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a pilot numerical model of the geminid meteoroid stream is presented. this model implies cometary origin of the stream. ejection of relatively small amount of particles (90 000 test meteoroids with masses 0.02, 0.003 and 0.0003 g) from the asteroid (3200) phaethon (the parent body) was simulated, and their evolution was followed till the present time. the particles close to the earth orbit were considered as the `shower'. it was found that the width of the model shower is at least twice less comparatively the real shower. the maximum activity of the model shower is dislocated and occurs about one day late. the most probable reason for both discrepancies is the drastic transformation of the parent body orbit during rapid release of the volatiles in the process of the stream initial formation. the dispersion of the model stream was evaluated in terms of the southworth-hawkins d-criterion. | a preliminary numerical model of the geminid meteoroid stream |
meteorite magnetizations can provide rare insight into early solar system evolution. such data take on new importance with recognition of the isotopic dichotomy between non-carbonaceous and carbonaceous meteorites, representing distinct inner and outer disk reservoirs, and the likelihood that parent body asteroids were once separated by jupiter and subsequently mixed. the arrival time of these parent bodies into the main asteroid belt, however, has heretofore been unknown. herein, we show that weak cv (vigarano type) and cm (mighei type) carbonaceous chondrite remanent magnetizations indicate acquisition by the solar wind 4.2 to 4.8 million years after ca-al-rich inclusion (cai) formation at heliocentric distances of ~2-4 au. these data thus indicate that the cv and cm parent asteroids had arrived near, or within, the orbital range of the present-day asteroid belt from the outer disk isotopic reservoir within the first 5 million years of solar system history. | arrival and magnetization of carbonaceous chondrites in the asteroid belt before 4562 million years ago |
nasa's lucy mission is designed to better understand the unique population of trojan asteroids. trojans were probably captured in jupiter's l4 and l5 points early in the solar system's evolution and little altered since then. a critical investigation of lucy is to use its highest-resolution camera, the lucy long range reconnaissance imager (l'lorri), to image trojans' surfaces to understand their geology and impact crater populations. through crater statistics, the population of smaller bodies that produced those impacts, relative age differences across the bodies, and other comparative investigations between bodies can be studied. mapping the crater population to the minimum diameters needed to achieve lucy's objectives might require image subsampling and deconvolution ("processing") to improve the spatial resolution, a process whereby multiple, slightly offset images are merged to create a single, better-sampled image and deconvolved with l'lorri's point-spread function. lucy's first earth gravity assist (ega1) provided an opportunity to test this process's accuracy using l'lorri images of the moon, whose crater population is well characterized and therefore provides ground-truth testing. specifically, the lunar crater imaging by l'lorri during ega1 allowed us to compare crater statistics derived from raw and processed l'lorri images with ground-truth statistics derived from higher-resolution lunar imaging from other missions. the results indicate the processing can improve impact crater statistics such that features can be identified and measured to ≈70% the diameter that they can otherwise be reliably mapped on native l'lorri images. this test's results will be used in the observation designs for the lucy flyby targets. | imaging lunar craters with the lucy long range reconnaissance imager (l'lorri): a resolution test for nasa's lucy mission |
the origin of fast radio bursts (frbs) is still a mystery. one model proposed to interpret the only known repeating object, frb 121102, is that the radio emission is generated from asteroids colliding with a highly magnetized neutron star (ns). with n-body simulations, we model a debris disc around a central star with an eccentric orbit intruding ns. as the ns approaches the first periastron passage, most of the comets are scattered away rather than being accreted by the ns. to match the observed frb rate, the debris belt would have to be at least 3 orders of magnitude more dense than the kuiper belt. we also consider the rate of collisions on to the central object but find that the density of the debris belt must be at least 4 orders of magnitude more dense than the kuiper belt. these discrepancies in the density arise even if (1) one introduces a kuiper belt-like comet belt rather than an asteroid belt and assume that comet impacts can also make frbs; (2) the ns moves ∼2 orders of magnitude slower than their normal proper-motion velocity due to supernova kicks; and (3) the ns orbit is coplanar to the debris belt, which provides the highest rate of collisions. | investigation of the asteroid-neutron star collision model for the repeating fast radio bursts |
a projectile accelerated by the hayabusa2 small carry-on impactor successfully produced an artificial impact crater with a final apparent diameter of 14.5 ± 0.8 m on the surface of the near-earth asteroid 162173 ryugu on april 5, 2019. at the time of cratering, deployable camera 3 took clear time-lapse images of the ejecta curtain, an assemblage of ejected particles forming a curtain-like structure emerging from the crater. focusing on the optical depth of the ejecta curtain and comparing it with a theoretical model, we infer the size of the ejecta particles. as a result, the typical size of the ejecta particles is estimated to be several centimeters to decimeters, although it slightly depends on the assumed size distribution. since the ejecta particles are expected to come from a depth down to ~1 m, our result suggests that the subsurface layer of ryugu is composed of relatively small particles compared to the uppermost layer on which we observe many meter-sized boulders. our result also suggests a deficit of particles of less than ~1 mm in the subsurface layer. these findings will play a key role in revealing the formation and surface evolution process of ryugu and other small solar system bodies. | size of particles ejected from an artificial impact crater on asteroid 162173 ryugu |
a recently discovered group of nearby co-orbital objects is an attractive location for extraterrestrial intelligence (eti) to locate a probe to observe earth while not being easily seen. these near-earth objects provide an ideal way to watch our world from a secure natural object. that provides resources an eti might need: materials, a firm anchor, and concealment. these have been little studied by astronomy and not at all by the search for extraterrestrial intelligence (seti) or planetary radar observations. i describe the objects found thus far and propose both passive and active observations of them as possible sites for extraterrestrial (et) probes. | looking for lurkers: co-orbiters as seti observables |
context. planetary debris is observed in the atmospheres of over 1000 white dwarfs, and two white dwarfs are now observed to contain orbiting minor planets. exoasteroids and planetary core fragments achieve orbits close to the white dwarf through scattering with major planets. however, the architectures that allow for this scattering to take place are time-consuming to explore with n-body simulations lasting ∼1010 yr; these long-running simulations restrict the amount of phase space that can be investigated.aims: here we use planar and three-dimensional (spatial) elliptic periodic orbits, as well as chaotic indicators through dynamical stability maps, as quick scale-free analytic alternatives to n-body simulations in order to locate and predict instability in white dwarf planetary systems that consist of one major and one minor planet on very long timescales. we then classify the instability according to ejection versus collisional events.methods: we generalized our previous work by allowing eccentricity and inclination of the periodic orbits to increase, thereby adding more realism but also significantly more degrees of freedom to our architectures. we also carried out a suite of computationally expensive 10 gyr n-body simulations to provide comparisons with chaotic indicators in a limited region of phase space.results: we compute dynamical stability maps that are specific to white dwarf planetary systems and that can be used as tools in future studies to quickly estimate pollution prospects and timescales for one-planet architectures. we find that these maps also agree well with the outcomes of our n-body simulations.conclusions: as observations of metal-polluted white dwarfs mount exponentially, particularly in the era of gaia, tools such as periodic orbits can help infer dynamical histories for ensembles of systems. | driving white dwarf metal pollution through unstable eccentric periodic orbits |
we analyzed data from the first year of a survey for near-earth objects (neos) that we are carrying out with the dark energy camera (decam) on the 4 m blanco telescope at the cerro tololo inter-american observatory. we implanted synthetic neos into the data stream to derive our nightly detection efficiency as a function of magnitude and rate of motion. using these measured efficiencies and the solar system absolute magnitudes derived by the minor planet center for the 1377 measurements of 235 unique neos detected, we directly derive, for the first time from a single observational data set, the neo size distribution from 1 km down to 10 m. we find that there are {10}6.6 neos larger than 10 m. this result implies a factor of 10 fewer small neos than some previous results, though our derived size distribution is in good agreement with several other estimates. | the size distribution of near-earth objects larger than 10 m |
all life on earth contains amino acids and carbonaceous chondrite meteorites have been suggested as their source at the origin of life on earth. while many meteoritic amino acids are considered indigenous, deciphering the extent of terrestrial contamination remains an issue. the ryugu asteroid fragments (jaxa hayabusa2 mission), represent the most uncontaminated primitive extraterrestrial material available. here, the concentrations of amino acids from two particles from different touchdown sites (td1 and td2) are reported. the concentrations show that n,n-dimethylglycine (dmg) is the most abundant amino acid in the td1 particle, but below detection limit in the other. the td1 particle mineral components indicate it experienced more aqueous alteration. furthermore, the relationships between the amino acids and the geochemistry suggest that dmg formed on the ryugu progenitor body during aqueous alteration. the findings highlight the importance of aqueous chemistry for defining the ultimate concentrations of amino acids in primitive extraterrestrial samples. | insights into the formation and evolution of extraterrestrial amino acids from the asteroid ryugu |
we report findings from a series of laser-simulated space weathering experiments on allende, a cv3 carbonaceous chondrite. the purpose of these experiments is to understand how spectra of anhydrous c-complex asteroids might vary as a function of micrometeorite bombardment. four 0.5-gram aliquots of powdered, unpacked allende meteorite were incrementally laser weathered with 30 mj pulses while under vacuum. radiative transfer modeling of the spectra and scanning transmission electron microscope (stem) analyses of the samples show lunar-like similarities and differences in response to laser-simulated space weathering. for instance, laser weathered allende exhibited lunar-like spectral changes. the overall spectra from visible to near infrared (vis-nir) redden and darken, and characteristic absorption bands weaken as a function of laser exposure. unlike lunar weathering, however, the continuum slope between 450-550 nm does not vary monotonically with laser irradiation. initially, spectra in this region redden with laser irradiation; then, the visible continua become less red and eventually spectrally bluer. stem analyses of less mature samples confirm submicroscopic iron metal (smfe) and micron sized sulfides. more mature samples reveal increased dispersal of fe-ni sulfides by the laser, which we infer to be the cause for the non-lunar-like changes in spectral behavior. spectra of laser weathered allende are a reasonable match to t- or possibly k-type asteroids; though the spectral match with a parent body is not exact. the key take away is, laser weathered allende looks spectrally different (i.e., darker, and redder or bluer depending on the wavelength region) than its unweathered spectrum. consequently, connecting meteorites to asteroids using unweathered spectra of meteorites would result in a different parent body than one matched on the basis of weathered spectra. further, spectra for these laser weathering experiments may provide an explanation for inconsistencies observed in both laboratory (e.g., hiroi et al., 2003, 2001; lazzarin et al., 2006; moroz et al., 2004, 1996; shingareva et al., 2004) and telescopic data (lazzarin et al., 2006; marchi et al., 2006; nesvorný et al., 2005). | incremental laser space weathering of allende reveals non-lunar like space weathering effects |
topological defects play a key role in two-dimensional active nematics, and a transient role in two-dimensional active polar fluids. in this paper, we study both the transient and long-time behavior of defects in two-dimensional active polar fluids in the limit of strong order and overdamped, compressible flow, and compare the defect dynamics with the corresponding active nematics model studied recently. one result is non-central interactions between defect pairs for active polar fluids, and by extending our analysis to allow orientation dynamics of defects, we find that the orientation of $+1$ defects, unlike that of $\pm 1/2$ defects in active nematics, is not locked to defect positions and relaxes to asters. moreover, using a scaling argument, we explain the transient feature of active polar defects and show that in the steady state, active polar fluids are either devoid of defects or consist of a single aster. we argue that for contractile (extensile) active nematic systems, $+1$ vortices (asters) should emerge as bound states of a pair of $+1/2$ defects, which has been recently observed. moreover, unlike the polar case, we show that for active nematics, a linear chain of equally spaced bound states of pairs of $+1/2$ defects can screen the activity term. a common feature in both models is the appearance of $+1$ defects (elementary in polar and composite in nematic) in the steady state. | defect dynamics in active polar fluids vs. active nematics |
we present near-infrared spectroscopy of the sporadically active asteroid (6478) gault collected on the 3 m nasa/infrared telescope facility observatory in late 2019 march/early april. long-exposure imaging with the 0.5 m near earth environment monitoring t05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. we confirm that gault is a silicate-rich (q- or s-type) object likely linked to the (25) phocaea collisional family. the asteroid exhibits substantial spectral variability over the 0.75-2.45 μm wavelength range, from unusual blue (s‧ = -13.5 ± 1.1% μm-1) to typical red (s‧ = +9.1 ± 1.2% μm-1) spectral slope, that does not seem to correlate with activity. spectral comparisons with samples of ordinary chondrite meteorites suggest that the blue color relates to the partial loss of the asteroid dust regolith, exposing a fresh, dust-free material at its surface. the existence of asteroids rotating close to rotational break-up limit and having similar spectral properties as gault further supports this interpretation. future spectroscopic observations of gault, when the tails dissipate, will help further testing of our proposed hypothesis. | active asteroid (6478) gault: a blue q-type surface below the dust? |
the geminid meteoroid stream and asteroid (3200) phaethon are generally recognized as being associated. it has been claimed that two other asteroids, namely (225416) 1999 yc and (155140) 2005 ud, might be the members of this complex. we aim to study this possibility, with the assumption that their separation happened within the last several thousand years. the stability of the orbits of the asteroids over the last 5000 yr was studied. the fragmentation was modelled assuming that the separation speed of the fragments was either 100 m s-1 or 1 km s-1. their orbits were integrated numerically till the present time. by analysing the orbital similarity and minimum orbit intersection distance, it is found that neither (225416) 1999 yc nor (155140) 2005 ud are members of the phaethon-geminid complex. | asteroid (3200) phaethon and the geminid meteoroid stream complex |
we consider a dynamical shake-up model to explain the low mass of mars and the lack of planets in the asteroid belt. in our scenario, a secular resonance with jupiter sweeps through the inner solar system as the solar nebula depletes, pitting resonant excitation against collisional damping in the sun’s protoplanetary disk. we report the outcome of extensive numerical calculations of planet formation from planetesimals in the terrestrial zone, with and without dynamical shake-up. if the sun’s gas disk within the terrestrial zone depletes in roughly a million years, then the sweeping resonance inhibits planet formation in the asteroid belt and substantially limits the size of mars. this phenomenon likely occurs around other stars with long-period massive planets, suggesting that asteroid belt analogs are common. | terrestrial planet formation: dynamical shake-up and the low mass of mars |
modelling and simulation of collisional particle breakage mechanisms are crucial in several physical phenomena (asteroid belts, molecular clouds, raindrop distribution etc.) and process industries (chemical, pharmaceutical, material etc.). this paper deals with the development and analysis of schemes to numerically solve the multi-dimensional nonlinear collisional fragmentation model. two numerical techniques are presented based on the finite volume discretization method. it is shown that the proposed schemes are consistent with the hypervolume conservation property. moreover, the number preservation property law also holds for one of them. detailed mathematical discussions are presented to establish the convergence analysis and consistency of the multi-dimensional schemes under predefined restrictions on the kernel and initial data. the proposed schemes are shown to be second-order convergent. finally, several numerical computations (one-, two- and three-dimensional fragmentation) are performed to validate the numerical schemes. | development and analysis of moments preserving finite volume schemes for multi-variate nonlinear breakage model |
the cybele and hilda dynamical groups delimit the outer edge of the asteroid belt. their compositional distribution is a key element to constrain evolutionary models of the solar system. in this paper, we present a compositional analysis of these populations using spectroscopic observations, sdss and neowise data. as part of the primass (primitive asteroids spectroscopic survey), we acquired visible spectra of 18 objects in hilda or cybele groups with the goodman high throughput spectrometer at the 4.1 m soar telescope and 20 near-ir spectra of hilda objects with near infrared camera spectrograph at the 3.56 m tng. the sample is enlarged with spectra taken from the literature in order to increase our statistical analysis. the spectra were inspected for aqueous alteration bands and other spectral features that can be linked to compositional constraints. the analysis shows a continuous distribution of compositions from the main-belt to the cybele, hilda and trojan regions. we also identify a population in the trojans group not present in hilda or cybele objects. | primass visits hilda and cybele groups |
the small asteroid itokawa was visited in 2005 by the japanese spacecraft hayabusa. the images of the surface showed a scenario different to previously visited asteroids. itokawa has a small number of large craters and many large boulders randomly distributed on most of the surface. we analyse images taken at different surface resolution and configurations corresponding to several regions on the asteroid's surface. by overlapping visual images and maps of the total potential and surface gravity, we observe a correlation between the distribution of boulders and these parameters. the boulders on the surface were identified by visual inspection of several images. after fitting ellipses to every boulder, we computed their size and the size distribution from decimeters to several meters at different locations in the surface. we found that the size distribution is correlated with the total potential and the surface gravity. a steeper size distribution shifted towards the small objects is observed in the low negative total potential (high surface gravity), which corresponds to the muses-c region. meanwhile, in the "head" and "bottom" regions of high potential (low surface gravity), we obtain a shallower size distribution, shifted towards the large boulders. we confirm there is a size segregation that is correlated with the gravity field which can be explained under the action of the brazil nut effect. there is a global relocation of boulders, with large ones going into the high potential regions and small ones into the low potential ones. a shape segregation is also observed on the location of the boulders: more rounded ones are found in the regions of high potential, while more elongated ones are frequent in regions of low potential. | distribution of boulders and the gravity potential on asteroid itokawa |
we describe a novel data-processing and analysis pipeline for optical observations of moving objects, either of natural (asteroids, meteors) or artificial origin (satellites, space debris). the monitoring of the space object populations requires reliable acquisition of observational data, to support the development and validation of population models and to build and maintain catalogues of orbital elements. the orbital catalogues are, in turn, needed for the assessment of close approaches (for asteroids, with the earth; for satellites, with each other) and for the support of contingency situations or launches. for both types of populations, there is also increasing interest to detect fainter objects corresponding to the small end of the size distribution. the esa-funded streakdet (streak detection and astrometric reduction) activity has aimed at formulating and discussing suitable approaches for the detection and astrometric reduction of object trails, or streaks, in optical observations. our two main focuses are objects in lower altitudes and space-based observations (i.e., high angular velocities), resulting in long (potentially curved) and faint streaks in the optical images. in particular, we concentrate on single-image (as compared to consecutive frames of the same field) and low-snr detection of objects. particular attention has been paid to the process of extraction of all necessary information from one image (segmentation), and subsequently, to efficient reduction of the extracted data (classification). we have developed an automated streak detection and processing pipeline and demonstrated its performance with an extensive database of semisynthetic images simulating streak observations both from ground-based and space-based observing platforms. the average processing time per image is about 13 s for a typical 2k-by-2k image. for long streaks (length >100 pixels), primary targets of the pipeline, the detection sensitivity (true positives) is about 90% for both scenarios for the bright streaks (snr > 1), while in the low-snr regime, the sensitivity is still 50% at snr = 0.5 . | streak detection and analysis pipeline for space-debris optical images |
from preliminary 2010-2011 results of the cameras for allsky meteor surveillance (cams) meteoroid orbit survey, which were combined with published 2007-2009 sonotaco video meteor network data, 55 new meteor showers (##448-502) were identified and added to the iau working list on meteor showers in 2012. these showers were identified based on an automated single-linked dsh-criterion analysis of a combined 105,000 orbits with high-threshold (a low dsh < 0.05), but low acceptable sample size (⩾6 members). three more years of cams and four more years of sonotaco observations have now increased the meteoroid orbit database four fold. the earlier detections are verified by searching for number density enhancements in drift-corrected radiant and orbital element maps. twenty showers are detected in both surveys and are now certain to exist. median orbital elements are presented. not detected in this manner were 19% of the fast vg > 40 km/s showers, 54% of the vg = 18-40 km/s showers, and 90% of the slow vg < 18 km/s showers. | cams verification of single-linked high-threshold d-criterion detected meteor showers |
this paper presents an overview of space mission concepts for disrupting or pulverizing hazardous asteroids, especially with warning time shorter than approximately 10 years. an innovative mission concept, referred to as a nuclear hypervelocity asteroid intercept vehicle (haiv) system, employs both a kinetic-energy impactor and nuclear explosive devices. a new mission concept of exploiting a multiple kinetic-energy impactor vehicle (mkiv) system that doesn't employ nuclear explosives is proposed in this paper, especially for asteroids smaller than approximately 150 m in diameter. the multiple shock wave interaction effect on disrupting or pulverizing a small asteroid is discussed using hydrodynamic simulation results. a multi-target terminal guidance problem and a planetary defense mission design employing a heavy-lift launch vehicle are also brie y discussed in support of the new non-nuclear mkiv mission concept. the nuclear haiv and non-nuclear mkiv systems complement to each other to effectively mitigate the various asteroid impact threats with short warning time. | planetary defense mission concepts for disrupting/pulverizing hazardous asteroids with short warning time |
by means of extensive three-dimensional contact dynamics simulations, we analyze the strength properties and microstructure of a granular asteroid, modeled as a self-gravitating cohesive granular aggregate composed of spherical particles, and subjected to diametrical compression tests. we show that, for a broad range of system parameters (shear rate, cohesive forces, asteroid diameter), the behavior can be described by a modified inertial number that incorporates interparticle cohesion and gravitational forces. at low inertial numbers, the behavior is ductile with a well-defined stress peak that scales with internal pressure with a prefactor ≃0.9 . as the inertial number increases, both the prefactor and fluctuations around the mean increase, evidencing a dynamical crisis resulting from the destabilizing effect of particle inertia. from a micromechanical description of the contact and force networks, we propose a model that accounts for solid fraction, local stress, particle connectivity, and granular texture. in the limit of small inertial numbers, we find a very good agreement of the theoretical estimate of compressive strength, evidencing the major role of these structural parameters for the modeled aggregates. | scaling behavior of cohesive self-gravitating aggregates |
jovian co-orbitals share jupiter's orbit in 1:1 mean motion resonance. this includes $>$10,000 so-called trojan asteroids surrounding the leading (l4) and trailing (l5) lagrange points, viewed as stable groups dating back to planet formation. via a massive numerical study we identify for the first time some trojans which are certainly only `metastable'; instead of being primordial, they are recent captures from heliocentric orbits into moderately long-lived (10 kyr - 100 myr) metastable states that will escape back to the scattering regime. we have also identified (1) the first two jovian horseshoe co-orbitals that exist for many resonant libration periods, and (2) eight jovian quasi-satellites with metastable lifetimes of 4-130 kyr. our perspective on the trojan population is thus now more complex as jupiter joins the other giant planets in having known metastable co-orbitals which are in steady-state equilibrium with the planet-crossing centaur and asteroid populations, in agreement with theoretical estimates. | jupiter's metastable companions |
the metal budgets in some white dwarf (wd) atmospheres reveal that volatile-rich circumstellar bodies must both exist in extrasolar systems and survive the giant branch phases of stellar evolution. the resulting behaviour of these active asteroids or comets which orbit wds is not well-understood, but may be strongly influenced by sublimation due to stellar radiation. here we develop a model, generally applicable to any extrasolar system with a main-sequence or wd star, that traces sublimation-induced orbital element changes in approximately km-sized extrasolar minor planets and comets travelling within hundreds of au. we derive evolution equations on orbital time-scales and for arbitrarily steep power-law sublimation dependences on distance, and place our model in a solar system context. we also demonstrate the importance of coupling sublimation and general relativity, and the orbital consequences of outgassing in arbitrary directions. we prove that non-gravitational accelerations alone cannot result in orbit crossing with the wd disruption radius, but may shrink or expand the orbit by up to several au after a single pericentre passage, potentially affecting subsequent interactions with remnant debris and planets. our analysis suggests that extant planets must exist in polluted wd systems. | sublimation-induced orbital perturbations of extrasolar active asteroids and comets: application to white dwarf systems |
using our photometric observations taken between april 1996 and january 2013 and other published data, we derived properties of the binary near-earth asteroid (175706) 1996 fg3 including new measurements constraining evolution of the mutual orbit with potential consequences for the entire binary asteroid population. we also refined previously determined values of parameters of both components, making 1996 fg3 one of the most well understood binary asteroid systems. with our 17-year long dataset, we determined the orbital vector with a substantially greater accuracy than before and we also placed constraints on a stability of the orbit. specifically, the ecliptic longitude and latitude of the orbital pole are 266 ° and - 83 ° , respectively, with the mean radius of the uncertainty area of 4 ° , and the orbital period is 16.1508 ± 0.0002 h (all quoted uncertainties correspond to 3σ). we looked for a quadratic drift of the mean anomaly of the satellite and obtained a value of 0.04 ± 0.20 deg /yr2 , i.e., consistent with zero. the drift is substantially lower than predicted by the pure binary yorp (byorp) theory of mcmahon and scheeres (mcmahon, j., scheeres, d. [2010]. icarus 209, 494-509) and it is consistent with the tigidity and quality factor of μq = 1.3 ×107 pa using the theory that assumes an elastic response of the asteroid material to the tidal forces. this very low value indicates that the primary of 1996 fg3 is a 'rubble pile', and it also calls for a re-thinking of the tidal energy dissipation in close asteroid binary systems. | the binary near-earth asteroid (175706) 1996 fg3 - an observational constraint on its orbital evolution |
the nature of the early martian climate has been the subject of debate for decades, with geologic evidence suggesting an environment with prolonged precipitation and flowing liquid water on the surface, while climate models have struggled to reproduce such conditions. in this paper, we test the impact heating hypothesis for warming early mars as presented in segura et al. (2008) using a new early mars version of the nasa ames research center 3-d mars global climate model. we simulate impacts of asteroids 30-, 50-, and 100- km in diameter into atmospheres possessing 150-mbar, 1-bar, and 2-bar surface pressure conditions, accounting for both radiatively active and radiatively inert water clouds. based on the scenarios simulated here, we find that the evolution of post-impact initially hot and moist conditions can be characterized in four phases: 1) a rapid radiative cooling phase, 2) a latent heat phase in which cloud formation and the radiative effects of water vapor induce a temporary warm period with significant precipitation, 3) a transition phase in which cooling accelerates due to sublimation at the surface and the lack of available water in the atmosphere for greenhouse warming and in which water vapor begins to contribute less to surface warming than water clouds, and 4) a steady state phase with mean annual surface temperatures below freezing and minimal precipitation. in these post-impact climate scenarios, global average surface temperatures remain above freezing for only 0.043 to 6.25 mars years, accompanied by 0.23 to 5.8 m of cumulative precipitation (global equivalent) falls during 10 simulated mars years. ultimately, periods of warm temperatures and significant precipitation are short-lived and even in the warmest cases, do not support sustained conditions in which valley networks are likely to form in the long run either by liquid precipitation or by seasonal melting of surface ice. scenarios with high surface pressures and radiatively active clouds experience the longest periods of above-freezing post-impact temperatures and result in the highest mean annual temperatures during the fourth phase (272.8 k in our warmest scenario), highlighting the potential significance of water clouds in the early martian climate and the importance of their careful physical treatment in models. future studies addressing sustained warm and wet early mars conditions should investigate the potential effects of obliquity, initial surface ice distribution, and possible delivery of reducing greenhouse gases on these post-impact climates. | testing the impact heating hypothesis for early mars with a 3-d global climate model |
the double asteroid redirection test (dart) mission will be the first test of a kinetic impactor as a means of planetary defense. in late 2022, dart will collide with dimorphos, the secondary in the didymos binary asteroid system. the impact will cause a momentum transfer from the spacecraft to the binary asteroid, changing the orbit period of dimorphos and forcing it to librate in its orbit. owing to the coupled dynamics in binary asteroid systems, the orbit and libration state of dimorphos are intertwined. thus, as the secondary librates, it also experiences fluctuations in its orbit period. these variations in the orbit period are dependent on the magnitude of the impact perturbation, as well as the system's state at impact and the moments of inertia of the secondary. in general, any binary asteroid system whose secondary is librating will have a nonconstant orbit period on account of the secondary's fluctuating spin rate. the orbit period variations are typically driven by two modes: a long period and a short period, each with significant amplitudes on the order of tens of seconds to several minutes. the fluctuating orbit period offers both a challenge and an opportunity in the context of the dart mission. orbit period oscillations will make determining the post-impact orbit period more difficult but can also provide information about the system's libration state and the dart impact. | libration-induced orbit period variations following the dart impact |
several pieces of evidence suggest that silicate grains in primitive meteorites are not interstellar grains but condensates formed in the early solar system. moreover, the size distribution of matrix grains in chondrites implies that these condensates might be formed as nanometer-sized grains. therefore, we propose a novel scenario for rocky planetesimal formation in which nanometer-sized silicate grains are produced by evaporation and recondensation events in early solar nebula, and rocky planetesimals are formed via aggregation of these nanograins. we reveal that silicate nanograins can grow into rocky planetesimals via direct aggregation without catastrophic fragmentation and serious radial drift, and our results provide a suitable condition for protoplanet formation in our solar system. | rocky planetesimal formation via fluffy aggregates of nanograins |
large language models (llms) have acquired ubiquitous attention for their performances across diverse domains. our study here searches through llms' cognitive abilities and confidence dynamics. we dive deep into understanding the alignment between their self-assessed confidence and actual performance. we exploit these models with diverse sets of questionnaires and real-world scenarios and extract how llms exhibit confidence in their responses. our findings reveal intriguing instances where models demonstrate high confidence even when they answer incorrectly. this is reminiscent of the dunning-kruger effect observed in human psychology. in contrast, there are cases where models exhibit low confidence with correct answers revealing potential underestimation biases. our results underscore the need for a deeper understanding of their cognitive processes. by examining the nuances of llms' self-assessment mechanism, this investigation provides noteworthy revelations that serve to advance the functionalities and broaden the potential applications of these formidable language models. | the confidence-competence gap in large language models: a cognitive study |
we present deep imaging observations, orbital dynamics, and dust-tail model analyses of the double-component asteroid p/2016 j1 (j1-a and j1-b). the observations were acquired at the gran telescopio canarias (gtc) and the canada-france-hawaii telescope (cfht) from mid-march to late july of 2016. a statistical analysis of backward-in-time integrations of the orbits of a large sample of clone objects of p/2016 j1-a and j1-b shows that the minimum separation between them occurred most likely ∼2300 days prior to the current perihelion passage, i.e., during the previous orbit near perihelion. this closest approach was probably linked to a fragmentation event of their parent body. monte carlo dust-tail models show that those two components became active simultaneously ∼250 days before the current perihelion, with comparable maximum loss rates of ∼0.7 and ∼0.5 kg s-1, and total ejected masses of 8 × 106 and 6 × 106 kg for fragments j1-a and j1-b, respectively. consequently, the fragmentation event and the present dust activity are unrelated. the simultaneous activation times of the two components and the fact that the activity lasted 6-9 months or longer, strongly indicate ice sublimation as the most likely mechanism involved in the dust emission process. | the splitting of double-component active asteroid p/2016 j1 (panstarrs) |
recent observations of water emission around ceres suggest the presence of an ice layer on or beneath the surface of this asteroid. several mechanisms have been suggested to explain these plumes, among which cometary-like sublimation seems to be plausible, since there is a correlation between the magnitude of the emission and the change in the heliocentric distance along the orbit. in this work, we applied a comet sublimation model to study the plausible scenarios that match with herschel observations of the water flux (1026 molecules s-1). each scenario is characterized by a well-defined set of physical and orbital parameters. moreover, a study of the dynamic evolution of the h2o plume has been performed, showing that an optically thin transient atmospheric envelope, with a typical timescale of some tens of days, can be maintained by the h2o surface emission. our simulations could be useful theoretical support for the dawn nasa mission by giving a better understanding of the physical conditions for water sublimation and ice stability. | ceres water regime: surface temperature, water sublimation and transient exo(atmo)sphere |
the origin of the jupiter trojan asteroids has long been a mystery. dynamically, the population, which is considerably smaller than the main asteroid belt, librates around jupiter's stable l4 and l5 lagrange points, 60 deg ahead and behind jupiter. it is thought that these bodies were captured into these orbits early in solar system history, but any capture mechanism must also explain why the trojans have an excited inclination distribution, with some objects reaching inclinations of 35°. the trojans themselves, individually and in aggregate, also have spectral and physical properties that appear consistent with many small bodies found in the outer solar system (e.g., irregular satellites, kuiper belt objects). in this review, we assemble what is known about the trojans and discuss various models for their origin and collisional evolution. it can be argued that the trojans are unlikely to be captured planetesimals from the giant planet zone, but instead were once denizens of the primordial kuiper belt, trapped by the events taking place during a giant planet instability. the lucy mission to the trojans is therefore well positioned to not only answer questions about these objects, but also about their place in planet formation and solar system evolution studies. | origin and evolution of jupiter's trojan asteroids |
the jaxa astromaterials science research group developed a web-based database system for the hayabusa2-returned samples from c-type asteroid ryugu. the ryugu sample database system database (rs-dbs) is designed as an online catalog for users of wide scientific communities to choose their preferred samples and propose the sample loan through the jaxa ryugu sample announcement of opportunity. ryugu samples can be sorted and given identification numbers as individual particles larger than 1 mm and aggregate samples consisting of less than 1 mm particle through the phase1 curation (i.e., the initial description). the rs-dbs lists all samples with analytical data such as a microscopy image, size, mass, spectroscopic data, and shape model obtained by the initial description at the jaxa curation facility. the list also includes research results conducted by previous projects (i.e., the hayabusa2 initial analysis team and phase2 curation teams). the rs-dbs, built with open-source technologies, archives the data securely and long-term on the data archives and transmission system (darts) at isas/jaxa. | ryugu sample database system (rs-dbs) on the data archives and transmission system (darts) by the jaxa curation |
we present fully covered phased light curves for 56 jovian trojan asteroids as observed by the k2 mission of the kepler space telescope. this set of objects has been monitored during campaign 6 and represents a nearly unbiased subsample of the population of small solar system bodies. we derived precise periods and amplitudes for all trojans, and found their distributions to be compatible with the previous statistics. we point out, however, that ground-based rotation periods are often unreliable above 20 h, and we find an overabundance of rotation periods above 60 h compared with other minor planet populations. from amplitude analysis we derive a rate of binarity of 20 ± 5%. our spin rate distribution confirms the previously obtained spin barrier of 5 h and the corresponding 0.5 g cm-3 cometary-like density limit, also suggesting a high internal porosity for jovian trojans. one of our targets, asteroid 65227 exhibits a double rotation period, which can either be due to binarity or the outcome of a recent collision. | the heart of the swarm: k2 photometry and rotational characteristics of 56 jovian trojan asteroids |
context. apart from thousands of "regular" exoplanet candidates, kepler satellite has discovered a small number of stars exhibiting peculiar eclipse-like events. they are most probably caused by disintegrating bodies transiting in front of the star. however, the nature of the bodies and obscuration events, such as those observed in kic 8462852, remain mysterious. a swarm of comets or artificial alien mega-structures have been proposed as an explanation for the latter object.aims: we explore the possibility that such eclipses are caused by the dust clouds associated with massive parent bodies orbiting the host star.methods: we assumed a massive object and a simple model of the dust cloud surrounding the object. then, we used the numerical integration to simulate the evolution of the cloud, its parent body, and resulting light-curves as they orbit and transit the star.results: we found that it is possible to reproduce the basic features in the light-curve of kic 8462852 with only four objects enshrouded in dust clouds. the fact that they are all on similar orbits and that such models require only a handful of free parameters provides additional support for this hypothesis.conclusions: this model provides an alternative to the comet scenario. with such physical models at hand, at present, there is no need to invoke alien mega-structures for an explanation of these light-curves. | mysterious eclipses in the light curve of kic8462852: a possible explanation |
the hamburg (h4) meteorite fell on 17 january 2018 at 01:08 ut approximately 10 km north of ann arbor, michigan. more than two dozen fragments totaling under 1 kg were recovered, primarily from frozen lake surfaces. the fireball initial velocity was 15.83 ± 0.05 km s-1, based on four independent records showing the fireball above 50 km altitude. the radiant had a zenith angle of 66.14 ± 0.29° and an azimuth of 121.56 ± 1.2°. the resulting low inclination (<1°) apollo-type orbit has a large aphelion distance and tisserand value relative to jupiter (tj) of 3. two major flares dominate the energy deposition profile, centered at 24.1 and 21.7 km altitude, respectively, under dynamic pressures of 5-7 mpa. the geostationary lightning mapper on the geostationary operational environmental satellite-16 also detected the two main flares and their relative timing and peak flux agree with the video-derived brightness profile. our preferred total energy for the hamburg fireball is 2-7 t tnt (8.4-28 × 109 j), which corresponds to a likely initial mass in the range of 60-225 kg or diameter between 0.3 and 0.5 m. based on the model of granvik et al. (2018), the meteorite originated in an escape route from the mid to outer asteroid belt. hamburg is the 14th known h chondrite with an instrumentally derived preatmospheric orbit, half of which have small (<5°) inclinations making connection with (6) hebe problematic. a definitive parent body consistent with all 14 known h chondrite orbits remains elusive. | the hamburg meteorite fall: fireball trajectory, orbit, and dynamics |
the crusts of the oldest protoplanets are virtually unknown due to the scarcity of samples. here, we describe the oldest known lava that crystallized ca. 4,565 ma ago and formed by partial melting of a chondritic parent body. 26al-26mg systematics suggest that the elapsed time between melting and crystallization was significant, on the order of several 105 y, probably due to the viscosity of the magma. although the first protoplanetary crusts were frequently not basaltic, their remains are not detected in the asteroid belt because their parent bodies served as the building blocks for larger rocky bodies or were nearly totally destroyed. | a 4,565-my-old andesite from an extinct chondritic protoplanet |
advancements in space exploration and sample return technology present a unique opportunity to leverage sample return capsules (srcs) towards studying atmospheric entry of meteoroids and asteroids. specifically engineered for the secure transport of valuable extraterrestrial samples from interplanetary space to earth, srcs offer unexpected benefits that reach beyond their intended purpose. as srcs enter the earth's atmosphere at hypervelocity, they are analogous to naturally occurring meteoroids and thus, for all intents and purposes, can be considered artificial meteors. furthermore, srcs are capable of generating shockwaves upon reaching the lower transitional flow regime, and thus can be detected by strategically positioned geophysical instrumentation. nasa's osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) src is one of only a handful of artificial objects to re-enter the earth's atmosphere from interplanetary space since the end of the apollo era and it will provide an unprecedented observational opportunity. this review summarizes past infrasound and seismic observational studies of src re-entries since the end of the apollo era and presents their utility towards the better characterization of meteoroid flight through the atmosphere. | a review of infrasound and seismic observations of sample return capsules since the end of the apollo era in anticipation of the osiris-rex arrival |
samples from the carbonaceous asteroid (162173) ryugu provide information on the chemical evolution of organic molecules in the early solar system. here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. sodium is the dominant electrolyte of the salt fraction extract. anions and nh4+ are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order so42− > cl− > s2o32− > no3− > nh4+. the salt fraction extracts contain anionic soluble sulfur-bearing species such as sn-polythionic acids (n < 6), cn-alkylsulfonates, alkylthiosulfonates, hydroxyalkylsulfonates, and hydroxyalkylthiosulfonates (n < 7). the sulfur-bearing soluble compounds may have driven the molecular evolution of prebiotic organic material transforming simple organic molecules into hydrophilic, amphiphilic, and refractory s allotropes. | chemical evolution of primordial salts and organic sulfur molecules in the asteroid 162173 ryugu |
in 2010 jewitt and li published a paper examining the behavior of "comet-asteroid transition object" 3200 phaethon, arguing it was asteroid-like in its behavior throughout most of its orbit, but that near its perihelion, at a distance of only 0.165 au from the sun, its dayside temperatures would be hot enough to vaporize rock (>1000 k, hanus et al. 2016). thus it would act like a "rock comet" as gases produced from evaporating rock were released from the body, in a manner similar to the more familiar sublimation of water ice into vacuum seen for comets coming within ~3 au of the sun. in this note we predict that the same thermal effects that would create "rock comet" behavior with qgas ~ 1022 mol/s at perihelion have also helped to greatly bluen phaethon's surface via preferential thermal alteration and sublimative removal of fe and refractory organics, known reddening and darkening agents. these predictions are testable by searching for signs of spectral bluening of the surfaces of other small bodies in phaethon-like small perihelion orbits, including comets, and by in situ measurements of phaethon's surface and coma composition near perihelion with the upcoming destiny+ mission (kawakatsu & itawa 2013, arai et al. 2018) to phaethon by jaxa. | thermal alteration and differential sublimation can create phaethon\'s "rock comet" activity and blue color |
the geminids meteoroid stream produces one of the most intense meteor showers at earth. it is an unusual stream in that its parent body is understood to be an asteroid, (3200) phaethon, unlike most streams, which are formed via ongoing cometary activity. until recently, our primary understanding of this stream came from earth-based measurements of the geminids meteor shower. however, the parker solar probe (psp) spacecraft has transited near the core of the stream close to its perihelion and provides a new platform to better understand this unique stream. here, we create a dynamical model of the geminids meteoroid stream, calibrate its total density to earth-based measurements, and compare this model to recent observations of the dust environment near the sun by psp. for the formation mechanisms considered, we find with the exception of very near perihelion the core of the meteoroid stream predominantly lies interior to the orbit of its parent body and we expect grains in the stream to be ≳10 μm in radius. data-model comparisons of the location of the stream relative to phaethon's orbit near perihelion are more consistent with a catastrophic formation scenario, with the core stream residing near or outside the orbit of its parent body consistent with psp observations. this is in contrast to a cometary formation mechanism, where even near the sun the meteoroid stream is interior to the orbit of its parent body. finally, while psp transits very near the core of the stream, the impact rate expected from geminids meteoroids is orders of magnitude below the impact rates observed by psp, and hence undetectable in situ. we similarly expect the upcoming destiny+ mission to be unable to detect appreciable quantities of geminids grains far from (3200) phaethon. | formation, structure, and detectability of the geminids meteoroid stream |
on october 4, 1957, homo sapiens crossed a new threshold of technological innovation after constructing an artifact capable of entering low earth orbit and effectively paving the way for a future of space exploration. this artifact was sputnik 1, launched by the soviet space program which triggered the "space race" of the mid‑20th century. over the past 65 years, we have continued to explore and populate our solar system with rockets and spacecraft including satellites, probes, landers, and rovers. this expansion into our solar system has left traces of our presence on several planets including the earth, mars, mercury, and venus along with earth's moon, titan, and several galaxy travelers in the form of asteroids and comets. today, we have entered the realm of a new privatized and global space race, effectively a "new space race" or "new space age." as we expand our material footprint into new extraterrestrial environments, there is a growing need to understand the types of unique site formation processes capable of altering, destroying, or preserving this rapidly increasing archaeological record known as space heritage. such understandings are germane to the subdiscipline of geoarchaeology, that part of archaeology dedicated to studying the interaction between humans, cultural heritage, and environmental systems from a geoscience perspective. closely aligned and partially overlapping with the subdisciplines of space archaeology, archaeological science, and planetary geology, we introduce a new subfield we call planetary geoarchaeology to open discussion about how geoarchaeologists can play a role in addressing current and future issues surrounding the preservation and management of space heritage. to demonstrate the potential of the subdiscipline, we focus on the current archaeological record of the moon, describe lunar site formation processes, and discuss the implications for the current and future preservation of space heritage in the lunar setting. planetary geoarchaeology can be applied to practically every type of extraterrestrial environment, provided humans have left behind a measurable record. we hope this paper will spur more research studying human–environment interaction in space. | planetary geoarchaeology as a new frontier in archaeological science: evaluating site formation processes on earth's moon |
context. most small asteroids (< 50 km in diameter) are the result of the breakup of a larger parent body and are often considered to be rubble-pile objects. similar structures are expected for the secondaries of small asteroid binaries, including dimorphos, the smaller component of the 65 803 didymos binary system and the target of nasa's double asteroid redirection test (dart) and esa's hera mission. the dart impact will occur on september 26, 2022, and will alter the orbital period of dimorphos around didymos.aims: in this work we assume dimorphos-like bodies with a rubble-pile structure and quantify the effects of boulder packing in its interior on the post-impact morphology, degree of shape change, and material ejection processes.methods: we used the bern smoothed particle hydrodynamics shock physics code to numerically model hypervelocity impacts on small, 160 m in diameter, rubble-pile asteroids with a variety of boulder distributions.results: we find that the post-impact target morphology is most sensitive to the mass fraction of boulders comprising the target, while the asteroid deflection efficiency depends on both the mass fraction of boulders on the target and on the boulder size distribution close to the impact point. our results may also have important implications for the structure of small asteroids. | reshaping and ejection processes on rubble-pile asteroids from impacts |
the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) spacecraft orbited the near-earth asteroid (101955) bennu to characterize the asteroid prior to sampling. one important aspect of this characterization was the creation of a high-resolution (5-7 cm) global shape model using the osiris-rex laser altimeter (ola). we describe the data collected by ola, along with the approach used to register overlapping topography using keypoints and keypoint descriptors in order to produce a globally self-consistent set of data. these globally registered sets of topographic scans were used to generate digital terrain models at both global and regional scales. we also describe efforts to correct for a change in behavior of the scanning mirror after the launch and highlight the improvements to the data after implementing an updated calibration of the mirror. the resulting model represents the highest-fidelity global ola data set. | building a high-resolution digital terrain model of bennu from laser altimetry data |
if very low mass primordial black holes (pbh) within the asteroid/moon-mass range indeed reside in galactic dark matter halos, they must necessarily collide with galactic neutron stars (nss). these collisions must, again necessarily, form light black holes (lbhs) with masses of typical nss, m lbh ≈ 1-2 m ⊙. lbhs may be behind events already detected by ground-based gravitational-wave detectors (gw170817, gw190425, and others such as a mixed stellar black hole-ns-mass event gw191219_163120), and most recently by microlensing (ogle-blg-2011-0462). although the status of these observations as containing lbhs is not confirmed, there is no question that gravitational-wave detectors and microlensing are in principle and in practice capable of detecting lbhs. we have calculated the creation rate of lbhs resulting from these light primordial black hole (pbh) collisions with nss. on this basis, we claim that if improved gravitational-wave detectors and microlensing statistics of the lbh events would indicate that the number of lbhs is significantly lower that what follows from the calculated creation rate, then this would be an unambiguous proof that there is no significant light pbh contribution to the galactic dark matter halos. otherwise, if observed and calculated numbers of lbhs roughly agree, then the hypothesis of primordial black hole existence gets strong observational support, and in addition their collisions with nss may be considered a natural creation channel for the lbhs, solving the problem of their origin, as it is known that they cannot be a product of standard stellar evolution. | a robust test of the existence of primordial black holes in galactic dark matter halos |
we describe the ambition project, a mission to return the first-ever cryogenically-stored sample of a cometary nucleus, that has been proposed for the esa science programme voyage 2050. comets are the leftover building blocks of giant planet cores and other planetary bodies, and fingerprints of solar system's formation processes. we summarise some of the most important questions still open in cometary science and solar system formation after the successful rosetta mission. we show that many of these scientific questions require sample analysis using techniques that are only possible in laboratories on earth. we summarize measurements, instrumentation and mission scenarios that can address these questions. we emphasize the need for returning a sample collected at depth or, still more challenging, at cryogenic temperatures while preserving the stratigraphy of the comet nucleus surface layers. we provide requirements for the next generation of landers, for cryogenic sample acquisition and storage during the return to earth. rendezvous missions to the main belt comets and centaurs, expanding our knowledge by exploring new classes of comets, are also discussed. the ambition project is discussed in the international context of comet and asteroid space exploration. | ambition - comet nucleus cryogenic sample return |
we present a technique for verifying or refuting exoplanet candidates from the transiting exoplanet survey satellite (tess) mission by searching for nearby eclipsing binary stars using higher-resolution archival images from ground-based telescopes. our new system is called detecting and evaluating a transit: finding its hidden source in time-domain archival records (deathstar). we downloaded time series of cutout images from two ground-based telescope surveys (the zwicky transient facility, or ztf, and the asteroid terrestrial-impact last alert system, or atlas), analyzed the images to create apertures and measure the brightness of each star in the field, and plotted the resulting light curves using custom routines. thus far, we have confirmed on-target transits for 17 planet candidates, and identified 35 false positives and located their actual transit sources. with future improvements to automation, deathstar will be scaleable to run on the majority of tois. | deathstar: a system for confirming planets and identifying false positive signals in tess data using ground-based time domain surveys |
this is an overview of recent research on meteors and the parent bodies from which they are produced. while many meteor showers result from material ejected by comets, two out of the three strongest annual showers (the geminids and the quadrantids) are associated with objects whose physical properties are apparently those of asteroids. in the last decades dynamical and observational studies have confirmed the existence of a number of asteroid-meteoroid complexes, comprising streams and several macroscopic, split fragments. spectroscopy of meteor showers has been utilized to investigate the perihelion-dependent thermal alteration while in interplanetary space. in this chapter, we review characteristics of the complexes, including those of some minor streams. the scientific interest is to trace the physical and dynamical properties of the complexes back to the evolutionary pathways to learn about the variety of production processes of meteoroids to form streams. we also discuss open questions in the field for the next decade. | asteroid-meteoroid complexes |
the samples returned from asteroid ryugu were collected both at its surface and at its subsurface by hayabusa2 and can, thus, provide information on the space weathering of c-type asteroids at different depths without terrestrial contamination. the near-infrared hyperspectral microscope micromega gathered data on the -oh feature at ~2.7 μm for 177 individual grains from the two collection sites. here, through a spectral analysis of these data, we show that the position of the band peak can be used as an indicator of the degree of space weathering. most subsurficial grains do not present space weathering features, indicating that ryugu's subsurface layers have never been exposed to the interplanetary medium. moreover, the ~2.7 μm feature for the ryugu samples is narrower than that observed for ci chondrites, which are the closest meteorite analogues to ryugu, suggesting that these contain more absorbed molecular water than ryugu due to terrestrial aqueous contamination. we conclude that ryugu samples should be considered as a reference for the primordial water abundance within primitive bodies. | space weathering record and pristine state of ryugu samples from micromega spectral analysis |
top-shaped asteroids have been observed among near-earth asteroids. about half of them are reported to have moons (on the order of ~1 wt.% of the top-shaped primary) and many of them have an equatorial ridge. a recent study has shown that the enigmatic top-shaped figure of asteroids (e.g., ryugu, bennu, and didymos) could result from an axisymmetric landslide of the primary during a fast spin-up near the breakup rotation period. such a landslide would inevitably form a particulate disk around an asteroid with a short timescale (~3 hr). however, the long-term full dynamical evolution is not investigated. here, we perform a continuous simulation (~700 hr) that investigates the sequence of events from the surface landslide that forms a top-shaped asteroid and a particulate disk to disk evolution. we show that the disk quickly spreads and produces moons (within ~300 hr). the mass of the formed moon is consistent with what is observed around the top-shaped asteroids. we also demonstrate that an equatorial ridge is naturally formed because a fraction of the disk particles re-accretes selectively onto the equatorial region of the primary. we envision that ryugu and bennu could once have an ancient moon that was later lost due to a successive moon's orbital evolution. alternatively, at a top-shaped asteroid that has a moon, such as didymos, no significant orbital evolution of the moon has occurred that would result in its loss. our study would also be qualitatively applicable to any rubble-pile asteroids near the breakup rotation period. | formation of moons and equatorial ridge around top-shaped asteroids after surface landslide |
we present heliolinc, a novel approach to the minor planet linking problem. our heliocentric transformation-and-propagation algorithm clusters tracklets at common epochs, allowing for the efficient identification of tracklets that represent the same minor planet. this algorithm scales as { \mathcal o }(n{log}n) with the number of tracklets n, a significant advance over standard methods, which scale as { \mathcal o }({n}3). this overcomes one of the primary computational bottlenecks faced by current and future asteroid surveys. we apply our algorithm to the minor planet center’s isolated tracklet file, establishing orbits for more than 200,000 new minor planets. a detailed analysis of the influence of false detections on the efficiency of our approach, along with an examination of detection biases, will be presented in future work. | heliolinc: a novel approach to the minor planet linking problem |
it is now widely accepted that the asteroid 4-vesta has an fe-rich metallic core, but the composition of the core and the conditions prevailing during core-mantle differentiation are poorly constrained. in light of new constraints on vesta's geophysical and geochemical properties obtained by the dawn mission, we have re-examined the conditions at which core-mantle differentiation in vesta may have occurred by linking the estimated mantle depletions of siderophile elements p, co, ni, cu, ga, ge, mo and w in the vestan mantle to newly derived predictive equations for core-mantle partitioning of these elements. we extend the number of elements previously considered in geochemical modeling of vestan core formation and use published metal-silicate partitioning data obtained at low pressures to characterize the dependence of metal/silicate partition coefficients (d) on pressure, temperature, oxygen fugacity and composition of the silicate and metallic melt. in our modeling we implement newly derived mantle depletions of p, co, ni and ga through analysis of published hed meteorite analyses and assess two contrasting bulk compositional models for vesta. modeling results using monte carlo simulations constrain vestan core formation to have occurred at mildly reducing conditions of approximately 2 log units below the iron-wüstite (iw) buffer (δiw = -2.05 ± 0.20) if the two most likely bulk compositions (binary mixtures of h + cm or h + cv chondritic meteorites) are considered, assuming a temperature range between 1725 and 1850 k and a sulfur-free pure fe core. if the core is assumed to be sulfur-rich (15 wt.% s) as predicted by the latter bulk compositional models, observed depletions for all eight siderophile elements can be simultaneously satisfied at δiw = -2.35 ± 0.10 and 1725-1850 k for the h + cv bulk composition and δiw = -2.30 ± 0.15 and 1725-1850 k for the h + cm bulk composition. more reducing conditions are not consistent with the observed siderophile element depletions in the vestan mantle, independent of the sulfur content of the vestan core and of the bulk compositional model chosen. our analysis shows that a previously proposed shallow magma ocean on vesta during core formation is not consistent with the observed mantle depletion of ga for the two considered bulk compositions irrespective of core composition. instead, our results are consistent with the existence of a deep magma ocean during core formation on vesta, requiring >50-100% mantle melting. | constraints on core formation in vesta from metal-silicate partitioning of siderophile elements |
planetary surfaces can be complex mixtures of coarse and fine particles that exhibit linear and nonlinear mixing behaviors at mid-infrared (mir) wavelengths. machine learning multivariate analysis can estimate modal mineralogy of mixtures and is favorable because it does not assume linear mixing across wavelengths. we used partial least squares (pls) and least absolute shrinkage and selection operator (lasso), two types of machine learning, to build mir spectral models to determine the surface mineralogy of the asteroid (101955) bennu using osiris-rex thermal emission spectrometer (otes) data. we find that pls models outperform lasso models. the cross-validated root-mean-square error of our final pls models (consisting of 317 unique spectra of samples derived from 13 analog mineral samples and eight meteorites) range from ∼4 to 13 vol% depending on the mineral group. pls predictions in vol% of bennu's average global composition are 78% phyllosilicate, 9% olivine, 11% carbonates, and 6% magnetite. pyroxene is not predicted for the global average spectrum, though it has been detected in small amounts on bennu. these mineral abundances confirm previous findings that the composition of bennu is consistent with ci/cm chondrites with high degrees of aqueous alteration. the predicted mineralogy of two previously identified otes spectral types vary minimally from the global average. in agreement with previous work, we interpret otes spectral differences as primarily caused by relative abundances of fine particulates rather than major compositional variations. | machine learning mid-infrared spectral models for predicting modal mineralogy of ci/cm chondritic asteroids and bennu |
the past decade has brought major improvements in large-scale asteroid discovery and characterization, with over half a million known asteroids, more than 100,000 of which have some measurement of physical characterization. this explosion of data has allowed us to create a new global picture of the main asteroid belt. put in context with meteorite measurements and dynamical models, a new and more complete picture of solar system evolution has emerged. the question has changed from "what was the original compositional gradient of the asteroid belt?" to "what was the original compositional gradient of small bodies across the entire solar system?" no longer is the leading theory that two belts of planetesimals are primordial, but instead those belts were formed and sculpted through evolutionary processes after solar system formation. this chapter reviews the advancements on the fronts of asteroid compositional characterization, meteorite measurements, and dynamical theories in the context of the heliocentric distribution of asteroid compositions seen in the main belt today. this chapter also reviews the major outstanding questions relating to asteroid compositions and distributions and summarizes the progress and current state of understanding of these questions to form the big picture of the formation and evolution of asteroids in the main belt. finally, we briefly review the relevance of asteroids and their compositions in their greater context within our solar system and beyond. | the compositional structure of the asteroid belt |
aims: the primary objective of this study is to utilize gaia dr3 asteroid astrometry to detect the yarkovsky effect, a non-gravitational acceleration that affects the orbits of small asteroids. we then computed the bulk densities for the sample of objects for which we obtained an estimation of the yarkovsky effect.methods: we used the version of the orbfit software that is currently developed at the minor planet center (mpc). we utilized the complete astrometric dataset from the mpc, encompassing all radar data and gaia dr3 observations. the orbital computation was performed for a total of 446 near-earth asteroids (neas; including 93 potentially hazardous asteroids (phas)), and 54094 inner main belt asteroids (imbas) as well as mars crossing asteroids. furthermore, we used a new validation method which involved computing the a2 (the yarkovsky effect) using different observational arcs to observe the stability of the result. we applied the yarkovsky effect to determine the density of the studied asteroids.results: thanks to gaia dr3 we significantly constrained orbital uncertainties and determined reliable a2 values for 49 near-earth asteroids, including 10 new detections and for all improvements in signal-to-noise ratio. additionally, we successfully determined the density, along with their uncertainties, for all of these objects. however, regarding imbas, although we have made progress, we do not detect yarkovsky drift for any asteroid in the main belt.conclusions: adding a relatively small amount of ultra-precise astrometry from gaia dr3 to the observations from the minor planet center (mpc) not only significantly improves the orbit of the asteroid but also enhances the detectability of non-gravitational parameters. utilizing this improved dataset, we were able to determine the densities, along with their uncertainties, for the studied asteroids. looking ahead, with the upcoming release of gaia dr4, we anticipate even more detections for neas and new detections for imba and mars crossing asteroids. | the yarkovsky effect and bulk density of near-earth asteroids from gaia dr3 |
cm carbonaceous chondrites can be used to constrain the abundance and h isotopic composition of water and oh in c-complex asteroids. previous measurements of the water/oh content of the cms are at the higher end of the compositional range of asteroids as determined by remote sensing. one possible explanation is that the indigenous water/oh content of meteorites has been overestimated due to contamination during their time on earth. here we have sought to better understand the magnitude and rate of terrestrial contamination through quantifying the concentration and h isotopic composition of telluric and indigenous water in cm falls by stepwise pyrolysis. these measurements have been integrated with published pyrolysis data from cm falls and finds. once exposed to earth's atmosphere cm falls are contaminated rapidly, with some acquiring weight percent concentrations of water within days. the amount of water added does not progressively increase with time because cm falls have a similar range of adsorbed water contents to finds. instead, the petrologic types of cms strongly influence the amount of terrestrial water that they can acquire. this relationship is probably controlled by mineralogical and/or petrophysical properties of the meteorites that affect their hygroscopicity. irrespective of the quantity of water that a sample adsorbs or its terrestrial age, there is minimal exchange of h in indigenous phyllosilicates with the terrestrial environment. the falls and finds discussed here contain 1.9-10.5 wt% indigenous water (average 7.0 wt%) that is consistent with recent measurements of c-complex asteroids including bennu. | the water content of cm carbonaceous chondrite falls and finds, and their susceptibility to terrestrial contamination |
carbonaceous chondrites contain widespread mineralogical evidence for water-rock interactions, indicating that the c-type asteroids from which they are derived had active hydrothermal systems. in comparison, ordinary chondrites contain secondary minerals that are predominantly anhydrous, suggesting that their parent s-type asteroids were relatively dry. the returned particles from the hayabusa mission allow us to probe directly the alteration history of s-type asteroid itokawa. here we report nanometre-sized nacl crystals identified in the interior of an itokawa particle. these crystals are intimately associated with secondary albitic plagioclase, indicating coupled formation. the nacl most likely formed through precipitation from an aqueous fluid prior to complete metamorphic dehydration on asteroid itokawa. our results therefore imply that asteroid itokawa supported an active hydrothermal system and suggest that the once-hydrated s-type asteroids could have potentially delivered water to terrestrial planets. | hydrothermal fluid activity on asteroid itokawa |
designing optimal transfer trajectories and reference orbit tracking in binary asteroid systems is both challenging and computationally expensive. this paper proposes a method of bypassing the high computational overhead by leveraging a collection of known techniques. indeed, the proposed framework is based on the combination of artificial intelligence techniques, such as the particle swarm optimization and neural networks, along with the inverse dynamics and the b-splines approximation of the trajectory. the real irregular shapes of the asteroids are considered in the free dynamics of the system, which are obtained via the mutual polyhedral model. the gravitational accelerations of the single asteroids acting on the spacecraft are approximated by using two single-layer neural networks trained via an extreme learning machine. by using a combination of these techniques, the computational time of the whole optimization is decreased from hours to minutes. the proposed approach is applied to the optimal trajectory design around the binary asteroid system, 1999 kw4, showing the feasibility of the proposed optimization approach, reducing the computational effort and time, and increasing the reliability of the obtained results. it is shown through a monte carlo analysis that our optimization strategy yields more accurate solutions than other optimization algorithms, such as the interior point and sequential quadratic programming methods, when a random initial guess is provided. finally, the proposed optimization approach can be used in combination with other techniques to provide a feasible and reliable initial guess for a better solution refinement.t | optimal maneuvers around binary asteroids using particle swarm optimization and machine learning |
we modeled the geometry and the three-dimensional orientation of the ejecta cone triggered by the impact of the dart spacecraft on the asteroid dimorphos. we used eight luke images of the impact acquired by the cubesat liciacube that flew by the didymos system shortly after the impact. these images, which show the ejecta cone in both face-on and side-on profiles, enabled us to reconstruct the ejecta cone in inertial space. we started our model as a simple cone with a circular base and developed it to a rotated cone with an elliptical base that best fit the data. the cone axis points to r.a., decl. (in j2000): ${147}_{-10^\circ }^{+1^\circ }$ , + ${16}_{-6^\circ }^{+4^\circ }$ . the cone is characterized by two perpendicular half-angles of $\eta ={69}_{-3^\circ }^{+1^\circ },\gamma ={51}_{-11^\circ }^{+1^\circ }$ and a rotation of ω = 12° around its axis. the apex of the cone is located near the center of dimorphos within 15 m. the intersection of the cone and the surface of dimorphos (surface enclosed by the cone) would correspond to a crater with a maximum radius of about 65 m. the characterization of the cone axis is directly related to the computation of the momentum enhancement factor (β) of the impact, and it hence proves the crucial need of studying impacts in the context of planetary defence scenarios. the results of this work could potentially be used to constrain whether the impact took place in a strength-dominated or a gravity-dominated regime. this work shows the important scientific return of the liciacube cubesat in the context of planetary defence. | characterization of the dart impact ejecta plume on dimorphos from liciacube observations |
hayabusa2 is a japanese sample return mission from the asteroid ryugu. the hayabusa2 spacecraft was launched on 3 december 2014 and arrived at ryugu on 27 june 2018. it stayed there until december 2019 for in situ observation and soil sample collection, and will return to the earth in november or december 2020. during the stay, the spacecraft performed the first touchdown operation on 22 february 2019 and the second touchdown on 11 july 2019, which were both completed successfully. because the surface of ryugu is rough and covered with boulders, it was not easy to find target areas for touchdown. there were several technical challenges to overcome, including demanding guidance, navigation, and control accuracy, to realize the touchdown operation. in this paper, strategies and technical details of the guidance, navigation, and control systems are presented. the flight results prove that the performance of the systems was satisfactory and largely contributed to the success of the operation. | guidance, navigation, and control of hayabusa2 touchdown operations |
certain debris disks have nonaxisymmetric shapes in scattered light which are unexplained. the appearance of a disk depends on how its constituent keplerian ellipses are arranged. the more the ellipses align apsidally, the more nonaxisymmetric the disk. apsidal alignment is automatic for fragments released from a catastrophic collision between solid bodies. we synthesize scattered light images, and thermal emission images, of such giant impact debris. depending on the viewing geometry, and if and how the initial apsidal alignment is perturbed, the remains of a giant impact can appear in scattered light as a one-sided or two-sided "fork," a lopsided "needle," or a set of "double wings." the last shape is difficult to reproduce in other scenarios involving gravitational forcing or gas drag, which do not align orbits as well. we compare our images with observations and offer a scorecard assessing whether the scattered light asymmetries in hd 15115, hd 32297, hd 61005, hd 111520, hd 106906, β pic, and au mic are best explained by giant impacts, gravitational perturbations, or sculpting by the interstellar medium. | giant impacts and debris disk morphology |
we present an observational and dynamical study of newly discovered main-belt comet 313p/gibbs. we find that the object is clearly active both in observations obtained in 2014 and in precovery observations obtained in 2003 by the sloan digital sky survey, strongly suggesting that its activity is sublimation-driven. this conclusion is supported by a photometric analysis showing an increase in the total brightness of the comet over the 2014 observing period, and dust modeling results showing that the dust emission persists over at least three months during both active periods, where we find start dates for emission no later than 2003 july 24 ± 10 for the 2003 active period and 2014 july 28 ± 10 for the 2014 active period. from serendipitous observations by the subaru telescope in 2004 when the object was apparently inactive, we estimate that the nucleus has an absolute r-band magnitude of hr = 17.1 ± 0.3, corresponding to an effective nucleus radius of re ∼ 1.00 ± 0.15 km. the object’s faintness at that time means we cannot rule out the presence of activity, and so this computed radius should be considered an upper limit. we find that 313p’s orbit is intrinsically chaotic, having a lyapunov time of tl = 12,000 yr and being located near two three-body mean-motion resonances with jupiter and saturn, 11j-1s-5a and 10j+12s-7a, yet appears stable over >50 myr in an apparent example of stable chaos. we furthermore find that 313p is the second main-belt comet, after p/2012 t1 (panstarrs), to belong to the ∼155 myr old lixiaohua asteroid family. | sublimation-driven activity in main-belt comet 313p/gibbs |
the surfaces of many planets and asteroids contain coarsely fragmental material generated by impacts or other geologic processes. the presence of such pre-existing structures may affect subsequent impacts, particularly when the width of the shock is comparable to or smaller than the size of pre-existing structures. reasonable theoretical predictions and low-speed (<300 m s-1) impact experiments suggest that in such targets the cratering process should be highly dissipative, which would reduce cratering efficiencies and cause a rapid decay in ejection speed as a function of distance from the impact point. in this study, we assess whether these results apply at impact speeds between 0.5 and 2.5 km s-1. this study shows little change in cratering efficiency when 3.18 mm diameter glass beads are launched into targets composed of these same beads. these impacts are very efficient, and ejection speed decays slowly as a function of distance from the impact point. this slow decay in ejection speed probably indicates a correspondingly slow decay of the shock stresses. however, these experiments reveal that initial interactions between projectile and target strongly influence the cratering process and lead to asymmetries in crater shape and ejection angles, as well as significant variations in ejection speed at a given launch position. such effects of asymmetric coupling could be further enhanced by heterogeneity in the initial distribution of grains in the target and by mechanical collisions between grains during excavation. these experiments help to explain why so few craters are seen on the rubble-pile asteroid itokawa: impacts into its coarsely fragmental surface by projectiles comparable to or smaller than the size of these fragments likely yield craters that are not easily recognizable. | impacts into coarse-grained spheres at moderate impact velocities: implications for cratering on asteroids and planets |
we present results from a suite of 169 hydrocode simulations of collisions between planetary bodies with radii from 100 to 1000 km. the simulation data are used to derive a simple scaling law for the threshold for catastrophic disruption, defined as a collision that leads to half the total colliding mass escaping the system post impact. for a target radius 100 ≤ rt ≤ 1000km and a mass mt and a projectile radius rp ≤ rt and mass mp we find that a head-on impact with velocity magnitude v is catastrophic if the kinetic energy of the system in the center of mass frame, k = 0.5mtmpv2 /(mt +mp) , exceeds a threshold value k* that is a few times u =(3 / 5) gmt2/rt +(3 / 5) gmp2/rp + gmtmp /(rt +rp) , the gravitational binding energy of the system at the moment of impact; g is the gravitational constant. in all head-on collision runs we find k* =(5.5 ± 2.9) u . oblique impacts are catastrophic when the fraction of kinetic energy contained in the volume of the projectile intersecting the target during impact exceeds ∼2 k* for 30° impacts and ∼3.5 k* for 45° impacts. we compare predictions made with this scaling to those made with existing scaling laws in the literature extrapolated from numerical studies on smaller targets. we find significant divergence between predictions where in general our results suggest a lower threshold for disruption except for highly oblique impacts with rp ≪ rt. this has implications for the efficiency of collisional grinding in the asteroid belt (morbidelli et al., [2009] icarus, 204, 558-573), kuiper belt (greenstreet et al., [2015] icarus, 258, 267-288), and early solar system accretion (chambers [2013], icarus, 224, 43-56). | impact disruption of gravity-dominated bodies: new simulation data and scaling |
how do planetary scientists analyze and interpret data from laboratory, telescopic, and spacecraft observations of planetary surfaces? what elements, minerals, and volatiles are found on the surfaces of our solar system's planets, moons, asteroids, and comets? this comprehensive volume answers these topical questions by providing an overview of the theory and techniques of remote compositional analysis of planetary surfaces. bringing together eminent researchers in solar system exploration, it describes state-of-the-art results from spectroscopic, mineralogical, and geochemical techniques used to analyze the surfaces of planets, moons, and small bodies. the book introduces the methodology and theoretical background of each technique, and presents the latest advances in space exploration, telescopic and laboratory instrumentation, and major new work in theoretical studies. this engaging volume provides a comprehensive reference on planetary surface composition and mineralogy for advanced students, researchers, and professional scientists. | remote compositional analysis: techniques for understanding spectroscopy, mineralogy, and geochemistry of planetary surfaces. |
linear dunes are among the world's most common desert dune types, and typically occur in dunefields arranged in remarkably organized patterns extending over hundreds of kilometers. the causes of the patterns, formed by dunes merging, bifurcating and terminating, are still poorly understood, although it is widely accepted that they are emergent properties of the complex system of interactions between the boundary layer and an often-vegetated erodible substrate. where such dunefields are vegetated, they are typically used as extensive rangeland, yet it is evident that many currently stabilized dunefields have been reactivated repeatedly during the late quaternary. it has been suggested that dunefield patterning and the temporal evolution of dunefields are related, and thus there is considerable interest in better understanding the boundary conditions controlling dune patterning, especially given the possibility of reactivation of currently-stabilized dunefields under 21st century climate change. however, the time-consuming process of manual dune mapping has hampered attempts at quantitative description of dunefield patterning. this study aims to develop and test methods for delineating linear dune trendlines automatically from freely-available remotely sensed datasets. the highest resolution free global topographic data presently available (aster gdem v2) proved to be of marginal use, as the topographic expression of the dunes is of the same order as the vertical precision of the dataset (∼10 m), but in regions with relatively simple patterning it defined dune trends adequately. analysis of spectral data (panchromatic landsat 8 data) proved more promising in five of the six test sites, and despite poor panchromatic signal/noise ratios for the sixth site, the reflectance in the deep blue/violet (landsat 8 band 1) offers an alternative method of delineating dune pattern. a new edge detection algorithm (linear dune optimized edge detection; lido) is proposed, based on sobel operators with directional filtering and topologically-constrained recursion to optimize the inclusion of marginal zones. the method offers the potential for rapid quantitative mapping of linear dunefield patterning, providing validation data for modeling studies, and offering for the first time the ability to readily remap dunefields to assess dune reorganization at the dunefield scale. | automated mapping of linear dunefield morphometric parameters from remotely-sensed data |
recycling opportunities for graphitic carbon from lithium-ion battery (lib) anodes have been neglected owing to the relative low value of application. in this study, the potential methods for removing toxic metals (lead, barium, and cadmium) and organic compounds (2,4-dinitrotoluene [dnt], 2,4,6-trinitrotoluene [tnt], hexahydro-1,3,5-trinitro-1,3,5-triazine [rdx], and 2,4-dichlorophenol [dcp]) with anode carbonaceous material (acm) obtained from the anodes of spent libs were evaluated. the sorption ability of acm for lead is higher (the maximal sorption capacity is 43.5 mg/g) than for barium and cadmium. similarly, the maximal sorption capacity of acm for dcp is 6.5 mg/g, which is higher than those for tnt and dnt (2.6 and 2.3 mg/l, respectively). as a catalyst, acm significantly enhances oxidation by persulfate with zero-valent iron and reduction by dithiothreitol (dtt) and hydrogen sulfides for nitro compounds. in addition, the graphitic properties enhance the redox reactions. the results suggest that acm from spent libs may be an effective sorbent and catalyst in redox processes for the remediation of contaminated water and soil. | anode carbonaceous material recovered from spent lithium-ion batteries in electric vehicles for environmental application |
examining the functional response of predators can provide insight into the role of predation in structuring prey populations and ecological communities. this study explored feeding behaviour and functional responses of planktivorous damselfishes when offered captive reared larvae of crown-of-thorns starfish, acanthaster sp., with the aim of determining whether these predators could ever play a role in moderating outbreaks of acanthaster sp. we examined predatory behaviour of 11 species of planktivorous damselfish, testing: (1) the relationship between predator size and predation rate, both within and among fish species; (2) consumption rates on larvae of acanthaster sp. versus larvae of a common, co-occurring coral reef asteroid linckia laevigata; (3) maximal feeding rates upon both acanthaster sp. and l. laevigata; and (4) functional responses of planktivorous fishes to increasing densities of acanthaster sp. consumption rates of crown-of-thorns larvae by damselfishes were independent of predator size; however, there was a significant negative relationship between predator size and consumption rate of l. laevigata, when pooling across all predatory species. some damselfishes, including acanthochromis polyacanthus and amblyglyphidodon curacao, consumed larval acanthaster sp. at a greater rate than for l. laevigata. most predatory species (all except a. curacao and pomacentrus amboinensis) exhibited a type ii functional response whereby the increasing feeding rate decelerated with increasing prey density. in addition to revealing that a wide range of planktivorous fishes can prey upon larvae of acanthaster sp., these data suggest that planktivorous damselfishes may have the capacity to buffer against population fluctuations of acanthaster sp. importantly, predators with type ii functional responses often contribute to stability of prey populations, though planktivorous fishes may be swamped by an abnormally high influx of larvae, potentially contributing to the characteristic population fluctuations of acanthaster sp. | predation on crown-of-thorns starfish larvae by damselfishes |
various simplified models have been investigated as a way to understand the complex dynamical environment near irregular asteroids. a dipole segment model is explored in this paper, one that is composed of a massive straight segment and two point masses at the extremities of the segment. given an explicitly simple form of the potential function that is associated with the dipole segment model, five topological cases are identified with different sets of system parameters. locations, stabilities, and variation trends of the system equilibrium points are investigated in a parametric way. the exterior potential distribution of nearly axisymmetrical elongated asteroids is approximated by minimizing the acceleration error in a test zone. the acceleration error minimization process determines the parameters of the dipole segment. the near-earth asteroid (8567) 1996 hw1 is chosen as an example to evaluate the effectiveness of the approximation method for the exterior potential distribution. the advantages of the dipole segment model over the classical dipole and the traditional segment are also discussed. percent error of acceleration and the degree of approximation are illustrated by using the dipole segment model to approximate four more asteroids. the high efficiency of the simplified model over the polyhedron is clearly demonstrated by comparing the cpu time. | the dipole segment model for axisymmetrical elongated asteroids |
many debris discs reveal a two-component structure, with a cold outer and a warm inner component. while the former are likely massive analogues of the kuiper belt, the origin of the latter is still a matter of debate. in this work, we investigate whether the warm dust may be a signature of asteroid belt analogues. in the scenario tested here, the current two-belt architecture stems from an originally extended protoplanetary disc, in which planets have opened a gap separating it into the outer and inner discs which, after the gas dispersal, experience a steady-state collisional decay. this idea is explored with an analytic collisional evolution model for a sample of 225 debris discs from a spitzer/irs catalogue that are likely to possess a two-component structure. we find that the vast majority of systems (220 out of 225, or 98 per cent) are compatible with this scenario. for their progenitors, original protoplanetary discs, we find an average surface density slope of -0.93 ± 0.06 and an average initial mass of (3.3^{+0.4}_{-0.3})× 10^{-3} solar masses, both of which are in agreement with the values inferred from submillimetre surveys. however, dust production by short-period comets and - more rarely - inward transport from the outer belts may be viable, and not mutually excluding, alternatives to the asteroid belt scenario. the remaining five discs (2 per cent of the sample: hip 11486, hip 23497, hip 57971, hip 85790, hip 89770) harbour inner components that appear inconsistent with dust production in an 'asteroid belt.' warm dust in these systems must either be replenished from cometary sources or represent an aftermath of a recent rare event, such as a major collision or planetary system instability. | does warm debris dust stem from asteroid belts? |
the spacecraft hayabusa2 was launched on december 3, 2014, to collect and return samples from a c-type asteroid, 162173 ryugu (provisional designation, 1999 ju3). it is expected that the samples collected contain organic matter and water-bearing minerals and have key information to elucidate the origin and history of the solar system and the evolution of bio-related organics prior to delivery to the early earth. in order to obtain samples with volatile species without terrestrial contamination, based on lessons learned from the hayabusa mission, the sample catcher and container of hayabusa2 were refined from those used in hayabusa. the improvements include (1) a mirror finish of the inner wall surface of the sample catcher and the container, (2) adoption of an aluminum metal sealing system, and (3) addition of a gas-sampling interface for gas collection and evacuation. the former two improvements were made to limit contamination of the samples by terrestrial atmosphere below 1 pa after the container is sealed. the gas-sampling interface will be used to promptly collect volatile species released from the samples in the sample container after sealing of the container. these improvements maintain the value of the returned samples. | hayabusa2 sample catcher and container: metal-seal system for vacuum encapsulation of returned samples with volatiles and organic compounds recovered from c-type asteroid ryugu |
aimusing three north american species invading europe (aster novi‑belgii, lupinus polyphyllus and solidago canadensis) and three european species invading north america (agrostis capillaris, bromus tectorum and cirsium arvense), we tested (1) whether the dominant species impact differs between its native and invaded ranges and (2) whether the impacts differ according to the direction of invasion (from europe to north america and vice versa).locationnorth america (usa) and central europe (czech republic).methodsthe dominance of the selected species was expressed as its relative cover, and its relationship to species richness was tested using marginal and mixed‑effect regression models.resultsall the three north american species invading europe suppressed species richness in the native range, while only two (a. novi‑belgii and l. polyphyllus) impacted native species richness in the invaded range. on the contrary, of the three european species invading north america, only a. capillaris was found to suppress species richness in its native range, while all three suppressed it in the invaded range. overall, the richness of native species responded significantly more negatively to the dominant species cover in its invaded rather than native range, regardless of the identity of the dominant species.main conclusionsinvasive species suppress diversity more in the invaded range, and european invaders have more profound impacts in north america than north american invaders in europe. we suggest that long‑term coexistence and species filtering are responsible for the lower impacts in the native range, while large‑scale evolutionary patterns are likely to be associated with the more profound impacts of selected european species as invaders in north america than vice versa. | dominance has a biogeographical component: do plants tend to exert stronger impacts in their invaded rather than native range? |
this study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the transantarctic mountain (tam) micrometeorite collection. for the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. we use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of <1.2 in the scheme of howard et al. (2015)) and reveal a range of alteration styles. two particles are found to contain pseudomorphic chondrules with thick fine-grained rims, while another micrometeorite contains several aqueously altered cais. their outlines range from well-defined to indistinct, demonstrating that the advanced stages of aqueous alteration progressively remove evidence of coarse-grained components. the remaining two micrometeorites entirely lack coarse-grained components but are similarly altered. thus, the combined chondrule-to-matrix ratio among these giant micrometeorites is extremely low (6.45 area%), and significantly below the average ratio found in typical cm or cr chondrites (∼20%, weisberg et al., 2006). our findings are consistent with previous analyses from smaller antarctic micrometeorites, which suggest that chondrules (and cais) derived from hydrated carbonaceous chondrite parent bodies are underrepresented among the micrometeorite flux, even when considering contributions from coarse-grained micrometeorites. therefore, to explain the relative paucity of anhydrous material, we propose that the flux of fine-grained micrometeorites is primarily derived from intensely aqueously altered, primitive c-type asteroids, which have lost the majority of their refractory coarse-grained components by replacement with secondary phyllosilicate minerals. | intense aqueous alteration on c-type asteroids: perspectives from giant fine-grained micrometeorites |
insoluble organic matter (iom) is the major organic component of chondritic meteorites and may be akin to organic materials from comets and interplanetary dust particles (idps). reflectance spectra of iom in the range 0.35-25 μm are presented as a tool for interpreting organic chemistry from remote measurements of asteroids, comets, idps, and other planetary bodies. absorptions in the iom spectra were strongly related to elemental h/c (atom) ratio. the aliphatic 3.4 μm absorption in iom spectra increased linearly in strength with increasing h/c for h/c > 0.4, but was absent at lower h/c values. when meteorite spectra from the reflectance experiment laboratory (relab) spectral catalog (n = 85) were reanalyzed at 3.4 μm, this detection limit (h/c > 0.4) persisted. aromatic absorption features seen in iom spectra were not observed in the meteorite spectra due to overlapping absorptions. however, the 3.4 μm aliphatic absorption strength for the bulk meteorites was correlated with both h/c of the meteorite's iom and bulk c (wt%). gaussian modeling of the 3 μm region provided an additional estimate of bulk c for the meteorites, along with bulk h (wt%), which is related to phyllosilicate abundance. these relationships lay the foundation for determining organic and phyllosilicate abundances from reflectance spectra. both the full iom spectra and the spectral parameters discussed here will aid in the interpretation of data from asteroid missions (e.g., osiris-rex, hayabusa2), and may be able to place unknown spectral samples within the context of the meteorite collection. | reflectance spectroscopy of insoluble organic matter (iom) and carbonaceous meteorites |
identification of linear features (streaks) in astronomical images is important for several reasons, including: detecting fast-moving near-earth asteroids; detecting or flagging faint satellites streaks; and flagging or removing diffraction spikes, pixel bleeding, line-like cosmic rays and bad-pixel features. here we discuss an efficient and optimal algorithm for the detection of such streaks. the optimal method to detect streaks in astronomical images is by cross-correlating the image with a template of a line broadened by the point-spread function of the system. to do so efficiently, the cross-correlation of the streak position and angle is performed using the radon transform, which is the integral of pixel values along all possible lines through an image. a fast version of the radon transform exists, which we here extend to efficiently detect arbitrarily short lines. while the brute force radon transform requires { \mathcal o }({n}3) operations for a n × n image, the fast radon transform has a complexity of { \mathcal o }({n}2{log}(n)). we apply this method to simulated images, recovering the theoretical signal-to-noise ratio, and to real images, finding long streaks of low-earth-orbit satellites and shorter streaks of global positioning system satellites. we detect streaks that are barely visible to the eye, out of hundreds of images, without a-priori knowledge of the streaks’ positions or angles. we provide implementation of this algorithm in python and matlab. | optimal and efficient streak detection in astronomical images |
context. determining the source regions of meteorites is one of the major goals of current research in planetary science. whereas asteroid observations are currently unable to pinpoint the source regions of most meteorite classes, observations of meteors with camera networks and the subsequent recovery of the meteorite may help make progress on this question. the main caveat of such an approach, however, is that the recovery rate of meteorite falls is low (<20%), implying that the meteoritic analogues of at least 80% of the observed falls remain unknown.aims: spectroscopic observations of incoming bolides may have the potential to mitigate this problem by classifying the incoming meteoritic material.methods: to probe the use of spectroscopy to determine the meteoritic analogues of incoming bolides, we collected emission spectra in the visible range (320-880 nm) of five meteorite types (h, l, ll, cm, and eucrite) acquired in atmospheric entry-like conditions in a plasma wind tunnel at the institute of space systems (irs) at the university of stuttgart (germany). a detailed spectral analysis including a systematic line identification and mass ratio determinations (mg/fe, na/fe) was subsequently performed on all spectra.results: it appears that spectroscopy, via a simple line identification, allows us to distinguish the three main meteorite classes (chondrites, achondrites and irons) but it does not have the potential to distinguish for example an h chondrite from a cm chondrite.conclusions: the source location within the main belt of the different meteorite classes (h, l, ll, cm, ci, etc.) should continue to be investigated via fireball observation networks. spectroscopy of incoming bolides only marginally helps precisely classify the incoming material (iron meteorites only). to reach a statistically significant sample of recovered meteorites along with accurate orbits (>100) within a reasonable time frame (10-20 years), the optimal solution may be the spatial extension of existing fireball observation networks. the movie associated to this article is available at http://www.aanda.org | probing the use of spectroscopy to determine the meteoritic analogues of meteors |
the polar cold traps of mercury host an estimated 1016-1018 g of water ice. the relative purity of the water-ice deposits could indicate they were emplaced over a short time interval, and sharp albedo boundaries suggest that the water ice could have been emplaced relatively recently. together, these lines of evidence are consistent with potential delivery by a single, large, young impact event. hokusai is the most prominent large young impact crater on mercury—if the bulk of mercury's water-ice inventory was indeed delivered by a single recent impact event, hokusai is the best candidate source crater. this study constrains the impact conditions that created hokusai from morphological and color observations of the crater and its ejecta. results show that the hokusai impact was recent and oblique. these parameters, coupled with retention and migration factors largely derived from existing lunar studies, are used to estimate the possible contribution of the hokusai impact to water ice on mercury. assuming water-rich asteroidal or cometary impactors, the hokusai impact event could account for the inventory of water ice on mercury for impact velocities less than 30 km/s, a velocity that is achieved by 24-32% of impacts into mercury, depending on the size distribution model employed. the single impact delivery scenario therefore remains viable for mercury. robust modeling of a single large impact event on mercury would supply critical insight into the feasibility of this scenario. | examining the potential contribution of the hokusai impact to water ice on mercury |
context. the rotation states of small asteroids are affected by a net torque arising from an anisotropic sunlight reflection and thermal radiation from the asteroids' surfaces. on long timescales, this so-called yorp effect can change asteroid spin directions and their rotation periods.aims: we analyzed lightcurves of four selected near-earth asteroids with the aim of detecting secular changes in their rotation rates that are caused by yorp or at least of putting upper limits on such changes.methods: we use the lightcurve inversion method to model the observed lightcurves and include the change in the rotation rate dω/ dt as a free parameter of optimization. to enlarge the time line of observations and to increase the sensitivity of the method, we collected more than 70 new lightcurves. for asteroids toro and cacus, we used thermal infrared data from the wise spacecraft and estimated their size and thermal inertia by means of a thermophysical model. we also used the currently available optical and radar astrometry of toro, ra-shalom, and cacus to infer the yarkovsky effect.results: we detected a yorp acceleration of dω/ dt = (1.9 ± 0.3) × 10-8 rad d-2 for asteroid cacus. the current astrometric data set is not sufficient to provide detection of the yarkovsky effect in this case. for toro, we have a tentative (2σ) detection of yorp from a significant improvement of the lightcurve fit for a nonzero value of dω/ dt = 3.0 × 10-9 rad d-2. we note an excellent agreement between the observed secular change of the semimajor axis da/ dt and the theoretical expectation for densities in the 2-2.5 g cm-3 range. for asteroid eger, we confirmed the previously published yorp detection with more data and updated the yorp value to (1.1 ± 0.5) × 10-8 rad d-2. we also updated the shape model of asteroid ra-shalom and put an upper limit for the change of the rotation rate to | dω/ dt | ≲ 1.5 × 10-8 rad d-2. ra-shalom has a greater than 3σ yarkovsky detection with a theoretical value consistent with observations assuming its size and/or density is slightly larger than the nominally expected values. using the convex shape models and spin parameters reconstructed from lightcurves, we computed theoretical yorp values and compared them with those measured. they agree with each other within the expected uncertainties of the model. | yorp and yarkovsky effects in asteroids (1685) toro, (2100) ra-shalom, (3103) eger, and (161989) cacus |
context. co-orbital bodies are the byproduct of planet formation and evolution, as we know from the solar system. although planet-size co-orbitals do not exists in our planetary system, dynamical studies show that they can remain stable for long periods of time in the gravitational well of massive planets. should they exist, their detection is feasible with the current instrumentation.aims: in this paper, we present new ground-based observations searching for these bodies co-orbiting with nine close-in (p < 5 days) planets, using various observing techniques. the combination of all of these techniques allows us to restrict the parameter space of any possible trojan in the system.methods: we used multi-technique observations, comprised of radial velocity, precision photometry, and transit timing variations, both newly acquired in the context of the troy project and publicly available, to constrain the presence of planet-size trojans in the lagrangian points of nine known exoplanets.results: we find no clear evidence of trojans in these nine systems through any of the techniques used down to the precision of the observations. however, this allows us to constrain the presence of any potential trojan in the system, especially in the trojan mass or radius vs. libration amplitude plane. in particular, we can set upper mass limits in the super-earth mass regime for six of the studied systems. based on observations collected at the centro astronómico hispano alemán (caha) at calar alto, operated jointly by the max-planck institut für astronomie and the instituto de astrofísica de andalucía (csic).partly based on data obtained with the stella robotic telescopes in tenerife, an aip facility jointly operated by aip and iac.based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programs 297.c-5051, 098.c-0440(a), and 298.c-5009 | the troy project. ii. multi-technique constraints on exotrojans in nine planetary systems |
the distributions of size and chemical composition in regolith on airless bodies provide clues to the evolution of the solar system. recently, the regolith on asteroid (25143) itokawa, visited by the jaxa hayabusa spacecraft, was observed to contain millimeter to centimeter sized particles. itokawa boulders commonly display well-rounded profiles and surface textures that appear inconsistent with mechanical fragmentation during meteorite impact; the rounded profiles have been hypothesized to arise from rolling and movement on the surface as a consequence of seismic shaking. this investigation provides a possible explanation of these observations by exploring the primary crack propagation mechanism during thermal fatigue of a chondrite. herein, we present the evolution of the full-field strains on the surface as a function of temperature and microstructure, and examine the crack growth during thermal cycling. our experimental results demonstrate that thermal-fatigue-driven fracture occurs under these conditions. the results suggest that the primary fatigue crack path preferentially follows the interfaces between monominerals, leaving the minerals themselves intact after fragmentation. these observations are explained through a microstructure-based finite element model that is quantitatively compared with our experimental results. these results on the interactions of thermal fatigue cracking with the microstructure may ultimately allow us to distinguish between thermally induced fragments and impact products. | the origins of asteroidal rock disaggregation: interplay of thermal fatigue and microstructure |
s. r. kulkarni on behalf of the zwicky transient facility (ztf) announces the first confirmed results from the project. ztf is led by the california institute of technology, us and includes ipac, us; los alamos national laboratory, us; university of maryland, us; university of wisconsin at milwaukee, us; university of washington, us; oskar-klein center of the university of stockholm, sweden; desy and humboldt university of berlin, germany; weizmann institute of science, israel; and the university system of taiwan, taiwan. | the zwicky transient facility (ztf) begins |
the alos world 3d - 30&thinsp;m (aw3d30), aster global dem version 2 (gdem2), and srtm-30&thinsp;m are digital elevation models (dems) that have been made available to the general public free of charge. an important feature of these dems is their unprecedented horizontal resolution of 30-m and almost global coverage. the very recent release of these dems, particularly aw3d30 and srtm- 30&thinsp;m, calls for opportunities for the conduct of localized assessment of the dem's quality and accuracy to verify their suitability for a wide range of applications in hydrology, geomorphology, archaelogy, and many others. in this study, we conducted a vertical accuracy assessment of these dems by comparing the elevation of 274 control points scattered over various sites in northeastern mindanao, philippines. the elevations of these control points (referred to the mean sea level, msl) were obtained through 3rd order differential levelling using a high precision digital level, and their horizontal positions measured using a global positioning system (gps) receiver. these control points are representative of five (5) land-cover classes namely brushland (45 points), built-up (32), cultivated areas (97), dense vegetation (74), and grassland (26). results showed that aw3d30 has the lowest root mean square error (rmse) of 5.68&thinsp;m, followed by srtm-30&thinsp;m (rmse&thinsp;=&thinsp;8.28&thinsp;m), and aster gdem2 (rmse&thinsp;=&thinsp;11.98&thinsp;m). while all the three dems overestimated the true ground elevations, the mean and standard deviations of the differences in elevations were found to be lower in aw3d30 compared to srtm-30&thinsp;m and aster gdem2. the superiority of aw3d30 over the other two dems was also found to be consistent even under different landcover types, with aw3d30's rmses ranging from 4.29&thinsp;m (built-up) to 6.75&thinsp;m (dense vegetation). for srtm-30&thinsp;m, the rmse ranges from 5.91&thinsp;m (built-up) to 10.42&thinsp;m (brushland); for aster gdem2, the rmse ranges from 9.27&thinsp;m (brushland) to 14.88&thinsp;m (dense vegetation). the results of the vertical accuracy assessment suggest that the aw3d30 is more accurate than srtm-30&thinsp;m and aster gdem2, at least for the areas considered in this study. on the other hand, the tendencies of the three dems to overestimate true ground elevation can be considered an important finding that users of the dems in the philippines should be aware of, and must be considered into decisions regarding use of these data products in various applications. | vertical accuracy assessment of 30-m resolution alos, aster, and srtm global dems over northeastern mindanao, philippines |
context. earlier work suggests that slowly rotating asteroids should have higher thermal inertias than faster rotators because the heat wave penetrates deeper into the subsurface. however, thermal inertias have been determined mainly for fast rotators due to selection effects in the available photometry used to obtain shape models required for thermophysical modelling (tpm).aims: our aims are to mitigate these selection effects by producing shape models of slow rotators, to scale them and compute their thermal inertia with tpm, and to verify whether thermal inertia increases with the rotation period.methods: to decrease the bias against slow rotators, we conducted a photometric observing campaign of main-belt asteroids with periods longer than 12 h, from multiple stations worldwide, adding in some cases data from wise and kepler space telescopes. for spin and shape reconstruction we used the lightcurve inversion method, and to derive thermal inertias we applied a thermophysical model to fit available infrared data from iras, akari, and wise.results: we present new models of 11 slow rotators that provide a good fit to the thermal data. in two cases, the tpm analysis showed a clear preference for one of the two possible mirror solutions. we derived the diameters and albedos of our targets in addition to their thermal inertias, which ranged between 3-3+33 and 45-30+60 j m-2 s-1/2 k-1.conclusions: together with our previous work, we have analysed 16 slow rotators from our dense survey with sizes between 30 and 150 km. the current sample thermal inertias vary widely, which does not confirm the earlier suggestion that slower rotators have higher thermal inertias. full table a.1 and photometric data from all individual nights are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/625/a139 | thermal properties of slowly rotating asteroids: results from a targeted survey |
we report on a multiobservatory campaign to examine asteroid 3200 phaethon during its 2017 december close approach to earth, in order to improve our measurements of its fundamental parameters, and to search for surface variations, cometary activity, and fragmentation. the mean colors of phaethon are b - v = 0.702 ± 0.004, v - r = 0.309 ± 0.003, and r - i = 0.266 ± 0.004, neutral to slightly blue, consistent with previous classifications of phaethon as a f-type or b-type asteroid. variations in phaethon’s b - v colors (but not v - r or r - i) with observer sublatitude are seen and may be associated with craters observed by the arecibo radar. high-cadence photometry over phases from 20° to 100° allows a fit to the values of the hg photometric parameters; h = 14.57 ± 0.02, 13.63 ± 0.02, 13.28 ± 0.02, 13.07 ± 0.02 g = 0.00 ± 0.01, -0.09 ± 0.01, -0.10 ± 0.01, -0.08 ± 0.01 in the bvri filters respectively; the negative g values are consistent with other observations of f-type asteroids. light-curve variations were seen that are also consistent with concavities reported by arecibo, indicative of large craters on phaethon’s surface whose ejecta may be the source of the geminid meteoroid stream. a search for gas/dust production sets an upper limit of 0.06 ± 0.02 kg s-1 when phaethon was 1.449 au from the sun, and 0.2 ± 0.1 kg s-1 at 1.067 au. a search for meter-class fragments accompanying phaethon did not find any whose on-sky motion was not also consistent with background main-belt asteroids. | asteroid (3200) phaethon: colors, phase curve, limits on cometary activity, and fragmentation |
we develop a fourth-order numerical integrator to simulate the coupled spin and orbital motions of two rigid bodies having arbitrary mass distributions under the influence of their mutual gravitational potential. we simulate the dynamics of components in well-characterized binary and triple near-earth asteroid systems and use surface of section plots to map the possible spin configurations of the satellites. for asynchronous satellites, the analysis reveals large regions of phase space where the spin state of the satellite is chaotic. for synchronous satellites, we show that libration amplitudes can reach detectable values even for moderately elongated shapes. the presence of chaotic regions in the phase space has important consequences for the evolution of binary asteroids. it may substantially increase spin synchronization timescales, explain the observed fraction of asychronous binaries, delay byorp-type evolution, and extend the lifetime of binaries. the variations in spin rate due to large librations also affect the analysis and interpretation of light curve and radar observations. | near-earth asteroid satellite spins under spin-orbit coupling |
we investigate numerically, by a hybrid lattice boltzmann method, the morphology and the dynamics of an emulsion made of a polar active gel, contractile or extensile, and an isotropic passive fluid. we focus on the case of a highly off-symmetric ratio between the active and passive components. in absence of any activity we observe an hexatic-ordered droplets phase, with some defects in the layout. we study how the morphology of the system is affected by activity both in the contractile and extensile case. in the extensile case a small amount of activity favors the elimination of defects in the array of droplets, while at higher activities, first aster-like rotating droplets appear, and then a disordered pattern occurs. in the contractile case, at sufficiently high values of activity, elongated structures are formed. energy and enstrophy behavior mark the transitions between the different regimes. | morphology and flow patterns in highly asymmetric active emulsions |
the formation of planetesimals was a key step in the assemblage of planetary bodies, yet many aspects of their formation remain poorly constrained. notably, the mechanism by which chondrules-submillimetric spheroids that dominate primitive meteorites-were incorporated into planetesimals remains poorly understood. here we classify and analyze particle-size distributions in various co carbonaceous chondrites found in the atacama desert. our results show that the average circle-equivalent diameters of chondrules define a positive trend with the petrographic grade, which reflects the progressive role of thermal metamorphism within the co parent body. we show that this relationship could not have been established by thermal metamorphism alone but rather by aerodynamic sorting during accretion. by modeling the self-gravitational contraction of clumps of chondrules, we show that (i) the accretion of the co parent body(ies) would have generated a gradual change of chondrule size with depth in the parent body, with larger chondrules being more centrally concentrated than smaller ones, and (ii) any subsequent growth by pebble accretion would have been insignificant. these findings give substantial support to the view that planetesimals formed via gravitational collapse. | constraints on planetesimal accretion inferred from particle-size distribution in co chondrites |
we study the optical properties of the solar gravitational lens (sgl) while treating the sun as an extended, axisymmetric and rotating body. the gravitational field of the sun is represented using a set of zonal harmonics. we develop an analytical description of the intensity of light that is observed in the image plane in the strong interference region of a realistic sgl. this formalism makes it possible to model not only the point-spread function of point sources, but also actual observables, images that form in the focal plane of an imaging telescope positioned in the image plane. perturbations of the monopole gravitational field of the sun are dominated by the solar quadrupole moment, which results in forming an astroid caustic on the image plane. consequently, an imaging telescope placed inside the astroid caustic observes four bright spots, forming the well-known pattern of an einstein cross. the relative intensities and positions of these spots change as the telescope is moved in the image plane, with spots merging into bright arcs when the telescope approaches the caustic boundary. outside the astroid caustic, only two spots remain and the observed pattern eventually becomes indistinguishable from the imaging pattern of a monopole lens at greater distances from the optical axis. we present results from extensive numerical simulations, forming the basis of our ongoing study of prospective exoplanet imaging with the sgl. these results are also applicable to describe a large class of gravitational lensing scenarios involving axisymmetric lenses that can be represented using zonal harmonics. | imaging point sources with the gravitational lens of an extended sun |
the growth of small planetesimals into large planetary embryos occurs far before the dispersal of the gas from the protoplanetary disk. the planetesimal-gaseous disk interactions give rise to migration and orbital evolution of the planetesimals/planets. small planetesimals are dominated by aerodynamic gas drag. large protoplanets, m∼ 0.1{m}\oplus , are dominated by type i migration differential torque. there is an additional mass range m∼ {10}21-{10}25 {{g}} of intermediate-mass planetesimals (imps), where gravitational interactions with the disk dominate over aerodynamic gas drag, but for which such interactions were typically neglected. here, we model these interactions using the gas dynamical friction (gdf) approach, previously used to study the disk-planet interactions at the planetary mass range. we find the critical size where gdf dominates over gas drag, and then we study the implications of gdf on single imps. we find that planetesimals with small inclinations rapidly become co-planar. eccentric orbits circularize within a few myr, provided the the planetesimal mass is large, m≳ {10}23 {{g}}, and that the initial eccentricity is low, e≲ 0.1. planetesimals of higher masses, m∼ {10}24-{10}25 {{g}}, inspiral on a timescale of a few myr, leading to an embryonic migration to the inner disk. this can lead to an overabundance of rocky material (in the form of imps) in the inner protoplanetary disk (\lt 1 {au}) and induce rapid planetary growth. this can explain the origin of super-earth planets. in addition, gdf damps the velocities of imps, thereby cooling the planetesimal disk and affecting its collisional evolution through quenching the effects of viscous stirring by the large bodies. | application of gas dynamical friction for planetesimals. i. evolution of single planetesimals |
while having a comet-like appearance, p/2012 f5 (gibbs) has an orbit native to the main asteroid belt, and physically is a km-sized asteroid which recently (mid 2011) experienced an impulsive mass ejection event. here we report new observations of this object obtained with the keck ii telescope on ut 2014 august 26. the data show previously undetected 200 m scale fragments of the main nucleus, and reveal a rapid nucleus spin with a rotation period of 3.24 ± 0.01 hr. the existence of large fragments and the fast nucleus spin are both consistent with rotational instability and partial disruption of the object. to date, many fast rotators have been identified among the minor bodies, which, however, do not eject detectable fragments at the present-day epoch, and also fragmentation events have been observed, but with no rotation period measured. p/2012 f5 is unique in that for the first time we detected fragments and quantified the rotation rate of one and the same object. the rapid spin rate of p/2012 f5 is very close to the spin rates of two other active asteroids in the main belt, 133p/elst-pizarro and (62412), confirming the existence of a population of fast rotators among these objects. but while p/2012 f5 shows impulsive ejection of dust and fragments, the mass loss from 133p is prolonged and recurrent. we believe that these two types of activity observed in the rapidly rotating active asteroids have a common origin in the rotational instability of the nucleus. the data presented herein were obtained at the w. m. keck observatory, which is operated as a scientific partnership among the california institute of technology, the university of california, and the national aeronautics and space administration. the observatory was made possible by the generous financial support of the w. m. keck foundation. | fast rotation and trailing fragments of the active asteroid p/2012 f5 (gibbs) |
understanding the collisional fragmentation and subsequent reaccumulation of fragments is crucial for studies of the formation and evolution of the small-body populations. using an sph / n-body approach, we investigate the size-frequency distributions (sfds) resulting from the disruption of 100 km-diameter targets consisting of porous material, including the effects of pore-crushing as well as friction. overall, the porous targets have a significantly higher impact strength (qd*) than the rubble-pile parent bodies investigated previously (benavidez et al., 2012) and show a behavior more similar to non-porous monolithic targets (durda et al., 2007). our results also confirm that for a given specific impact energy, the sfds resulting from a parent body disruption are strongly dependent on the size scale. | fragment properties from large-scale asteroid collisions: i: results from sph/n-body simulations using porous parent bodies and improved material models |
a discontinuous galerkin time-domain (dgtd) method based on dynamically adaptive cartesian meshes (acm) is developed for a full-wave analysis of electromagnetic fields in dispersive media. hierarchical cartesian grids offer simplicity close to that of structured grids and the flexibility of unstructured grids while being highly suited for adaptive mesh refinement (amr). the developed dgtd-acm achieves a desired accuracy by refining non-conformal meshes near material interfaces to reduce stair-casing errors without sacrificing the high efficiency afforded with uniform cartesian meshes. moreover, dgtd-acm can dynamically refine the mesh to resolve the local variation of the fields during propagation of electromagnetic pulses. a local time-stepping scheme is adopted to alleviate the constraint on the time-step size due to the stability condition of the explicit time integration. simulations of electromagnetic wave diffraction over conducting and dielectric cylinders and spheres demonstrate that the proposed method can achieve a good numerical accuracy at a reduced computational cost compared with uniform meshes. for simulations of dispersive media, the auxiliary differential equation (ade) and recursive convolution (rc) methods are implemented for a local drude model and tested for a cold plasma slab and a plasmonic rod. with further advances of the charge transport models, the dgtd-acm method is expected to provide a powerful tool for computations of electromagnetic fields in complex geometries for applications to high-frequency electronic devices, plasmonic thz technologies, as well as laser-induced and microwave plasmas. | a discontinuous galerkin time-domain method with dynamically adaptive cartesian mesh for computational electromagnetics |
context. meteoroid streams are fragments of matter produced by comets or asteroids which intersects the orbit of earth. meteor showers are produced when earth intersects these streams of matter. the discoveries of active asteroids and extinct comets open a new view of the relation between these objects as possible parent bodies at the origin of meteor showers.aims: the aim of this work is to identify the asteroids that can produce or re-populate meteoroid streams by determining the similarity of their orbits and orbital evolution over 10 000 yr.methods: the identification was carried out by evaluating several well known d-criteria metrics, the orbits being taken from the iau meteor data center database and from iau minor planet center. finally, we analyzed the physical properties and the orbital stability (in the lyapunov time sense) of the candidates as well as their possible relationship with meteorites.results: 206 near-earth asteroids (neas) were associated as possible parent bodies with 28 meteor showers, according to at least two of the criterion used. 50 of them satisfied all the criteria. notable finds are: binary asteroid 2000ug11 associated with andromedids (and), while the tumbling asteroid (4179)toutatis could be associated with october capricornids (occ). other possible good candidates are 2004tg10, 2008ey5, 2010cf55, 2010tu149 and 2014oy1. these objects have low albedo, therefore can be primitive objects. asteroid 2007lw19 which is a fast rotator and most probably has monolithic structure and so its physical characteristic does not support the association found based on the dynamical criteria. | association between meteor showers and asteroids using multivariate criteria |
aims: we perform light curve inversion for 491 asteroids to retrieve phase curve parameters, rotation periods, pole longitudes and latitudes, and convex and triaxial ellipsoid shapes by using the sparse photometric observations from gaia data release 2 and the dense ground-based observations from the damit database. we develop a method for the derivation of reference absolute magnitudes and phase curves from the gaia data, allowing for comparative studies involving hundreds of asteroids.methods: for both general convex shapes and ellipsoid shapes, we computed least-squares solutions using either the levenberg-marquardt optimization algorithm or the nelder-mead downhill simplex method. virtual observations were generated by adding gaussian random errors to the observations, and, later on, a markov chain monte carlo method was applied to sample the spin, shape, and scattering parameters. absolute magnitude and phase curve retrieval was developed for the reference geometry of equatorial illumination and observations based on model magnitudes averaged over rotational phase.results: the derived photometric slope values showed wide variations within each assumed tholen class. the computed gaia g-band absolute magnitudes matched notably well with the v-band absolute magnitudes retrieved from the jet propulsion laboratory small-body database. finally, the reference phase curves were well fitted with the h, g1, g2 phase function. the resulting g1, g2 distribution differed, in an intriguing way, from the g1, g2 distribution that is based on the phase curves corresponding to light curve brightness maxima. phase curve data 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/649/a98 | asteroid absolute magnitudes and phase curve parameters from gaia photometry |
jan hendrik oort hypothesized the existence of a distant cloud of cometary objects that orbit the sun based on a spike in the reciprocal orbital separation at 1∕a ≲ 10−4 au−1. the oort cloud is the source of long-period comets, but has not been observed directly, and its origin remains theoretical. theories on its origin evoke a sequence of events that have been tested individually but never as a consistent chronology. we present a chronology of the formation and early evolution of the oort cloud, and test the sequence of events by simulating the formation process in subsequent amalgamated steps. these simulations start with the solar system being born with planets and asteroids in a stellar cluster orbiting the galactic center. upon ejection from its birth environment, we continue to follow the evolution of the solar system while it navigates the galaxy as an isolated planetary system. we conclude that the range in semi-major axis between ~100 au and several ~103 au still bears the signatures of the sun being born in a ≳1000 m⊙ pc−3 star cluster, and that most of the outer oort cloud formed after the solar system was ejected. the ejection of the solar system, we argue, happened between ~20 myr and 50 myr after its birth. trailing and leading trails of asteroids and comets along the sun's orbit in the galactic potential are the by-product of the formation of the oort cloud. these arms are composed of material that became unbound from the solar system when the oort cloud formed. today, the bulk of the material in the oort cloud (~70%) originates from the region in the circumstellar disk that was located between ~15 au and ~35 au, near the current location of the ice giants and the centaur family of asteroids. according to our simulations, this population is eradicated if the ice-giant planets are born in orbital resonance. planet migration or chaotic orbital reorganization occurring while the solar system is still a cluster member is, according to our model, inconsistent with the presence of the oort cloud. about half the inner oort cloud, between 100 and 104 au, and a quarter of the material in the outer oort cloud, ≳104 au, could be non-native to the solar system but was captured from free-floating debris in the cluster or from the circumstellar disks of other stars in the birth cluster. characterizing this population will help us to reconstruct the history of the solar system. the source code, input files, and simulation data for this manuscript are available at 10.6084/m9.figshare.13214471. a tutorial on how to run the various codes in amuse is available at https://github.com/spzwart/amuse-tutorial. | oort cloud ecology. ii. the chronology of the formation of the oort cloud |
composition of terrestrial planets records planetary accretion, core-mantle and crust-mantle differentiation, and surface processes. here we compare the compositional models of earth and mars to reveal their characteristics and formation processes. earth and mars are equally enriched in refractory elements (1.9 $\times$ ci), although earth is more volatile-depleted and less oxidized than mars. their chemical compositions were established by nebular fractionation, with negligible contributions from post-accretionary losses of moderately volatile elements. the degree of planetary volatile element depletion might correlate with the abundances of chondrules in the accreted materials, planetary size, and their accretion timescale, which provides insights into composition and origin of mercury, venus, the moon-forming giant impactor, and the proto-earth. during its formation before and after the nebular disk's lifetime, the earth likely accreted more chondrules and less matrix-like materials than mars and chondritic asteroids, establishing its marked volatile depletion. a giant impact of an oxidized, differentiated mars-like (i.e., composition and mass) body into a volatile-depleted, reduced proto-earth produced a moon-forming debris ring with mostly a proto-earth's mantle composition. chalcophile and some siderophile elements in the silicate earth added by the mars-like impactor were extracted into the core by a sulfide melt. in contrast, the composition of mars indicates its rapid accretion of lesser amounts of chondrules under nearly uniform oxidizing conditions. mars' rapid cooling and early loss of its dynamo likely led to the absence of plate tectonics and surface water, and the present-day low surface heat flux. these similarities and differences between the earth and mars made the former habitable and the other inhospitable to uninhabitable. | earth and mars – distinct inner solar system products |
we present diameters and albedos computed for the near-earth and main belt asteroids (mbas) observed by the near-earth object wide-field infrared survey explorer (neowise) spacecraft during the sixth and seventh years of its reactivation mission. these diameters and albedos are calculated from fitting thermal models to neowise observations of 199 near-earth objects (neos) and 5851 mbas detected during the sixth year of the survey and 175 neos and 5861 mbas from the seventh year. comparisons of the neo diameters derived from reactivation data with those derived from the wise cryogenic mission data show a ~30% relative uncertainty. this larger uncertainty compared to data from the cryogenic mission is due to the need to assume a beaming parameter for the fits to the shorter-wavelength data that the reactivation mission is limited to. we also present an analysis of the orbital parameters of the mbas that have been discovered by neowise during reactivation, finding that these objects tend to be on orbits that result in their perihelia being far from the ecliptic, and thus missed by other surveys. to date, the neowise reactivation survey has provided thermal fits of 1415 unique neos. including the mission phases before spacecraft hibernation increases the count of unique neos characterized to 1845 from wise's launch to the present. | asteroid diameters and albedos from neowise reactivation mission years six and seven |
the polana-eulalia family complex is located in the inner part of the asteroid belt, bounded by the ν6 and the 3:1 resonances, where we can find another three collisional families of primitive asteroids (erigone, clarissa, and sulamitis), and a low-albedo population of background objects. this region of the belt is believed to be the most likely origin of the two primitive near-earth asteroids that are the current targets of two sample return missions: nasa's osiris-rex and jaxa's hayabusa 2 to asteroids (101955) bennu and (162173) ryugu (also known as 1999 ju3), respectively. therefore, understanding these families will enhance the scientific return of these missions. we present the results of a spectroscopic survey of asteroids in the region of the polana-eulalia family complex, and also asteroids from the background population of low-albedo, low-inclination objects. we obtained visible spectra of a total of 65 asteroids, using the 10.4 m gran telescopio canarias (gtc) and the 3.6 m telescopio nazionale galileo (tng), both located at the el roque de los muchachos observatory, in the island of la palma (spain), and the 3.6 m new technology telescope (ntt), located at the european southern observatory of la silla, in chile. from the spectral analysis of our sample we found that, in spite of the presence of distinct dynamical groups, the asteroids in this region present spectral homogeneity at visible wavelengths, showing a continuum of spectral slopes, from blue to moderately red, typical of primitive asteroids classified as b- and c-types. we conclude that visible spectra cannot be used to distinguish between members of the polana and the eulalia families, or members of the background population. the visible spectra of the two targets of sample return missions, asteroids bennu and ryugu, are compatible with the spectra of the asteroids in this region, supporting previous studies that suggested either the polana family or the background population as the most likely origins of these neas. | visible spectroscopy of the polana-eulalia family complex: spectral homogeneity |
metallic potassium (k) is a desirable anode for potassium secondary batteries due to its low electrode potential in nonaqueous electrolytes and high theoretical capacity. nevertheless, instability caused by dendritic growth, large volume changes, and parasitic side reactions hamper its practical application. here, an anode containing metallic k is fabricated by infiltrating an aligned carbon nanotube membrane (acm) with molten k because of its good wettability to molten k due to the strong capillary forces. the k metal is spatially distributed on the 3d acm framework, which offers sufficient electrode/electrolyte contact for charge transfer. the robust acm host provides a large number of k nucleation sites and physically confines the k deposited there, thus mitigating dimensional changes during cycling. the pathways for electrons and ions in the anode are associated to form a mixed conducting network, which is beneficial for the electrochemical redox. consequently, the anode shows stable plating/stripping profiles with low polarization in symmetric cells using conventional carbonate‑based electrolytes. in addition, dendrite growth is suppressed, and the anode demonstrates excellent suitability when paired with a prussian blue cathode in a full cell. this design strategy is expected to provide a way to address the problems with using metallic k anodes. | capillary encapsulation of metallic potassium in aligned carbon nanotubes for use as stable potassium metal anodes |
a method for computing the components of the euler-poinsot tensors up to the fourth order in the expansion of the gravitational potential is described. the results are illustrated by the example of asteroid 433 eros. | computation of attraction potential of asteroid (433) eros with an accuracy up to the terms of the fourth order |
generally, terrestrial rocks, martian and chondritic meteorites exhibit a relatively narrow range in bulk and apatite cl isotope compositions, with δ37cl (per mil deviation from standard mean ocean chloride) values between -5.6 and +3.8‰. lunar rocks, however, have more variable bulk and apatite δ37cl values, ranging from ∼-4 to +40‰. as the howardite-eucrite-diogenite (hed) meteorites represent the largest suite of crustal and sub-crustal rocks available from a differentiated basaltic asteroid (4 vesta), studying them for their volatiles may provide insights into planetary differentiation processes during the earliest solar system history. here the abundance and isotopic composition of cl in apatite were determined for seven eucrites representing a broad range of textural and petrological characteristics. apatite cl abundances range from ∼25 to 4900 ppm and the δ37cl values range from -3.98 to +39.2‰. samples with lower apatite h2o contents were typically also enriched in 37cl but no systematic correlation between δ37cl and δd values was observed across samples. modelled rayleigh fractionation and a strong positive correlation between bulk δ66zn and apatite δ37cl support the hypothesis that cl degassed as metal chlorides from eucritic magmas, in a hydrogen-poor environment. in the case of lunar samples, it has been noted that δ37cl values of apatite positively correlate with bulk la/yb ratio. interestingly, most eucrites show a negative correlation with bulk la/yb ratio. recently, isotopically light cl values have been suggested to record the primary solar nebular signature. if this is the case then 4 vesta, which accreted rapidly and early in solar system history, could also record this primary nebular signature corresponding to the lightest cl values measured here. the significant variation in cl isotope composition observed within the eucrites are likely related to degassing of metal chlorides. | investigating magmatic processes in the early solar system using the cl isotopic systematics of eucrites |
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