abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
we propose that several short-duration events observed in past stellar occultations by chiron were produced by ring material. some similarities between these events and the characteristics of chariklo's rings could indicate common mechanisms around centaurs. from a reanalysis of the stellar occultation data in the literature, we determined two possible orientations of the pole of chiron's rings, with ecliptic coordinates λ = (352 ± 10)°, β = (37 ± 10)° or λ = (144 ± 10)°, β = (24 ± 10)°. the mean radius of the rings is (324 ± 10) km. one can use the rotational lightcurve amplitude of chiron at different epochs to distinguish between the two solutions for the pole. both solutions imply a lower lightcurve amplitude in 2013 than in 1988, when the rotational lightcurve was first determined. we derived chiron's rotational lightcurve in 2013 from observations at the 1.23 m caha telescope, and indeed its amplitude was smaller than in 1988. we also present a rotational lightcurve in 2000 from images taken at the casleo 2.15 m telescope that is consistent with our predictions. out of the two poles, the λ = (144 ± 10)°, β = (24 ± 10)° solution provides a better match to a compilation of rotational lightcurve amplitudes from the literature and those presented here. we also show that using this preferred pole orientation, chiron's long-term brightness variations are compatible with a simple model that incorporates the changing brightness of the rings while the tilt angle with respect to the earth is changing with time. also, the variability of the water ice band in chiron's spectra as seen in the literature can be explained to a large degree by an icy ring system whose tilt angle changes with time and whose composition includes water ice, analogously to the case of chariklo. we present several possible formation scenarios for the rings from qualitative points of view and speculate on why rings might be common in centaurs. we also speculate on whether the known bimodal color distribution of the centaurs could be due to centaurs with rings and centaurs without rings. table 1 is 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/576/a18 | possible ring material around centaur (2060) chiron |
the recently discovered minor body 1i/2017 u1 (‘oumuamua) is the first known object in our solar system that is not bound by the sun’s gravity. its hyperbolic orbit (eccentricity greater than unity) strongly suggests that it originated outside our solar system; its red color is consistent with substantial space weathering experienced over a long interstellar journey. we carry out a simple calculation of the probability of detecting such an object. we find that the observed detection rate of 1i-like objects can be satisfied if the average mass of ejected material from nearby stars during the process of planetary formation is ∼20 earth masses, similar to the expected value for our solar system. the current detection rate of such interstellar interlopers is estimated to be 0.2 yr-1, and the expected number of detections over the past few years is almost exactly one. when the large synoptic survey telescope begins its wide, fast, deep all-sky survey, the detection rate will increase to 1 yr-1. those expected detections will provide further constraints on nearby planetary system formation through a better estimate of the number and properties of interstellar objects. | implications for planetary system formation from interstellar object 1i/2017 u1 (‘oumuamua) |
we present follow-up photometry and spectroscopy of ztf j0328-1219, strengthening its status as a white dwarf exhibiting transiting planetary debris. using tess and zwicky transient facility photometry, along with follow-up high-speed photometry from various observatories, we find evidence for two significant periods of variability at 9.937 and 11.2 hr. we interpret these as most likely the orbital periods of different debris clumps. changes in the detailed dip structures within the light curves are observed on nightly, weekly, and monthly timescales, reminiscent of the dynamic behavior observed in the first white dwarf discovered to harbor a disintegrating asteroid, wd 1145+017. we fit previously published spectroscopy along with broadband photometry to obtain new atmospheric parameters for the white dwarf, with m⋆ = 0.731 ± 0.023 m⊙, teff = 7630 ± 140 k, and [ca/he] = - 9.55 ± 0.12. with new high-resolution spectroscopy, we detect prominent and narrow na d absorption features likely of circumstellar origin, with velocities 21.4 ± 1.0 km s-1 blueshifted relative to atmospheric lines. we attribute the periodically modulated photometric signal to dusty effluents from small orbiting bodies such as asteroids or comets, but we are unable to identify the most likely material that is being sublimated, or otherwise ejected, as the environmental temperatures range from roughly 400 to 700 k. | recurring planetary debris transits and circumstellar gas around white dwarf ztf j0328-1219 |
the surface mineralogy of dwarf planet ceres appears to be dominated by products of rock-fluid interactions, such as phyllosilicates—some of which are nh4-bearing—and carbonates1-3. elemental concentrations derived from the inferred mineral mixing fractions, however, do not match measurements of h, c, k and fe on ceres4. a complicating factor in assessing ceres's unique surface composition is the secular accretion of asteroids typical of chondritic compositions. here we show that ceres's mineral and elemental data can be explained by the presence of carbonaceous chondritic-like materials ( 50-60 vol%), possibly due to infalling asteroids, admixed with aqueously altered endogenic materials that contain higher-than-chondritic concentrations of carbon. we find that ceres's surface may contain up to 20 wt% of carbon, which is more than five times higher than in carbonaceous chondrites. the coexistence of phyllosilicates, magnetite, carbonates and a high carbon content implies rock-water alteration played an important role in promoting widespread carbon chemistry. these findings unveil pathways for the synthesis of organic matter, with implications for their transport across the solar system. | an aqueously altered carbon-rich ceres |
we present a new analysis of the diffuse soft γ -ray emission toward the inner galaxy as measured by the spectrometer aboard the integral satellite (spi) with 16 years of data taking. the analysis implements a spatial template fit of spi data and an improved instrumental background model. we characterize the contribution of primordial black holes (pbh) as dark matter (dm) candidates evaporating into o (1 ) mev photons by including, for the first time to our knowledge, the spatial distribution of their signal into the fitting procedure. no pbh signal is detected, and we set the strongest limit on pbh dm for masses up to 4 ×1017 g , significantly closing in to the so-called asteroid mass range. | strong constraints on primordial black hole dark matter from 16 years of integral/spi observations |
the qinghai lake basin (qlb) is an ideal region to explore the interaction between climate change, vegetation evolution, and anthropogenic activities during the holocene epoch. this is due to the basin's particular sensitivity to global climate changes along with its densely distributed archeological sites, present since the last deglaciation. to date, a full understanding of the lakeshore terrestrial fossil pollen record is lacking and few studies have explored the human signals in the pollen spectra of the northeast qinghai-tibetan plateau. here, we present fossil pollen and charcoal records from over 8500 years ago obtained from a high resolution-dated aeolian section in the southeastern margin of the qlb. these results show that the pollen spectra are dominated by herbaceous and shrubby pollen taxa, while arboreal pollen taxa are rare. from approximately 8.5-7.2 ka, artemisia- and poaceae- dominated temperate steppe developed in the region, suggesting relatively warm and dry climatic conditions. comparatively, regional vegetation shifted to cyperaceae-dominated alpine meadow from approximately 7.2-3.4 ka, which reflected cooler and wetter climatic conditions. thereafter, the amount of asteraceae, artemisia, and chenopodiaceae notably increased from approximately 3.4-1.8 ka, suggesting that temperate steppe dominated the region under relative drier climate. noticeably, an interval between approximately 1.8-0.6 ka was characterized by an increase of hippophae pollen, reflecting a comparatively warmer episode; alpine meadow then reoccupied the region since approximately 0.6 ka. combining the variations of charcoal concentrations (20-50 μm and >50 μm) with human-related pollen taxa (aster-type, chenopodiaceae, plantago, and hordeum-type), we inferred that prehistoric humans were extensively using fire for hunting and subsistence during 7.2-3.5 ka, which strongly impacted the local vegetation during the middle holocene; regional grazing activities intensified and caused grassland degradation since approximately 3.5 ka, which manifested with a significant increase in aster-type and chenopodiaceae pollen. after this period, hordeum-type pollen as well as charcoal concentration of >50 μm increased significantly since approximately 2.2 ka, suggesting an intensifying agricultural cultivation in the region. | climate change and anthropogenic activities in qinghai lake basin over the last 8500 years derived from pollen and charcoal records in an aeolian section |
the cm carbonaceous chondrite meteorites provide a record of low temperature (<150 °c) aqueous reactions in the early solar system. a number of cm chondrites also experienced short-lived, post-hydration thermal metamorphism at temperatures of ∼200 °c to >750 °c. the exact conditions of thermal metamorphism and the relationship between the unheated and heated cm chondrites are not well constrained but are crucial to understanding the formation and evolution of hydrous asteroids. here we have used position-sensitive-detector x-ray diffraction (psd-xrd), thermogravimetric analysis (tga) and transmission infrared (ir) spectroscopy to characterise the mineralogy and water contents of 14 heated cm and ungrouped carbonaceous chondrites. we show that heated cm chondrites underwent the same degree of aqueous alteration as the unheated cms, however upon thermal metamorphism their mineralogy initially (300-500 °c) changed from hydrated phyllosilicates to a dehydrated amorphous phyllosilicate phase. at higher temperatures (>500 °c) we observe recrystallisation of olivine and fe-sulphides and the formation of metal. thermal metamorphism also caused the water contents of heated cm chondrites to decrease from ∼13 wt% to ∼3 wt% and a subsequent reduction in the intensity of the 3 μm feature in ir spectra. we estimate that the heated cm chondrites have lost ∼15 - >65% of the water they contained at the end of aqueous alteration. if impacts were the main cause of metamorphism, this is consistent with shock pressures of ∼20-50 gpa. however, not all heated cm chondrites retain shock features suggesting that some were instead heated by solar radiation. evidence from the hayabusa2 and orsirs-rex missions suggest that dehydrated materials may be common on the surfaces of primitive asteroids and our results will support upcoming analysis of samples returned from asteroids ryugu and bennu. | thermal alteration of cm carbonaceous chondrites: mineralogical changes and metamorphic temperatures |
we use a dynamical model to characterize the monthly and yearly variations of the lunar meteoroid environment for meteoroids originating from short and long-period comets and the main-belt asteroids. our results show that if we assume the meteoroid mass flux of 43.3 tons per day at earth, inferred from previous works, the mass flux of meteoroids impacting the moon is 30 times smaller, approximately 1.4 tons per day, and shows variations of the order of 10% over a year. the mass flux difference is due to the combined effect of the smaller cross-section of the moon (factor of 13.46) and earth's larger gravitational focusing (factor of 2-2.5). the lunar surface is vaporized by these impactors at an average impact vaporization flux of 11.6 × 10-16 g·cm-2·s-1, providing a significant source for the rarefied lunar exosphere. our model predicts acceptable vaporization rates and reproduces the local time dependence of observations of the dust ejecta cloud, measured by the lunar dust experiment on board nasa's lunar atmosphere and dust environment (ladee) satellite. however, the predicted density of the lunar ejecta cloud is four orders of magnitude larger than reported values by ladee. this discrepancy might be attributed to a much lower yield from meteoroid impacts on fluffy lunar regolith and/or a lower detection efficiency of the ladee dust detector. we suggest an upper limit of 30 cm per million years for the soil gardening rate from small meteoroids. | meteoroids at the moon: orbital properties, surface vaporization, and impact ejecta production |
samples from asteroid ryugu returned by the hayabusa2 mission contain evidence of extensive alteration by aqueous fluids and appear related to the ci chondrites. to understand the sources of the fluid and the timing of chemical reactions occurring during the alteration processes, we investigated the oxygen, carbon and 53mn-53cr systematics of carbonate and magnetite in two ryugu particles. we find that the fluid was initially between 0 and 20 °c and enriched in 13c, 17o and 18o, and subsequently evolved towards lighter carbon and oxygen isotopic compositions as alteration proceeded. carbonate ages show that this fluid-rock interaction took place within approximately the first 1.8 million years of solar system history, requiring early accretion either in a planetesimal less than ∼20 km in diameter or within a larger body that was disrupted and reassembled. | early fluid activity on ryugu inferred by isotopic analyses of carbonates and magnetite |
we report high-resolution spectroscopic observations of wd 1145+017—a white dwarf that was recently found to be transitted by multiple asteroid-sized objects within its tidal radius. we discovered numerous circumstellar absorption lines with linewidths of ∼300 km s-1 from mg, ca, ti, cr, mn, fe, and ni, possibly from several gas streams produced by collisions among the actively disintegrating objects. the atmosphere of wd 1145+017 is polluted with 11 heavy elements, including o, mg, al, si, ca, ti, v:, cr, mn, fe, and ni. evidently, we are witnessing the active disintegration and subsequent accretion of an extrasolar asteroid. the data presented herein were obtained at the w.m. keck observatory, which is operated as a scientific partnership among caltech, the university of california, and nasa. the observatory was made possible by the generous financial support of the w.m. keck foundation. | evidence for gas from a disintegrating extrasolar asteroid |
the jaxa hayabusa-2 mission was approved in 2010 and launched on december 3, 2014. the spacecraft will arrive at the near-earth asteroid 162173 ryugu (1999 ju3) in 2018 where it will perform a survey, land and obtainsurface material, then depart in december 2019 and return to earth in december 2020. we observed ryugu with the herschel space observatory in april 2012 at far-infrared thermal wavelengths, supported by several ground-based observations to obtain optical lightcurves. we reanalysed previously published subaru-comics and akari-irc observations and merged them with a spitzer-irs data set. in addition, we used a large set of spitzer-irac observations obtained in the period january to may, 2013. the data set includes two complete rotational lightcurves and a series of ten "point-and-shoot" observations, all at 3.6 and 4.5 μm. the almost spherical shape of the target together with the insufficient lightcurve quality forced us to combine radiometric and lightcurve inversion techniques in different ways to find the object's spin-axis orientation, its shape and to improve the quality of the key physical and thermal parameters. handling thermal data in inversion techniques remains challenging: thermal inertia, roughness or local structures influence the temperature distribution on the surface. the constraints for size, spin or thermal properties therefore heavily depend on the wavelengths of the observations. we find that the solution which best matches our data sets leads to this c class asteroid having a retrograde rotation with a spin-axis orientation of (λ = 310°-340°; β = -40° ± 15°) in ecliptic coordinates, an effective diameter (of an equal-volume sphere) of 850 to 880 m, a geometric albedo of 0.044 to 0.050 and a thermal inertia in the range 150 to 300 j m-2 s-0.5 k-1. based on estimated thermal conductivities of the top-layer surface in the range 0.1 to 0.6 w k-1 m-1, we calculated that the grain sizes are approximately equal to between 1 and 10 mm. the finely constrained values for this asteroid serve as a "design reference model", which is currently used for various planning, operational and modelling purposes by the hayabusa-2 team. this work includes space data from (i) herschel, an esa space observatory with science instruments provided by european-led principal investigator consortia and with important participation from nasa; (ii) spitzer space telescope, which is operated by the jet propulsion laboratory, california institute of technology under a contract with nasa; (iii) akari, a jaxa project with the participation of esa. | hayabusa-2 mission target asteroid 162173 ryugu (1999 ju3): searching for the object's spin-axis orientation |
we present the results of a monte carlo technique to calculate the absolute magnitudes (h) and slope parameters (g) of ∼240,000 asteroids observed by the pan-starrs1 telescope during the first 15 months of its 3-year all-sky survey mission. the system's exquisite photometry with photometric errors ≲ 0.04mag , and well-defined filter and photometric system, allowed us to derive accurate h and g even with a limited number of observations and restricted range in phase angles. our monte carlo method simulates each asteroid's rotation period, amplitude and color to derive the most-likely h and g, but its major advantage is in estimating realistic statistical + systematic uncertainties and errors on each parameter. the method was tested by comparison with the well-established and accurate results for about 500 asteroids provided by pravec et al. (pravec, p. et al. [2012]. icarus 221, 365-387) and then applied to determining h and g for the pan-starrs1 asteroids using both the muinonen et al. (muinonen, k. et al. [2010]. icarus 209, 542-555) and bowell et al. (bowell, e. et al. [1989]. asteroids iii, chapter application of photometric models to asteroids. university of arizona press, pp. 524-555) phase functions. our results confirm the bias in mpc photometry discovered by jurić et al. (jurić, m. et al. [2002]. astrophys. j. 124, 1776-1787). | absolute magnitudes and slope parameters for 250,000 asteroids observed by pan-starrs ps1 - preliminary results |
the low velocity of interstellar asteroid 1i/'oumuamua with respect to our galaxy's local standard of rest implies that it is young. adopting the young age hypothesis, we assess possible origin systems for this interstellar asteroid and for 2i/borisov, though the latter's higher speed means it is unlikely to be young. first, their past trajectories are modeled under gravitational scattering by galactic components ("disk heating") to assess how far back one can trace them. the stochastic nature of disk heating means that a back integration can only expect to be accurate to within 15 pc and 2 km s-1 at -10 myr, dropping steeply to 400 pc and 10 km s-1 at -100 myr, sharply limiting our ability to determine a precise origin. nevertheless, we show that 'oumuamua's origin system likely is currently within 1 kpc of earth, in the local orion arm. second, we back integrate 'oumuamua's trajectory in order to assess source regions, emphasizing young systems and moving groups. though disk heating allows for only a statistical link to source regions, 'oumuamua passed through a considerable subset of the carina and columba moving groups when those groups were forming. this makes them perhaps the most plausible source region, if 'oumuamua was ejected during planet formation or via intra-cluster interactions. we find three stars in the ursa major group, one brown dwarf, and seven other stars to have plausible encounters with 2i/borisov, within 2 pc and 30 km s-1. these encounters' high relative speeds mean none are likely to be the home of 2i/borisov. | the dynamics of interstellar asteroids and comets within the galaxy: an assessment of local candidate source regions for 1i/'oumuamua and 2i/borisov |
the collision of the nasa dart spacecraft with asteroid dimorphos resulted in the formation of a distinctive and long-lived debris trail, formed by the action of solar radiation pressure on ejected particles. this trail briefly displayed a double appearance, which has been interpreted as the result of a double ejection. we present a model that can produce a transient double trail without the need to assume a double ejection. our model explains the appearance of the double trail as a projection of the cone walls when viewed from a large angle to the cone axis and avoids the problem of producing dust in two epochs from a single, instantaneous impact. the particles follow a broken power-law size distribution, with differential indices q = 2.7 ± 0.2 (1 μm ≤ a ≤ 2 mm), 3.9 ± 0.1 (2 mm < a ≤ 1 cm), and 4.2 ± 0.2 (1 cm < a ≤ 20 cm). we find that the total trail mass in particles from 1 μm to 20 cm in size (for an assumed density 3500 kg m-3) is ~1.7 × 107 kg, rising to 2.2 × 107 kg, when extended to boulders up to 3.5 m in radius. this corresponds to 0.4%-0.6% of the mass of dimorphos. | a single ejection model of the dart/dimorphos debris trail |
the cm chondrites are samples of primitive water-rich asteroids formed during the early solar system. they record significant interaction between liquid water and silicate rock, resulting in a mineralogy dominated by hydrated secondary phases. their similarity to the near-earth asteroids bennu and ryugu - targets of current sample return space missions - makes the analysis of cm chondrites essential to the interpretation of these enigmatic bodies. here, we review the aqueous alteration history of the cm chondrite group. initially, amorphous silicate, metal and sulphides within the matrix were converted into fe-cronstedtite and tochilinite. later, the serpentinization of refractory coarse-grained inclusions led to the addition of mg to the fluid phase. this is reflected in the cation composition of secondary phases which evolved from fe-rich to mg-rich. although most cm meteorites are classified as cm2 chondrites and retain some unaltered anhydrous silicates, a few completely altered cm1s exist (∼4.2% [meteoritical bulletin, 2021]). the extent of aqueous alteration can be quantified through various techniques, all of which trace the progression of secondary mineralization. early attempts employed petrographic criteria to assign subtypes - most notably the browning and rubin scales have been widely adopted. alternatively, bulk techniques evaluate alteration either by measuring the ratio of phyllosilicate to anhydrous silicate (this can be with x-ray diffraction [xrd] or infrared spectroscopy [ir]) or by measuring the combined h abundance/δd compositions. the degree of aqueous alteration appears to correlate with petrofabric strength (most likely arising due to shock deformation). this indicates that aqueous alteration may have been driven primarily by impact rather than by radiogenic heating. alteration extent and bulk o-isotope compositions show a complex relationship. among cm2 chondrites higher initial water contents correspond to more advanced alteration. however, the cm1s have lighter-than-expected bulk compositions. although further analyses are needed these findings could suggest either differences in alteration conditions or initial isotopic compositions - the latter scenario implies that the cm1 chondrites formed on a separate asteroid from the cm2 chondrites. secondary phases (primarily calcite) act as proxies for the conditions of aqueous alteration and demonstrate that alteration was prograde, with an early period at low temperatures (<70 °c), while later alteration operated at higher temperatures of 100-250 °c. estimates for the initial water-to-rock ratios (w/r) vary between 0.2-0.7. they are based either on isotopic mass balance or mineral stoichiometry calculations - variability reflects uncertainties in the primordial water and protolith compositions and whether alteration was open or closed system. some cm chondrites (<36%) experienced a later episode of post-hydration thermal metamorphism, enduring peak temperatures <900 °c and resulting in a dehydrated mineralogy and depleted volatile element abundances. heating was likely short-duration and caused by impact events. the presence of cm chondrite material embedded in other meteorites, their prominence among the micrometeorite flux and the link between cms and rubble-pile c-type near-earth asteroids (e.g. bennu and ryugu) implies that the cm parent body was disrupted, leaving second-generation cm asteroids to supply material to earth. | the aqueous alteration of cm chondrites, a review |
this paper proposes a new nonlinear guidance algorithm applicable for asteroid both hovering and landing. with the new guidance, a spacecraft achieves its target position and velocity in finite-time without the requirement of reference trajectories. the global stability is proven for the controlled system. a parametric analysis is conducted to illustrate the parameters' effects on the guidance algorithm. simulations of straight landing, hovering to hovering and landing with a prior hovering phase of the highly irregular asteroid 2063 bacchus are presented and the effectiveness of the proposed method is demonstrated. | finite-time control for asteroid hovering and landing via terminal sliding-mode guidance |
the exoplanetary system of hr 8799 is one of the rare systems in which multiple planets have been directly imaged. its architecture is strikingly similar to that of the solar system, with the four imaged giant planets surrounding a warm dust belt analogous to the asteroid belt, and themselves being surrounded by a cold dust belt analog to the kuiper belt. previous observations of this cold belt with alma in band 6 (1.3 mm) revealed its inner edge, but analyses of the data differ on its precise location. it was therefore unclear whether or not the outermost planet hr 8799 b was dynamically sculpting it. we present here new alma observations of this debris disk in band 7 (340 ghz, 880 μm). these are the most detailed observations of this disk obtained so far, with a resolution of 1″ (40 au) and sensitivity of 9.8 μjy beam-1, which allowed us to recover the disk structure with high confidence. in order to constrain the disk morphology, we fit its emission using radiative transfer models combined with a markov chain monte carlo procedure. we find that this disk cannot be adequately represented by a single power law with sharp edges. it exhibits a smoothly rising inner edge and smoothly falling outer edge, with a peak in between, as expected from a disk that contains a high-eccentricity component, hence confirming previous findings. whether this excited population and inner edge shape stem from the presence of an additional planet remains, however, an open question. | a detailed characterization of hr 8799's debris disk with alma in band 7 |
extraterrestrial iron sulfide is a major mineral reservoir of the cosmochemically and astrobiologically important elements iron and sulfur. sulfur depletion on asteroids is a long-standing, yet unresolved phenomenon that is of fundamental importance for asteroid evolution and sulfur delivery to the earth. understanding the chemistry of such environments requires insight into the behavior of iron sulfides exposed to space. here we show that troilite (fes) grains recovered from the regolith of asteroid 25143 itokawa have lost sulfur during long-term space exposure. we report the wide-spread occurrence of metallic iron whiskers as a decomposition product formed through irradiation of the sulfide by energetic ions of the solar wind. whisker growth by ion irradiation is a novel and unexpected aspect of space weathering. it implies that sulfur loss occurs rapidly and, furthermore, that ion irradiation plays an important role in the redistribution of sulfur between solids and gas of the interstellar medium. | iron whiskers on asteroid itokawa indicate sulfide destruction by space weathering |
some years ago, the consensus was that asteroid (16) psyche was almost entirely metal. new data on density, radar properties, and spectral signatures indicate that the asteroid is something perhaps even more enigmatic: a mixed metal and silicate world. here we combine observations of psyche with data from meteorites and models for planetesimal formation to produce the best current hypotheses for psyche's properties and provenance. psyche's bulk density appears to be between 3,400 and 4,100 kg m-3. psyche is thus predicted to have between ~30 and ~60 vol% metal, with the remainder likely low-iron silicate rock and not more than ~20% porosity. though their density is similar, mesosiderites are an unlikely analog to bulk psyche because mesosiderites have far more iron-rich silicates than psyche appears to have. cb chondrites match both psyche's density and spectral properties, as can some pallasites, although typical pallasitic olivine contains too much iron to be consistent with the reflectance spectra. final answers, as well as resolution of contradictions in the data set of psyche physical properties, for example, the thermal inertia measurements, may not be resolved until the nasa psyche mission arrives in orbit at the asteroid. despite the range of compositions and formation processes for psyche allowed by the current data, the science payload of the psyche mission (magnetometers, multispectral imagers, neutron spectrometer, and a gamma-ray spectrometer) will produce data sets that distinguish among the models. | observations, meteorites, and models: a preflight assessment of the composition and formation of (16) psyche |
context. asteroid (101955) bennu is the target of nasa's origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission. the spacecraft's instruments have characterized bennu at global and local scales to select a sampling site and provide context for the sample that will be returned to earth. these observations include thermal infrared spectral characterization by the osiris-rex thermal emission spectrometer (otes).aims: to understand the degree of compositional and particle size variation on bennu, and thereby predict the nature of the returned sample, we studied otes spectra, which are diagnostic of these properties.methods: we created and mapped spectral indices and compared them with the distribution of geomorphic features. comparison to laboratory spectra of aqueously altered carbonaceous chondrites constrains the amount of compositional variability that is observable.results: the otes spectra exhibit two end-member shapes (or types), and compositional variability appears limited at the spatial resolution of the observations. the global distribution of these spectral types corresponds with the locations of regions composed of (i) large, dark, relatively rough boulders and (ii) relatively smooth regions lacking large boulders.conclusions: the two spectral types appear to be diagnostic primarily of particle size variations, with contributions from other properties. the spectra resemble experimental data of solid substrates with very thin accumulations (a few to tens of microns) of fine particles (<~65-100 μm). the dustier surfaces commonly correspond with rougher rocks that may produce and/or act as traps for the particles. anhydrous silicates are limited in abundance, and the bulk mineralogy is consistent with the most aqueously altered carbonaceous chondrites. we expect the returned samples to include these physical and mineralogical characteristics. | evidence for limited compositional and particle size variation on asteroid (101955) bennu from thermal infrared spectroscopy |
stereophotoclinometry (spc) is a technique to extract topographic information from images acquired by spacecraft. it combines stereophotogrammetry and photoclinometry to produce a product that has the accuracy of stereo with the resolution of photoclinometry without the restrictions common to both. we describe the implementation of this technique in the context of digital terrain model (dtm) generation for a small-body mission. we detail the process and the data used to generate spc-derived dtms at progressively increasing resolutions. the highest-quality dtms are generated using four images optimized for topography, a 30° emission angle with the emission azimuth (spacecraft position) to the north, east, south, and west of the target, and one image optimized for albedo (a low incidence angle such that most of the image pixels' digital numbers are based upon albedo rather than topography). we discuss implications for mission planning and how spc-based dtm generation can support spacecraft navigation. as a case study, we share outcomes from the modeling performed for the osiris-rex mission to asteroid bennu. | practical stereophotoclinometry for modeling shape and topography on planetary missions |
prompt learning is a new paradigm in the natural language processing (nlp) field which has shown impressive performance on a number of natural language tasks with common benchmarking text datasets in full, few-shot, and zero-shot train-evaluation setups. recently, it has even been observed that large but frozen pre-trained language models (plms) with prompt learning outperform smaller but fine-tuned models. however, as with many recent nlp trends, the performance of even the largest plms such as gpt-3 do not perform well on specialized domains (e.g. medical text), and the common practice to achieve state of the art (sota) results still consists of pre-training and fine-tuning the plms on downstream tasks. the reliance on fine-tuning large plms is problematic in clinical settings where data is often held in non-gpu environments, and more resource efficient methods of training specialized domain models is crucial. we investigated the viability of prompt learning on clinically meaningful decision tasks and directly compared with more traditional fine-tuning methods. results are partially in line with the prompt learning literature, with prompt learning able to match or improve on traditional fine-tuning with substantially fewer trainable parameters and requiring less training data. we argue that prompt learning therefore provides lower computational resource costs applicable to clinical settings, that can serve as an alternative to fine-tuning ever increasing in size plms. complementary code to reproduce experiments presented in this work can be found at: https://github.com/ntaylorox/public_clinical_prompt. | clinical prompt learning with frozen language models |
large metal stable isotopic variations have been observed in both extraterrestrial and terrestrial samples. for example, ca exhibits large mass-dependent isotopic variation in terrestrial igneous rocks and mantle minerals (on the order of ∼2‰ variation in 44ca/40ca). a thorough assessment and understanding of such isotopic variations in peridotites provides important constraints on the evolution and compositon of the earth's mantle. in order to better understand the ca and fe isotopic variations in terrestrial silicate rocks, we report ca isotopic compositions in a set of peridotitic xenoliths from north china craton (ncc), which have been studied for fe isotopes. these ncc peridotites have large ca and fe isotopic variations, with δ44/40ca ranging from -0.08 to 0.92 (delta value relative to srm915a) and δ57/54fe (delta value relative to irmm-014) ranging from -0.61 to 0.16, and these isotopic variations are correlated with large mg# (100 × mg/(mg + fe) molar ratio) variation, ranging from 80 to 90. importantly, ncc fe-rich peridotites have the lowest 44ca/40ca and 57fe/54fe ratios in all terrestrial silicate rocks. in contrast, although ureilites, mantle rocks from a now broken differentiated asteroid(s), have large mg# variation, from 70 to 92, they have very limited δ57fe/54fe variation (0.03-0.21, delta value relative to irmm-014). our model calculations show that the coupled extremely light ca-fe isotopic signatures in ncc fe-rich peridotites most likely reflect kinetic isotopic fractionation during melt-peridotite reaction on a timescale of several to 104 years. in addition, our new data and compiled literature data show a possible compositional effect on the inter-mineral ca isotopic fractionation between co-existing clinopyroxene and orthopyroxene pairs. | coupled extremely light ca and fe isotopes in peridotites |
we study possibilities to explain the whole dark matter abundance by primordial black holes (pbhs) or to explain the merger rate of binary black holes estimated from the gravitational wave detections by ligo/virgo. we assume that the pbhs are originated in a radiation- or matter-dominated era from large primordial curvature perturbation generated by inflation. we take a simple model-independent approach considering inflation with large running spectral indices which are parametrized by , and consistent with the observational bounds. the merger rate is fitted by pbhs with masses of produced in the radiation-dominated era. then the running of running should be , which can be tested by future observation. on the other hand, the whole abundance of dark matter is consistent with pbhs with masses of asteroids () produced in an early matter-dominated era if a set of running parameters are properly realized. | primordial black hole dark matter and ligo/virgo merger rate from inflation with running spectral indices: formation in the matter- and/or radiation-dominated universe |
knowledge of water in the solar system is important for the understanding of a wide range of evolutionary processes and the thermal history of the solar system. to explore the existence of water in the solar system, it is indispensable to investigate hydrated minerals and/or water ice on asteroids. these water-related materials show absorption features in the 3 μm band (wavelengths from 2.7 to 3.1 μm). we conducted a spectroscopic survey of asteroids in the 3 μm band using the infrared camera (irc) on board the japanese infrared satellite akari. in the warm mission period of akari, 147 pointed observations were performed for 66 asteroids in the grism mode for wavelengths from 2.5 to 5 μm. according to these observations, most c-complex asteroids have clear absorption features (>10% with respect to the continuum) related to hydrated minerals at a peak wavelength of approximately 2.75 μm, while s-complex asteroids have no significant features in this wavelength range. the present data are released to the public as the asteroid catalog using akari spectroscopic observations (acua-spec). | akari/irc near-infrared asteroid spectroscopic survey: acua-spec |
we are performing a wide and deep survey for extreme distant solar system objects. our goal is to understand the high-perihelion objects sedna and 2012 vp113 and determine if an unknown massive planet exists in the outer solar system. the discovery of new extreme objects from our survey of some 1080 square degrees of sky to over 24th magnitude in the r-band are reported. two of the new objects, 2014 sr349 and 2013 ft28, are extreme detached trans-neptunian objects, which have semimajor axes greater than 150 au and perihelia well beyond neptune (q > 40 au). both new objects have orbits with arguments of perihelia within the range of the clustering of this angle seen in the other known extreme objects. one of these objects, 2014 sr349, has a longitude of perihelion similar to the other extreme objects, but 2013 ft28 is about 180° away or anti-aligned in its longitude of perihelion. we also discovered the first outer oort cloud object with a perihelion beyond neptune, 2014 fe72. we discuss these and other interesting objects discovered in our ongoing survey. all the high semimajor axis (a > 150 au) and high-perihelion (q > 35 au) bodies follow the previously identified argument of perihelion clustering as first reported and explained as being from an unknown massive planet in 2014 by trujillo & sheppard, which some have called planet x or planet nine. with the discovery of 2013 ft28 on the opposite side of the sky, we now report that the argument of perihelion is significantly correlated with the longitude of perihelion and orbit pole angles for extreme objects and find there are two distinct extreme clusterings anti-aligned with each other. this previously unnoticed correlation is further evidence of an unknown massive planet on a distant eccentric inclined orbit, as extreme eccentric objects with perihelia on opposite sides of the sky (180° longitude of perihelion differences) would approach the inclined planet at opposite points in their orbits, thus making the extreme objects prefer to stay away from opposite ecliptic latitudes to avoid the planet (i.e., opposite argument of perihelia or orbit pole angles). | new extreme trans-neptunian objects: toward a super-earth in the outer solar system |
we know that planetary systems are just as common around white dwarfs as around main-sequence stars. however, self-consistently linking a planetary system across these two phases of stellar evolution through the violent giant branch poses computational challenges, and previous studies restricted architectures to equal-mass planets. here, we remove this constraint and perform over 450 numerical integrations over a hubble time (14 gyr) of packed planetary systems with unequal-mass planets. we characterize the resulting trends as a function of planet order and mass. we find that intrusive radial incursions in the vicinity of the white dwarf become less likely as the dispersion amongst planet masses increases. the orbital meandering which may sustain a sufficiently dynamic environment around a white dwarf to explain observations is more dependent on the presence of terrestrial-mass planets than any variation in planetary mass. triggering unpacking or instability during the white dwarf phase is comparably easy for systems of unequal-mass planets and systems of equal-mass planets; instabilities during the giant branch phase remain rare and require fine-tuning of initial conditions. we list the key dynamical features of each simulation individually as a potential guide for upcoming discoveries. | full-lifetime simulations of multiple unequal-mass planets across all phases of stellar evolution |
context. the populations of small bodies of the solar system (asteroids, comets, kuiper-belt objects) are used to constrain the origin and evolution of the solar system. both their orbital distribution and composition distribution are required to track the dynamical pathway from their regions of formation to their current locations.aims: we aim at increasing the sample of solar system objects that have multi-filter photometry and compositional taxonomy.methods: we search for moving objects in the archive of the sloan digital sky survey. we attempt at maximizing the number of detections by using loose constraints on the extraction. we then apply a suite of filters to remove false-positive detections (stars or galaxies) and mark out spurious photometry and astrometry.results: we release a catalog of 1 542 522 entries, consisting of 1 036 322 observations of 379 714 known and unique ssos together with 506 200 observations of moving sources not linked with any known ssos. the catalog completeness is estimated to be about 95% and the purity to be above 95% for known ssos. the catalog is 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/652/a59 | a million asteroid observations in the sloan digital sky survey |
context. the gaia mission of the european space agency (esa) has been routinely observing solar system objects (ssos) since the beginning of its operations in august 2014. the gaia data release three (dr3) includes, for the first time, the mean reflectance spectra of a selected sample of 60 518 ssos, primarily asteroids, observed between august 5, 2014, and may 28, 2017. each reflectance spectrum was derived from measurements obtained by means of the blue and red photometers (bp/rp), which were binned in 16 discrete wavelength bands. for every spectrum, the dr3 also contains additional information about the data quality for each band.aims: we describe the processing of the gaia spectral data of ssos, explaining both the criteria used to select the subset of asteroid spectra published in gaia dr3, and the different steps of our internal validation procedures. in order to further assess the quality of gaia sso reflectance spectra, we carried out external validation against sso reflectance spectra obtained from ground-based and space-borne telescopes and available in the literature; we present our validation approach.methods: for each selected sso, an epoch reflectance was computed by dividing the calibrated spectrum observed by the bp/rp at each transit on the focal plane by the mean spectrum of a solar analogue. the latter was obtained by averaging the gaia spectral measurements of a selected sample of stars known to have very similar spectra to that of the sun. finally, a mean of the epoch reflectance spectra was calculated in 16 spectral bands for each sso. results.gaia sso reflectance spectra are in general agreement with those obtained from a ground-based spectroscopic campaign specifically designed to cover the same spectral interval as gaia and mimic the illumination and observing geometry characterising gaia sso observations. in addition, the agreement between gaia mean reflectance spectra and those available in the literature is good for bright ssos, regardless of their taxonomic spectral class. we identify an increase in the spectral slope of s-type ssos with increasing phase angle. moreover, we show that the spectral slope increases and the depth of the 1 μm absorption band decreases for increasing ages of s-type asteroid families. the latter can be interpreted as proof of progressive ageing of s-type asteroid surfaces due to their exposure to space weathering effects. this article is dedicated to the memory of dimitri pourbaix, who laid the foundations and directed thef coordination unit 4 (cu4) of the data processing and analysis consortium (dpac) of the esa mission gaia. | gaia data release 3. reflectance spectra of solar system small bodies |
abstract the timing and mechanisms of the climatic and environmental perturbations induced by the emplacement of the deccan traps large igneous province (india) and their contribution to the cretaceous-paleogene (k-pg) mass extinction are still debated. in many marine sediment archives, mercury (hg) enrichments straddling the k-pg boundary have been interpreted as the signature of deccan traps volcanism, but hg may also have been derived from the chicxulub (mexico) impact. we investigated the hg isotope composition, as well as the behavior of iridium (ir) and other trace elements, in k-pg sediments from the bidart section in southwest france. above the k-pg boundary, ir content gradually decreases to background values in the danian carbonates, which is interpreted to indicate the erosion and redistribution of ir-rich fallouts. no significant enrichment in ir and w, or zn and cu, is observed just below the k-pg boundary, excluding the hypothesis of downward remobilization of hg from the boundary clay layer. positive δ199hg and slightly negative values in the upper maastrichtian and lower part of the early danian are consistent with the signature of sediments supplied by atmospheric hg2+ deposition and volcanic emissions. up section, large shifts to strongly negative mass-dependent fractionation values (δ202hg) result from the remobilization of hg formerly sourced by the impactor or by a mixture of different sources including biomass burning, volcanic eruption, and asteroid impact, requiring further investigation. our results provide additional support for the interpretation that the largest eruptions of the deccan traps began just before, and encompassed, the k-pg boundary and therefore may have contributed to the k-pg mass extinction. | volcanic origin of the mercury anomalies at the cretaceous-paleogene transition of bidart, france |
phobos and deimos, the two small satellites of mars, are thought either to be asteroids captured by the planet or to have formed in a disc of debris surrounding mars following a giant impact. both scenarios, however, have been unable to account for the current mars system. here we use numerical simulations to suggest that phobos and deimos accreted from the outer portion of a debris disc formed after a giant impact on mars. in our simulations, larger moons form from material in the denser inner disc and migrate outwards due to gravitational interactions with the disc. the resulting orbital resonances spread outwards and gather dispersed outer disc debris, facilitating accretion into two satellites of sizes similar to phobos and deimos. the larger inner moons fall back to mars after about 5 million years due to the tidal pull of the planet, after which the two outer satellites evolve into phobos- and deimos-like orbits. the proposed scenario can explain why mars has two small satellites instead of one large moon. our model predicts that phobos and deimos are composed of a mixture of material from mars and the impactor. | accretion of phobos and deimos in an extended debris disc stirred by transient moons |
the utilization of natural resources from asteroids is an idea that is older than the space age. the technologies are now available to transform this endeavor from an idea into reality. the asteroid redirect mission (arm) is a mission concept which includes the goal of robotically returning a small near-earth asteroid (nea) or a multi-ton boulder from a large nea to cislunar space in the mid-2020s using an advanced solar electric propulsion (sep) vehicle and currently available technologies. the paradigm shift enabled by the arm concept would allow in-situ resource utilization (isru) to be used at the human mission departure location (i.e., cislunar space) versus exclusively at the deep-space mission destination. this approach drastically reduces the barriers associated with utilizing isru for human deep-space missions. the successful testing of isru techniques and associated equipment could enable large-scale commercial isru operations to become a reality and enable a future space-based economy utilizing processed asteroidal materials. this paper provides an overview of the arm concept and discusses the mission objectives, key technologies, and capabilities associated with the mission, as well as how the arm and associated operations would benefit humanity's quest for the exploration and settlement of space. | asteroid redirect mission concept: a bold approach for utilizing space resources |
two events share the stage as main drivers of the cretaceous-paleogene mass extinction—deccan traps volcanism, and an asteroid impact recorded by the chicxulub crater. we contribute to refining knowledge of the volcanic stressor by providing sulfur and fluorine budgets of deccan lavas from the western ghats (india), which straddle the cretaceous-paleogene boundary. volcanic fluorine budgets were variable (400 to 3000 parts per million) and probably sufficient to affect the environment, albeit only regionally. the highest sulfur budgets (up to 1800 parts per million) are recorded in deccan lavas emplaced just prior (within 0.1 million years) to the extinction interval, whereas later basalts are generally sulfur-poor (up to 750 parts per million). independent evidence suggests the deccan flood basalts erupted in high-flux pulses. our data suggest that volcanic sulfur degassing from such activity could have caused repeated short-lived global drops in temperature, stressing the ecosystems long before the bolide impact delivered its final blow at the end of the cretaceous. late cretaceous deccan basalts were sulfur- and fluorine-rich. degassing potentially caused cold spells and ecosystem damage. | recurring volcanic winters during the latest cretaceous: sulfur and fluorine budgets of deccan traps lavas |
the mineralogy and geochemistry of ceres, as constrained by dawn's instruments, are broadly consistent with a carbonaceous chondrite (cm/ci) bulk composition. differences explainable by ceres's more advanced alteration include the formation of mg-rich serpentine and ammoniated clay; a greater proportion of carbonate and lesser organic matter; amounts of magnetite, sulfide, and carbon that could act as spectral darkening agents; and partial fractionation of water ice and silicates in the interior and regolith. ceres is not spectrally unique, but is similar to a few other c-class asteroids, which may also have suffered extensive alteration. all these bodies are among the largest carbonaceous chondrite asteroids, and they orbit in the same part of the main belt. thus, the degree of alteration is apparently related to the size of the body. although the ammonia now incorporated into clay likely condensed in the outer nebula, we cannot presently determine whether ceres itself formed in the outer solar system and migrated inward or was assembled within the main belt, along with other carbonaceous chondrite bodies. | carbonaceous chondrites as analogs for the composition and alteration of ceres |
white dwarfs are routinely observed to have polluted atmospheres, and sometimes significant infrared excesses, that indicate ongoing accretion of circumstellar dust and rocky debris. typically this debris is assumed to be in the form of a (circular) disc, and to originate from asteroids that passed close enough to the white dwarf to be pulled apart by tides. however, theoretical considerations suggest that the circularisation of the debris, which initially occupies highly eccentric orbits, is very slow. we therefore hypothesise that the observations may be readily explained by the debris remaining on highly eccentric orbits, and we explore the properties of such debris. for the generic case of an asteroid originating at several au from the white dwarf, we find that all of the tidal debris is always bound to the white dwarf and that the orbital energy distribution of the debris is narrow enough that it executes similar elliptical orbits with only a narrow spread. assuming that the tidal field of the white dwarf is sufficient to minimise the effects of self-gravity and collisions within the debris, we estimate the time over which the debris spreads into a single elliptical ring, and we generate toy spectra and lightcurves from the initial disruption to late times when the debris distribution is essentially time steady. finally we speculate on the connection between these simple considerations and the observed properties of these systems, and on additional physical processes that may change this simple picture. | emission from elliptical streams of dusty debris around white dwarfs |
we have discovered two epochs of activity on quasi-hilda 2009 dq118. small bodies that display comet-like activity, such as active asteroids and active quasi-hildas, are important for understanding the distribution of water and other volatiles throughout the solar system. through our nasa partner citizen science project, active asteroids, volunteers classified archival images of 2009 dq118 as displaying comet-like activity. by performing an in-depth archival image search, we found over 20 images from ut 2016 march 8-9 with clear signs of a comet-like tail. we then carried out follow-up observations of 2009 dq118 using the 3.5 m astrophysical research consortium telescope at apache point observatory, sunspot, new mexico, usa and the 6.5 m magellan baade telescope at las campanas observatory, chile. these images revealed a second epoch of activity associated with the ut 2023 april 22 perihelion passage of 2009 dq118. we performed photometric analysis of the tail and find that it had a similar apparent length and surface brightness during both epochs. we also explored the orbital history and future of 2009 dq118 through dynamical simulations. these simulations show that 2009 dq118 is currently a quasi-hilda and that it frequently experiences close encounters with jupiter. we find that 2009 dq118 is currently on the boundary between asteroidal and cometary orbits. additionally, it has likely been a jupiter family comet or centaur for much of the past 10 kyr and will be in these same regions for the majority of the next 10 kyr. since both detected epochs of activity occurred near perihelion, the observed activity is consistent with sublimation of volatile ices. 2009 dq118 is currently observable until ~mid-october 2023. further observations would help to characterize the observed activity. | recurring activity discovered on quasi-hilda 2009 dq118 |
we performed a statistical analysis of the astrometric errors for the major asteroid surveys. we analyzed the astrometric residuals as a function of observation epoch, observed brightness and rate of motion, finding that astrometric errors are larger for faint observations and some stations improved their astrometric quality over time. based on this statistical analysis we develop a new weighting scheme to be used when performing asteroid orbit determination. the proposed weights result in ephemeris predictions that can be conservative by a factor as large as 1.5. however, the new scheme is robust with respect to outliers and handles the larger errors for faint detections. | statistical analysis of astrometric errors for the most productive asteroid surveys |
when plate tectonics began on the earth has been long debated and here we argue this topic based on the records of earth-moon geology and asteroid belt to conclude that the onset of plate tectonics was during the middle hadean (4.37-4.20 ga). the trigger of the initiation of plate tectonics is the abel bombardment, which delivered oceanic and atmospheric components on a completely dry reductive earth, originally comprised of enstatite chondrite-like materials. through the accretion of volatiles, shock metamorphism processed with vaporization of both ci chondrite and supracrustal rocks at the bombarded location, and significant recrystallization went through under wet conditions, caused considerable eclogitization in the primordial continents composed of felsic upper crust of 21 km thick anorthosite, and 50 km or even thicker kreep lower crust. eclogitization must have yielded a powerful slab-pull force to initiate plate tectonics in the middle hadean. another important factor is the size of the bombardment. by creating pacific ocean class crater by 1000 km across impactor, rigid plate operating stagnant lid tectonics since the early hadean was severely destroyed, and oceanic lithosphere was generated to have bi-modal lithosphere on the earth to enable the operation of plate tectonics. considering the importance of the abel bombardment event which initiated plate tectonics including the appearance of ocean and atmosphere, we propose that the hadean eon can be subdivided into three periods: (1) early hadean (4.57-4.37 ga), (2) middle hadean (4.37-4.20 ga), and (3) late hadean (4.20-4.00 ga). | initiation of plate tectonics in the hadean: eclogitization triggered by the abel bombardment |
blockchain technology (bct) has emerged in the last decade and added a lot of interest in the healthcare sector. the purpose of this systematic literature review (slr) is to explore the potential paradigm shift in healthcare utilizing bct. the study is compiled by reviewing research articles published in nine well-reputed venues such as ieee xplore, acm digital library, springs link, scopus, taylor & francis, science direct, psycinfo, ovid medline, and mdpi between january 2016 to august 2021. a total of 1,192 research studies were identified out of which 51 articles were selected based on inclusion criteria for this slr that presents the modern information on the recent implications and gaps in the use of bct for enhancing the healthcare procedures. according to the outcomes, bct is being applied to design the novel and advanced interventions to enrich the current protocol of managing, distributing, and processing clinical records and personal medical information. bct is enduring the conceptual development in the healthcare domain, where it has summed up the substantial elements through better and enhanced efficiency, technological innovation, access control, data privacy, and security. a framework is developed to address the probable field where future researchers can add considerable value, such as data protection, system architecture, and regulatory compliance. finally, this slr concludes that the upcoming research can support the pervasive implementation of bct to address the critical dilemmas related to health diagnostics, enhancing the patient healthcare process in remote monitoring or emergencies, data integrity, and avoiding fraud. | blockchain technology in healthcare: a systematic review |
we present atacama large millimeter/submillimeter array (alma) observations of the dust continuum emission at 1.3 mm and 12co j=2\to 1 line emission of the transitional disk around dm tau. dm tau’s disk is thought to possess a dust-free inner cavity inside a few au, from the absence of near-infrared excess on its spectral energy distribution (sed). previous submillimeter observations were, however, unable to detect the cavity; instead, a dust ring ∼20 au in radius was seen. the excellent angular resolution achieved in the new alma observations, 43 × 31 mas, allows discovery of a 4 au radius inner dust ring, confirming previous sed modeling results. this inner ring is symmetric in continuum emission, but asymmetric in 12co emission. the known (outer) dust ring at ∼20 au is recovered and shows azimuthal asymmetry with a strong-weak side contrast of ∼1.3. the gap between these two rings is depleted by a factor of ∼40 in dust emission relative to the outer ring. an extended outer dust disk is revealed, separated from the outer ring by another gap. the location of the inner ring is comparable to that of the main asteroid belt in the solar system. as a disk with a “proto-asteroid belt,” the dm tau system offers valuable clues to disk evolution and planet formation in the terrestrial-planet-forming region. | a spatially resolved au-scale inner disk around dm tau |
mass-independent isotopic anomalies of carbonaceous and noncarbonaceous meteorites show a clear dichotomy suggesting an efficient separation of the inner and outer solar system. observations show that ring-like structures in the distribution of millimeter-sized pebbles in protoplanetary disks are common. these structures are often associated with drifting pebbles being trapped by local pressure maxima in the gas disk. similar structures may also have existed in the sun's natal disk, which could naturally explain the meteorite/planetary isotopic dichotomy. here, we test the effects of a strong pressure bump in the outer disk (e.g., ~5 au) on the formation of the inner solar system. we model dust coagulation and evolution, planetesimal formation, as well as embryo growth via planetesimal and pebble accretion. our results show that terrestrial embryos formed via planetesimal accretion rather than pebble accretion. in our model, the radial drift of pebbles fosters planetesimal formation. however, once a pressure bump forms, pebbles in the inner disk are lost via drift before they can be efficiently accreted by embryos growing at ⪆1 au. embryos inside ~0.5-1.0 au grow relatively faster and can accrete pebbles more efficiently. however, these same embryos grow to larger masses so they should migrate inwards substantially, which is inconsistent with the current solar system. therefore, terrestrial planets most likely accreted from giant impacts of moon to roughly mars-mass planetary embryos formed around ⪆1.0 au. finally, our simulations produce a steep radial mass distribution of planetesimals in the terrestrial region, which is qualitatively aligned with formation models suggesting that the asteroid belt was born low mass. | the effect of a strong pressure bump in the sun's natal disk: terrestrial planet formation via planetesimal accretion rather than pebble accretion |
inner oort cloud objects (iocs) are trans-plutonian for their entire orbits. they are beyond the strong gravitational influences of the known planets, yet close enough to the sun that outside forces are minimal. here we report the discovery of the third known ioc after sedna and 2012 vp113, called 2015 tg387. this object has a perihelion of 65 ± 1 au and semimajor axis of 1170 ± 70 au. the longitude of perihelion angle, \bar{ω }, for 2015 tg387 is between that of sedna and 2012 vp113 and thus similar to the main group of clustered extreme trans-neptunian objects (etnos), which may be shepherded into similar orbital angles by an unknown massive distant planet called planet x, or planet nine. the orbit of 2015 tg387 is stable over the age of the solar system from the known planets and galactic tide. when including outside stellar encounters over 4 gyr, 2015 tg387's orbit is usually stable, but its dynamical evolution depends on the stellar encounter scenarios used. surprisingly, when including a massive planet x beyond a few hundred au on an eccentric orbit that is antialigned in longitude of perihelion with most of the known etnos, we find that 2015 tg387 is typically stable for planet x orbits that render the other etnos stable as well. notably, 2015 tg387's argument of perihelion is constrained, and its longitude of perihelion librates about 180° from planet x’s longitude of perihelion, keeping 2015 tg387 antialigned with planet x over the age of the solar system. | a new high perihelion trans-plutonian inner oort cloud object: 2015 tg387 |
expected to be of the highest survey power telescope in the northern hemisphere, the wide field survey telescope (wfst) will begin its routine observations of the northern sky since 2023. wfst will produce a lot of scientific data to support the researches of time-domain astronomy, asteroids and the solar system, galaxy formation and cosmology and so on. we estimated that the 5σ limiting magnitudes of wfst with 30 s exposure are u = 22.31 mag, g = 23.42 mag, r = 22.95 mag, i = 22.43 mag, z = 21.50 mag, w = 23.61 mag. the above values are calculated for the conditions of airmass = 1.2, seeing = 0.″75, precipitable water vapor = 2.5 mm and moon-object separation = 45° at the darkest new moon night of the lenghu site (v = 22.30 mag, moon phase θ = 0°). the limiting magnitudes in different moon phase conditions are also calculated. the calculations are based on the empirical transmittance data of wfst optics, the vendor provided ccd quantum efficiency, the atmospherical model transmittance and spectrum of the site. in the absence of measurement data such as sky transmittance and spectrum, we use model data. | limiting magnitudes of the wide field survey telescope (wfst) |
graph product structure theory expresses certain graphs as subgraphs of the strong product of much simpler graphs. in particular, an elegant formulation for the corresponding structural theorems involves the strong product of a path and of a bounded treewidth graph, and allows to lift combinatorial results for bounded treewidth graphs to graph classes for which the product structure holds, such as to planar graphs [dujmović et al., j. acm, 67(4), 22:1-38, 2020]. in this paper, we join the search for extensions of this powerful tool beyond planarity by considering the h-framed graphs, a graph class that includes 1-planar, optimal 2-planar, and k-map graphs (for appropriate values of h). we establish a graph product structure theorem for h-framed graphs stating that the graphs in this class are subgraphs of the strong product of a path, of a planar graph of treewidth at most 3, and of a clique of size $3\lfloor h/2 \rfloor +\lfloor h/3 \rfloor -1$. this allows us to improve over the previous structural theorems for 1-planar and k-map graphs. our results constitute significant progress over the previous bounds on the queue number, non-repetitive chromatic number, and p-centered chromatic number of these graph classes, e.g., we lower the currently best upper bound on the queue number of 1-planar graphs and k-map graphs from 495 to 81 and from 32225k(k-3) to 61k, respectively. we also employ the product structure machinery to improve the current upper bounds of twin-width of planar and 1-planar graphs from 183 to 37, and from o(1) to 80, respectively. all our structural results are constructive and yield efficient algorithms to obtain the corresponding decompositions. | graph product structure for h-framed graphs |
rocky asteroids and planets display nucleosynthetic isotope variations that are attributed to the heterogeneous distribution of stardust from different stellar sources in the solar protoplanetary disk. here we report new high-precision palladium isotope data for six iron meteorite groups. the palladium data display smaller nucleosynthetic isotope variations than the more refractory neighbouring elements. based on this observation, we present a model in which thermal destruction of interstellar dust in the inner solar system results in an enrichment of s-process-dominated stardust in regions closer to the sun. we propose that stardust is depleted in volatile elements due to incomplete condensation of these elements into dust around asymptotic giant branch stars. this led to the smaller nucleosynthetic variations for pd reported here and the lack of such variations for more volatile elements. the smaller magnitude variations measured in heavier refractory elements suggest that material from high-metallicity asymptotic giant branch stars is the dominant source of stardust in the solar system. these stars produce fewer heavy s-process elements (proton number z ≥ 56) compared with the bulk solar system composition. | the origin of s-process isotope heterogeneity in the solar protoplanetary disk |
earth is continually impacted by very small asteroids and debris, and a larger object, though uncommon, could produce a severe natural hazard. during impact crater formation the ballistic ejection of material out of the crater is a major process, which holds significance for an impact study into the deflection of asteroids. in this study we numerically simulate impacts into low-gravity, strength dominated asteroid surfaces using the isale shock physics code, and consider the double asteroid redirection test (dart) mission as a case study. we find that target cohesion, initial porosity, and internal friction coefficient greatly influence ejecta mass/velocity/launch-position distributions and hence the amount by which an asteroid can be deflected. our results show that as the cohesion is decreased the ratio of ejected momentum to impactor momentum, β - 1, increases; β - 1 also increases as the initial porosity and internal friction coefficient of the asteroid surface decrease. using nominal impactor parameters and reasonable estimates for the material properties of the didymos binary asteroid, the dart target, our simulations show that the ejecta produced from the impact can enhance the deflection by a factor of 2 to 4. we use numerical impact simulations that replicate conditions in several laboratory experiments to demonstrate that our approach to quantify ejecta properties is consistent with impact experiments in analogous materials. finally, we investigate the self-consistency between the crater size and ejection speed scaling relationships previously derived from the point-source approximation for impacts into the same target material. | the role of asteroid strength, porosity and internal friction in impact momentum transfer |
planetesimals—the initial stage of the planetary formation process—are considered to be initially very porous aggregates of dusts1,2, and subsequent thermal and compaction processes reduce their porosity3. the hayabusa2 spacecraft found that boulders on the surface of asteroid (162173) ryugu have an average porosity of 30-50% (refs. 4-6), higher than meteorites but lower than cometary nuclei7, which are considered to be remnants of the original planetesimals8. here, using high-resolution thermal and optical imaging of ryugu's surface, we discovered, on the floor of fresh small craters (<20 m in diameter), boulders with reflectance (~0.015) lower than the ryugu average6 and porosity >70%, which is as high as in cometary bodies. the artificial crater formed by hayabusa2's impact experiment9 is similar to these craters in size but does not have such high-porosity boulders. thus, we argue that the observed high porosity is intrinsic and not created by subsequent impact comminution and/or cracking. we propose that these boulders are the least processed material on ryugu and represent remnants of porous planetesimals that did not undergo a high degree of heating and compaction3. our multi-instrumental analysis suggests that fragments of the highly porous boulders are mixed within the surface regolith globally, implying that they might be captured within collected samples by touch-down operations10,11. | anomalously porous boulders on (162173) ryugu as primordial materials from its parent body |
we consider the long-term collisional and dynamical evolution of solid material orbiting in a narrow annulus near the roche limit of a white dwarf. with orbital velocities of 300 {km} {{{s}}}-1, systems of solids with initial eccentricity e≳ {10}-3 generate a collisional cascade where objects with radii r ≲ 100{--}300 {km} are ground to dust. this process converts 1-100 km asteroids into 1 μm particles in 102-106 yr. throughout this evolution, the swarm maintains an initially large vertical scale height h. adding solids at a rate \dot{m} enables the system to find an equilibrium where the mass in solids is roughly constant. this equilibrium depends on \dot{m} and {r}0, the radius of the largest solid added to the swarm. when {r}0 ≲ 10 km, this equilibrium is stable. for larger {r}0, the mass oscillates between high and low states; the fraction of time spent in high states ranges from 100% for large \dot{m} to much less than 1% for small \dot{m}. during high states, the stellar luminosity reprocessed by the solids is comparable to the excess infrared emission observed in many metallic line white dwarfs. | numerical simulations of collisional cascades at the roche limits of white dwarf stars |
primordial black holes (pbhs) in the asteroid-mass range $(10^{-17}$--$10^{-12})~m_{\odot}$ almost entirely escape constraints as dark matter candidates. in the early universe, however, the schwarzschild metric is no longer applicable and we must carefully consider pbh metrics with a proper cosmological embedding. in particular, the thakurta solution stands out as perhaps the most adequate such solution. notably, the thakurta metric contains a time-dependent apparent horizon, proportional to the cosmological scale-factor. we show that this implies the pbhs are hotter than in the standard schwarzschild case, and so evaporate significantly faster via hawking radiation. by matter-radiation equality, pbhs up to masses of $\sim 10^{-12}~m_{\odot}$ have totally evaporated, and so cannot be a viable dark matter candidate. | navigating the asteroid field: new evaporation constraints for primordial black holes as dark matter |
the examination of the physical properties of chondrules has generally received less emphasis than other properties of meteorites such as their mineralogy, petrology, and chemical and isotopic compositions. among the various physical properties of chondrules, chondrule size is especially important for the classification of chondrites into chemical groups, since each chemical group possesses a distinct size-frequency distribution of chondrules. knowledge of the physical properties of chondrules is also vital for the development of astrophysical models for chondrule formation, and for understanding how to utilize asteroidal resources in space exploration. to examine our current knowledge of chondrule sizes, we have compiled and provide commentary on available chondrule dimension literature data. we include all chondrite chemical groups as well as the acapulcoite primitive achondrites, some of which contain relict chondrules. we also compile and review current literature data for other astrophysically-relevant physical properties (chondrule mass and density). finally, we briefly examine some additional physical aspects of chondrules such as the frequencies of compound and 'cratered' chondrules. a purpose of this compilation is to provide a useful resource for meteoriticists and astrophysicists alike. | chondrule size and related physical properties: a compilation and evaluation of current data across all meteorite groups |
owing to the ever-present solar wind, our vast solar system is full of plasmas. the turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and phenomena in the solar atmosphere all the way to the earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in-situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. additionally high technology ground-based instrumentation has led to new and greater knowledge of solar and auroral features. as a result, a new branch of space physics, i.e., space weather, has emerged since many of the space physics processes have a direct or indirect influence on humankind. after briefly reviewing the major space physics discoveries before rockets and satellites, we aim to review all our updated understanding on coronal holes, solar flares and coronal mass ejections, which are central to space weather events at earth, solar wind, storms and substorms, magnetotail and substorms, emphasizing the role of the magnetotail in substorm dynamics, radiation belts/energetic magnetospheric particles, structures and space weather dynamics in the ionosphere, plasma waves, instabilities, and wave-particle interactions, long-period geomagnetic pulsations, auroras, geomagnetically induced currents (gics), planetary magnetospheres and solar/stellar wind interactions with comets, moons and asteroids, interplanetary discontinuities, shocks and waves, interplanetary dust, space dusty plasmas and solar energetic particles and shocks, including the heliospheric termination shock. this paper is aimed to provide a panoramic view of space physics and space weather. | space plasma physics: a review |
the double asteroid redirection test (dart) spacecraft will impact into the asteroid dimorphos on 2022 september 26 as a test of the kinetic impactor technique for planetary defense. the efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. currently, very little is known about dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. the dart impact modeling working group (iwg) is responsible for using impact simulations to better understand the results of the dart impact. pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. this insight provides a basis for predicting the effects of the dart impact and the first understanding of how to interpret results following the encounter. following the dart impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of dimorphos and β resulting from dart's impact. this paper summarizes, at a high level, what has been learned from the iwg simulations and experiments in preparation for the dart impact. while unknown, estimates for reasonable potential material properties of dimorphos provide predictions for β of 1-5, depending on end-member cases in the strength regime. | effects of impact and target parameters on the results of a kinetic impactor: predictions for the double asteroid redirection test (dart) mission |
we report a systematic oxygen isotopic survey of ca-carbonates in nine different cm chondrites characterized by different degrees of alteration, from the least altered known to date (paris, 2.7-2.8) to the most altered (alh 88045, cm1). our data define a continuous trend that crosses the terrestrial fractionation line (tfl), with a general relationship that is indistinguishable within errors from the trend defined by both matrix phyllosilicates and bulk o-isotopic compositions of cm chondrites. this bulk-matrix-carbonate (bmc) trend does not correspond to a mass-dependent fractionation (i.e., slope 0.52) as it would be expected during fluid circulation along a temperature gradient. it is instead a direct proxy of the degree of o-isotopic equilibration between 17,18o-rich fluids and 16o-rich anhydrous minerals. our o-isotopic survey revealed that, for a given cm, no carbonate is in o-isotopic equilibrium with its respective surrounding matrix. this precludes direct calculation of the temperature of carbonate precipitation. however, the o-isotopic compositions of alteration water in different cms (inferred from isotopic mass-balance calculation and direct measurements) define another trend (cmw for cm water), parallel to bmc but with a different intercept. the distance between the bmc and cmw trends is directly related to the temperature of cm alteration and corresponds to average carbonates and serpentine formation temperatures of 110 °c and 75 °c, respectively. however, carbonate o-isotopic variations around the bmc trend indicate that they formed at various temperatures ranging between 50 and 300 °c, with 50% of the carbonates studied here showing precipitation temperature higher than 100 °c. the average δ17o and the average carbonate precipitation temperature per chondrite are correlated, revealing that all cms underwent similar maximum temperature peaks, but that altered cms experienced protracted carbonate precipitation event(s) at lower temperatures than the least altered cms. our data suggest that the δ17o value of ca-carbonates could be a reliable proxy of the degree of alteration experienced by cm chondrites. | oxygen isotope constraints on the alteration temperatures of cm chondrites |
we present the results of the first-ever visible spectroscopic survey fully dedicated to the small (absolute magnitude h ≥ 20) near-earth asteroid (nea) population. observations have been performed at the new technology telescope (ntt) of the european southern observatory (eso), during a 30-night guaranteed time observations programme, in the framework of the european commission financed neoshield-2 project. the visible spectra of 147 objects have been obtained and taxonomically classified. they show a peculiar taxonomic distribution, with respect to larger neas. in particular, olivine-rich a-types and organic-rich d-types are more abundant than what could be expected by extrapolating the taxonomic distribution of larger neas. such results have implications for the investigation of the first phases of solar system history, including the delivery of prebiotic material on the early earth. having been obtained over a large range of solar phase angles, our data allowed us to evidence peculiar phase reddening behaviours for asteroids belonging to different taxonomic types. low-albedo asteroids display no or limited phase reddening, compared to moderate- and high-albedo objects. this result suggests a promising novel way to distinguish primitive asteroids in the x-complex. in agreement with previous laboratory experiments, olivine-rich surfaces are the most affected by phase reddening. | a spectroscopic survey of the small near-earth asteroid population: peculiar taxonomic distribution and phase reddening |
chondrule-like objects and ca-al-rich inclusions (cais) are discovered in the retuned samples from asteroid ryugu. here we report results of oxygen isotope, mineralogical, and compositional analysis of the chondrule-like objects and cais. three chondrule-like objects dominated by mg-rich olivine are 16o-rich and -poor with δ17o (=δ17o - 0.52 × δ18o) values of ~ -23‰ and ~ -3‰, resembling what has been proposed as early generations of chondrules. the 16o-rich objects are likely to be melted amoeboid olivine aggregates that escaped from incorporation into 16o-poor chondrule precursor dust. two cais composed of refractory minerals are 16o-rich with δ17o of ~ -23‰ and possibly as old as the oldest cais. the discovered objects (<30 µm) are as small as those from comets, suggesting radial transport favoring smaller objects from the inner solar nebula to the formation location of the ryugu original parent body, which is farther from the sun and scarce in chondrules. the transported objects may have been mostly destroyed during aqueous alteration in the ryugu parent body. | chondrule-like objects and ca-al-rich inclusions in ryugu may potentially be the oldest solar system materials |
initial analyses showed that asteroid ryugu's composition is close to ci (ivuna-like) carbonaceous chondrites (ccs) - the chemically most primitive meteorites, characterized by near-solar abundances for most elements. however, some isotopic signatures (for example, ti, cr) overlap with other cc groups, so the details of the link between ryugu and the ci chondrites are not yet fully clear. here we show that ryugu and ci chondrites have the same zinc and copper isotopic composition. as the various chondrite groups have very distinct zn and cu isotopic signatures, our results point at a common genetic heritage between ryugu and ci chondrites, ruling out any affinity with other cc groups. since ryugu's pristine samples match the solar elemental composition for many elements, their zn and cu isotopic compositions likely represent the best estimates of the solar composition. earth's mass-independent zn isotopic composition is intermediate between ryugu/cc and non-carbonaceous chondrites (ncs), suggesting a contribution of ryugu-like material to earth's budgets of zn and other moderately volatile elements. | contribution of ryugu-like material to earth's volatile inventory by cu and zn isotopic analysis |
the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) spacecraft arrived at its target, near-earth asteroid (101955) bennu, in december 2018. observations by the onboard instruments revealed an asteroid substantially different from pre-encounter expectations, including a rough and rugged terrain that complicated the mission's objective of collecting a sample. the team altered the mission profile to accommodate the reality of the target and incorporate lessons learned during operations. the data acquired by the osiris-rex spacecraft at bennu characterized this primitive asteroid's physical, chemical, and geological properties and provided critical context for the collected sample. in december 2019, after a year of operating in proximity, the team selected primary and backup sites for sample collection. in october 2020, osiris-rex descended to the bennu surface and collected a sample from the primary site, nightingale. the spacecraft departs bennu in 2021 and will return the sample to earth in september 2023. | chapter 8 - osiris-rex at bennu: overcoming challenges to collect a sample of the early solar system |
we present a new `supercalibration' technique for measuring systematic distortions in the wavelength scales of high-resolution spectrographs. by comparing spectra of `solar twin' stars or asteroids with a reference laboratory solar spectrum, distortions in the standard thorium-argon calibration can be tracked with ∼10 m s-1 precision over the entire optical wavelength range on scales of both echelle orders (∼50-100 å) and entire spectrographs arms (∼1000-3000 å). using archival spectra from the past 20 yr, we have probed the supercalibration history of the very large telescope-ultraviolet and visible echelle spectrograph (vlt-uves) and keck-high resolution echelle spectrograph (hires) spectrographs. we find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically ±200 m s-1 per 1000 å. we apply a simple model of these distortions to simulated spectra that characterize the large uves and hires quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, α. the spurious deviations in α produced by the model closely match important aspects of the vlt-uves quasar results at all redshifts and partially explain the hires results, though not self-consistently at all redshifts. that is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in α from quasar absorption lines. | impact of instrumental systematic errors on fine-structure constant measurements with quasar spectra |
the origin and abundance of water accreted by carbonaceous asteroids remains underconstrained, but would provide important information on the dynamic of the protoplanetary disk. here we report the in situ oxygen isotopic compositions of aqueously formed fayalite grains in the kaba and mokoia cv chondrites. cv chondrite bulk, matrix and fayalite o-isotopic compositions define the mass-independent continuous trend (δ17o = 0.84 ± 0.03 × δ18o - 4.25 ± 0.1), which shows that the main process controlling the o-isotopic composition of the cv chondrite parent body is related to isotopic exchange between 16o-rich anhydrous silicates and 17o- and 18o-rich fluid. similar isotopic behaviors observed in cm, cr and co chondrites demonstrate the ubiquitous nature of o-isotopic exchange as the main physical process in establishing the o-isotopic features of carbonaceous chondrites, regardless of their alteration degree. based on these results, we developed a new approach to estimate the abundance of water accreted by carbonaceous chondrites (quantified by the water/rock ratio) with cm (0.3-0.4) ≥ cr (0.1-0.4) ≥ cv (0.1-0.2) > co (0.01-0.10). the low water/rock ratios and the o-isotopic characteristics of secondary minerals in carbonaceous chondrites indicate they (i) formed in the main asteroid belt and (ii) accreted a locally derived (inner solar system) water formed near the snowline by condensation from the gas phase. such results imply low influx of d- and 17o- and 18o-rich water ice grains from the outer part of the solar system. the latter is likely due to the presence of a jupiter-induced gap in the protoplanetary disk that limited the inward drift of outer solar system material at the exception of particles with size lower than 150 μm such as presolar grains. among carbonaceous chondrites, cv chondrites show o-isotopic features suggesting potential contribution of 17-18o-rich water that may be related to their older accretion relative to other hydrated carbonaceous chondrites. | origin and abundance of water in carbonaceous asteroids |
1i/‘oumuamua is the first known interstellar small body, probably being only about 100 m in size. against expectations based on comets, ‘oumuamua does not show any activity and has a very elongated figure, and it also exhibits undamped rotational tumbling. in contrast, ‘oumuamua’s trajectory indicates that it was moving with the local stars, as expected from a low-velocity ejection from a relatively nearby system. here, i assume that ‘oumuamua is typical of 100 m interstellar objects and speculate on its origins. i find that giant planets are relatively inefficient at ejecting small bodies from inner solar systems of main-sequence stars, and that binary systems offer a much better opportunity for ejections of non-volatile bodies. i also conclude that ‘oumuamua is not a member of a collisional population, which could explain its dramatic difference from small asteroids. i observe that 100 m small bodies are expected to carry little mass in realistic collisional populations and that occasional events, when whole planets are disrupted in catastrophic encounters, may dominate the interstellar population of 100 m fragments. unlike the sun or jupiter, red dwarf stars are very dense and are capable of thoroughly tidally disrupting terrestrial planets. i conclude that ‘oumuamua may have originated as a fragment from a planet that was tidally disrupted and then ejected by a dense member of a binary system, which could explain its peculiarities. | 1i/‘oumuamua as a tidal disruption fragment from a binary star system |
using the most recent prototypes, design, and as-built system information, we test and quantify the capability of the large synoptic survey telescope (lsst) to discover potentially hazardous asteroids (phas) and near-earth objects (neos). we empirically estimate an expected upper limit to the false detection rate in lsst image differencing, using measurements on decam data and prototype lsst software and find it to be about 450 deg-2. we show that this rate is already tractable with current prototype of the lsst moving object processing system (mops) by processing a 30-day simulation consistent with measured false detection rates. we proceed to evaluate the performance of the lsst baseline survey strategy for phas and neos using a high-fidelity simulated survey pointing history. we find that lsst alone, using its baseline survey strategy, will detect 66% of the pha and 61% of the neo population objects brighter than h = 22 , with the uncertainty in the estimate of ± 5 percentage points. by generating and examining variations on the baseline survey strategy, we show it is possible to further improve the discovery yields. in particular, we find that extending the lsst survey by two additional years and doubling the mops search window increases the completeness for phas to 86% (including those discovered by contemporaneous surveys) without jeopardizing other lsst science goals (77% for neos). this equates to reducing the undiscovered population of phas by additional 26% (15% for neos), relative to the baseline survey. | the large synoptic survey telescope as a near-earth object discovery machine |
the younger dryas (yd) impact hypothesis posits that fragments of a large, disintegrating asteroid/comet struck north america, south america, europe, and western asia 12,800 years ago. multiple airbursts/impacts produced the yd boundary layer (ydb), depositing peak concentrations of platinum, high-temperature spherules, meltglass, and nanodiamonds, forming an isochronous datum at >50 sites across 50 million km² of earth's surface. this proposed event triggered extensive biomass burning, brief impact winter, yd climate change, and contributed to extinctions of late pleistocene megafauna. in the most extensive investigation south of the equator, we report on a 12,800-year-old sequence at pilauco, chile ( 40°s), that exhibits peak yd boundary concentrations of platinum, gold, high-temperature iron- and chromium-rich spherules, and native iron particles rarely found in nature. a major peak in charcoal abundance marks an intense biomass-burning episode, synchronous with dramatic changes in vegetation, including a high-disturbance regime, seasonality in precipitation, and warmer conditions. this is anti-phased with northern-hemispheric cooling at the yd onset, whose rapidity suggests atmospheric linkage. the sudden disappearance of megafaunal remains and dung fungi in the ydb layer at pilauco correlates with megafaunal extinctions across the americas. the pilauco record appears consistent with ydb impact evidence found at sites on four continents. | sedimentary record from patagonia, southern chile supports cosmic-impact triggering of biomass burning, climate change, and megafaunal extinctions at 12.8 ka |
meteorites originating from primitive c-type asteroids are composed of materials from the sun's protoplanetary disk, including up to a few per cent organic carbon. in contrast, some interplanetary dust particles and micrometeorites have much higher carbon contents, up to >90%, and are thought to originate from icy outer solar system bodies and comets. here we report an approximately 100-µm-diameter very carbon-rich clast, with highly primitive characteristics, in the matrix of a cr2 chondrite, lapaz icefield 02342. the clast may represent a cometary building block, largely unsampled in meteorite collections, that was captured by a c-type asteroid during the early stages of planet formation. the existence of this cometary microxenolith supports the idea of a radially inward transport of materials from the outer protoplanetary disk into the cr chondrite reservoir during the formation of planetesimals. moreover, the h-isotopic composition of the clast is suggestive of a temporal evolution of organic isotopic compositions in the comet-forming region of the disk. | a cometary building block in a primitive asteroidal meteorite |
in the past few decades, observations have revealed signatures of metals polluting the atmospheres of white dwarfs. the diffusion time-scale for metals to sink from the atmosphere of a white dwarf is of the order of days for a hydrogen-dominated atmosphere. thus, there must be a continuous supply of metal-rich material accreting onto these white dwarfs. we investigate the role of secular resonances that excite the eccentricity of asteroids allowing them to reach star-grazing orbits leading them to tidal disruption and the formation of a debris disc. changes in the planetary system during the evolution of the star lead to a change in the location of secular resonances. in our solar system, the engulfment of the earth will cause the ν6 resonance to shift outwards which will force previously stable asteroids to undergo secular resonant perturbations. with analytic models and n-body simulations we show that secular resonances driven by two outer companions can provide a source of continuous pollution. secular resonances are a viable mechanism for the pollution of white dwarfs in a variety of exoplanetary system architectures. | white dwarf pollution by asteroids from secular resonances |
we report new high-precision stable k isotope data for three martian meteorites, one lunar meteorite, one ordinary chondrite, four terrestrial igneous united states geological survey (usgs) reference materials, and twenty howardite-eucrite-diogenite [hed] meteorites. the three martian meteorites define a relatively narrow δ41k range with an average of -0.36 ± 0.12‰ (2 sd) that is slightly heavier than the bulk silicate earth (bse) k isotopic composition (-0.48 ± 0.03‰). except for the four northwest africa samples which were terrestrially contaminated, all hed meteorites reveal substantial 41k enrichment compared to bse, lunar samples, martian meteorites, and chondrites. we propose that the average δ41k (+0.36 ± 0.16‰) obtained from hed meteorites is representative of bulk silicate 4-vesta. the coupled volatile depletion and heavy k isotope enrichment in 4-vesta could be attributed to both nebula-scale processes and parent-body events. the asteroid 4-vesta is likely to have accreted from planetary feedstocks that have been significantly volatile-depleted prior to the major phases of planetary accretion in the early solar system, with secondary effects of k loss during accretionary growth and magma ocean degassing. | potassium isotopic compositions of howardite-eucrite-diogenite meteorites |
in early 2019, nasa's osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission surveyed asteroid (101955) bennu with a collection of instruments, including the osiris-rex camera suite (ocams) polycam imager. using polycam panchromatic images, we constructed a globally controlled basemap of bennu at an approximate ground sample distance of 5 cm with a mean spatial accuracy of ~30 cm. the basemap was photometrically normalized using a minneart phase angle correction. new mapping methods were developed to combine images of bennu's irregular shape and extremely rough surface into a nearly seamless mosaic. here we present the global basemap of bennu and discuss the image processing techniques used to construct a high-resolution mosaic of an irregular small body. | a high-resolution global basemap of (101955) bennu |
we present a global spectrophotometric characterization of the ceres surface using dawn framing camera (fc) images. we identify the photometric model that yields the best results for photometrically correcting images. corrected fc images acquired on approach to ceres were assembled into global maps of albedo and color. generally, albedo and color variations on ceres are muted. the albedo map is dominated by a large, circular feature in vendimia planitia, known from hst images (li et al., 2006), and dotted by smaller bright features mostly associated with fresh-looking craters. the dominant color variation over the surface is represented by the presence of "blue" material in and around such craters, which has a negative spectral slope over the visible wavelength range when compared to average terrain. we also mapped variations of the phase curve by employing an exponential photometric model, a technique previously applied to asteroid vesta (schröder et al., 2013b). the surface of ceres scatters light differently from vesta in the sense that the ejecta of several fresh-looking craters may be physically smooth rather than rough. high albedo, blue color, and physical smoothness all appear to be indicators of youth. the blue color may result from the desiccation of ejected material that is similar to the phyllosilicates/water ice mixtures in the experiments of poch et al. (2016). the physical smoothness of some blue terrains would be consistent with an initially liquid condition, perhaps as a consequence of impact melting of subsurface water ice. we find red terrain (positive spectral slope) near ernutet crater, where de sanctis et al. (2017) detected organic material. the spectrophotometric properties of the large vendimia planitia feature suggest it is a palimpsest, consistent with the marchi et al. (2016) impact basin hypothesis. the central bright area in occator crater, cerealia facula, is the brightest on ceres with an average visual normal albedo of about 0.6 at a resolution of 1.3 km per pixel (six times ceres average). the albedo of fresh, bright material seen inside this area in the highest resolution images (35 m per pixel) is probably around unity. cerealia facula has an unusually steep phase function, which may be due to unresolved topography, high surface roughness, or large average particle size. it has a strongly red spectrum whereas the neighboring, less-bright, vinalia faculae are neutral in color. we find no evidence for a diurnal ground fog-type haze in occator as described by nathues et al. (2015). we can neither reproduce their findings using the same images, nor confirm them using higher resolution images. fc images have not yet offered direct evidence for present sublimation in occator. | resolved spectrophotometric properties of the ceres surface from dawn framing camera images |
this book deals with an effect in celestial mechanics that has become quite important in exoplanet research. the lidov-kozai effect reveals itself in coherent periodic variations (which can be very large) of the inclination and eccentricity of an orbiting body in the presence of an inclined perturber. the effect is known to be important in the motion of many asteroids and planetary satellites. what is more, now it attracts more and more interest in the astronomical and astrophysical community due to its relevance for many exoplanetary systems. recent years witnessed major advancements in its theory. it would be no exaggeration to say that nowadays the lidov-kozai effect becomes one of the most studied astrophysical effects. this book covers the multitude of the lidov-kozai effect's modern applications and its theory developments. it will be useful for researchers and students working in astrophysics, celestial mechanics, stellar dynamics, theoretical mechanics, space missions design, depending on the interests of the reader. the book is self-contained. it provides the full detailed coverage of the effect's theory and applications. | the lidov-kozai effect - applications in exoplanet research and dynamical astronomy |
ryugu is a carbonaceous rubble-pile asteroid visited by the hayabusa2 spacecraft. small rubble pile asteroids record the thermal evolution of their much larger parent bodies. however, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. hayabusa2 remote-sensing observations find that on the asteroid (162173) ryugu both north and south pole regions preserve the material least processed by space weathering, which is spectrally blue carbonaceous chondritic material with a 0-3% deep 0.7-µm band absorption, indicative of fe-bearing phyllosilicates. here we report that spectrally blue ryugu's parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570-670 k (300-400 °c), suggesting that ryugu's parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2-2.5 ma. the samples being brought to earth by hayabusa2 will give us our first insights into this epoch in solar system history. | spectrally blue hydrated parent body of asteroid (162173) ryugu |
we give a nearly linear-time algorithm to approximately sample satisfying assignments in the random $k$-sat model when the density of the formula scales exponentially with $k$. the best previously known sampling algorithm for the random $k$-sat model applies when the density $\alpha=m/n$ of the formula is less than $2^{k/300}$ and runs in time $n^{\exp(\theta(k))}$ (galanis, goldberg, guo and yang, siam j. comput., 2021). here $n$ is the number of variables and $m$ is the number of clauses. our algorithm achieves a significantly faster running time of $n^{1 + o_k(1)}$ and samples satisfying assignments up to density $\alpha\leq 2^{0.039 k}$. the main challenge in our setting is the presence of many variables with unbounded degree, which causes significant correlations within the formula and impedes the application of relevant markov chain methods from the bounded-degree setting (feng, guo, yin and zhang, j. acm, 2021; jain, pham and vuong, 2021). our main technical contribution is a $o_k(\log n )$ bound of the sum of influences in the $k$-sat model which turns out to be robust against the presence of high-degree variables. this allows us to apply the spectral independence framework and obtain fast mixing results of a uniform-block glauber dynamics on a carefully selected subset of the variables. the final key ingredient in our method is to take advantage of the sparsity of logarithmic-sized connected sets and the expansion properties of the random formula, and establish relevant properties of the set of satisfying assignments that enable the fast simulation of this glauber dynamics. | fast sampling of satisfying assignments from random $k$-sat |
sixty-six million years ago, the end-cretaceous mass extinction ended the reign of the dinosaurs. flood basalt eruptions and an asteroid impact are widely discussed causes, yet their contributions remain debated. modeling the environmental changes after the chicxulub impact can shed light on this question. existing studies, however, focused on the effect of dust or used one-dimensional, noncoupled atmosphere models. here we explore the longer-lasting cooling due to sulfate aerosols using a coupled climate model. depending on aerosol stratospheric residence time, global annual mean surface air temperature decreased by at least 26°c, with 3 to 16 years subfreezing temperatures and a recovery time larger than 30 years. the surface cooling triggered vigorous ocean mixing which could have resulted in a plankton bloom due to upwelling of nutrients. these dramatic environmental changes suggest a pivotal role of the impact in the end-cretaceous extinction. | baby, it's cold outside: climate model simulations of the effects of the asteroid impact at the end of the cretaceous |
to better understand earth's present tectonic style-plate tectonics-and how it may have evolved from single plate (stagnant lid) tectonics, it is instructive to consider how common it is among similar bodies in the solar system. plate tectonics is a style of convection for an active planetoid where lid fragment (plate) motions reflect sinking of dense lithosphere in subduction zones, causing upwelling of asthenosphere at divergent plate boundaries and accompanied by focused upwellings, or mantle plumes; any other tectonic style is usefully called "stagnant lid" or "fragmented lid". in 2015 humanity completed a 50+ year effort to survey the 30 largest planets, asteroids, satellites, and inner kuiper belt objects, which we informally call "planetoids" and use especially images of these bodies to infer their tectonic activity. the four largest planetoids are enveloped in gas and ice (jupiter, saturn, uranus, and neptune) and are not considered. the other 26 planetoids range in mass over 5 orders of magnitude and in diameter over 2 orders of magnitude, from massive earth down to tiny proteus; these bodies also range widely in density, from 1000 to 5500 kg/m3. a gap separates 8 silicate planetoids with ρ = 3000 kg/m3 or greater from 20 icy planetoids (including the gaseous and icy giant planets) with ρ = 2200 kg/m3 or less. we define the "tectonic activity index" (tai), scoring each body from 0 to 3 based on evidence for recent volcanism, deformation, and resurfacing (inferred from impact crater density). nine planetoids with tai = 2 or greater are interpreted to be tectonically and convectively active whereas 17 with tai <2 are inferred to be tectonically dead. we further infer that active planetoids have lithospheres or icy shells overlying asthenosphere or water/weak ice. tai of silicate (rocky) planetoids positively correlates with their inferred rayleigh number. we conclude that some type of stagnant lid tectonics is the dominant mode of heat loss and that plate tectonics is unusual. to make progress understanding earth's tectonic history and the tectonic style of active exoplanets, we need to better understand the range and controls of active stagnant lid tectonics. | stagnant lid tectonics: perspectives from silicate planets, dwarf planets, large moons, and large asteroids |
the cameras for allsky meteor surveillance (cams) video-based meteoroid orbit survey adds 60 newly identified showers to the iau working list of meteor showers (numbers 427, 445-446, 506-507, and part of 643-750). 28 of these are also detected in the independent sonotaco survey. in total, 230 meteor showers and shower components are identified in cams data, 177 of which are detected in at least two independent surveys. from the power-law size frequency distribution of detected showers, we extrapolate that 36% of all cams-observed meteors originated from ∼700 showers above the n = 1 per 110,000 shower limit. 71% of mass falling to earth from streams arrives on jupiter-family type orbits. the transient geminids account for another 15%. all meteoroids not assigned to streams form a sporadic background with highest detected numbers from the apex source, but with 98% of mass falling in from the antihelion source. even at large ∼7-mm sizes, a poynting-robertson drag evolved population is detected, which implies that the grün et al. collisional lifetimes at these sizes are underestimated by about a factor of 10. while these large grains survive collisions, many fade on a 104-y timescale, possibly because they disintegrate into smaller particles by processes other than collisions, leaving a more resilient population to evolve. | cams newly detected meteor showers and the sporadic background |
we review the evidence for buried ice in the asteroid belt; specifically the questions around the so-called main belt comets (mbcs). we summarise the evidence for water throughout the solar system, and describe the various methods for detecting it, including remote sensing from ultraviolet to radio wavelengths. we review progress in the first decade of study of mbcs, including observations, modelling of ice survival, and discussion on their origins. we then look at which methods will likely be most effective for further progress, including the key challenge of direct detection of (escaping) water in these bodies. | the main belt comets and ice in the solar system |
meteorites have long been considered as reflections of the compositional diversity of main belt asteroids and consequently they have been used to decipher their origin, formation, and evolution. however, while some meteorites are known to sample the surfaces of metallic, rocky and hydrated asteroids (about one-third of the mass of the belt), the low-density icy asteroids (c-, p-, and d-types), representing the rest of the main belt, appear to be unsampled in our meteorite collections. here we provide conclusive evidence that the surface compositions of these icy bodies are compatible with those of the most common extraterrestrial materials (by mass), namely anhydrous interplanetary dust particles (idps). given that these particles are quite different from known meteorites, it follows that the composition of the asteroid belt consists largely of more friable material not well represented by the cohesive meteorites in our collections. in the light of our current understanding of the early dynamical evolution of the solar system, meteorites likely sample bodies formed in the inner region of the solar system (0.5-4 au) whereas chondritic porous idps sample bodies that formed in the outer region (>5 au). | interplanetary dust particles as samples of icy asteroids |
conditions for regolith landslides to occur on spinning, gravitating spheroidal asteroids and their aftermath are studied. these conditions are developed by application of classical granular mechanics stability analysis to the asteroid environment. as part of our study we determine how slopes evolve across the surface of these bodies as a function of spin rate, the dynamical fate of material that exceeds the angle of repose, and an analysis of how the shape of the body may be modified based on these results. we find specific characteristics for body surfaces and shapes when spun near the surface disruption limit and develop what their observable implications are. the small, oblate and rapidly spinning asteroids such as 1999 kw4 alpha and 2008 ev5 exhibit some of these observable traits. the detailed mechanisms outlined here can also provide insight and constraints on the recently observed active asteroids such as p/2013 p5, and the creation of asteroidal meteor streams. | landslides and mass shedding on spinning spheroidal asteroids |
understanding the nature and origin of the precursor material to terrestrial planets is key to deciphering the mechanisms and timescales of planet formation1. nucleosynthetic variability among rocky solar system bodies can trace the composition of planetary building blocks2-5. here we report the nucleosynthetic composition of silicon (μ30si), the most abundant refractory planet-building element, in primitive and differentiated meteorites to identify terrestrial planet precursors. inner solar system differentiated bodies, including mars, record μ30si deficits of −11.0 ± 3.2 parts per million to −5.8 ± 3.0 parts per million whereas non-carbonaceous and carbonaceous chondrites show μ30si excesses from 7.4 ± 4.3 parts per million to 32.8 ± 2.0 parts per million relative to earth. this establishes that chondritic bodies are not planetary building blocks. rather, material akin to early-formed differentiated asteroids must represent a major planetary constituent. the μ30si values of asteroidal bodies correlate with their accretion ages, reflecting progressive admixing of a μ30si-rich outer solar system material to an initially μ30si-poor inner disk. mars' formation before chondrite parent bodies is necessary to avoid incorporation of μ30si-rich material. in contrast, earth's μ30si composition necessitates admixing of 26 ± 9 per cent of μ30si-rich outer solar system material to its precursors. the μ30si compositions of mars and proto-earth are consistent with their rapid formation by collisional growth and pebble accretion less than three million years after solar system formation. finally, earth's nucleosynthetic composition for s-process sensitive (molybdenum and zirconium) and siderophile (nickel) tracers are consistent with pebble accretion when volatility-driven processes during accretion and the moon-forming impact are carefully evaluated. | silicon isotope constraints on terrestrial planet accretion |
ejecta from dimorphos following the dart mission impact significantly increased the brightness of the didymos-dimorphos system, allowing us to examine subsurface material. we report daily near-ir spectroscopic observations of the didymos system using nasa's irtf that follow the evolution of the spectral signature of the ejecta cloud over 1 week, from 1 day before the impact. overall, the spectral features remained fixed (s-type classification) while the ejecta dissipated, confirming that both didymos and dimorphos are constructed from the same silicate material. this novel result strongly supports binary asteroid formation models that include the breaking up of a single body due to rotational breakup of kilometer-wide bodies. at impact time +14 and +38 hr, the spectral slope decreased, but the following nights presented an increasing spectral slope that almost returned to the preimpact slope. however, the parameters of the 1 μm band remained fixed, and no "fresh"/q-type-like spectrum was measured. we interpret this as follows. (1) the ejecta cloud is the main contributor (60%-70%) to the overall light during the ~40 hr after impact. (2) coarser debris (≥100 μm) dominated the ejecta cloud, decreasing the spectral slope (after radiation pressure removed the fine grains ≤10 hr after impact). (3) after approximately 1 week, the ejecta cloud dispersed enough to make the fine grains on didymos's surface the dominant part of the light, increasing the spectral slope to the preimpact level. (4) a negligible amount of nonweathered material was ejected from dimorphos's subsurface, suggesting that dimorphos was accumulated from weathered material ejected from didymos's surface. | near-ir spectral observations of the didymos system: daily evolution before and after the dart impact indicates that dimorphos originated from didymos |
we performed photometric observations of the binary near-earth asteroid (65803) didymos in support of the double asteroid redirection test (dart) mission that will test the kinetic impactor technology for diverting dangerous asteroids. it will hit the didymos secondary, called dimorphos, on 2022 september 26. we observed didymos with 11 telescopes with diameters from 3.5 to 10.4 m during four apparitions in 2015-2021, obtaining data with rms residuals from 0.006 to 0.030 mag. we analyzed the light-curve data and decomposed them into the primary rotational and secondary orbital light curves. we detected 37 mutual eclipse/occultation events between the binary system components. the data presented here, in combination with 18 mutual events detected in 2003, provide the basis for modeling the dimorphos orbit around the didymos primary. the orbit modeling is discussed in detail by scheirich & pravec and naidu et al. the primary light curves were complex, showing multiple extrema on some epochs. they suggest a presence of complex topography on the primary's surface that is apparent in specific viewing/illumination geometries; the primary shape model by naidu et al. (icarus 348, 113777, 2020) needs to be refined. the secondary rotational light-curve data were limited and did not provide a clear solution for the rotation period and equatorial elongation of dimorphos. we define the requirements for observations of the secondary light curve to provide the needed information on dimorphos's rotation and elongation when didymos is bright in 2022 july-september before the dart impact. | photometric observations of the binary near-earth asteroid (65803) didymos in 2015-2021 prior to dart impact |
main-belt comets are small solar system bodies located in the asteroid belt that repeatedly exhibit comet-like activity (that is, dust comae or tails) during their perihelion passages, strongly indicating ice sublimation1,2. although the existence of main-belt comets implies the presence of extant water ice in the asteroid belt, no gas has been detected around these objects despite intense scrutiny with the world's largest telescopes3. here we present james webb space telescope observations that clearly show that main-belt comet 238p/read has a coma of water vapour, but lacks a significant co2 gas coma. our findings demonstrate that the activity of comet read is driven by water-ice sublimation, and implies that main-belt comets are fundamentally different from the general cometary population. whether or not comet read experienced different formation circumstances or evolutionary history, it is unlikely to be a recent asteroid belt interloper from the outer solar system. on the basis of these results, main-belt comets appear to represent a sample of volatile material that is currently unrepresented in observations of classical comets and the meteoritic record, making them important for understanding the early solar system's volatile inventory and its subsequent evolution. | spectroscopic identification of water emission from a main-belt comet |
the nasa's double-asteroid redirection test (dart) was a unique planetary defence and technology test mission, the first of its kind. the main spacecraft of the dart mission impacted the target asteroid dimorphos, a small moon orbiting the asteroid didymos (65803), on 2022 september 26. the impact brought up a mass of ejecta which, together with the direct momentum transfer from the collision, caused an orbital period change of 33 ± 1 minutes, as measured by ground-based observations. we report here the outcome of the optical monitoring campaign of the didymos system from the danish 1.54 m telescope at la silla around the time of impact. the observations contributed to the determination of the changes in the orbital parameters of the didymos-dimorphos system, as reported by thomas et al., but in this paper we focus on the ejecta produced by the dart impact. we present photometric measurements from which we remove the contribution from the didymos-dimorphos system using an h-g photometric model. using two photometric apertures we determine the fading rate of the ejecta to be 0.115 ± 0.003 mag day-1 (in a 2″ aperture) and 0.086 ± 0.003 mag day-1 (5″) over the first week postimpact. after about 8 days postimpact we note the fading slows down to 0.057 ± 0.003 mag day-1 (2″ aperture) and 0.068 ± 0.002 mag day-1 (5″). we include deep-stacked images of the system to illustrate the ejecta evolution during the first 18 days, noting the emergence of dust tails formed from ejecta pushed in the antisolar direction, and measuring the extent of the particles ejected sunward to be at least 4000 km. | optical monitoring of the didymos-dimorphos asteroid system with the danish telescope around the dart mission impact |
we collected data on rotations and elongations of 46 secondaries of binary and triple systems among near-earth, mars-crossing and small main belt asteroids. 24 were found or are strongly suspected to be synchronous (in 1:1 spin-orbit resonance), and the other 22, generally on more distant and/or eccentric orbits, were found or are suggested to have asynchronous rotations. for 18 of the synchronous secondaries, we constrained their librational angles, finding that their long axes pointed to within 20° of the primary on most epochs. the observed anti-correlation of secondary synchroneity with orbital eccentricity and the limited librational angles agree with the theories by ćuk and nesvorný (ćuk, m., nesvorný, d. [2010]. icarus 207, 732-743) and naidu and margot (naidu, s.p., margot, j.-l. [2015]. astron. j. 149, 80). a reason for the asynchronous secondaries being on wider orbits than synchronous ones may be longer tidal circularization time scales at larger semi-major axes. the asynchronous secondaries show relatively fast spins; their rotation periods are typically < 10 h. an intriguing observation is a paucity of chaotic secondary rotations; with an exception of (35107) 1991 vh, the secondary rotations are single-periodic with no signs of chaotic rotation and their periods are constant on timescales from weeks to years. the secondary equatorial elongations show an upper limit of a2 /b2 ∼ 1.5 . the lack of synchronous secondaries with greater elongations appears consistent, considering uncertainties of the axis ratio estimates, with the theory by ćuk and nesvorný that predicts large regions of chaotic rotation in the phase space for a2 /b2 ≳√{ 2 } . alternatively, secondaries may not form or stay very elongated in gravitational (tidal) field of the primary. it could be due to the secondary fission mechanism suggested by jacobson and scheeres (jacobson, s.a., scheeres, d.j. [2011]. icarus 214, 161-178), as its efficiency is correlated with the secondary elongation. sharma (sharma, i. [2014]. icarus 229, 278-294) found that rubble-pile satellites with a2 /b2 ≲ 1.5 are more stable to finite structural perturbations than more elongated ones. it appears that more elongated secondaries, if they originally formed in spin fission of parent asteroid, are less likely to survive intact and they more frequently fail or fission. | binary asteroid population. 3. secondary rotations and elongations |
one of the most promising techniques to capture large debris on orbit consists in the use of tether-nets. with this concept currently at a medium technological readiness level only, numerical studies on tether-net removal missions are still needed. this paper presents a versatile simulator developed with the aim of gaining insight into the dynamics of tether-net capture of space debris. its modular architecture supports multiple modeling choices and allows simulating diverse capture scenarios with different system designs. simulation results are shown for the capture of a realistic launcher upper stage with the representation of the main components of the system, consisting in chaser, main tether, net, and two possible configurations of a closing mechanism. it is shown that only a closing mechanism with more than one attachment to each side of the net can guarantee containment of this type of debris after capture. it is also observed that a safer capture scenario is one in which the axis of rotation of the target is parallel to the direction of ejection of the net. additional simulation results suggest that tether-nets could be used to capture not only large debris, but also small asteroids, and that this simulator could enable future studies. | simulation of tether-nets for capture of space debris and small asteroids |
the primordial black hole (pbh) productions from the inflationary potential with an inflection point usually rely heavily on the fine-tuning of the model parameters. we propose in this work a new kind of the α-attractor inflation with asymmetric double poles that naturally and easily lead to a period of non-attractor inflation, during which the pbh productions are guaranteed with less fine-tuning the model parameters. this double-pole inflation can be tested against the observational data in the future with rich phenomenological signatures: (1) the enhanced curvature perturbations at small scales admit a distinctive feature of ultraviolet oscillations in the power spectrum; (2) the quasi-monochromatic mass function of the produced pbhs can be made compatible to the asteroid-mass pbhs as the dominant dark matter component, the planet-mass pbhs as the ogle ultrashort-timescale microlensing events, and the solar-mass pbhs as the ligo-virgo events; (3) the induced gravitational waves can be detected by the gravitational-wave detectors in space and pulsar timing array/square kilometer array. | primordial black holes and induced gravitational waves from double-pole inflation |
we investigate the quantum annealing of the ferromagnetic p -spin model in a dissipative environment (p =5 and p =7 ). this model, in the large-p limit, codifies grover's algorithm for searching in an unsorted database [l. k. grover, proceedings of the 28th annual acm symposium on theory of computing (acm, new york, 1996), pp. 212-219]. the dissipative environment is described by a phonon bath in thermal equilibrium at finite temperature. the dynamics is studied in the framework of a lindblad master equation for the reduced density matrix describing only the spins. exploiting the symmetries of our model hamiltonian, we can describe many spins and extrapolate expected trends for large n and p . while at weak system-bath coupling the dissipative environment has detrimental effects on the annealing results, we show that in the intermediate-coupling regime, the phonon bath seems to speed up the annealing at low temperatures. this improvement in the performance is likely not due to thermal fluctuation but rather arises from a correlated spin-bath state and persists even at zero temperature. this result may pave the way to a new scenario in which, by appropriately engineering the system-bath coupling, one may optimize quantum annealing performances below either the purely quantum or the classical limit. | dissipative environment may improve the quantum annealing performances of the ferromagnetic p -spin model |
we report arecibo s-band (2380 mhz; 12.6 cm) radar observations of near-earth asteroid (3200) phaethon during the december 2017 apparition when phaethon passed within 0.07 au of earth. radar images with a resolution of 75 m per pixel reveal a roughly spheroidal shape more than 6 km in diameter at the equator with several discernible surface features hundreds of meters in extent. these include a possible crater more than 1 km across located below 30∘ latitude and a roughly 600-m radar-dark region near one of the poles. overall, the radar images of phaethon are reminiscent of those of (101955) bennu, target of the osiris-rex mission. as such, the shape of phaethon is suspected to have an equatorial ridge similar to the top-shaped models of several other radar-observed near-earth asteroids as well as the optical images of (162173) ryugu returned by the hayabusa2 spacecraft. preliminary analysis of the radar data finds no satellites and gives no indication of a dusty coma at the time of these observations. | arecibo radar observations of near-earth asteroid (3200) phaethon during the 2017 apparition |
context. disk-integrated photometric data of asteroids do not contain accurate information on shape details or size scale. additional data such as disk-resolved images or stellar occultation measurements further constrain asteroid shapes and allow size estimates.aims: we aim to use all the available disk-resolved images of approximately forty asteroids obtained by the near-infrared camera (nirc2) mounted on the w.m. keck ii telescope together with the disk-integrated photometry and stellar occultation measurements to determine their volumes. we can then use the volume, in combination with the known mass, to derive the bulk density.methods: we downloaded and processed all the asteroid disk-resolved images obtained by the nirc2 that are available in the keck observatory archive (koa). we combined optical disk-integrated data and stellar occultation profiles with the disk-resolved images and use the all-data asteroid modeling (adam) algorithm for the shape and size modeling. our approach provides constraints on the expected uncertainty in the volume and size as well.results: we present shape models and volume for 41 asteroids. for 35 of these asteroids, the knowledge of their mass estimates from the literature allowed us to derive their bulk densities. we see a clear trend of lower bulk densities for primitive objects (c-complex) and higher bulk densities for s-complex asteroids. the range of densities in the x-complex is large, suggesting various compositions. we also identified a few objects with rather peculiar bulk densities, which is likely a hint of their poor mass estimates. asteroid masses determined from the gaia astrometric observations should further refine most of the density estimates. | volumes and bulk densities of forty asteroids from adam shape modeling |
a working timeline for the history of ordinary chondrites includes chondrule formation as early as 0-2 ma after our solar system's earliest forming solids (cais), followed by rapid accretion into undifferentiated planetesimals that were heated internally by 26al decay and cooled over a period of tens of millions of years. there remains conflict, however, between metallographic cooling rate (ni-metal) and radioisotopic thermochronometric data over the sizes and lifetimes of the chondrite parent bodies, as well as the timing of impact related disruptions. the importance of establishing the timing of parent body disruption is heightened by the use of meteorites as recorders of asteroid belt wide disruption events and their use to interpret solar system dynamical models. here we attempt to resolve these records by contributing new 207pb-206pb data obtained on phosphates isolated from nine previously unstudied ordinary chondrites. these new results, along with previously published pb-phosphate, ni-metal and thermometry data, are interpreted with a series of numerical models designed to simulate the thermal evolution for a chondrite parent body that either remains intact or is disrupted by impact prior to forming smaller unsorted "rubble piles". our thermal model and previously published thermometry data limit accretion time to 2.05-2.25 ma after cais. measured pb-phosphate data place minimum estimates on parent body diameters of ∼260-280 km for both the l and h chondrite parent bodies. they also consistently show that petrologic type 6 (highest thermal metamorphism) chondrites from both the h and l bodies have younger ages and, therefore, cooled more slowly than type 5 (lesser metamorphism) chondrites. this is interpreted as evidence for type 5 chondrite origination from shallower depths than type 6 chondrites within initially concentrically zoned bodies. this contrasts metallographic cooling rate data that are inconsistent with such a simple onion shell scenario. one model that can reconcile these two data sets takes into account subtle differences in temperature to which each system responds. this working model requires that disruption occur early enough such that the ni-metal system can record the cooling rate associated with a rubble pile (<70 ma), yet late enough that the pb-phosphate system can record an onion shell structure (>30 ma). for this 30-70 ma timeline, reaccretion into smaller rubble piles will ensure that the originally deeply buried and hot type 6 samples will always cool faster as a result of disruption, yielding nearly uniform ages that record the time of parent body disruption. this is consistent with the available pb-phosphate data, where all but one type 6 chondrite (h, n = 3; l, n = 4) yields a cooling age within a narrow 4505 ± 5 ma timeframe. these data collectively imply that both the h and l chondrite parent bodies were catastrophically disrupted at ∼60 ma. in addition, combined ni-metal and pb-phosphate models confirm that a subset of type 4 chondrites record early rapid cooling likely associated with erosional impacting of the h and l parent bodies on ∼5 ma timescales. | the accretion and impact history of the ordinary chondrite parent bodies |
interplanetary dust particles and meteoroids mostly originate from comets and asteroids. understanding their distribution in the solar system, their dynamical behavior and their properties, sheds light on the current state and the dynamical behavior of the solar system. dust particles can endanger earth-orbiting satellites and deep-space probes, and a good understanding of the spatial density and velocity distribution of dust and meteoroids in the solar system is important for designing proper spacecraft shielding. the study of interplanetary dust and meteoroids provides clues to the formation of the solar system. particles having formed 4.5 billion years ago can survive planetary accretion and those that survived until now did not evolve significantly since then. meteoroids and interplanetary dust can be observed by measuring the intensity and polarization of the zodiacal light, by observing meteors entering the earth's atmosphere, by collecting them in the upper atmosphere, polar ices and snow, and by detecting them with in-situ detectors on space probes. | interplanetary dust, meteoroids, meteors and meteorites |
the trans-neptunian objects (tnos) preserve evidence of planet building processes in their orbital and size distributions. while all populations show steep size distributions for large objects, a relative deficit of neptunian trojans and scattering objects with diameters of d < 100 km has been detected. we investigated this deficit with a 32 square degree survey, in which we detected 77 tnos that are brighter than a limiting r-band magnitude of 24.6. our plutino sample (18 objects in 3:2 mean-motion resonance with neptune) shows a deficit of d < 100 km objects, rejecting a single power-law size distribution at >99% confidence. combining our survey with the canada-france ecliptic plane survey, we perform a detailed analysis of the allowable parameters for the plutino size distribution, including knees and divots. we surmise the existence of 9000 ± 3000 plutinos with an absolute magnitude of hr≤ 8.66 and {37000}-10000+12000 with hr≤ 10.0 (95% confidence). our survey also discovered one temporary uranian trojan, one temporary neptunian trojan, and one stable neptunian trojan, for which we estimate populations of {110}-100+500, {210}-200+900, and {150}-140+600 with hr≤ 10.0, respectively. all three populations are thus less numerous than the main belt asteroids (592 asteroids with hr≤ 10.0). with such population sizes, the temporary neptunian trojans cannot be previously stable trojans diffusing out of the resonance now; they must be recently captured centaurs or scattering objects. as the bias against the detection of objects grows with larger semimajor axes, our discovery of three 3:1 resonators and one 4:1 resonator adds to the growing evidence that the high-order resonances are far more populated than is typically predicted. | a carefully characterized and tracked trans-neptunian survey: the size distribution of the plutinos and the number of neptunian trojans |
the optical navigation cameras (onc-t, onc-w1, onc-w2) onboard hayabusa2 are also being used for scientific observations of the mission target, c-complex asteroid 162173 ryugu. science observations and analyses require rigorous instrument calibrations. in order to meet this requirement, we have conducted extensive inflight observations during the 3.5 years of cruise after the launch of hayabusa2 on 3 december 2014. in addition to the first inflight calibrations by suzuki et al. (2018), we conducted an additional series of calibrations, including read-out smear, electronic-interference noise, bias, dark current, hot pixels, sensitivity, linearity, flat-field, and stray light measurements for the onc. moreover, the calibrations, especially flat-fields and sensitivities, of onc-w1 and -w2 are updated for the analysis of the low-altitude (i.e., high-resolution) observations, such as the gravity measurement, touchdowns, and the descents for mascot and minerva-ii payload releases. the radiometric calibration for onc-t is also updated in this study based on star and moon observations. our updated inflight sensitivity measurements suggest the accuracy of the absolute radiometric calibration contains <1.8% error for the ul-, b-, v-, na-, w-, and x-bands based on star calibration observations and 5% for the p-band based on lunar calibration observations. the radiance spectra of the moon, jupiter, and saturn from the onc-t show good agreement with the spacecraft-based observations of the moon from sp/selene and wac/lroc and with ground-based telescopic observations for jupiter and saturn. our calibration results suggest that the 0.7-μm absorption band typically observed on ch and cgh asteroids at the 3-4% level can be detected with the onc's signal-to-noise ratio (snr) of 2. we also demonstrate a decrease in snr due to ccd temperature increases caused by radiant heat when the spacecraft is close to the surface, as the snr is measured to be 150 at a ccd temperature of 20 °c (the worst case scenario). since ryugu may possess a significant amount of internal volatiles, a sodium atmosphere around ryugu is considered to be highly plausible. we evaluated the upper limit of detectability of a sodium atmosphere around jupiter using the na-filter as 100 r with 100 images. this implies that the onc-t can detect a sodium atmosphere of several 10s kr based on a single image set of v- and na-bands and of several 100 s r based on 100 image sets. finally, we report the first inflight observation of ryugu by onc-t from 1.3 × 106 km away on 26 february 2018. the onc-t v-band photometric observation displays consistency with ground-based observation, which confirms the capability of onc-t. | updated inflight calibration of hayabusa2's optical navigation camera (onc) for scientific observations during the cruise phase |
chondrites consist of three major components: refractory inclusions (ca,al-rich inclusions [cais] and amoeboid olivine aggregates), chondrules, and matrix. here, i summarize recent results on the mineralogy, petrology, oxygen, and aluminum-magnesium isotope systematics of the chondritic components (mainly cais in carbonaceous chondrites) and their significance for understanding processes in the protoplanetary disk (ppd) and on chondrite parent asteroids. cais are the oldest solids originated in the solar system: their u-corrected pb-pb absolute age of 4567.3 ± 0.16 ma is considered to represent time 0 of its evolution. cais formed by evaporation, condensation, and aggregation in a gas of approximately solar composition in a hot (ambient temperature >1300 k) disk region exposed to irradiation by solar energetic particles, probably near the protosun; subsequently, some cais were melted in and outside their formation region during transient heating events of still unknown nature. in unmetamorphosed, type 2-3.0 chondrites, cais show large variations in the initial 26al/27al ratios, from <5 × 10-6 to ~5.25 × 10-5. these variations and the inferred low initial abundance of 60fe in the ppd suggest late injection of 26al by a wind from a nearby wolf-rayet star into the protosolar molecular cloud core prior to or during its collapse. although there are multiple generations of cais characterized by distinct mineralogies, textures, and isotopic (o, mg, ca, ti, mo, etc.) compositions, the 26al heterogeneity in the cai-forming region(s) precludes determining the duration of cais formation using 26al-26mg systematics. the existence of multiple generations of cais and the observed differences in cai abundances in carbonaceous and noncarbonaceous chondrites may indicate that cais were episodically formed and ejected by a disk wind from near the sun to the outer solar system and then spiraled inward due to gas drag. in type 2-3.0 chondrites, most cais surrounded by wark-lovering rims have uniform δ17o (= δ17o-0.52 × δ18o) of ~ -24‰; however, there is a large range of δ17o (from ~-40 to ~ -5‰) among them, suggesting the coexistence of 16o-rich (low δ17o) and 16o-poor (high δ17o) gaseous reservoirs at the earliest stages of the ppd evolution. the observed variations in δ17o of cais may be explained if three major o-bearing species in the solar system (co, h2o, and silicate dust) had different o-isotope compositions, with h2o and possibly silicate dust being 16o-depleted relative to both the genesis solar wind δ17o of -28.4 ± 3.6‰ and even more 16o-enriched co. oxygen isotopic compositions of co and h2o could have resulted from co self-shielding in the protosolar molecular cloud (pmc) and the outer ppd. the nature of 16o-depleted dust at the earliest stages of ppd evolution remains unclear: it could have either been inherited from the pmc or the initially 16o-rich (solar-like) mc dust experienced o-isotope exchange during thermal processing in the ppd. to understand the chemical and isotopic composition of the protosolar mc material and the degree of its thermal processing in ppd, samples of the primordial silicates and ices, which may have survived in the outer solar system, are required. in metamorphosed co3 and cv3 chondrites, most cais exhibit o-isotope heterogeneity that often appears to be mineralogically controlled: anorthite, melilite, grossite, krotite, perovskite, and zr- and sc-rich oxides and silicates are 16o-depleted relative to corundum, hibonite, spinel, al,ti-diopside, forsterite, and enstatite. in texturally fine-grained cais with grain sizes of ~10-20 μm, this o-isotope heterogeneity is most likely due to o-isotope exchange with 16o-poor (δ17o ~0‰) aqueous fluids on the co and cv chondrite parent asteroids. in co3.1 and cv3.1 chondrites, this process did not affect al-mg isotope systematics of cais. in some coarse-grained igneous cv cais, o-isotope heterogeneity of anorthite, melilite, and igneously zoned al,ti-diopside appears to be consistent with their crystallization from melts of isotopically evolving o-isotope compositions. these cais could have recorded o-isotope exchange during incomplete melting in nebular gaseous reservoir(s) with different o-isotope compositions and during aqueous fluid-rock interaction on the cv asteroid. | refractory inclusions in carbonaceous chondrites: records of early solar system processes |
we report on the petrology, magnesium isotopes and mass-independent 54cr/52cr compositions (μ54cr) of 42 chondrules from cv (vigarano and nwa 3118) and cr (nwa 6043, nwa 801 and lap 02342) chondrites. all sampled chondrules are classified as type ia or type iab, have low 27al/24mg ratios (0.04-0.27) and display little or no evidence for secondary alteration processes. the cv and cr chondrules show variable 25mg/24mg and 26mg/24mg values corresponding to a range of mass-dependent fractionation of ∼500 ppm (parts per million) per atomic mass unit. this mass-dependent mg isotope fractionation is interpreted as reflecting mg isotope heterogeneity of the chondrule precursors and not the result of secondary alteration or volatility-controlled processes during chondrule formation. the cv and cr chondrule populations studied here are characterized by systematic deficits in the mass-independent component of 26mg (μ26mg∗) relative to the solar value defined by ci chondrites, which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26al compared to the canonical 26al/27al of ∼5 × 10-5. model initial 26al/27al values of cv and cr chondrules vary from (1.5 ± 4.0) × 10-6 to (2.2 ± 0.4) × 10-5. the cv chondrules display significant μ54cr variability, defining a range of compositions that is comparable to that observed for inner solar system primitive and differentiated meteorites. in contrast, cr chondrites are characterized by a narrower range of μ54cr values restricted to compositions typically observed for bulk carbonaceous chondrites. collectively, these observations suggest that the cv chondrules formed from precursors that originated in various regions of the protoplanetary disk and were then transported to the accretion region of the cv parent asteroid whereas cr chondrule predominantly formed from precursor with carbonaceous chondrite-like μ54cr signatures. the observed μ54cr variability in chondrules from cv and cr chondrites suggest that the matrix and chondrules did not necessarily formed from the same reservoir. the coupled μ26mg∗ and μ54cr systematics of cr chondrules establishes that these objects formed from a thermally unprocessed and 26al-poor source reservoir distinct from most inner solar system asteroids and planetary bodies, possibly located beyond the orbits of the gas giants. in contrast, a large fraction of the cv chondrules plot on the inner solar system correlation line, indicating that these objects predominantly formed from thermally-processed, 26al-bearing precursor material akin to that of inner solar system solids, asteroids and planets. | magnesium and 54cr isotope compositions of carbonaceous chondrite chondrules - insights into early disk processes |
the colours of the outer solar system origins survey is acquiring near-simultaneous g, r, and j photometry of unprecedented precision with the gemini north telescope, targeting nearly 100 trans-neptunian objects (tnos) brighter than mr= 23.6 mag discovered in the outer solar system origins survey. combining the optical and near-infrared photometry with the well-characterized detection efficiency of the colours of the outer solar system origins survey target sample will provide the first flux-limited compositional dynamical map of the outer solar system. in this paper, we describe our observing strategy and detail the data reduction processes we employ, including techniques to mitigate the impact of rotational variability. we present optical and near-infrared colors for 35 tnos. we find two taxonomic groups for the dynamically excited tnos, the neutral and red classes, which divide at g - r ≃ 0.75. based on simple albedo and orbital distribution assumptions, we find that the neutral class outnumbers the red class, with a ratio of 4:1 and potentially as high as 11:1. including in our analysis constraints from the cold classical objects, which are known to exhibit unique albedos and r - z colors, we find that within our measurement uncertainty our observations are consistent with the primordial solar system protoplanetesimal disk being neutral class dominated, with two major compositional divisions in grj color space. | col-ossos: the colors of the outer solar system origins survey |
surface shedding of an asteroid is a failure mode where surface materials fly off due to strong centrifugal forces beyond the critical spin period, while the internal structure does not deform significantly. this paper proposes a possible structure of an asteroid interior that leads to surface shedding due to rapid rotation rates. a rubble pile asteroid is modeled as a spheroid composed of a surface shell and a concentric internal core, the entire assembly called the test body. the test body is assumed to be uniformly rotating around a constant rotation axis. we also assume that while the bulk density and the friction angle are constant, the cohesion of the surface shell is different from that of the internal core. first, developing an analytical model based on limit analysis, we provide the upper and lower bounds for the actual surface shedding condition. second, we use a soft-sphere discrete element method (ssdem) to study dynamical deformation of the test body due to a quasi-static spin-up. in this paper we show the consistency of both approaches. additionally, the ssdem simulations show that the initial failure always occurs locally and not globally. in addition, as the core becomes larger, the size of lofted components becomes smaller. these results imply that if there is a strong core in a progenitor body, surface shedding is the most likely failure mode. | internal structure of asteroids having surface shedding due to rotational instability |
we present a detailed study of the metal-polluted db white dwarf sdss j0845+2257 (ton 345). using high-resolution hubble space telescope/cosmic origins spectrograph and very large telescope spectroscopy, we have detected hydrogen and 11 metals in the atmosphere of the white dwarf. the origin of these metals is almost certainly the circumstellar disc of dusty and gaseous debris from a tidally disrupted planetesimal, accreting at a rate of 1.6 × 1010 g s-1. studying the chemical abundances of the accreted material demonstrates that the planetesimal had a composition similar to the earth, dominated by rocky silicates and metallic iron, with a low water content. the mass of metals within the convection zone of the white dwarf corresponds to an asteroid of at least ∼130-170 km in diameter, although the presence of ongoing accretion from the debris disc implies that the planetesimal was probably larger than this. while a previous abundance study of the accreted material has shown an anomalously high mass fraction of carbon (15 per cent) compared to the bulk earth, our independent analysis results in a carbon abundance of just 2.5 per cent. enhanced abundances of core material (fe, ni) suggest that the accreted object may have lost a portion of its mantle, possibly due to stellar wind stripping in the asymptotic giant branch. time series spectroscopy reveals variable emission from the orbiting gaseous disc, demonstrating that the evolved planetary system at sdss j0845+2257 is dynamically active. | the composition of a disrupted extrasolar planetesimal at sdss j0845+2257 (ton 345) |
post-main-sequence planetary science has been galvanized by the striking variability, depth and shape of the photometric transit curves due to objects orbiting white dwarf wd 1145+017, a star which also hosts a dusty debris disc and circumstellar gas, and displays strong metal atmospheric pollution. however, the physical properties of the likely asteroid which is discharging disintegrating fragments remain largely unconstrained from the observations. this process has not yet been modelled numerically. here, we use the n-body code pkdgrav to compute dissipation properties for asteroids of different spins, densities, masses and eccentricities. we simulate both homogeneous and differentiated asteroids, for up to 2 yr, and find that the disruption time-scale is strongly dependent on density and eccentricity, but weakly dependent on mass and spin. we find that primarily rocky differentiated bodies with moderate (∼3-4 g cm-3) bulk densities on near-circular (e ≲ 0.1) orbits can remain intact while occasionally shedding mass from their mantles. these results suggest that the asteroid orbiting wd 1145+017 is differentiated, resides just outside of the roche radius for bulk density but just inside the roche radius for mantle density, and is more akin physically to an asteroid like vesta instead of one like itokawa. | explaining the variability of wd 1145+017 with simulations of asteroid tidal disruption |
near-earth asteroid population models predict the existence of bodies located inside the orbit of venus. despite searches up to the end of 2019, none had been found. we report discovery and follow-up observations of (594913) 'ayló'chaxnim, an asteroid with an orbit entirely interior to venus. (594913) 'ayló'chaxnim has an aphelion distance of ~0.65 au, is ~2 km in diameter and is red in colour. the detection of such a large asteroid inside the orbit of venus is surprising given their rarity according to near-earth asteroid population models. as the first officially numbered and named asteroid located entirely within the orbit of venus, we propose that the class of interior to venus asteroids be referred to as 'ayló'chaxnim asteroids. | the discovery and characterization of (594913) 'ayló'chaxnim, a kilometre sized asteroid inside the orbit of venus |
unlike the other terrestrial planets, earth has a substantial silica-rich continental crust with a bulk andesitic composition. a small number of meteorites with andesitic bulk compositions have been identified that are thought to be the products of partial melting of chondritic protoliths, a mode of petrogenesis distinct from that of earth's continental crust. here we show, using geochemical analyses, that unlike other known andesitic meteorites, erg chech 002 has strongly fractionated and low abundances of the highly siderophile elements and mineralogy consistent with origin from a melt. the meteorite's bulk composition, which is similar to terrestrial andesites, cannot be explained by partial melting of basaltic lithologies and instead requires a metal-free chondritic source. we argue that erg chech 002 probably formed by ~15-25% melting of the mantle of an alkali-undepleted differentiated asteroid. our findings suggest that extensive silicate differentiation after metal-silicate equilibration of chondritic parent bodies was already occurring within the first 2.25 million years of solar system history and that andesitic crust formation does not necessarily require plate tectonics. | early silicic magmatism on a differentiated asteroid |
japan aerospace exploration agency (jaxa) launched the asteroid exploration probe "hayabusa2" in december 3rd, 2014, following the 1st hayabusa mission. with technological and scientific improvements from the hayabusa probe, we plan to visit the c-type asteroid 162137 ryugu (1999 ju3), and to sample surface materials of the c-type asteroid that is likely to be different from the s-type asteroid itokawa and contain more pristine materials, including organic matter and/or hydrated minerals, than s-type asteroids. we developed the hayabusa2 sampler to collect a minimum of 100 mg of surface samples including several mm-sized particles at three surface locations without any severe terrestrial contamination. the basic configuration of the sampler design is mainly as same as the 1st hayabusa (yano et al. in science, 312(5778):1350-1353, 2006), with several minor but important modifications based on lessons learned from the hayabusa to fulfill the scientific requirements and to raise the scientific value of the returned samples. | hayabusa2 sampler: collection of asteroidal surface material |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.