-nebula dust or a very diverse sampling of inner solar system compositional reservoirs that accreted along with a large number of inner-solar-system rocks to form comet wild 2. | oxygen isotopic composition of coarse- and fine-grained material from comet 81p/wild 2 |
the large synoptic survey telescope (lsst) will be a ground-based, optical, all-sky, rapid cadence survey project with tremendous potential for discovering and characterizing asteroids. with lsst's large 6.5m diameter primary mirror, a wide 9.6 square degree field of view 3.2 gigapixel camera, and rapid observational cadence, lsst will discover more than 5 million asteroids over its ten year survey lifetime. with a single visit limiting magnitude of 24.5 in r band, lsst will be able to detect asteroids in the main belt down to sub-kilometer sizes. the current strawman for the lsst survey strategy is to obtain two visits (each `visit' being a pair of back-to-back 15s exposures) per field, separated by about 30 minutes, covering the entire visible sky every 3-4 days throughout the observing season, for ten years. the catalogs generated by lsst will increase the known number of small bodies in the solar system by a factor of 10-100 times, among all populations. the median number of observations for main belt asteroids will be on the order of 200-300, with near earth objects receiving a median of 90 observations. these observations will be spread among ugrizy bandpasses, providing photometric colors and allow sparse lightcurve inversion to determine rotation periods, spin axes, and shape information. these catalogs will be created using automated detection software, the lsst moving object processing system (mops), that will take advantage of the carefully characterized lsst optical system, cosmetically clean camera, and recent improvements in difference imaging. tests with the prototype mops software indicate that linking detections (and thus `discovery') will be possible at lsst depths with our working model for the survey strategy, but evaluation of mops and improvements in the survey strategy will continue. all data products and software created by lsst will be publicly available. | asteroid discovery and characterization with the large synoptic survey telescope |
we determine the absolute magnitude (h) distribution (or size-frequency distribution, sfd; n(h)∝10αh where α is the slope of the distribution) for near-earth objects (neo) with 13 < h < 30 and asteroid retrieval mission (arm) targets with 27 < h < 31 that were detected by the 1st telescope of the panoramic survey telescope and rapid response system (pan-starrs1; e.g. kaiser et al., 2002; kaiser, 2004; hodapp et al., 2004). the neo and arm target detection efficiencies were calculated using the greenstreet et al. (2012) neo orbit distribution. the debiased pan-starrs1 neo absolute magnitude distribution is more complex than a single slope power law - it shows two transitions - at h ∼ 16 from steep to shallow slope, and in the 21 < h < 23 interval from a shallow to steep slope, which is consistent with other recent works (e.g. mainzer et al., 2011c; brown et al., 2013; harris and d'abramo, 2015). we fit α = 0.48 ± 0.02 for neos with 13 < h < 16, α = 0.33 ± 0.01 for neos with 16 < h < 22, and α = 0.62 ± 0.03 for the smaller objects with h > 22. there is also another change in slope from steep to shallow around h = 27. the three arm target candidates detected by pan-starrs1 in one year of surveying have a corrected sfd with slope α = 0.40-0.45+0.33. we also show that the window for follow up observations of small (h≳ 22) neos with the nasa irtf telescope and arecibo and goldstone radars are extremely short - on order of days, and procedures for fast response must be implemented in order to measure physical characteristics of small earth-approaching objects. cfht's megacam and pan-starrs1 have longer observing windows and are capable of following-up more neos due to their deeper limiting magnitudes and wider fields of view. | the size-frequency distribution of h > 13 neos and arm target candidates detected by pan-starrs1 |
dormant comets in the near-earth object (neo) population are thought to be involved in the terrestrial accretion of water and organic materials. identification of dormant comets is difficult as they are observationally indistinguishable from their asteroidal counterparts, however, they may have produced dust during their final active stages which potentially are detectable today as weak meteor showers at the earth. here we present the result of a reconnaissance survey looking for dormant comets using 13 567 542 meteor orbits measured by the canadian meteor orbit radar (cmor). we simulate the dynamical evolution of the hypothetical meteoroid streams originated from 407 near-earth asteroids in cometary orbits that resemble orbital characteristics of jupiter-family comets (jfcs). out of the 44 hypothetical showers that are predicted to be detectable by cmor, we identify five positive detections that are statistically unlikely to be chance associations, including three previously known associations. this translates to a lower limit to the dormant comet fraction of 2.0 ± 1.7 per cent in the neo population and a dormancy rate of ∼10-5 yr-1 per comet. the low dormancy rate confirms disruption and dynamical removal as the dominant end state for near-earth jfcs. we also predict the existence of a significant number of meteoroid streams whose parents have already been disrupted or dynamically removed. | dormant comets among the near-earth object population: a meteor-based survey |
we show that the rate of pollution of white dwarfs by asteroidal material implies a concomitant rate of material ejection that can contribute significantly to the population of interstellar minor bodies. we note also that the irradiation during post main sequence evolution implies that much of this ejected material may lose volatiles, providing a rationale for the curious properties of the recently discovered interstellar object oumuamua. | ejection of material—“jurads”—from post-main-sequence planetary systems |
main belt asteroid (6478) gault has been dynamically linked with two overlapping asteroid families: phocaea, dominated by s-type asteroids, and tamara, dominated by low-albedo c-types. this object has recently become an interesting case for study after images obtained in late 2018 revealed that it was active and displaying a comet-like tail. previous authors have proposed that the most likely scenarios to explain the observed activity on gault were rotational excitation or merger of near-contact binaries. here we use new photometric and spectroscopic data of gault to determine its physical and compositional properties. lightcurves derived from the photometric data showed little variation over three nights of observations, which prevented us from determining the rotation period of the asteroid. using wise observations of gault and the near-earth asteroid thermal model (neatm) we determined that this asteroid has a diameter <6 km. near-infrared spectroscopic data obtained with the infrared telescope facility showed a spectrum similar to that of s-complex asteroids, and a surface composition consistent with h chondrite meteorites. these results favor a compositional affinity between gault and asteroid (25) phocaea, and rules out a compositional link with the tamara family. from the spectroscopic data we found no evidence of fresh material that could have been exposed during the outburst episodes. | physical characterization of active asteroid (6478) gault |
the existence of earth's trojan asteroids is not well constrained and represents a major gap in our inventory of small bodies in near-earth space. their discovery would be of high scientific and human interest. | the case for a deep search for earth's trojan asteroids |
we present v-band photometry of the 20 000 brightest asteroids using data from the all-sky automated survey for supernovae (asas-sn) between 2012 and 2018. we were able to apply the convex inversion method to more than 5000 asteroids with more than 60 good measurements in order to derive their sidereal rotation periods, spin axis orientations, and shape models. we derive unique spin state and shape solutions for 760 asteroids, including 163 new determinations. this corresponds to a success rate of about 15%, which is significantly higher than the success rate previously achieved using photometry from surveys. we derive the first sidereal rotation periods for additional 69 asteroids. we find good agreement in spin periods and pole orientations for objects with prior solutions. we obtain a statistical sample of asteroid physical properties that is sufficient for the detection of several previously known trends, such as the underrepresentation of slow rotators in current databases, and the anisotropic distribution of spin orientations driven by the nongravitational forces. we also investigate the dependence of spin orientations on the rotation period. since 2018, asas-sn has been observing the sky with higher cadence and a deeper limiting magnitude, which will lead to many more new solutions in just a few years. full tables a.1-a.4 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/654/a48 | v-band photometry of asteroids from asas-sn. finding asteroids with slow spin |
asteroid 162173 ryugu has numerous craters. the initial measurement of impact craters on ryugu, by sugita et al. (2019), is based on hayabusa2 onc images obtained during the first month after the arrival of hayabusa2 in june 2018. utilizing new images taken until february 2019, we constructed a global impact crater catalogue of ryugu, which includes all craters larger than 20 m in diameter on the surface of ryugu. as a result, we identified 77 craters on the surface of ryugu. ryugu shows variation in crater density which cannot be explained by the randomness of cratering; there are more craters at lower latitudes and fewer at higher latitudes, and fewer craters in the western bulge (160°e - 290°e) than in the region around the meridian (300°e - 30°e). this variation implies a complicated geologic history for ryugu. it seems that the variation in crater density indicates that the equatorial ridge located in the western hemisphere is relatively young, while that located in the eastern hemisphere is a fossil structure formed during the short rotational period in the distant past. | the spatial distribution of impact craters on ryugu |
using viscoelastic mass/spring model simulations, we explore tidal evolution and migration of compact binary asteroid systems. we find that after the secondary is captured into a spin-synchronous state, non-principal axis rotation in the secondary can be long-lived. the secondary's long axis can remain approximately aligned along the vector connecting secondary to primary while the secondary rocks back and forth about its long axis. inward orbital semi-major axis migration can also resonantly excite non-principal axis rotation. by estimating solar radiation forces on triangular surface meshes, we show that the magnitude of the byorp effect induced torque is sensitive to the secondary's spin state. non-principal axis rotation within the 1:1 spin-orbit resonance can reduce the byorp torque or cause frequent reversals in its direction. | non-principal axis rotation in binary asteroid systems and how it weakens the byorp effect |
we give new decomposition theorems for classes of graphs that can be transduced in first-order logic from classes of sparse graphs -- more precisely, from classes of bounded expansion and from nowhere dense classes. in both cases, the decomposition takes the form of a single colored rooted tree of bounded depth where, in addition, there can be links between nodes that are not related in the tree. the constraint is that the structure formed by the tree and the links has to be sparse. using the decomposition theorem for transductions of nowhere dense classes, we show that they admit low-shrubdepth covers of size $o(n^\varepsilon)$, where $n$ is the vertex count and $\varepsilon>0$ is any fixed~real. this solves an open problem posed by gajarský et al. (acm tocl '20) and also by briański et al. (sidma '21). | treelike decompositions for transductions of sparse graphs |
a widely held assumption is that each single white dwarf containing observable rocky debris requires the presence of at least one terrestrial or giant planet to have gravitationally perturbed the progenitor of the debris into the star. however, these planets could have been previously engulfed by the star or escaped the system, leaving behind asteroids, boulders, cobbles, pebbles, sand, and dust. these remaining small bodies could then persist throughout the host star's evolution into a white dwarf at ≈2-100 au scales, and then be radiatively dragged into the white dwarf without the help of a planet. here, we identify the parameter space and cooling ages for which this one metal-pollution mechanism is feasible by, for the first time, coupling poynting-robertson drag, the yarkovsky effect, and the yorp effect solely from rapidly dimming white dwarf radiation. we find that this no-planet pollution scenario is efficient for remnant 10-5 to 10-4 m dust up to about 80 au, 10-4 to 10-3 m sand up to about 25 au, and 10-3 to 10-2 m small pebbles up to about 8 au, and perhaps 10-1 to 100 m small boulders up to tens of au. further, young white dwarf radiation can spin-up large strengthless boulders with radii of 102-103 m to destruction, breaking them down into smaller fragments that then can be dragged towards the white dwarf. our work hence introduces a planetless metal-pollution mechanism that may be active in some fraction of white dwarf planetary systems. | orbit decay of 2-100 au planetary remnants around white dwarfs with no gravitational assistance from planets |
in a work by raz (j. acm and focs 16), it was proved that any algorithm for parity learning on $n$ bits requires either $\omega(n^2)$ bits of classical memory or an exponential number (in~$n$) of random samples. a line of recent works continued that research direction and showed that for a large collection of classical learning tasks, either super-linear classical memory size or super-polynomially many samples are needed. however, these results do not capture all physical computational models, remarkably, quantum computers and the use of quantum memory. it leaves the possibility that a small piece of quantum memory could significantly reduce the need for classical memory or samples and thus completely change the nature of the classical learning task. in this work, we prove that any quantum algorithm with both, classical memory and quantum memory, for parity learning on $n$ bits, requires either $\omega(n^2)$ bits of classical memory or $\omega(n)$ bits of quantum memory or an exponential number of samples. in other words, the memory-sample lower bound for parity learning remains qualitatively the same, even if the learning algorithm can use, in addition to the classical memory, a quantum memory of size $c n$ (for some constant $c>0$). our results refute the possibility that a small amount of quantum memory significantly reduces the size of classical memory needed for efficient learning on these problems. our results also imply improved security of several existing cryptographical protocols in the bounded-storage model (protocols that are based on parity learning on $n$ bits), proving that security holds even in the presence of a quantum adversary with at most $c n^2$ bits of classical memory and $c n$ bits of quantum memory (for some constant $c>0$). | memory-sample lower bounds for learning with classical-quantum hybrid memory |
context. it is well known that asteroids and comets fall into the sun. metal pollution of white dwarfs and transient spectroscopic signatures of young stars like β-pic provide growing evidence that extra solar planetesimals can attain extreme orbital eccentricities and fall into their parent stars.aims: we aim to develop a general, implementable, semi-analytical theory of secular eccentricity excitation of small bodies (planetesimals) in mean motion resonances with an eccentric planet valid for arbitrary values of the eccentricities and including the short-range force due to general relativity.methods: our semi-analytic model for the restricted planar three-body problem does not make use of series expansion and therefore is valid for any eccentricity value and semi-major axis ratio. the model is based on the application of the adiabatic principle, which is valid when the precession period of the longitude of pericentre of the planetesimal is much longer than the libration period in the mean motion resonance. in resonances of order larger than 1 this is true except for vanishingly small eccentricities. we provide prospective users with a mathematica notebook with implementation of the model allowing direct use.results: we confirm that the 4:1 mean motion resonance with a moderately eccentric (e' ≲ 0.1) planet is the most powerful one to lift the eccentricity of planetesimals from nearly circular orbits to star-grazing ones. however, if the planet is too eccentric, we find that this resonance is unable to pump the planetesimal's eccentricity to a very high value. the inclusion of the general relativity effect imposes a condition on the mass of the planet to drive the planetesimals into star-grazing orbits. for a planetesimal at ~ 1 au around a solar mass star (or white dwarf), we find a threshold planetary mass of about 17 earth masses. we finally derive an analytical formula for this critical mass.conclusions: planetesimals can easily fall into the central star even in the presence of a single moderately eccentric planet, but only from the vicinity of the 4:1 mean motion resonance. for sufficiently high planetary masses the general relativity effect does not prevent the achievement of star-grazing orbits. the mathematica notebook is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/605/a23 | extreme secular excitation of eccentricity inside mean motion resonance. small bodies driven into star-grazing orbits by planetary perturbations |
mean motion resonances (mmrs) play an important role in the formation and evolution of planetary systems and have significantly influenced the orbital properties and distribution of planets and minor planets in the solar system and in exoplanetary systems. most previous theoretical analyses have focused on the low- to moderate-eccentricity regime, but with new discoveries of high-eccentricity resonant minor planets and even exoplanets, there is increasing motivation to examine mmrs in the high-eccentricity regime. here we report on a study of the high-eccentricity regime of mmrs in the circular planar restricted three-body problem. numerical analyses of the 2:1 and the 3:2 interior resonances are carried out for a wide range of planet-to-star mass ratio μ, and for a wide range of eccentricity of the test particle. the surface-of-section technique is used to study the phase space structure near resonances. we find that new stable libration zones appear at higher eccentricity at libration centers that are shifted from those at low eccentricities. we provide physically intuitive explanations for these transitions in phase space, and we present novel results on the mass and eccentricity dependence of the resonance widths. our results show that mmrs have sizable libration zones at high eccentricities, comparable to those at lower eccentricities. | mean motion resonances at high eccentricities: the 2:1 and the 3:2 interior resonances |
asteroid families are groups of asteroids that are the product of collisions or of the rotational fission of a parent object. these groups are mainly identified in proper elements or frequencies domains. because of robotic telescope surveys, the number of known asteroids has increased from ${\simeq}10\, 000$ in the early 1990s to more than $750\, 000$ nowadays. traditional approaches for identifying new members of asteroid families, like the hierarchical clustering method (hcm), may struggle to keep up with the growing rate of new discoveries. here we used machine learning classification algorithms to identify new family members based on the orbital distribution in proper (a, e, sin (i)) of previously known family constituents. we compared the outcome of nine classification algorithms from stand-alone and ensemble approaches. the extremely randomized trees (extratree) method had the highest precision, enabling to retrieve up to 97 per cent of family members identified with standard hcm. | machine learning classification of new asteroid families members |
we report near-infrared (0.7-2.5 μm) reflectance spectra for each of the six target asteroids of the forthcoming nasa discovery-class mission lucy. five jupiter trojans (the binary (617) patroclus system, (3548) eurybates, (21900) orus, (11351) leucus, and (15094) polymele) are well characterized, with measurable spectral differences. we also report a survey-quality spectrum for main-belt asteroid (52246) donaldjohanson. we measured a continuum of spectral slopes including “red” (orus, leucus), “less red” (eurybates, patroclus-menoetius), and intermediate (polymele), indicating a range of compositional end-members or geological histories. we perform radiative transfer modeling of several possible surface compositions. we find that the mild-sloped spectra and low albedo of patroclus and eurybates imply similar compositions. eurybates (∼7 wt.% water ice) and patroclus (∼4 wt.% water ice) are consistent with a hydrated surface. models for orus and leucus are consistent with each other and require a significantly more reddening agent (e.g., iron-rich silicates or tholin-like organics). polymele has a linear spectrum like patroclus, but a higher albedo more closely aligned with orus/leucus, defying simple grouping. solar system formation models generally predict that the jovian trojans accreted in the outer solar system. our observations and analysis are generally consistently with this expectation, although not uniquely so. | compositional constraints for lucy mission trojan asteroids via near-infrared spectroscopy |
a new era of up-close asteroid exploration has been entered in the 21st century. however, the widely rugged terrain and microgravity field of asteroids still pose significant challenges to the stable landing of spacecraft and may even directly lead to the escape of the explorer. owing to the substantial energy dissipation arising from the interaction among multiple bodies, the flexible net, which is a typical multibody system, may be capable of overcoming the above problems. in this study, a dynamical model was established to analyze the movement of the flexible net spacecraft (fns) near and on the asteroid comprehensively. first, we investigated the dynamical environment of the target asteroid by combining the polyhedron method and spherical harmonics parametric surface modeling approach. thereafter, we constructed the multibody dynamics model of the explorer using the linear kelvin-voigt method. subsequently, we studied the collision process between the fns and asteroid based on the spring-damper contact dynamics model. the trajectory and speed of the fns could be derived by solving the system dynamic equations in parallel. finally, we analyzed the deformation, descent, jumping motion, and surface movement process of the fns during the movement. consequently, a promising scheme is provided for asteroid exploration missions in the future. | dynamical behavior of flexible net spacecraft for landing on asteroid |
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