abstract stringlengths 3 192k | title stringlengths 4 857 |
|---|---|
tidal flats on the north coast of vietnam suffer diurnal tide with a tide range varying between 0.3 m and 3.5 m. along the 350 km long coastline, the diversity of environmental conditions induces various tidal flats with different characteristics. this study applies the waterline method for multi-temporal satellite images to build digital elevation models (dems) of tidal flats during the last 25 years. 117 landsat images acquired with tm, etm+, and oli have been processed to construct tidal flat dems in 1989, 2000, and 2014. waterlines extracted from single spectral bands (near-infrared [nir], short wave infrared [swir]) or band ratios (normalized difference water index [ndwi], normalized difference vegetation index [ndvi], green/swir) of the landsat data have been compared with waterlines digitalized on spot, aster and worldview 2 images. this experiment allows us to determine the best band (or band ratio) for extracting waterlines depending on local conditions. consequently, the study shows that the green/swir ratio image is a good solution for extracting waterlines in the black coal tidal flats of cam pha. however, the ndwi index appears to be a better choice for the other parts of the study area. the vertical accuracy of the tidal flat dems reaches 0.144 m. the change analysis of the dems also emphasizes the tidal flat evolution in both vertical and horizontal dimensions, i.e. erosion or accretion. the erosion of the tidal flats along the northern coast of vietnam is particularly developed in the area extending from yen hung to mong cai, especially in mong cai with an amount of about 50 × 106 m3 of sediments lost between 1989 and 2014. on the contrary, the tidal flats in the south of the study area show a high rate of deposition due to the sediments fed by red and thai binh rivers. about 35 × 106 m3 of sediments deposited in the tidal flat surrounding the red river mouth between 1989 and 2014. this study represents a development of the waterline extraction method to investigate the evolution of tidal flat at a large scale and a diversified coastal environment using optical satellite images and fieldwork. | an optimal waterline approach for studying tidal flat morphological changes using remote sensing data: a case of the northern coast of vietnam |
we combine photometry of eris from a 6 month campaign on the palomar 60 inch telescope in 2015, a 1 month hubble space telescope wfc3 campaign in 2018, and dark energy survey data spanning 2013-2018 to determine a light curve of definitive period 15.771 ± 0.008 days (1σ formal uncertainties), with nearly sinusoidal shape and peak-to-peak flux variation of 3%. this is consistent at part-per-thousand precision with the p = 15.785 90 ± 0.00005 day sidereal period of dysnomia's orbit around eris, strengthening the recent detection of synchronous rotation of eris by szakáts et al. with independent data. photometry from gaia are consistent with the same light curve. we detect a slope of 0.05 ± 0.01 mag per degree of eris's brightness with respect to illumination phase averaged across g, v, and r bands, intermediate between pluto's and charon's values. variations of 0.3 mag are detected in dysnomia's brightness, plausibly consistent with a double-peaked light curve at the synchronous period. the synchronous rotation of eris is consistent with simple tidal models initiated with a giant-impact origin of the binary, but is difficult to reconcile with gravitational capture of dysnomia by eris. the high albedo contrast between eris and dysnomia remains unexplained in the giant-impact scenario. | synchronous rotation in the (136199) eris-dysnomia system |
the rare ci carbonaceous chondrites are the most aqueously altered and chemically primitive meteorites but due to their porous nature and high abundance of volatile elements are susceptible to terrestrial weathering. the ivuna meteorite, type specimen for the ci chondrites, is the largest twentieth-century ci fall and probably the ci chondrite least affected by terrestrial alteration that is available for study. the main mass of ivuna (bm2008 m1) has been stored in a nitrogen atmosphere at least since its arrival at the natural history museum (nhm), london, in 2008 (70 years after its fall) and could be considered the most pristine ci chondrite stone. we report the mineralogy, petrography and bulk elemental composition of bm2008 m1 and a second ivuna stone (bm1996 m4) stored in air within wooden cabinets. we find that both ivuna stones are breccias consisting of multiple rounded, phyllosilicate-rich clasts that formed through aqueous alteration followed by impact processing. a polished thin section of bm2008 m1 analysed immediately after preparation was found to contain sulphate-bearing veins that formed when primary sulphides reacted with oxygen and atmospheric water. a section of bm1996 m4 lacked veins but had sulphate grains on the surface that formed in ≤6 years, ∼3 times faster than previous reports for ci chondrite sections. differences in the extent of terrestrial alteration recorded by bm2008 m1 and bm1996 m4 probably reflect variations in the post-recovery curation history of the stones prior to entering the nhm collection, and indicate that where possible pristine samples of hydrated carbonaceous should be kept out of the terrestrial environment in a stable atmosphere to avoid modification. the bulk elemental composition of the two ivuna stones show some variability due to their heterogeneous nature but in general are similar to previous analyses of ci chondrites. we combine our elemental abundances with literature values to calculate a new average composition for the ivuna meteorite, which we find is in good agreement with existing compilations of element compositions in the ci chondrites and the most recent solar photospheric abundances. | terrestrial modification of the ivuna meteorite and a reassessment of the chemical composition of the ci type specimen |
the geostationary lightning mapper (glm) instrument onboard the goes 16 and 17 satellites can be used to detect bolides in the atmosphere. this capacity is unique because glm provides semi-global, continuous coverage and releases its measurements publicly. here, six filters are developed that are aggregated into an automatic algorithm to extract bolide signatures from the glm level 2 data product. the filters exploit unique bolide characteristics to distinguish bolide signatures from lightning and other noise. typical lightning and bolide signatures are introduced and the filter functions are presented. the filter performance is assessed on 144845 glm l2 files (equivalent to 34 days-worth of data) and the algorithm selected 2252 filtered files (corresponding to a pass rate of 1.44%) with bolide-similar signatures. the challenge of identifying frequent but small, decimeter-sized bolide signatures is discussed as glm reaches its resolution limit for these meteors. the effectiveness of the algorithm is demonstrated by its ability to extract confirmed and new bolide discoveries. we provide discovery numbers for november 2018 when seven likely bolides were discovered of which four are confirmed by secondary observations. the cuban meteor on feb 1st 2019 serves as an additional example to demonstrate the algorithms capability and the first light curve as well as correct ground track was available within 8.5 hours based on glm data for this event. the combination of the automatic bolide extraction algorithm with glm can provide a wealth of new measurements of bolides in earth's atmosphere to enhance the study of asteroids and meteors. | an algorithmic approach for detecting bolides with the geostationary lightning mapper |
ongoing spectroscopic reconnaissance of the osiris-rex target asteroid (101955) bennu was performed in july 2011 and may 2012. near-infrared spectra taken during these apparitions display slightly more positive ("redder") spectral slopes than most previously reported measurements. while observational systematic effects can produce such slope changes, and these effects cannot be ruled out, we entertain the hypothesis that the measurements are correct. under this assumption, we present laboratory measurements investigating a plausible explanation that positive spectral slopes indicate a finer grain size for the most directly observed sub-earth region on the asteroid. in all cases, the positive spectral slopes correspond to sub-earth latitudes nearest to the equatorial ridge of bennu. if confirmed by osiris-rex in situ observations, one possible physical implication is that if the equatorial ridge is created by regolith migration during episodes of rapid rotation, that migration is most strongly dominated by finer grain material. alternatively, after formation of the ridge (by regolith of any size distribution), larger-sized equatorial material may be more subject to loss due to centrifugal acceleration relative to finer grain material, where cohesive forces can preferentially retain the finest fraction (rozitis, b., maclennan, e., emery, j.p. [2014]. nature 512, 174-176). | spectral slope variations for osiris-rex target asteroid (101955) bennu: possible evidence for a fine-grained regolith equatorial ridge |
asteroid (2) pallas is the largest main-belt object not yet visited by a spacecraft, making its surface geology largely unknown and limiting our understanding of its origin and collisional evolution. previous ground-based observational campaigns returned different estimates of its bulk density that are inconsistent with one another, one measurement1 being compatible within error bars with the icy ceres (2.16 ± 0.01 g cm-3)2 and the other3 compatible within error bars with the rocky vesta (3.46 ± 0.03 g cm-3)4. here we report high-angular-resolution observations of pallas performed with the extreme adaptive optics-fed sphere imager5 on the very large telescope. pallas records a violent collisional history, with numerous craters larger than 30 km in diameter populating its surface and two large impact basins that could be related to a family-forming impact. monte carlo simulations of the collisional evolution of the main belt correlate this cratering record to the high average impact velocity of ~11.5 km s-1 on pallas—compared with an average of ~5.8 km s-1 for the asteroid belt—induced by pallas's high orbital inclination (i = 34.8°) and orbital eccentricity (e = 0.23). compositionally, pallas's derived bulk density of 2.89 ± 0.08 g cm-3 (1σ uncertainty) is fully compatible with a cm chondrite-like body, as suggested by its spectral reflectance in the 3 μm wavelength region6. a bright spot observed on its surface may indicate an enrichment in salts during an early phase of aqueous alteration, compatible with pallas's relatively high albedo of 12-17% (refs. 7,8), although alternative origins are conceivable. | the violent collisional history of aqueously evolved (2) pallas |
the finding by the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission that its target (101955) bennu is an active asteroid has raised questions as to whether the observed particle ejection events are driven by temperature. to investigate sublimation of water ice and rock thermal fracture as possible temperature-driven causes, we modeled the global temperatures of bennu and searched for correlations with the identified ejection points on the asteroid surface. we computed temperatures with the advanced thermophysical model and the 75-cm-resolution global shape model of bennu derived by the osiris-rex mission. we find that ~1,856 m2 of bennu's polar regions have orbit-averaged temperatures that are sufficiently cold to enable water ice, if buried within the top few meters of the surface, to remain stable over geological timescales. millimeter thick layers of surface water ice are also stable over ~103-year timescales within polar centimeter-scale cold traps. however, we do not find evidence of conditions enabling ice stability in the warmer equatorial regions, where ejection events have been observed, implying that sublimation of water ice is not the cause of particle ejection. conversely, rock thermal fracture remains a possible mechanism of particle ejection. we find high amplitudes of diurnal temperature variation, a proxy for the efficacy of thermal fracturing, at all latitudes on bennu due to its extreme ruggedness. therefore, if rock thermal fracture is the mechanism, particles could be ejected from any latitude, which is consistent with the continued observations of particle ejection by osiris-rex. | implications for ice stability and particle ejection from high-resolution temperature modeling of asteroid (101955) bennu |
micrometeoroid bombardments are one of the causes of space weathering on airless bodies. we have simulated micrometeoroid bombardments on the surfaces of c-type asteroids by pulse-laser irradiation experiments on murchison cm2 chondrite samples. in this letter, we focus in particular on the effect of lower-energy irradiation compared to our previous study, where the laser energy range was set to 5-15 mj, causing spectral flattening and water absorption band suppression. murchison powder samples were irradiated with pulse lasers of various laser intensities (0.7, 1, 2, and 5 mj). the irradiation energies are equivalent to micrometeoroid bombardments on the main-belt asteroids for ∼5.7 × 107 yr for 5 mj and ∼7.9 × 106 yr for 0.7 mj, respectively. we measured reflectance spectra and analyzed chemical compositions and microstructures of the surface of the laser-irradiated murchison samples. laser-irradiated murchison spectra show flattening and darkening in the ultraviolet (uv)-visible (vis)-infrared (ir) range. as the laser energy was increased up to 5 mj, the 3 and 0.7 μm band depths decreased by 12% and 50%, respectively. the particle surface in the 5 mj irradiated area shows melted and vesiculated structures, indicating high-temperature heating by laser irradiation followed by rapid cooling. the chemical composition of the melted and bubbled portions is similar to fes-rich amorphous silicate particles observed in the high-energy laser irradiation case. each mineralogical change of murchison due to short-duration heating would cause spectral bluing, darkening, and absorption band suppression. | space weathering simulation with low-energy laser irradiation of murchison cm chondrite for reproducing micrometeoroid bombardments on c-type asteroids |
lake el'gygytgyn in far east russia is a 3.6 myr old impact crater lake. located in an area that has never been affected by cenozoic glaciations nor desiccation, the unique sediment record of the lake represents the longest continuous sediment archive of the terrestrial arctic. the surrounding crater is the only impact structure on earth developed in mostly acid volcanic rocks. recent studies on the impactite, permafrost, and sediment sequences recovered within the framework of the icdp "el'gygytgyn drilling project" and multiple pre-site surveys yielded new insight into the bedrock origin and cratering processes as well as permafrost dynamics and the climate and environmental history of the terrestrial arctic back to the mid-pliocene. results from the impact rock section recovered during the deep drilling clearly confirm the impact genesis of the el'gygytgyn crater, but indicate an only very reduced fallback impactite sequence without larger coherent melt bodies. isotope and element data of impact melt samples indicate a f-type asteroid of mixed composition or an ordinary chondrite as the likely impactor. the impact event caused a long-lasting hydrothermal activity in the crater that is assumed to have persisted for c. 300 kyr. geochemical and microbial analyses of the permafrost core indicate a subaquatic formation of the lower part during lake-level highstand, but a subaerial genesis of the upper part after a lake-level drop after the allerød. the isotope signal and ion compositions of ground ice is overprinted by several thaw-freeze cycles due to variations in the talik underneath the lake. modeling results suggest a modern permafrost thickness in the crater of c. 340 m, and further confirm a pervasive character of the talik below lake el'gygytgyn. the lake sediment sequences shed new leight into the pliocene and pleistocene climate and environmental evolution of the arctic. during the mid-pliocene, significantly warmer and wetter climatic conditions in western beringia than today enabled dense boreal forests to grow around lake el'gygytgyn and, in combination with a higher nutrient flux into the lake, promoted primary production. the exceptional warmth during the mid-pliocene is in accordance with other marine and terrestrial records from the arctic and indicates a period of enhanced "arctic amplification". the favourable conditions during the mid-pliocene were repeatedly interrupted by climate deteriorations, e.g., during marine isotope stage (mis) m2, when pollen data and sediment proxies indicate a major cooling and the onset of local permafrost around the lake. a gradual vegetation change after c. 3.0 ma points to the onset of a long-term cooling trend during the late pliocene that culminated in major temperature drops, first during mis g6, and later during mis 104. these cold events coincide with the onset of an intensified northern hemisphere (nh) glaciation and the largest extent of the cordilleran ice sheet, respectively. after the pliocene/pleistocene transition, local vegetation and primary production in lake el'gygtygyn experienced a major change from relatively uniform conditions to a high-amplitude glacial-to-interglacial cyclicity that fluctuated on a dominant 41 kyr obliquity band, but changed to a 100 kyr eccentricity dominance during the middle pleistocene transition (mpt) at c. 1.2-0.6 ma. periods of exceptional warming in the pleistocene record of lake el'gygytgyn with dense boreal forests around and peaks of primary production in the lake are assigned to so-called "super-interglacial" periods. the occurrence of these super-interglacials well corresponds to collapses of the west antarctic ice sheet (wais) recorded in ice-free periods in the andrill core, which suggests strong intrahemispheric teleconnections presumably driven by changes in the thermocline ocean circulation. | impact processes, permafrost dynamics, and climate and environmental variability in the terrestrial arctic as inferred from the unique 3.6 myr record of lake el'gygytgyn, far east russia - a review |
abiotic synthesis of biomolecules is an essential step for the chemical origin of life. many attempts have succeeded in synthesizing biomolecules, including amino acids and nucleobases (e.g., via spark discharge, impact shock, and hydrothermal heating), from reduced compounds that may have been limited in their availabilities on hadean earth and noachian mars. on the other hand, formation of amino-acids and nucleobases from co2 and n2 (i.e., the most abundant c and n sources on earth during the hadean) has been limited via spark discharge. here, we demonstrate the synthesis of amino acids by laboratory impact-induced reactions among simple inorganic mixtures: fe, ni, mg2sio4, h2o, co2, and n2, by coupling the reduction of co2, n2, and h2o with the oxidation of metallic fe and ni. these chemical processes simulated the possible reactions at impacts of fe-bearing meteorites/asteroids on oceans with a co2 and n2 atmosphere. the results indicate that hypervelocity impact was a source of amino acids on the earth during the hadean and potentially on mars during the noachian. amino acids formed during such events could more readily polymerize in the next step of the chemical evolution, as impact events locally form amino acids at the impact sites. | impact-induced amino acid formation on hadean earth and noachian mars |
we report on the mineralogy, petrology, and in situ measured oxygen-isotope compositions of three fluffy type a ca,al-rich inclusions (fta cais) and two amoeboid olivine aggregates (aoas) from the cv3.1 carbonaceous chondrite kaba. the fta cais are aggregates of several inclusions composed of spinel, al,ti-diopside, and gehlenitic melilite replaced to various degrees by anorthite; they are surrounded by the wark-lovering rim layers made of spinel, anorthite, al-diopside, and forsterite. one of fta cais contains a relict ultrarefractory inclusion composed of sc-rich al,ti-pyroxene, spinel, and zr-rich oxides. the aoas are aggregates of ca- and/or al-rich minerals (spinel, anorthite, and al,ti-diopside) surrounded by forsterite ± fe,ni-metal condensates; fe,ni-metal is almost entirely replaced by magnetite and fe,ni-sulfides. neither the fta cais nor the aoas show evidence for being melted after aggregation, and contain very minor secondary alteration minerals resulted from fluid-rock interaction on the cv parent asteroid. these include magnetite, fayalite, hedenbergite, phyllosilicates, and fe-bearing ti-free al-diopside; secondary anorthite of asteroidal origin is absent in kaba cais and aoas. there are large variations in δ17o (deviation from the terrestrial fractionation line = δ17o - 0.52 × δ18o) within the individual fta cais and aoas: anorthite and melilite are systematically 16o-depleted (δ17o range from ∼-14 to ∼-2‰) relative to the uniformly 16o-rich forsterite and al,ti-diopside (δ17o ∼ -25 to -20 ± 2‰, 2σ). scandium-rich al,ti-pyroxene has 16o-poor composition (δ17o ∼ -4‰). many anorthite and melilite analyses plot close to or along mass-dependent fractionation line with δ17o of -1.5 ± 1‰ (average ± 2sd) defined by the aqueously-formed magnetite and fayalite from kaba, and, therefore, corresponding to δ17o of an aqueous fluid that operated on the cv parent asteroid. we conclude that anorthite and probably melilite in the kaba fta cais and aoas experienced postcrystallization oxygen-isotope exchange with this fluid. the similar process must have affected plagioclase/plagioclase mesostasis and probably melilite in refractory inclusions and chondrules from cv3 chondrites of higher petrologic types [e.g., allende (cvoxa3.6) and efremovka (cvred3.1-3.4)], which appear to have experienced higher temperature metasomatic alteration than kaba and were subsequently metamorphosed. we conclude that the carbonaceous chondrite anhydrous mineral (ccam) line defined by oxygen-isotope compositions of whole-rock and mineral separates of allende cais and having a slope of 0.94 is not the primary nebular line. instead this line results from superposition of the nebular slope-1 line recorded by the primitive chondrule mineral (pcm) line, the mass-dependent fractionation line with slope of ∼0.5 defined by the secondary minerals, and the minerals which experienced oxygen-isotope exchange with an aqueous fluid. | evidence for oxygen-isotope exchange in refractory inclusions from kaba (cv3.1) carbonaceous chondrite during fluid-rock interaction on the cv parent asteroid |
cm chondrites are the most common type of hydrated meteorites, making up ∼1.5% of all falls. whereas most cm chondrites experienced only low-temperature (∼0°c-120°c) aqueous alteration, the existence of a small fraction of cm chondrites that suffered both hydration and heating complicates our understanding of the early thermal evolution of the cm parent body(ies). here, we provide new constraints on the collisional and thermal history of cm-like bodies from a comparison between newly acquired spectral measurements of main-belt ch/cgh-type asteroids (70 objects) and existing laboratory spectral measurements of cm chondrites. it first appears that the spectral variation observed among cm-like bodies is essentially due to variations in the average regolith grain size. second, the spectral properties of the vast majority (unheated) of cm chondrites resemble both the surfaces and the interiors of cm-like bodies, implying a “low” temperature (<300°c) thermal evolution of the cm parent body(ies). it follows that an impact origin is the likely explanation for the existence of heated cm chondrites. finally, similarly to s-type asteroids and (2) pallas, the surfaces of large (d > 100 km)—supposedly primordial—ch/cgh-type main-belt asteroids likely expose the interiors of the primordial cm parent bodies, a possible consequence of impacts by small asteroids (d < 10 km) in the early solar system. | compositional homogeneity of cm parent bodies |
the dwarf planet ceres (diameter 939 km) is the largest object in the main asteroid belt. recent investigations suggest that ceres is a thermally evolved, volatile-rich body with potential geological activity, a body which was never completely molten but possibly differentiated into a rocky core, an ice-rich mantle, and which may contain remnant internal liquid water. thermal alteration and exogenic material infall contribute to producing a (dark) carbonaceous chondritic-like surface containing ammoniated phyllosilicates. here we report imaging and spectroscopic analyses of occator crater derived from the framing camera and the visible and infrared spectrometer onboard dawn. we found that the central bright spot (cerealia facula) of occator is ∼30 myr younger than the crater itself. the central spot is located in a central pit which contains a dome that is spectrally homogenous, exhibiting absorption features that are consistent with carbonates. multiple radial fractures across the dome indicate an extrusive formation process. our results lead us to conclude that the floor region was subject to past endogenic activity. dome and bright material in its vicinity formed likely due to a long-lasting, periodic, or episodic ascent of bright material from a subsurface reservoir rich in carbonates. originally triggered by an impact event, gases, possibly dissolved from a subsurface water/brine layer, enabled material rich in carbonates to ascend through fractures and be deposited onto the surface. | evolution of occator crater on (1) ceres |
exploratory missions to investigate accessible near earth asteroids (neas) can benefit from leveraging dynamics associated with a solar sail-based spacecraft. as a part of this effort, nea scout is a solar sail mission designed to propel a 6u cubesat by harnessing solar radiation pressure from the sun. the spacecraft will be launched as a secondary payload on nasa's space launch system (sls) exploration mission one (em-1). as the launch of em-1 has recently been rescheduled for december 2019, alternative target neas are identified. additionally, solar sail-based trajectories for the nea scout mission also need to be reevaluated. in this study, high-fidelity trajectories for the nea scout mission are investigated for varying launch dates under the assumption of the failure of a critical propulsive maneuver. furthermore, feasible trajectory solutions are presented for multiple candidate asteroids. | high-fidelity contingency trajectory design and analysis for nasa's near-earth asteroid (nea) scout solar sail mission |
fifteen h, l, and ll ordinary chondrites of petrologic types 4-6 have been analyzed for hf-w isotope systematics to constrain the chronology, internal structure, and thermal history of their parent bodies. for most samples coarse-grained metals plot below the isochrons defined by silicate-dominated fractions which consist of variable mixtures of silicate minerals with tiny metal inclusions. this offset results from an earlier hf-w closure in the large metal grains and provides a new means for simultaneously determining cooling rates and hf-w closure ages for individual samples. for most type 5 and 6 samples, cooling rates and hf-w ages are inversely correlated, indicating that these samples derive from concentrically zoned bodies in which more strongly metamorphosed samples derive from greater depth. these data, therefore, provide strong evidence for a common 'onion shell' structure for the h, l, and ll chondrite parent bodies. the cooling rates and hf-w ages of some type 5 and 6 chondrites overlap, indicating that the hf-w systematics provide a more robust measure of the thermal history and burial depth of a given sample than the simple petrographic distinction between types 5 and 6. two type 6 samples deviate from the correlation between cooling rates and hf-w ages and cooled much faster than expected for their hf-w age. these samples likely were excavated by impacts that occurred during high-temperature metamorphism and prior to complete closure of the hf-w system at ∼10 ma after cai formation. as these impacts would have disturbed the asteroid's cooling history, these samples likely derive from different bodies than samples with undisturbed cooling histories, implying that ordinary chondrites derive from more than just three parent bodies. the hf-w data reveal that metal-silicate fractionation among the h, l, and ll groups occurred between ∼2 and ∼2.7 ma after cai formation and, hence, was about coeval to chondrule formation. as both metal-silicate fractionation and chondrule formation occurred prior to chondrite parent body accretion, there should be no ordinary chondrite chondrules that are younger than ∼2.7 ma. finally, ordinary chondrite precursors had lower hf/w ratios than carbonaceous chondrites, suggesting that inner and outer solar system materials, respectively, were chemically distinct even for refractory elements. | hf-w chronology of ordinary chondrites |
the caltech high-speed multi-colour camera (chimera) is a new instrument that has been developed for use at the prime focus of the hale 200-inch telescope. simultaneous optical imaging in two bands is enabled by a dichroic beam splitter centred at 567 nm, with sloan u' and g' bands available on the blue arm and sloan r', i' and z_s bands available on the red arm. additional narrow-band filters will also become available as required. an electron multiplying ccd (emccd) detector is employed for both optical channels, each capable of simultaneously delivering sub-electron effective read noise under multiplication gain and frame rates of up to 26 fps full frame (several 1000 fps windowed), over a fully corrected 5 × 5 arcmin field of view. chimera was primarily developed to enable the characterization of the size distribution of sub-km kuiper belt objects via stellar occultation, a science case that motivates the frame-rate, the simultaneous multi-colour imaging and the wide field of view of the instrument. in addition, it also has unique capability in the detection of faint near-earth asteroids and will be used for the monitoring of short-duration transient and periodic sources, particularly those discovered by the intermediate palomar transient factory (iptf), and the upcoming zwicky transient facility (ztf). | chimera: a wide-field, multi-colour, high-speed photometer at the prime focus of the hale telescope |
asteroids and other small solar system bodies (sssbs) are of high general and scientific interest in many aspects. the origin, formation, and evolution of our solar system (and other planetary systems) can be better understood by analysing the constitution and physical properties of small bodies in the solar system. currently, two space missions (hayabusa2, osiris-rex) have recently arrived at their respective targets and will bring a sample of the asteroids back to earth. other small body missions have also been selected by, or proposed to, space agencies. the threat posed to our planet by near-earth objects (neos) is also considered at the international level, and this has prompted dedicated research on possible mitigation techniques. the dart mission, for example, will test the kinetic impact technique. even ideas for industrial exploitation have risen during the last years. lastly, the origin of water and life on earth appears to be connected to asteroids. hence, future space mission projects will undoubtedly target some asteroids or other sssbs. in all these cases and research topics, specific knowledge of the structure and mechanical behaviour of the surface as well as the bulk of those celestial bodies is crucial. in contrast to large telluric planets and dwarf planets, a large proportion of such small bodies is believed to consist of gravitational aggregates (`rubble piles') with no—or low—internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges). bodies with such structure can sustain some plastic deformation without being disrupted in contrast to the classical visco-elastic models that are generally valid for planets, dwarf planets, and large satellites. these sssbs are hence better described through granular mechanics theories, which have been a subject of intense theoretical, experimental, and numerical research over the last four decades. this being the case, it has been necessary to use the theoretical, numerical and experimental tools developed within soil mechanics, granular dynamics, celestial mechanics, chemistry, condensed matter physics, planetary and computer sciences, to name the main ones, in order to understand the data collected and analysed by observational astronomy (visible, thermal, and radio), and different space missions. in this paper, we present a review of the multi-disciplinary research carried out by these different scientific communities in an effort to study sssbs. | small solar system bodies as granular media |
context. when we wish to understand planetesimal formation, the only data set we have is our own solar system. the solar system is particularly interesting because so far, it is the only planetary system we know of that developed life. understanding the conditions under which the solar nebula evolved is crucial in order to understand the different processes in the disk and the subsequent dynamical interaction between (proto-)planets after the gas disk has dissolved.aims: protoplanetary disks provide a plethora of different parameters to explore. the question is whether this parameter space can be constrained, allowing simulations to reproduce the solar system.methods: models and observations of planet formation provide constraints on the initial planetesimal mass in certain regions of the solar nebula. by making use of pebble flux-regulated planetesimal formation, we performed a parameter study with nine different disk parameters such as the initial disk mass, the initial disk size, the initial dust-to-gas ratio, the turbulence level, and others.results: we find that the distribution of mass in planetesimals in the disk depends on the timescales of planetesimal formation and pebble drift. multiple disk parameters can affect the pebble properties and thus planetesimal formation. however, it is still possible to draw some conclusions on potential parameter ranges.conclusions: pebble flux-regulated planetesimal formation appears to be very robust, allowing simulations with a wide range of parameters to meet the initial planetesimal constraints for the solar nebula. this means that it does not require much fine-tuning. | constraining the parameter space for the solar nebula. the effect of disk properties on planetesimal formation |
(60558) 174p/echeclus is an unusual object that belongs to a class of minor planets called centaurs, which may be intermediate between kuiper belt objects and jupiter family comets. it is sporadically active throughout its orbit at distances too far for water ice, the source of activity for most comets, to sublimate. thus, its coma must be triggered by another mechanism. in 2005, echeclus had a strong outburst with peculiar behavior that raised questions about the nucleus’ homogeneity. to test nucleus models, we performed the most sensitive search to date for the highly volatile co molecule via its j = 2-1 emission toward echeclus during 2016 may-june (at 6.1 astronomical units from the sun) using the arizona radio observatory 10 m submillimeter telescope. we obtained a 3.6σ detection with a slightly blueshifted (δv = -0.55 ± 0.10 km s-1) and narrow (δv fwhm = 0.53 ± 0.23 km s-1) line. the data are consistent with emission from a cold gas from the sunward side of the nucleus, as seen in two other comets at 6 au. we derive a production rate of q(co) = (7.7 ± 3.3) × {10}26 mol s-1, which is capable of driving the estimated dust production rates. echeclus’ co outgassing rate is ∼40 times lower than what is typically seen for another centaur at this distance, 29p/schwassmann-wachmann 1. we also used the iram 30 m telescope to search for the co j = 2-1 line, and derive an upper limit that is above the smt detection. compared with the relatively unprocessed comet c/1995 o1 (hale-bopp), echeclus produces significantly less co, as do chiron and four other centaurs. | carbon monoxide in the distantly active centaur (60558) 174p/echeclus at 6 au |
northwest africa (nwa) 7325 is an ungrouped achondrite that has recently been recognized as a sample of ancient differentiated crust from either mercury or a previously unknown asteroid. in this work we augment data from previous investigations on petrography and mineral compositions, mid-ir spectroscopy, and oxygen isotope compositions of nwa 7325, and add constraints from cr and ti isotope compositions on the provenance of its parent body. in addition, we identify and discuss notable similarities between nwa 7325 and clasts of a rare xenolithic lithology found in polymict ureilites. nwa 7325 has a medium grained, protogranular to poikilitic texture, and consists of 10-15 vol.% mg-rich olivine (fo 98), 25-30 vol.% diopside (wo 45, mg# 98), 55-60 vol.% ca-rich plagioclase (an 90), and trace cr-rich sulfide and fe,ni metal. we interpret this meteorite to be a cumulate that crystallized at ⩾1200 °c and very low oxygen fugacity (similar to the most reduced ureilites) from a refractory, incompatible element-depleted melt. modeling of trace elements in plagioclase suggests that this melt formed by fractional melting or multi-stage igneous evolution. a subsequent event (likely impact) resulted in plagioclase being substantially remelted, reacting with a small amount of pyroxene, and recrystallizing with a distinctive texture. the bulk oxygen isotope composition of nwa 7325 plots in the range of ureilites on the ccam line, and also on a mass-dependent fractionation line extended from acapulcoites. the ɛ54cr and ɛ50ti values of nwa 7325 exhibit deficits relative to terrestrial composition, as do ordinary chondrites and most achondrites. its ɛ54cr value is distinct from that of any analyzed ureilite, but is not resolved from that of acapulcoites (as represented by acapulco). in terms of all these properties, nwa 7325 is unlike any known achondrite. however, a rare population of clasts found in polymict ureilites ("the magnesian anorthitic lithology") are strikingly similar to nwa 7325 in mineralogy and mineral compositions, oxygen isotope compositions, and internal textures in plagioclase. these clasts are probably xenolithic in polymict ureilites, and could be pieces of nwa 7325-like meteorites. using constraints from chromium, titanium and oxygen isotopes, we discuss two possible models for the provenance of the nwa 7325 parent body: (1) accretion in the inner solar system from a reservoir similar to that of acapulcoites in δ17o, ɛ54cr and ɛ50ti; or (2) early (<1 ma after cai formation) accretion in the outer solar system (beyond the snow line), before 54cr and 50ti anomalies were introduced to this region of the solar system. the mid-ir emission spectrum of nwa 7325 obtained in this work matches its modal mineralogy, and so can be compared with spectra of new meteorites or asteroids/planets to help identify similar materials and/or the parent body of nwa 7325. | petrogenesis and provenance of ungrouped achondrite northwest africa 7325 from petrology, trace elements, oxygen, chromium and titanium isotopes, and mid-ir spectroscopy |
periodic orbits are important keys to understand the motion of a massless particle in the vicinity of a binary asteroid system. due to the complex gravity generated by the irregular-shaped asteroids, it is difficult to generate periodic orbits with an analytical method, except with the linearized dynamics in a small region around the libration points. this paper has presented a numerical method to search the three-dimensional periodic orbits in a global space. the grid searching method is used to find nearly periodic orbits, and then the shooting method is used to get the accurate periodic orbits. the method is applied to the binary asteroid (66391) 1999 kw4 to solve the periodic orbits in the vicinity. the periodic orbits are then classified into five categories according to their shapes and locations. the search method can also be used to find periodic orbits in the vicinity of other binary systems. | global search for periodic orbits in the irregular gravity field of a binary asteroid system |
context. the nasa origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission has obtained thousands of spectra of asteroid (101955) bennu with the osiris-rex visible and infrared spectrometer.aims: we present a spectral search for minor absorption bands and determine compositional variations on the surface of bennu.methods: reflectance spectra with low and high spatial resolutions were analyzed for evidence of weak absorption bands. spectra were also divided by a global average spectrum to isolate unique spectral features, and variations in the strongest band depths were mapped on a surface shape model. the global visible to near-ir spectrum of bennu shows evidence of several weak absorption bands with depths of a few percent.results: several observed bands are consistent with phyllosilicates, and their distribution correlates with the stronger 2.74-μm hydration band. a 0.55-μm band is consistent with iron oxides and is deepest in the spectrally reddest areas on bennu. the presence of hydrated phyllosilicates and iron oxides indicates substantial aqueous alteration in bennu's past.conclusions: bennu's spectra are not identical to a limited set of carbonaceous chondrite spectra, possibly due to compositional properties and spatial scale differences; however, returned samples should contain a mixture of common chondrite materials. | weak spectral features on (101995) bennu from the osiris-rex visible and infrared spectrometer |
secular oscillations in multiplanet systems can drive chaotic evolution of a small inner body through non-linear resonant perturbations. this 'secular chaos' readily pushes the inner body to an extreme eccentricity, triggering tidal interactions or collision with the central star. we present a numerical study of secular chaos in systems with two planets and test particles using the ring-averaging method, with emphasis on the relationship between the planets' properties and the time-scale and efficiency of chaotic diffusion. we find that secular chaos can excite extreme eccentricities on time-scales spanning several orders of magnitude in a given system. we apply our results to the evolution of planetary systems around white dwarfs (wds), specifically the tidal disruption and high-eccentricity migration of planetesimals and planets. we find that secular chaos in a planetesimal belt driven by large (≳10 m⊕), distant ($\gtrsim 10 \, \mathrm{au}$) planets can sustain metal accretion on to a wd over gyr time-scales. we constrain the total mass of planetesimals initially present within the chaotic zone by requiring that the predicted mass delivery rate to the roche limit be consistent with the observed metal accretion rates of wds with atmospheric pollution throughout the cooling sequence. based on the occurrence of long-period exoplanets and exo-asteroid belts, we conclude that secular chaos can be a significant (perhaps dominant) channel for polluting solitary wds. secular chaos can also produce short-period planets and planetesimals around wds in concert with various circularization mechanisms. we discuss prospects for detecting exoplanets driving secular chaos around wds using direct imaging and microlensing. | secular chaos in white dwarf planetary systems: origins of metal pollution and short-period planetary companions |
aims: the goal of this study is to simulate space weathering processes on primitive bodies. we use ion implantation as a simulation of solar wind irradiation, which has been suggested by several authors to be the major component of space weathering on main belt asteroids. the laboratory analogs we irradiate and analyze are carbonaceous chondrites; we started the study with the allende cv meteorite and in this companion paper we present results on the murchison cm meteorite.methods: we performed irradiations on pressed pellets of murchison with 40 kev he+ and ar+ ions using fluences up to 3 × 1016 ions/cm2. reflectance spectra were acquired ex situ before and after irradiation in the visible to mid-infrared range (0.4-16 μm). a raman analysis was also performed to investigate the modifications of the aromatic carbonaceous component.results: our results indicate that spectral variations after irradiation within the visible range are smaller than spectral variations due to sample grain size or viewing geometry of the murchison meteorite. the aqueous alteration band profile near 3 μm changes after irradiation, as adsorbed water is removed, and phyllosilicates are affected. raman spectroscopy highlights the insoluble organic matter (iom) modification under irradiation. we observe a shift of the silicates band at 9.9 μm, probably due to a preferential loss of mg (compared to fe, the lighter mg is more easily sputtered backward) and/or amorphization of mg-rich materials. we compare our results to previous experiments on organic-rich materials (like asphaltite or carbonaceous chondrites), and on ordinary chondrites and olivine grains. we find that the reddening/darkening trend observed on silicate-rich surfaces is not valid for all carbonaceous chondrites, and that the spectral modifications after irradiation are a function of the initial albedo. | ion irradiation of the murchison meteorite: visible to mid-infrared spectroscopic results |
the hopping dynamics of a lander in single-tidal-locked binary asteroid systems is explored. a coupled orbit-attitude dynamical model of the lander in the body-fixed frame of the secondary is established by considering the non-spherical perturbations from the two bodies. as an approximate model, the binary system is treated as an oblate spheroid-ellipsoid system. lander deployment to the secondary is numerically simulated to examine the motion characteristics by varying the primary mass and system period. two dynamical parameters related to the characteristic properties of the binary system are introduced to reveal the intrinsic reasons for different landing trajectory evolutions. these two dynamical parameters can effectively provide a measure to estimate the hopping evolution in different binary systems. | natural landing dynamics near the secondary in single-tidal-locked binary asteroids |
aims: we present a library of low-resolution meteor spectra that includes sporadic meteors, members of minor meteor showers, and major meteor showers. these meteors are in the magnitude range from +2 to -3, corresponding to meteoroid sizes from 1 mm to 10 mm.methods: parallel double-station video observations allowed us to compute heliocentric orbits for all meteors. most observations were performed during the periods of activity of major meteor showers in the years between 2006 and 2012. spectra are classified according to relative intensities of the low-temperature emission lines of mg, na, and fe.results: shower meteors were found to be of normal composition, except for southern δ aquariids and some members of the geminid shower, neither of which have na in the meteor spectra. variations in na content are typical for the geminid shower. three populations of na-free mereoroids were identified. the first population are iron meteorites, which have an asteroidal-chondritic origin, but one meteoroid with low perihelion (0.11 au) was found among the iron meteorites. the second population were sun-approaching meteoroids in which sodium is depleted by thermal desorption. the third population were na-free meteoroids of cometary origin. long exposure to cosmic rays on the surface of comets in the oort cloud and disintegration of this crust might be the origin of this population of meteoroids. spectra (figs. 17-30) are only, tables 4-6 are also 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/580/a67 | catalogue of representative meteor spectra |
rubble pile asteroids such as (162173) ryugu have large bulk porosities, which are believed to result from void spaces in between the constituent boulders (macroporosity) as well as void spaces within the boulders themselves (microporosity). in general, both macroporosity and microporosity are estimated based on comparisons between the asteroid bulk density and both the bulk and grain density of meteorite analogs, and relatively large macroporosities are usually obtained. here we use semiempirical models for the macroporosity of multicomponent mixtures to determine ryugu's macroporosity based on the observed size-frequency distribution (sfd) of boulders on the surface. we find that ryugu's macroporosity can be significantly smaller than usually assumed, as the observed sfd allows for an efficient packing of boulders, resulting in a macroporosity of 16% ± 3%. therefore, we confirm that ryugu's high bulk porosity is a direct consequence of a very large boulder microporosity. furthermore, using estimates of boulder microporosity of around 50% as derived from in situ measurements, the average grain density in boulders is 2,848 ± 152 kg m-3, similar to values obtained for cm and the tagish lake meteorites. ryugu's bulk porosity corresponding to the above values is 58%. thus, the macroporosity of rubble pile asteroids may have been systematically overestimated in the past. | macroporosity and grain density of rubble pile asteroid (162173) ryugu |
the dynamical environment in the close-proximity of small celestial bodies is characterized by a very weak and irregular gravity field. in this low-acceleration deep-space environment, small dynamical perturbations might affect significantly the dynamics of a spacecraft hovering near the surface of such objects. this poses a challenge to the efficient design of trajectories of space probes for space missions aimed at the exploration of small solar system bodies. this applies especially to cubesats, small spacecraft with limited autonomy and maneuvering capabilities. in this case, a careful and efficient design of the operational trajectory is mandatory to accomplish the objective of the mission. as a representative and timely case study, we investigate the dynamics around binary asteroid (65803) didymos, the target of nasa's double asteroid redirection test (dart) and esa's hera missions. we analyze all the relevant dynamical contributions concurring to the acceleration environment near didymos and provide a subdivision of it into subregions, each identified by a different dynamical regime. with reference to the hera milani cubesat mission scenario, we describe the methodology and design approach to find trajectories in the dayside of didymos system. finally, we provide examples of suitable trajectory options to host the operational phase of the hera milani cubesat. | trajectory options for hera's milani cubesat around (65803) didymos |
pinpoint landing is challenging for future mars and asteroid exploration missions. vision-based navigation scheme based on feature detection and matching is practical and can achieve the required precision. however, existing algorithms are computationally prohibitive and utilize poor-performance measurements, which pose great challenges for the application of visual navigation. this paper proposes an innovative visual navigation scheme using crater edge curves during descent and landing phase. in the algorithm, the edge curves of the craters tracked from two sequential images are utilized to determine the relative attitude and position of the lander through a normalized method. then, considering error accumulation of relative navigation, a method is developed. that is to integrate the crater-based relative navigation method with crater-based absolute navigation method that identifies craters using a georeferenced database for continuous estimation of absolute states. in addition, expressions of the relative state estimate bias are derived. novel necessary and sufficient observability criteria based on error analysis are provided to improve the navigation performance, which hold true for similar navigation systems. simulation results demonstrate the effectiveness and high accuracy of the proposed navigation method. | visual navigation using edge curve matching for pinpoint planetary landing |
the akari irc all-sky survey provided more than twenty thousand thermal infrared observations of over five thousand asteroids. diameters and albedos were obtained by fitting an empirically calibrated version of the standard thermal model to these data. after the publication of the flux catalogue in october 2016, our aim here is to present the akari irc all-sky survey data and discuss valuable scientific applications in the field of small body physical properties studies. as an example, we update the catalogue of asteroid diameters and albedos based on akari using the near-earth asteroid thermal model (neatm). we fit the neatm to derive asteroid diameters and, whenever possible, infrared beaming parameters. we fit groups of observations taken for the same object at different epochs of the survey separately, so we compute more than one diameter for approximately half of the catalogue. we obtained a total of 8097 diameters and albedos for 5170 asteroids, and we fitted the beaming parameter for almost two thousand of them. when it was not possible to fit the beaming parameter, we used a straight line fit to our sample's beaming parameter-versus-phase angle plot to set the default value for each fit individually instead of using a single average value. our diameters agree with stellar-occultation-based diameters well within the accuracy expected for the model. they also match the previous akari-based catalogue at phase angles lower than 50°, but we find a systematic deviation at higher phase angles, at which near-earth and mars-crossing asteroids were observed. the akari irc all-sky survey is an essential source of information about asteroids, especially the large ones, since, it provides observations at different observation geometries, rotational coverages and aspect angles. for example, by comparing in more detail a few asteroids for which dimensions were derived from occultations, we discuss how the multiple observations per object may already provide three-dimensional information about elongated objects even based on an idealised model like the neatm. finally, we enumerate additional expected applications for more complex models, especially in combination with other catalogues. full table 1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/612/a85 | the akari irc asteroid flux catalogue: updated diameters and albedos |
a high-fidelity approach for simulating the aerothermodynamic environments of meteor entries was developed, which allows the commonly assumed heat transfer coefficient of 0.1 to be assessed. this model uses chemically reacting computational fluid dynamics (cfd), coupled with radiation transport and surface ablation. coupled radiation accounts for the impact of radiation on the flowfield energy equations, while coupled ablation explicitly models the injection of ablation products within the flowfield and radiation simulations. for a meteoroid with a velocity of 20 km/s, coupled radiation is shown to reduce the stagnation point radiative heating by over 60%. the impact of coupled ablation (with coupled radiation) is shown to provide at least a 70% reduction in the radiative heating relative to cases with only coupled radiation. this large reduction is partially the result of the low ionization energies of meteoric ablation products relative to air species. the low ionization energies of ablation products, such as mg and ca, provide strong photoionization and atomic line absorption in regions of the spectrum that air species do not. mgo and cao are also shown to provide significant absorption. turbulence is shown to impact the distribution of ablation products through the shock-layer, which results in up to a 100% increase in the radiative heating downstream of the stagnation point. to create a database of heat transfer coefficients, the developed model was applied to a range of cases. this database considered velocities ranging from 14 to 20 km/s, altitudes ranging from 20 to 50 km, and nose radii ranging from 1 to 100 m. the heat transfer coefficients from these simulations are below 0.045 for the range of cases, for both laminar and turbulent, which is significantly lower than the canonical value of 0.1. when the new heat transfer model is applied to a tunguska-like 15 mt entry, the effect of the new model is to lower the height of burst by up to 2 km, depending on assumed entry angle. this, in turn, results in a significantly larger ground damage footprint than when the canonical heating assumption is used. | radiative heating of large meteoroids during atmospheric entry |
cm/ci meteorites range in degree of aqueous alteration suggesting differences in initially accreted materials including water ice and possible spatial heterogeneities within their parent bodies. as alteration progresses, the total abundance and magnesium content of phyllosilicates increases. in this paper we present the results of a coordinated spectral-mineralogical study of a well-characterized suite of cm/ci meteorites that range from 60 to 90% alteration. by acquiring spectra the same meteorite powders as howard et al. (howard, k.t., benedix, g.k., bland, p.a., cressey, g. [2009]. geochim. cosmochim. acta 73, 4576-4589; howard, k.t., benedix, g.k., bland, p.a., cressey, g. [2011]. geochim. cosmochim. acta 75, 2735-2751) and bland et al. (bland, p.a., cressey, g., menzies, o.n. [2004]. meteorit. planet. sci. 39(1), 3-16), we are able for the first time to directly correlate mineralogy with features in reflectance spectra. at visible/near-infrared wavelength, the presence of a 0.7-μm charge transfer band is indicative of aqueous alteration. however, not all altered cm/ci meteorites exhibit this feature; thus the lack of a 0.7 μm absorption band in asteroids does not necessarily signify a lack of aqueous alteration. furthermore, the position and depth of 0.7-μm charge transfer band shows no correlation with the mineralogical changes associated with aqueous alteration. similarly, the near-infrared slope, which is not directly related to the mineralogic progression associated with increasing alteration, is not unambiguously related to degree of alteration in the cm/ci meteorites studied. however, the mid-infrared reflectance spectra of cm/ci meteorites contain a broad absorption feature in the 10-13-μm region, which is a convolution of vibrational features due to mg-rich phyllosilicates and unaltered olivine. the overall feature continuously changes with total phyllosilicate abundance from a shorter wavenumber/longer wavelength peak (815 cm-1, 12.3-μm) for less altered meteorites to a longer wavenumber/shorter wavelength (875 cm-1, 11.4-μm) peak in the highly altered meteorites, with roughly equal spectral contributions producing a doublet in intermediately altered meteorites, using the results from the mid-infrared analyses of meteorite spectra, it is possible to estimate the degree of alteration on dark primitive asteroids. we find asteroid (24) themis to have a 1000-700 cm-1 (10-13-μm) peak at longer wavelengths suggesting themis has a complex surface mineralogy with approximately 70 vol.% phyllosilicates and 25 vol.% anhydrous silicates. | aqueous alteration on asteroids: linking the mineralogy and spectroscopy of cm and ci chondrites |
asteroid (514107) 2015 bz509 was discovered recently in jupiter's co-orbital region with a retrograde motion around the sun. the known chaotic dynamics of the outer solar system have so far precluded the identification of its origin. here, we perform a high-resolution statistical search for stable orbits and show that asteroid (514107) 2015 bz509 has been in its current orbital state since the formation of the solar system. this result indicates that (514107) 2015 bz509 was captured from the interstellar medium 4.5 billion years in the past as planet formation models cannot produce such a primordial large-inclination orbit with the planets on nearly coplanar orbits interacting with a coplanar debris disc that must produce the low-inclination small-body reservoirs of the solar system such as the asteroid and kuiper belts. this result also implies that more extrasolar asteroids are currently present in the solar system on nearly polar orbits. | an interstellar origin for jupiter's retrograde co-orbital asteroid |
the asteroid belt was dynamically shaped during and after planet formation. despite representing a broad ring of stable orbits, the belt contains less than one one-thousandth of an earth mass. the asteroid orbits are dynamically excited with a wide range in eccentricity and inclination and their compositions are diverse, with a general trend toward dry objects in the inner belt and more water-rich objects in the outer belt. here we review models of the asteroid belt's origins and dynamical history. the classical view is that the belt was born with several earth masses in planetesimals, then strongly depleted. however, it is possible that very few planetesimals ever formed in the asteroid region and that the belt's story is one of implantation rather than depletion. a number of processes may have implanted asteroids from different regions of the solar system, dynamically removed them, and excited their orbits. during the gaseous disk phase these include the effects of giant planet growth and migration and sweeping secular resonances. after the gaseous disk phase these include scattering from resident planetary embryos, chaos in the giant planets' orbits, the giant planet instability, and long-term dynamical evolution. different global models for solar system formation imply contrasting dynamical histories of the asteroid belt. vesta and ceres may have been implanted from opposite regions of the solar system -- ceres from the jupiter-saturn region and vesta from the terrestrial planet region -- and could therefore represent very different formation conditions. | origin and dynamical evolution of the asteroid belt |
recently, a nitrogen iceberg was proposed as a possible origin for the first interstellar object, 1i/2017 u1, also known as 'oumuamua. here, we show that the mass budget in exo-pluto planets necessary to explain the detection of 'oumuamua as a nitrogen iceberg chipped off from a planetary surface requires a mass of heavy elements exceeding the total quantity locked in stars with 95% confidence, making the scenario untenable because only a small fraction of the mass in stars ends in exo-plutos. | the mass budget necessary to explain 'oumuamua as a nitrogen iceberg |
mars express, the first european interplanetary mission, carries the mars advanced radar for subsurface and ionosphere sounding (marsis) to search for ice and water in the martian subsurface. developed by an italian-us team, marsis transmits low-frequency, wide-band radio pulses penetrating below the surface and reflected by dielectric discontinuities linked to structural or compositional changes. marsis is also a topside ionosphere sounder, transmitting a burst of short, narrow-band pulses at different frequencies that are reflected by plasma with varying densities at different altitudes. the radar operates since july 2005, after the successful deployment of its 40 m antenna, acquiring data at altitudes lower than 1200 km. subsurface sounding (ss) data are processed on board by stacking together a batch of echoes acquired at the same frequency. on ground, ss data are further processed by correlating the received echo with the transmitted waveform and compensating de-focusing caused by the dispersive ionosphere. ground processing of active ionospheric sounding (ais) data consists in the reconstruction of the electron density profile as a function of altitude. marsis observed the internal structure of planum boreum outlining the basal unit, an icy deposit lying beneath the north polar layered deposits thought to have formed in an epoch in which climate was markedly different from the current one. the total volume of ice in polar layered deposits could be estimated, and parts of the southern residual ice cap were revealed to consist of ≈ 10 m of co2 ice. radar properties of the vastitas borealis formation point to the presence of large quantities of ice buried beneath the surface. observations of the ionosphere revealed the complex interplay between plasma, crustal magnetic field and solar wind, contributing to space weather studies at mars. the presence of three-dimensional plasma structures in the ionosphere was revealed for the first time. marsis could successfully operate at phobos, becoming the first instrument of its kind to observe an asteroid-like body. the main goal pursued by marsis, the search for liquid water beneath the surface, remains elusive. however, because of the many factors affecting detection and of the difficulties in identifying water in radar echoes, a definitive conclusion on its presence cannot yet be drawn. | mars advanced radar for subsurface and ionospheric sounding (marsis) after nine years of operation: a summary |
in this paper, we present masses of 103 asteroids deduced from their perturbations on the orbits of the inner planets, in particular mars and the earth. these determinations and the inpop19a planetary ephemerides are improved by the recent mars orbiter navigation data and the updated orbit of jupiter based on the juno mission data. more realistic mass estimates are computed by a new method based on random monte carlo sampling that uses up-to-date knowledge of asteroid bulk densities. we provide masses with uncertainties better than 33{{ per cent}} for 103 asteroids. deduced bulk densities are consistent with those observed within the main spectroscopic complexes. | asteroid masses obtained with inpop planetary ephemerides |
cloud initialization is a challenge in numerical weather prediction. probably the most relevant observations for this task come from geostationary satellites. these satellites provide the cloud mask with high spatio-temporal resolution and low latencies. the low latency is an attractive option for nowcasting systems such as the solar irradiance nowcasting model mad-wrf. in this study we examine the potential of using the cloud mask from the goes-16 satellite over the contiguous u.s. for this particular application. with this aim, the goes-16 cloud mask product is compared against calipso retrievals during a two year period. both the goes-16 data and the calipso retrievals are interpolated to a grid that covers the contiguous u.s. at 9 km of horizontal grid spacing that is being used in mad-wrf nowcasts. results indicate a probability of detection, or accuracy, of all sky conditions of 86.0%. however, the accuracy is higher for cloud detections, 90.9% than for clear sky detections 74.8%. the lower performance of clear sky retrievals is a result of missdetections during daytime. this is especially clear for summer, and for regions to the north of parallel 36 during winter. however, regions to the south of parallel 36 show acceptable performance during both daytime and nighttime. it is over these regions wherein the cloud mask product should show its largest potential to enhance the cloud initialization in the mad-wrf model. | assessment of the goes-16 clear sky mask product over the contiguous usa using calipso retrievals |
a novel amplitude control method (acm) is proposed to construct multiple self-excited or hidden attractors by scaling partial or total variables without changing their dynamic and topological properties. various attractors including nested attractor, axisymmetric attractor, and centrosymmetric attractor can be obtained by multiplying signals with different amplitudes. an universal pulse control module is designed to realize the amplitude scale. different number of scrolls can be adjusted by regulating the pulse signals without redesigning the nonlinear circuit. the classical lorenz system and jerk system are employed as examples to generate nested hidden multi-butterfly and multiscroll attractors. some novel properties of acm, such as nested morphology, amplitude modulation, and constant lyapunov exponential spectrum, are analyzed theoretically and simulated numerically. the circuit design and pspice simulation results are implemented to verify the availability and feasibility of the proposed approach. | a novel amplitude control method for constructing nested hidden multi-butterfly and multiscroll chaotic attractors |
delivery of water and organics by asteroid and comet impacts may have influenced prebiotic chemistry on the early earth. some recent prebiotic chemistry experiments emphasize hydrogen cyanide (hcn) as a feedstock molecule for the formation of sugars, ribonucleotides, amino acids, and lipid precursors. here, we assess how much hcn originally contained in a comet would survive impact, using parametric temperature and pressure profiles together with a time-dependent chemistry model. we find that hcn survival mainly depends on whether the impact is hot enough to thermally decompose h2o into reactive radicals, and hcn is therefore rather insensitive to the details of the chemistry. in the most favorable impacts (low impact angle, low velocity, small radius), this temperature threshold is not reached, and intact delivery of hcn is possible. we estimate the global delivery of hcn during a period of early and late heavy bombardment of the early earth, as well as local hcn concentrations achieved by individual impacts. in the latter case, comet impacts can provide prebiotically interesting hcn levels for thousands to millions of years, depending on properties of the impactor and of the local environment. | cometary delivery of hydrogen cyanide to the early earth |
the asteroid (16) psyche may be the metal-rich remnant of a differentiated planetesimal, or it may be a highly reduced, metal-rich asteroidal material that never differentiated. the nasa psyche mission aims to determine psyche's provenance. here we describe the possible solar system regions of origin for psyche, prior to its likely implantation into the asteroid belt, the physical and chemical processes that can enrich metal in an asteroid, and possible meteoritic analogs. the spacecraft payload is designed to be able to discriminate among possible formation theories. the project will determine psyche's origin and formation by measuring any strong remanent magnetic fields, which would imply it was the core of a differentiated body; the scale of metal to silicate mixing will be determined by both the neutron spectrometers and the filtered images; the degree of disruption between metal and rock may be determined by the correlation of gravity with composition; some mineralogy (e.g., modeled silicate/metal ratio, and inferred existence of low-calcium pyroxene or olivine, for example) will be detected using filtered images; and the nickel content of psyche's metal phase will be measured using the grns. | distinguishing the origin of asteroid (16) psyche |
context. the jaxa hayabusa2 mission will perform the first ever sample return from a primitive asteroid. the target near-earth asteroid (162173) ryugu will be reached in mid-2018 and its samples will be returned to the earth by the end of 2020.aims: we want to improve the current knowledge of the compositional and rotational properties of ryugu, which are still presenting some uncertainties that might affect the mission operations and scientific return.methods: we acquired high-quality photometric time-series data with the fors2 instrument at the very large telescope of the european southern observatory (eso-vlt, chile). we also acquired four fors2 visible spectra and three x-shooter spectra in the 0.35-2.15 μm range, at different rotational phases.results: we obtained the currently highest-quality visual light-curve of ryugu. a best solution of ~7.63 h is found for the rotational period, while a short-period solution (i.e., p ≈ 3.8 h) is ruled out by the clearly non-symmetric light-curve. the obtained spectra are generally similar and featureless, but present a drop-off of the reflectance at <0.45 μm, suggesting the presence of aqueously altered minerals on ryugu. the best meteorite analogs for ryugu are represented by thermally altered cm carbonaceous chondrites.conclusions: our new photometric data help to refine the target reference model used by the hayabusa2 team for the mission preparation and implementation, improving our knowledge of ryugu's spin properties. our new spectra constrain the compositional and geological context of the ryugu's surface in order to prepare the planning of mission observations and support the working group for the selection of possible landing and sampling sites. based on observations collected at the european organisation for astronomical research in the southern hemisphere under eso programme 097.c-0248. | spectral and rotational properties of near-earth asteroid (162173) ryugu, target of the hayabusa2 sample return mission |
the annual flux of extraterrestrial material on earth is largely dominated by sub-millimetre particles. the mass distribution and absolute value of this cosmic dust flux at the earth's surface is however still uncertain due to the difficulty in monitoring both the collection efficiency and the exposure parameter (i.e. the area-time product in m2.yr). in this paper, we present results from micrometeorite collections originating from the vicinity of the concordia station located at dome c (antarctica), where we performed several independent melts of large volumes of ultra-clean snow. the regular precipitation rate and the exceptional cleanliness of the snow from central antarctica allow a unique control on both the exposure parameter and the collection efficiency. a total of 1280 unmelted micrometeorites (umms) and 808 cosmic spherules (css) with diameters ranging from 30 to 350 μm were identified. within that size range, we measured mass fluxes of 3.0 μg.m-2.yr-1 for umms and 5.6 μg.m-2.yr-1 for css. extrapolated to the global flux of particles in the 12-700 μm diameter range, the mass flux of dust at earth's surface is 5 , 200 ±12001500 tons.yr-1 (1 , 600 ± 500 and 3 , 600 ±7001000 tons.yr-1 of umms and css, respectively). we indicate the statistical uncertainties expected for collections with exposure parameters in the range of 0.1 up to 105 m2.yr. in addition, we estimated the flux of altered and unaltered carbon carried by heated and un-heated particles at earth's surface. the mass distributions of css and umms larger than 100 μm are fairly well reproduced by the cabmod-zody model that includes melting and evaporation during atmospheric entry of the interplanetary dust flux. these numerical simulations suggest that most of the umms and css originate from jupiter family comets and a minor part from the main asteroid belt. the total dust mass input before atmospheric entry is estimated at 15,000 tons.yr-1. the existing discrepancy between the flux data and the model for umms below 100 μm suggests that small fragile umms may evade present day collections, and/or that the amount of small interplanetary particles at 1 au may be smaller than expected. | the micrometeorite flux at dome c (antarctica), monitoring the accretion of extraterrestrial dust on earth |
optical observations of faint meteors (10-7 < mass < 10-4 kg) were collected by the canadian automated meteor observatory between 2010 april and 2014 may. these high-resolution (metre scale) observations were combined with two-station light-curve observations and the meteoroid orbit to classify meteors and attempt to answer questions related to meteoroid fragmentation, strength, and light-curve shape. the f parameter was used to classify the meteor light-curve shape; the observed morphology was used to classify the fragmentation mode; and the tisserand parameter described the origin of the meteoroid. we find that most meteor light curves are symmetric (mean f parameter 0.49), show long distinct trails (continuous fragmentation), and are cometary in origin. meteors that show no obvious fragmentation (presumably single body objects) show mostly symmetric light curves, surprisingly, and this indicates that light-curve shape is not an indication of fragility or fragmentation behaviour. approximately 90 per cent of meteors observed with high-resolution video cameras show some form of fragmentation. our results also show, unexpectedly, that meteors which show negligible fragmentation are more often on high-inclination orbits (i > 60°) than low-inclination ones. we also find that dynamically asteroidal meteors fragment as often as dynamically cometary meteors, which may suggest mixing in the early solar system, or contamination between the dynamic groups. | physical characteristics of faint meteors by light curve and high-resolution observations, and the implications for parent bodies |
detailed observations of the solar system planets reveal a wide variety of local atmospheric conditions. astronomical observations have revealed a variety of extrasolar planets none of which resembles any of the solar system planets in full. instead, the most massive amongst the extrasolar planets, the gas giants, appear very similar to the class of (young) brown dwarfs which are amongst the oldest objects in the universe. despite this diversity, solar system planets, extrasolar planets and brown dwarfs have broadly similar global temperatures between 300 and 2500 k. in consequence, clouds of different chemical species form in their atmospheres. while the details of these clouds differ, the fundamental physical processes are the same. further to this, all these objects were observed to produce radio and x-ray emissions. while both kinds of radiation are well studied on earth and to a lesser extent on the solar system planets, the occurrence of emissions that potentially originate from accelerated electrons on brown dwarfs, extrasolar planets and protoplanetary disks is not well understood yet. this paper offers an interdisciplinary view on electrification processes and their feedback on their hosting environment in meteorology, volcanology, planetology and research on extrasolar planets and planet formation. | atmospheric electrification in dusty, reactive gases in the solar system and beyond |
thermal inertia is a useful property to characterize a planetary surface, since it can be used as a qualitative measure of the regolith grain size. it is expected to vary with heliocentric distance because of its dependence on temperature. however, no previous investigation has conclusively observed a change in thermal inertia for any given planetary body. we have addressed this by using neowise data and the advanced thermophysical model to study the thermophysical properties of the near-earth asteroids (1036) ganymed, (1580) betulia, and (276 049) 2002 ce26 as they moved around their highly eccentric orbits. we confirm that the thermal inertia values of ganymed and 2002 ce26 do vary with heliocentric distance, although the degree of variation observed depends on the spectral emissivity assumed in the thermophysical modelling. we also confirm that the thermal inertia of betulia did not change for three different observations obtained at the same heliocentric distance. depending on the spectral emissivity, the variations for ganymed and 2002 ce26 are potentially more extreme than that implied by theoretical models of heat transfer within asteroidal regoliths, which might be explained by asteroids having thermal properties that also vary with depth. accounting for this variation reduces a previously observed trend of decreasing asteroid thermal inertia with increasing size, and suggests that the surfaces of small and large asteroids could be much more similar than previously thought. furthermore, this variation can affect yarkovsky orbital drift predictions by a few tens of per cent. | observing the variation of asteroid thermal inertia with heliocentric distance |
much attention has been given in the literature to the effects of astrophysical events on human and land-based life. however, little has been discussed on the resilience of life itself. here we instead explore the statistics of events that completely sterilise an earth-like planet with planet radii in the range 0.5-1.5r⊕ and temperatures of ∼300 k, eradicating all forms of life. we consider the relative likelihood of complete global sterilisation events from three astrophysical sources - supernovae, gamma-ray bursts, large asteroid impacts, and passing-by stars. to assess such probabilities we consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in earth's oceans. surprisingly we find that although human life is somewhat fragile to nearby events, the resilience of ecdysozoa such as milnesium tardigradum renders global sterilisation an unlikely event. | the resilience of life to astrophysical events |
micromega is a near-ir hyperspectral microscope designed to characterize in situ the texture and composition of the surface materials of the hayabusa2 target asteroid. micromega is implemented within the mascot lander (ho et al. in space sci. rev., 2016, this issue, doi:10.1007/s11214-016-0251-6). the spectral range (0.99-3.65 μm) and the spectral sampling (20 cm^{-1}) of micromega have been chosen to allow the identification of most potential constituent minerals, ices and organics, within each 25 μm pixel of the 3.2× 3.2 mm2 fov. such an unprecedented characterization will (1) enable the identification of most major and minor phases, including the potential organic phases, and ascribe their mineralogical context, as a critical set of clues to decipher the origin and evolution of this primitive body, and (2) provide the ground truth for the orbital measurements as well as a reference for the analyses later performed on returned samples. | the micromega investigation onboard hayabusa2 |
in fluid dynamics, an important problem is linked to the knowledge of the fluid pressure. recently, another approach to study incompressible fluid flow was suggested. it consists in using a general pressure equation (gpe) derived from compressible navier-stokes equation. in this paper, gpe is considered and compared with the chorin's artificial compressibility method (acm) and the entropically damped artificial compressibility (edac) method. the three methods are discretized in a staggered grid system with second order centered schemes in space and a third order runge-kutta scheme in time. three test cases are realized: two-dimensional taylor-green vortex flow, the traveling wave and the doubly periodic shear layers. it is demonstrated that gpe is accurate and efficient to capture the correct behavior for unsteady incompressible flows. the numerical results obtained by gpe are in excellent agreement with those obtained by acm, edac and a classical finite volume method with a poisson equation. furthermore, gpe convergence is better than acm convergence. the proposed general pressure equation (gpe) allows to solve general, time-accurate, incompressible navier-stokes flows. finally, the parametric study realized in terms of mach and prandtl numbers shows that the velocity divergence can be limited by an arbitrary maximum and that acoustic waves can be damped. | numerical simulations of unsteady viscous incompressible flows using general pressure equation |
the timing and extent to which the initial interstellar material was thermally processed provide fundamental constraints for models of the formation and early evolution of the solar protoplanetary disk. we argue that the nonsolar (solar δ17o ≈ -29‰) and near-terrestrial (δ17o ≈ 0‰) o-isotopic compositions of the earth and most extraterrestrial materials (moon, mars, asteroids, and comet dust) were established very early by heating of regions of the disk that were modestly enriched (dust/gas ≥ 5-10 times solar) in primordial silicates (δ17o ≈ -29‰) and water-dominated ice (δ17o ≈ 24‰) relative to the gas. such modest enrichments could be achieved by grain growth and settling of dust to the midplane in regions where the levels of turbulence were modest. the episodic heating of the disk associated with fu orionis outbursts were the likely causes of this early thermal processing of dust. we also estimate that at the time of accretion the ci chondrite and interplanetary dust particle parent bodies were composed of 5-10% of pristine interstellar material. the matrices of all chondrites included roughly similar interstellar fractions. whether this interstellar material avoided the thermal processing experienced by most dust during fu orionis outbursts or was accreted by the disk after the outbursts ceased to be important remains to be established. | measuring the level of interstellar inheritance in the solar protoplanetary disk |
bright materials have been reported in association with impact craters on ceres. the abundant na2co3 and some ammonium salts, nh4hco3 and/or nh4cl, were detected in bright deposits within occator crater with dawn near infrared spectroscopy. the composition and appearance of the salts suggest their aqueous mobilization and emplacement after formation of the crater. here we consider origins of the bright deposits through calculation of speciation in the h-c-n-o-na-cl water-salt type system constrained by the mass balance of observed salts. calculations of chemical equilibria show that initial solutions had the ph of ∼10. the temperature and salinity of solutions could have not exceeded ∼273 k and ∼100 g per kg h2o, respectively. freezing models reveal an early precipitation of na2co3·10h2o followed by minor nahco3. ammonium salts precipitate near eutectic from brines enriched in nh4+, cl- and na+. a late-stage precipitation of nacl·2h2o is modeled for solution compositions with added nacl. calculated eutectics are above 247 k. the apparently unabundant ammonium and chloride salts in occator's deposits imply a rapid emplacement without a compositional evolution of solution. salty ice grains could have deposited from post-impact ballistic plumes formed through low-pressure boiling of subsurface solutions. hydrated and ammonium salts are unstable at maximum temperatures of ceres' surface and could decompose through space weathering. occator's ice-free salt deposits formed through a post-depositional sublimation of ice followed by dehydration of na2co3·10h2o and nahco3 to na2co3. in other regions, excavated and exposed bright materials could be salts initially deposited from plumes and accumulated at depth via post-impact boiling. the lack of detection of sulfates and an elevated carbonate/chloride ratio in ceres' materials suggest an involvement of compounds abundant in the outer solar system. | aqueous origins of bright salt deposits on ceres |
among solar system materials there are variable degrees of depletion in moderately volatile elements (mves, such as na, k, rb, cu, and zn) relative to the proto-solar composition. whether these depletions are due to nebular and/or parent-body (asteroidal or planetary) processes is still under debate. in order to help decipher the mve abundances in early solar system materials, we conducted a systematic study of high-precision k stable isotopic compositions of a suite of whole-rock samples of well-characterized carbonaceous and ordinary chondrites. we analyzed 16 carbonaceous chondrites (cm1-2, co3, cv3, cr2, ck4-5 and ch3) and 28 ordinary chondrites covering petrological types 3- 6 and chemical groups h, l, and ll. we observed significant k isotope (δ41k) variations (-1.54 to 0.70‰) among the carbonaceous and ordinary chondrites. in general, the two major chondrite groups are distinct: the k isotope compositions of carbonaceous chondrites are largely higher than the bulk silicate earth (bse) value, whereas ordinary chondrites show k isotope compositions that are typically lower than the bse value. neither carbonaceous nor ordinary chondrites show clear/resolvable correlations between k isotopes and chemical groups, petrological types, shock levels, cosmic-ray exposure ages, fall/find occurrence, or terrestrial weathering. importantly, the lack of a clear trend between k isotopes and k content among chondrites indicates that the k isotope fractionations were decoupled from the relative elemental k depletions, which is inconsistent with a single-stage partial vaporization or condensation process to account for these mve depletion patterns among chondrites. the range of k isotope variations in the carbonaceous chondrites in this study is consistent with a four-component (chondrule, refractory inclusion, matrix and water) mixing model that is able to explain the bulk elemental and isotopic compositions of the main carbonaceous chondrite groups, but requires a fractionation in k isotopic compositions in chondrules. we propose that the major control of the isotopic compositions of group averages is condensation and/or vaporization in pre-accretional (nebular) environments that is preserved in the compositional variation of chondrules. parent-body processes, such as aqueous alteration, thermal metamorphism, and metasomatism, can mobilize k and affect the k isotopes in individual samples. in the case of the ordinary chondrites, the full range of k isotopic variations can only be explained by the combined effects of the size and relative abundances of chondrules, parent-body aqueous and thermal alteration, and possible sampling bias. | potassium isotope compositions of carbonaceous and ordinary chondrites: implications on the origin of volatile depletion in the early solar system |
we review the construction of almost contact metric (three-) structures, abbreviated acm(3)s, on manifolds with a $g_2$ structure. these are of interest for certain supersymmetric configurations in string and m-theory. we compute the torsion of the $su(3)$ structure associated to an acms and apply these computations to heterotic $g_2$ systems and supersymmetry enhancement. we initiate the study of the space of acm3ss, which is an infinite dimensional space with a local product structure and interesting topological features. tantalising links between acm3ss and associative and coassociative submanifolds are observed. | almost contact structures on manifolds with a $g_2$ structure |
we present time-resolved visible spectrophotometry of 2020 cd3, the second known minimoon. the spectrophotometry was taken with the keck i/low resolution imaging spectrometer between wavelengths 434 and 912 nm in the b, g, v, r, i, and rg850 filters as it was leaving the earth-moon system on 2020 march 23 utc. the spectrum of 2020 cd3 resembles v-type asteroids and some lunar rock samples with a 434-761 nm reddish slope of ∼18%/100 nm (g-r = 0.62 ± 0.08 and r-i = 0.21 ± 0.06) with an absorption band at ∼900 nm corresponding to i-z = -0.54 ± 0.10. combining our measured h of 31.9 ± 0.1 with an albedo of 0.35 typical for v-type asteroids, we determine 2020 cd3's diameter to be ∼0.9 ± 0.1 m, making it the first minimoon and one of the smallest asteroids to be spectrally studied. we use our time-series photometry to detect significant periodic light-curve variations with a period of ∼573 s and amplitude of ∼1. in addition, we extend the observational arc of 2020 cd3 to 37 days, to 2020 march 23 utc. from the improved orbital solution for 2020 cd3, we estimate the likely duration of its capture to be ∼2 yr and the nongravitational perturbation on its orbit due to radiation pressure with an area-to-mass ratio of (6.9 ± 2.4) × 10-4 m2 kg-1 implying a density of 2.3 ± 0.8 g cm-3, broadly compatible with other meter-scale asteroids and lunar rock. we searched for prediscovery detections of 2020 cd3 in the zwicky transient facility archive as far back as 2018 october but were unable to locate any positive detections. | characterization of temporarily captured minimoon 2020 cd3 by keck time-resolved spectrophotometry |
the discovery of the intact minor planet embedded in the debris disc orbiting sdss j1228+1040 raises questions about the dynamical history of the system. further, the recent passage of the potentially interstellar object 1i/'oumuamua within the solar system has re-ignited interest in minor body flux through exoplanetary systems. here, we utilize the new analytical formalism from grishin et al. (2019) to estimate the rate at which the gaseous components of typical white dwarf discs trap an exo-planetesimal. we compare the types of captured orbits which arise from planetesimals originating from the interstellar medium, exo-kuiper belts, and exo-oort clouds. we find that the rate of interstellar medium injection is negligible, whereas capture of both exo-kuiper and exo-oort cloud planetesimals is viable, but strongly size-dependent. for a gaseous disc which extends much beyond its roche limit, capture is more probable than disruption at the roche limit. we find that the capture probability linearly increases with the radial extent of the disc. even in systems without minor planets, capture of smaller bodies will change the disc size distribution and potentially its temporal variability. our formalism is general enough to be applied to future discoveries of embedded planetesimals in white dwarf debris discs. | embedding planetesimals into white dwarf discs from large distances |
aims: the near-earth asteroid population suggests the existence of an inner main belt source of asteroids that belongs to the spectroscopic x complex and has moderate albedos. the identification of such a source has been lacking so far. we argue that the most probable source is one or more collisional asteroid families that have escaped discovery up to now.methods: we apply a novel method to search for asteroid families in the inner main-belt population of asteroids belonging to the x complex with moderate albedo. instead of searching for asteroid clusters in orbital element space, which could be severely dispersed when older than some billions of years, our method looks for correlations between the orbital semimajor axis and the inverse size of asteroids. this correlation is the signature of members of collisional families that have drifted from a common centre under the effect of the yarkovsky thermal effect.results: we identify two previously unknown families in the inner main belt among the moderate-albedo x-complex asteroids. one of them, whose lowest numbered asteroid is (161) athor, is 3 gyr old, whereas the second one, whose lowest numbered object is (689) zita, could be as old as the solar system. members of this latter family have orbital eccentricities and inclinations that spread them over the entire inner main belt, which is an indication that this family could be primordial, that is, it formed before the giant planet orbital instability.conclusions: the vast majority of moderate-albedo x-complex asteroids of the inner main belt are genetically related, as they can be included into a few asteroid families. only nine x-complex asteroids with moderate albedo of the inner main belt cannot be included in asteroid families. we suggest that these bodies formed by direct accretion of the solids in the protoplanetary disc, and are thus surviving planetesimals. this work is dedicated to the memory of andrea milani, who put the foundation and devoted his scientific career on the study of asteroid families. | ancient and primordial collisional families as the main sources of x-type asteroids of the inner main belt |
context. the asteroid terrestrial-impact last alert system (atlas) is an all-sky survey primarily aimed at detecting potentially hazardous near-earth asteroids. apart from the astrometry of asteroids, it also produces their photometric measurements that contain information about asteroid rotation and their shape.aims: to increase the current number of asteroids with a known shape and spin state, we reconstructed asteroid models from atlas photometry that was available for approximately 180 000 asteroids observed between 2015 and 2018.methods: we made use of the light-curve inversion method implemented in the asteroids@home project to process atlas photometry for roughly 100 000 asteroids with more than a hundred individual brightness measurements. by scanning the period and pole parameter space, we selected those best-fit models that were, according to our setup, a unique solution for the inverse problem.results: we derived ~2750 unique models, 950 of them were already reconstructed from other data and published. the remaining 1800 models are new. about half of them are only partial models, with an unconstrained pole ecliptic longitude. together with the shape and spin, we also determined for each modeled asteroid its color index from the cyan and orange filter used by the atlas survey. we also show the correlations between the color index, albedo, and slope of the phase-angle function.conclusions: the current analysis is the first inversion of atlas asteroid photometry, and it is the first step in exploiting the huge scientific potential that atlas photometry has. atlas continues to observe, and in the future, this data, together with other independent photometric measurements, can be inverted to produce more refined asteroid models. tables a.1-a.4 are only available in electronic form at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/643/a59 | asteroid models reconstructed from atlas photometry |
asteroid mining has been proposed as an approach to complement earth-based supplies of rare earth metals and to supply resources in space, such as water. however, existing studies on the economic viability of asteroid mining do not provide much guidance on which technological improvements would be needed for increasing its economic viability. this paper develops a techno-economic analysis of asteroid mining with the objective of providing basic recommendations for future technology development and performance improvements. both, providing water in space as well as returning platinum to earth are considered. starting from first principles of techno-economic analysis, gradually additional economic and technological factors are added to the analysis model. applied to mining missions involving spacecraft reuse, learning curve effect, and multiple spacecraft, their economic viability is assessed. a sensitivity analysis with respect to throughput rate, spacecraft mass, and resource price is performed. furthermore, a sample asteroid mining architecture for volatiles based on small cubesat-class spacecraft is presented. it is concluded that key technological drivers for asteroid mining missions are throughput rate, number of spacecraft per mission, and the rate in which successive missions are conducted. furthermore, for returning platinum to earth, market reaction strongly influences its economic viability and it seems to be economically viable only under unlikely conditions. | a techno-economic analysis of asteroid mining |
subsequent to the moon's formation, late accretion to the terrestrial planets strongly modified the physical and chemical nature of their silicate crusts and mantles. here, we combine dynamical n-body and monte carlo simulations to determine impact probabilities, impact velocities, and expected mass augmentation onto the terrestrial planets from four sources: planetesimals left over from primary accretion, asteroids from the hypothetical e-belt, the main asteroid belt, and comets arriving from the outer solar system. we present new estimates of the amount of cometary material striking the terrestrial planets in an early (ca. 4480 ma) episode of planetesimal-driven giant planet migration (mojzsis et al., 2019). we conclude that the moon and mars suffer proportionally higher cometary accretion than venus and earth. we further conclude that the background mass addition from small leftover planetesimals to earth and mars is far less than independent estimates based on their respective mantle abundances of highly-siderophile elements and terrestrial tungsten isotopes. this supports the theory that both planets were struck by single large bodies that delivered most of their terminal mass augmentation since primary accretion, rather than a throng of smaller impactors. our calculated lunar, martian and mercurian chronologies use the impacts recorded onto the planets from dynamical simulations rather than relying on the decline of the population as a whole. we present fits to the impact chronologies valid from 4500 ma to ca. 3700 ma by which time the low number of planetesimals remaining in the dynamical simulations causes the impact rate to drop artificially. the lunar timeline obtained from these dynamical simulations using nominal values for the masses of each contributing reservoir is at odds with both the calibrated neukum (neukum et al., 2001) and werner (werner et al., 2014; werner, 2019) chronologies. for mars, the match with its calibrated werner chronology is no better; by increasing the mass of the e-belt by a factor of four the dynamical lunar and martian chronologies are in line with that of werner (2019) and match constraints from the current population of hungaria asteroids. yet, neither of our dynamical timelines fit well with that of neukum. the dynamical lunar and martian chronologies are also different from each other. consequently, the usual extrapolation of such chronologies from one planetary body to the other is technically inappropriate. | impact bombardment chronology of the terrestrial planets from 4.5 ga to 3.5 ga |
we report the mineralogy, petrography, and in situ measured 26al-26mg systematics in chondrules from the least metamorphosed cv3 (vigarano-type) chondrites, kaba and yamato (y) 980145. two y 980145 chondrules measured show no resolvable excesses in 26mg (26mg∗), a decay product of a short-lived (t1/2 ∼0.7 ma) radionuclide 26al. plagioclase in one of the chondrules is replaced by nepheline, indicative of thermal metamorphism. the lack of 26mg∗ in the y 980145 chondrules is most likely due to disturbance of their 26al-26mg systematics during the metamorphism. although kaba experienced extensive metasomatic alteration (<300 °c), it largely avoided subsequent thermal metamorphism, and the 26al-26mg systematics of its chondrules appear to be undisturbed. all eight kaba chondrules measured show 26mg∗, corresponding to the initial 26al/27al ratios [(26al/27al)0] ranging from (2.9 ± 1.7) × 10-6 to (6.3 ± 2.7) × 10-6. if cv parent asteroid accreted rapidly after chondrule formation, the inferred (26al/27al)0 ratios in kaba chondrules provide an upper limit on 26al available in this asteroid at the time of its accretion. the estimated initial abundance of 26al in the cv asteroid is too low to melt it and contradicts the existence of a molten core in this body suggested from the paleomagnetic records of allende [carporzen et al. (2011) magnetic evidence for a partially differentiated carbonaceous chondrite parent body. proc. natl. acad. sci. usa108, 6386-6389] and kaba [gattacceca et al. (2013) more evidence for a partially differentiated cv parent body from the meteorite kaba. lunar planet. sci.44, abstract#1721]. | 26al-26mg systematics in chondrules from kaba and yamato 980145 cv3 carbonaceous chondrites |
aims: we explore the performance of neural networks in automatically classifying asteroids into their taxonomic spectral classes. we particularly focus on what the methodology could offer the esa gaia mission.methods: we constructed an asteroid dataset that can be limited to simulating gaia samples. the samples were fed into a custom-designed neural network that learns how to predict the samples' spectral classes and produces the success rate of the predictions. the performance of the neural network is also evaluated using three real preliminary gaia asteroid spectra.results: the overall results show that the neural network can identify taxonomic classes of asteroids in a robust manner. the success in classification is evaluated for spectra from the nominal 0.45-2.45 μm wavelength range used in the bus-demeo taxonomy, and from a limited range of 0.45-1.05 μm following the joint wavelength range of gaia observations and the bus-demeo taxonomic system.conclusions: the obtained results indicate that using neural networks to execute automated classification is an appealing solution for maintaining asteroid taxonomies, especially as the size of the available datasets grows larger with missions like gaia. | asteroid spectral taxonomy using neural networks |
we introduce adam, the all-data asteroid modelling algorithm. adam is simple and universal since it handles all disk-resolved data types (adaptive optics or other images, interferometry, and range-doppler radar data) in a uniform manner via the 2d fourier transform, enabling fast convergence in model optimization. the resolved data can be combined with disk-integrated data (photometry). in the reconstruction process, the difference between each data type is only a few code lines defining the particular generalized projection from 3d onto a 2d image plane. occultation timings can be included as sparse silhouettes, and thermal infrared data are efficiently handled with an approximate algorithm that is sufficient in practice because of the dominance of the high-contrast (boundary) pixels over the low-contrast (interior) pixels. this is of particular importance to the raw alma data that can be directly handled by adam without having to construct the standard image. we study the reliability of the inversion, using the independent shape supports of function series and control-point surfaces. when other data are lacking, one can carry out fast non-convex lightcurve-only inversions, but any shape models resulting from it should only be taken as illustrative large-scale models. the code 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/a8 | adam: a general method for using various data types in asteroid reconstruction |
we performed pulsed laser irradiation to simulate the progressive space weathering of three individual chips of the cm2 murchison meteorite. after irradiation, we performed two-step laser desorption mass spectrometry to analyze alterations in the concentration, distribution, and functional group chemistry of organics in the samples. these results indicate an increase in the concentration of aromatic organic species in the irradiated regions of the samples compared to the unirradiated areas. we utilized optical reflectance spectroscopy, fourier-transform infrared spectroscopy, and mössbauer spectroscopy to investigate changes in the spectral characteristics of the samples as a result of simulated progressive space weathering. we observed an overall decrease in reflectance spectra of the irradiated samples. the spectra also exhibit a bluing trend after irradiation, the degree of which weakens with progressive laser exposure. finally, we used scanning electron microscopy and transmission electron microscopy to examine changes in microstructure and chemistry of the irradiated samples. we observed vesicles and nanoparticles in the melt layers produced by laser irradiation. our results indicate that the nanoparticle compositions evolve with increasing laser irradiation, progressing from a mineralogically diverse group towards a population dominated by fe-ni-sulfides. radiative transfer models were used to examine the influence of various nanoparticle compositions on sample spectral properties, the results of which indicate nanoparticle size and mineralogy may result in competing spectral effects. we discuss the implications these experiments have for the space weathering of primitive, organic-rich asteroids. | the effect of progressive space weathering on the organic and inorganic components of a carbonaceous chondrite |
determining compositional trends among individual minerals is key to understanding the thermodynamic conditions under which they formed and altered, and is also essential to maximizing the scientific value of small extraterrestrial samples, including returned samples and meteorites. here we report the chemical compositions of fe-sulfides, focusing on the pyrrhotite-group sulfides, which are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and in small solar system bodies. our data show that while there are trends with the at.% fe/s ratio of pyrrhotite with thermal and aqueous alteration in some meteorite groups, there is a universal trend between the fe/s ratio and degree of oxidation. relatively reducing conditions led to the formation of troilite during: (1) chondrule formation in the protoplanetary disk (i.e., pristine chondrites) and (2) parent body thermal alteration (i.e., ll4 to ll6, cr1, cm, and cy chondrites). oxidizing and sulfidizing conditions led to the formation of fe-depleted pyrrhotite with low fe/s ratios during: (1) aqueous alteration (i.e., cm and ci chondrites), and (2) thermal alteration (i.e., ck and r chondrites). the presence of troilite in highly aqueously altered carbonaceous chondrites (e.g., cy, cr1, and some cm chondrites) indicates they were heated after aqueous alteration. the presence of troilite, fe-depleted pyrrhotite, or pyrite in a chondrite can provide an estimate of the oxygen and sulfur fugacities at which it was formed or altered. the data reported here can be used to estimate the oxygen fugacity of formation and potentially the aqueous and/or thermal histories of sulfides in extraterrestrial samples, including those returned by the hayabusa2 mission and due to be returned by the osiris-rex mission in the near future. | the fe/s ratio of pyrrhotite group sulfides in chondrites: an indicator of oxidation and implications for return samples from asteroids ryugu and bennu |
antarctic carbonaceous chondrite (cc) meteorite chip samples in the japanese and us collections have been studied by an ultraviolet (uv), visible (vis), and near-infrared (nir) (uvvnir) spectrometer and a fourier-transform infrared (ftir) spectrometer, targeting small areas of about 2-6 mm in diameter. uvvnir and ftir reflectance spectra of 169 spots on 148 cc chips were measured on their naturally broken surfaces with no sample preparation. among them, 83 spectra were accepted as reasonably free of terrestrial weathering or surface texture effects. x-ray diffraction (xrd) and ftir measurements of a weathered sample revealed that gypsum likely formed on its surface after recovery from antarctica. principal component analysis (pca) of the uvvnir-ftir combined spectra allowed distinguishing powder and chip or surface texture and identifying their class and thermal metamorphism. gaussian fitting of the 3 μm absorption band of hydrous cc samples allowed for removal of the spectral effects of adsorbed h2o and for the extraction of structural absorption bands which are characteristic of cc classes and degree of aqueous alteration. these results suggest that cc-like rocks on small asteroids without fine regolith can be identified through spectral reflectance measurements by spacecraft, landers, or rovers. | uv-visible-infrared spectral survey of antarctic carbonaceous chondrite chips |
the arrival of the robustly hyperbolic asteroid a/2017 u1 has potentially interesting ramifications for the planet-formation process. although extrapolations from a sample size of one are necessarily uncertain, order-of-magnitude estimates suggest that the galaxy contains a substantial mass in similar bodies. we argue that despite its lack of coma, a/2017 u1 likely contained a significant mass fraction of volatile components, and we argue that its presence can be used to infer a potentially large population of as-yet undetected neptune-like extrasolar planets. | on the consequences of the detection of an interstellar asteroid |
we report on the results of a systematic search for associated asteroid families for all active asteroids known to date. we find that 10 out of 12 main-belt comets (mbcs) and five out of seven disrupted asteroids are linked with known or candidate families, rates that have ∼0.1% and ∼6% probabilities, respectively, of occurring by chance, given the overall family association rate of 37% for asteroids in the main asteroid belt. we find previously unidentified family associations between 238p/read and the candidate gorchakov family, 311p/panstarrs and the candidate behrens family, 324p/la sagra and the alauda family, 354p/linear and the baptistina family, p/2013 r3-b (catalina-panstarrs) and the mandragora family, p/2015 x6 (panstarrs) and the aeolia family, p/2016 g1 (panstarrs) and the adeona family, and p/2016 j1-a/b (panstarrs) and the theobalda family. all mbcs with family associations belong to families that contain asteroids with primitive taxonomic classifications and low average reported albedos (\overline{{p}v}≲ 0.10), while disrupted asteroids with family associations belong to families that contain asteroids that span wider ranges of taxonomic types and average reported albedos (0.06< \overline{{p}v}< 0.25). these findings are consistent with mbc activity being closely correlated to composition (i.e., whether an object is likely to contain ice), while disrupted asteroid activity is not as sensitive to composition. given our results, we describe a sequence of processes by which the formation of young asteroid families could lead to the production of present-day mbcs. | asteroid family associations of active asteroids |
the acapulcoites and lodranites are rare groups of primitive achondrites that originate from a common parent body and are of particular interest since they experienced only partial melting. we calculated thermal evolution and differentiation models of the parent body of the acapulco-lodran meteorite clan. the models were compared to the maximum metamorphic temperatures, differentiation degree, and thermo-chronological data available. an optimized set of parameters which fits to the data was determined: a radius of ≈ 260 km, a formation time of ≈ 1.7 ma after cais and an initial temperature of ≈ 250 k. the burial depths derived are 7-13 km. the respective layers experienced minor melting and small-scale melt migration, matching the differentiation degree of the meteorites. the resulting structure has an iron core, a silicate mantle, a partially differentiated layer, and an undifferentiated outer shell. our results indicate a larger size, an earlier formation time, and a formation closer to the sun of the parent body of acapulcoites and lodranites than typical estimates for ordinary chondritic parent bodies, consistent with a stronger thermal metamorphism. the burial depths support excavation by a single impact. the presence of core and mantle indicates that these meteorites could share a common parent body with differentiated stony and iron meteorites. | modeling the evolution of the parent body of acapulcoites and lodranites: a case study for partially differentiated asteroids |
a fast radio burst (frb) was recently detected to be associated with a hard x-ray burst from the galactic magnetar sgr 1935+2154. scenarios involving magnetars for frbs are hence highly favored. in this work, we suggest that the impact between an asteroid and a magnetar could explain such a detection. according to our calculations, an asteroid of mass 1020 g will be disrupted at a distance of 7 × 109 cm when approaching the magnetar. the accreted material will flow along the magnetic field lines from the alfvén radius ∼107 cm. after falling onto the magnetar's surface, an instant accretion column will be formed, producing a comptonized x-ray burst and an frb in the magnetosphere. we show that all the observational features of frb 200428 could be interpreted self-consistently in this scenario. we predict quasi-periodic oscillations in this specific x-ray burst, which can serve as an independent observational test. | frb 200428: an impact between an asteroid and a magnetar |
this pds data set represents a compilation of published diameters, optical albedos, near-infrared albedos, and beaming parameters for minor planets detected by neowise during the fully cryogenic, 3-band cryo, post-cryo and neowise-reactivation years 1 through 3 operations. it contains data covering near-earth asteroids, main belt asteroids, active main belt objects, hildas, jupiter trojans, centaurs, and jovian and saturnian irregular satellites. methodology for physical property determination is described in the referenced articles. | neowise diameters and albedos v2.0 |
photometry from the helios and stereo spacecraft revealed regions of enhanced sky surface-brightness suggesting a narrow circumsolar ring of dust associated with venus’s orbit. we model this phenomenon by integrating the orbits of 10,000,000+ dust particles subject to gravitational and non-gravitational forces, considering several different kinds of plausible dust sources. we find that only particles from a hypothetical population of venus co-orbital asteroids can produce enough signal in a narrow ring to match the observations. previous works had suggested such objects would be dynamically unstable. however, we re-examined the stability of asteroids in 1:1 resonance with venus and found that ∼8% should survive for the age of the solar system, enough to supply the observed ring. | co-orbital asteroids as the source of venus's zodiacal dust ring |
our knowledge of white dwarf planetary systems predominately arises from the region within a few solar radii of the white dwarfs, where minor planets breakup, form rings and discs, and accrete on to the star. the entry location, angle, and speed into this roche sphere has rarely been explored but crucially determines the initial geometry of the debris, accretion rates on to the photosphere, and ultimately the composition of the minor planet. here, we evolve a total of over 105 asteroids with single-planet n-body simulations across the giant branch and white dwarf stellar evolution phases to quantify the geometry of asteroid injection into the white dwarf roche sphere as a function of planetary mass and eccentricity. we find that lower planetary masses increase the extent of anisotropic injection and decrease the probability of head-on (normal to the roche sphere) encounters. our results suggest that one can use dynamical activity within the roche sphere to make inferences about the hidden architectures of these planetary systems. | the entry geometry and velocity of planetary debris into the roche sphere of a white dwarf |
we describe the fall of annama meteorite occurred in the remote kola peninsula (russia) close to finnish border on 2014 april 19 (local time). the fireball was instrumentally observed by the finnish fireball network. from these observations the strewnfield was computed and two first meteorites were found only a few hundred metres from the predicted landing site on 2014 may 29 and 30, so that the meteorite (an h5 chondrite) experienced only minimal terrestrial alteration. the accuracy of the observations allowed a precise geocentric radiant to be obtained, and the heliocentric orbit for the progenitor meteoroid to be calculated. backward integrations of the orbits of selected near-earth asteroids and the annama meteoroid showed that they rapidly diverged so that the annama meteorites are unlikely related to them. the only exception seems to be the recently discovered 2014ur116 that shows a plausible dynamic relationship. instead, analysis of the heliocentric orbit of the meteoroid suggests that the delivery of annama onto an earth-crossing apollo-type orbit occurred via the 3:1 mean motion resonance with jupiter or the nu6 secular resonance, dynamic mechanisms that are responsible for delivering to earth most meteorites studied so far. | orbit and dynamic origin of the recently recovered annama's h5 chondrite |
the rubble pile spin barrier is an upper limit on the rotation rate of asteroids larger than ∼200-300 m. among thousands of asteroids with diameters larger than ∼300 m, only a handful of asteroids are known to rotate faster than 2.0 h, all are in the sub-km range (⩽0.6 km). here we present photometric measurements suggesting that (60716) 2000 gd65, an s-complex, inner-main belt asteroid with a relatively large diameter of 2.3-0.7+0.6km , completes one rotation in 1.9529 ± 0.0002h . its unique diameter and rotation period allow us to examine scenarios about asteroid internal structure and evolution: a rubble pile bound only by gravity; a rubble-pile with strong cohesion; a monolithic structure; an asteroid experiencing mass shedding; an asteroid experiencing yorp spin-up/down; and an asteroid with a unique octahedron shape results with a four-peak lightcurve and a 3.9 h period. we find that the most likely scenario includes a lunar-like cohesion that can prevent (60716) 2000 gd65 from disrupting without requiring a monolithic structure or a unique shape. due to the uniqueness of (60716) 2000 gd65, we suggest that most asteroids typically have smaller cohesion than that of lunar regolith. | a 2 km-size asteroid challenging the rubble-pile spin barrier - a case for cohesion |
discs of bodies orbiting a much more massive central object are extremely common in astrophysics. when the orbits comprising such discs are eccentric, we show they are susceptible to a new dynamical instability. gravitational forces between bodies in the disc drive exponential growth of their orbital inclinations and clustering in their angles of pericentre, expanding an initially thin disc into a conical shape by giving each orbit an identical `tilt' with respect to the disc plane. this new instability dynamically produces the unusual distribution of orbits observed for minor planets beyond neptune, suggesting that the instability has shaped the outer solar system. it also implies a large disc mass (∼ 1-10 earth masses) of scattered bodies at hundreds of au; we predict increasing numbers of detections of minor planets clustered in their angles of pericentre with high inclinations. | a new inclination instability reshapes keplerian discs into cones: application to the outer solar system |
the most dramatic phases of terrestrial planet formation are thought to be oligarchic and chaotic growth, on timescales of up to 100-200 myr, when violent impacts occur between large planetesimals of sizes up to protoplanets. such events are marked by the production of large amounts of debris, as has been observed in some exceptionally bright and young debris disks (termed extreme debris disks). here we report five years of spitzer measurements of such systems around two young solar-type stars: id8 and p1121. the short-term (weekly to monthly) and long-term (yearly) disk variability is consistent with the aftermaths of large impacts involving large asteroid-sized bodies. we demonstrate that an impact-produced clump of optically thick dust, under the influence of the dynamical and viewing geometry effects, can produce short-term modulation in the disk light curves. the long-term disk flux variation is related to the collisional evolution within the impact-produced fragments once released into a circumstellar orbit. the time-variable behavior observed in the p1121 system is consistent with a hypervelocity impact prior to 2012 that produced vapor condensates as the dominant impact product. two distinct short-term modulations in the id8 system suggest two violent impacts at different times and locations. its long-term variation is consistent with the collisional evolution of two different populations of impact-produced debris dominated by either vapor condensates or escaping boulders. the bright, variable emission from the dust produced in large impacts from extreme debris disks provides a unique opportunity to study violent events during the era of terrestrial planet formation. | extreme debris disk variability: exploring the diverse outcomes of large asteroid impacts during the era of terrestrial planet formation |
the properties of the first-discovered interstellar object (iso), 1i/2017 ('oumuamua), differ from both solar system asteroids and comets, casting doubt on a protoplanetary disk origin. in this study, we investigate the possibility that it formed with a substantial h2 ice component in the starless core of a giant molecular cloud. while interstellar solid hydrogen has yet to be detected, this constituent would explain a number of the iso's properties. we consider the relevant processes required to build decameter-sized, solid hydrogen bodies and assess the plausibility of growth in various size regimes. via an energy balance argument, we find the most severe barrier to formation is the extremely low temperature required for the favorability of molecular hydrogen ice. however, if deposition occurs, we find that the turbulence within starless cores is conducive for growth into kilometer-sized bodies on sufficiently short timescales. then, we analyze mass loss in the interstellar medium and determine the necessary size for a hydrogen object to survive a journey to the solar system as a function of iso age. finally, we discuss the implications if the h2 explanation is correct, and we assess the future prospects of iso science. if hydrogen ice isos do exist, our hypothesized formation pathway would require a small population of porous, 100 μm dust in a starless core region that has cooled to 2.8 k via adiabatic expansion of the surrounding gas and excellent shielding from electromagnetic radiation and cosmic rays. | assessing the formation of solid hydrogen objects in starless molecular cloud cores |
the k2 mission of the kepler space telescope allowed the observations of light curves of small solar system bodies throughout the whole solar system. in this paper, we present the results of a collection of k2 trans-neptunian object observations between campaigns c03 (2014 november-2015 february) and c19 (2018 august-september), which includes 66 targets. due to the faintness of our targets, the detectability rate of a light-curve period is ~56%, notably lower than in the case of other small-body populations, like hildas or jovian trojans. we managed to obtain light-curve periods with an acceptable confidence for 37 targets; the majority of these cases are new identifications. we were able to give light-curve amplitude upper limits for the other 29 targets. several of the newly detected light-curve periods are longer than ~24 hr, in many cases close to ~80 hr; i.e., these targets are slow rotators. this relative abundance of slowly rotating objects is similar to that observed among hildas, jovian trojans, and centaurs in the k2 mission, as well as among main belt asteroids measured with the tess space telescope. trans-neptunian objects show notably higher light-curve amplitudes at large (d ≳ 300 km) sizes than found among large main belt asteroids, in contrast to the general expectation that due to their lower compressive strength, they reach hydrostatic equilibrium at smaller sizes than their inner solar system counterparts. | light curves of trans-neptunian objects from the k2 mission of the kepler space telescope |
although solar system bodies exhibit large variations in their volatile element abundances, the mechanisms and conditions that lead to these variations remain ambiguous. the howardite-eucrite-diogenite (hed) meteorites that likely sample the asteroid 4 vesta, provide evidence for extensive volatile depletion on their parent body. isotopic variations in moderately volatile elements, such as zn, have been used to track the origin of such volatile loss. although not nominally volatile, cr is useful because it has several oxidized gas species that render it volatile under the oxidizing conditions that characterize planetary accretion. as such, volatile loss of cr has the potential to produce an isotopically light evaporation residue under an equilibrium regime. this contrasts with other moderately volatile elements that show heavy isotope enrichments in the residue following both kinetic or equilibrium fractionation. here, we report the cr stable isotope composition of 11 eucrites and four diogenites. the eucrites possess systematically lighter cr isotope compositions than diogenites, which is onset by the accumulation of isotopically heavy cr3+-rich orthopyroxene and spinel in diogenites during their magmatic evolution. we estimate for the primary eucrite melt with mg# ≈ 50, a δ53cr (53cr/52cr deviation relative to nist srm 979 in per mile) of -0.22 ± 0.03‰ (2sd), lighter than any chondritic meteorite group by ∼0.1‰. this deficit may result from either partial melting with residual cr3+-bearing phases (e.g. chromite) that retain heavy isotopes, or from vapor loss that occurred at equilibrium with a magma ocean on vesta. isotopic fractionation during partial melting would necessitate implausibly high cr contents in the vestan mantle, and oxygen fugacities high enough to stabilize chromite in the mantle source. isotopic fractionation during evaporation would require an oxidized vapor and a reduced residue, as predicted by thermodynamic constraints on the composition of the vapor phase above a silicate magma ocean. therefore, this cr isotopic deficit between vesta and chondrites may be caused by cr loss at relatively high oxygen fugacity in a gas phase at equilibrium with the liquid from which it evolved. temperatures of volatile loss are estimated to be lower than 2300 k, consistent with loss from a large-scale magma ocean model for formation of vesta, which may be a common evolutionary stage in accreting planetesimals. | tracking the volatile and magmatic history of vesta from chromium stable isotope variations in eucrite and diogenite meteorites |
we present an analysis of new and published data on p/2013 r3, the first asteroid detected while disintegrating. thirteen discrete components are measured in the interval between ut 2013 october 01 and 2014 february 13. we determine a mean, pair-wise velocity dispersion among these components of δv = 0.33 ± 0.03 m s-1 and find that their separation times are staggered over an interval of ∼5 months. dust enveloping the system has, in the first observations, a cross-section of ∼30 km2 but fades monotonically at a rate consistent with the action of radiation pressure sweeping. the individual components exhibit comet-like morphologies and also fade except where secondary fragmentation is accompanied by the release of additional dust. we find only upper limits to the radii of any embedded solid nuclei, typically ∼100-200 m (geometric albedo 0.05 assumed). combined, the components of p/2013 r3 would form a single spherical body with a radius of ≲ 400 m, which is our best estimate of the size of the precursor object. the observations are consistent with rotational disruption of a weak (cohesive strength of ∼50 to 100 n m-2) parent body, ∼400 m in radius. estimated radiation (yorp) spin-up times of this parent are ≲ 1 {myr}, shorter than the collisional lifetime. if present, water ice sublimating at as little as 10-3 kg s-1 could generate a torque on the parent body rivaling the yorp torque. under conservative assumptions about the frequency of similar disruptions, the inferred asteroid debris production rate is ≳103 kg s-1, which is at least 4% of the rate needed to maintain the zodiacal cloud. | anatomy of an asteroid breakup: the case of p/2013 r3 |
this paper aims to propose a novel approach to classify acoustic emission (ae) signals deriving from corrosion experiments, even if embedded into a noisy environment. to validate this new methodology, synthetic data are first used throughout an in-depth analysis, comparing random forests (rf) to the k-nearest neighbor (k-nn) algorithm. moreover, a new evaluation tool called the alter-class matrix (acm) is introduced to simulate different degrees of uncertainty on labeled data for supervised classification. then, tests on real cases involving noise and crevice corrosion are conducted, by preprocessing the waveforms including wavelet denoising and extracting a rich set of features as input of the rf algorithm. to this end, a software called rf-cam has been developed. results show that this approach is very efficient on ground truth data and is also very promising on real data, especially for its reliability, performance and speed, which are serious criteria for the chemical industry. | classification of acoustic emission signals using wavelets and random forests : application to localized corrosion |
the propagation of hopping trajectories with uncertainties is investigated over the surface of small celestial bodies. an intuitive geometric description of the accessible area referred to as the potential hop reachable domain, is provided when considering the uncertainties of the hopping rover's state variables as well as the asteroid's system parameters. a method to solve the envelope of the potential hop reachable domain is proposed by taking into account multi-hopping trajectories, which is applied to the asteroid 101955 bennu. the influences of the state variables and asteroid physical parameters' uncertainties on the propagation of hopping trajectories are discussed in detail. a comparison between the solved potential hop reachable domain and the monte carlo simulation is carried out to show the effectiveness of the method in this paper. | potential hop reachable domain over surfaces of small bodies |
china will launch in the forthcoming years a sample return mission called zhenghe, to asteroid 469219 kamo`oalewa (provisional designation 2016ho3) and comet 133p/elst-pizarro. the mission will consist of an orbiter and a nano-lander. one of zhenghe's investigations is the radio science experiment, whose main objective is the asteroid gm estimate. in this paper, we conduct full numerical simulations of the radio science experiment using the wudogs software package, developed by wuhan university. in addition to two-way doppler measurements, we also include one-way on-board distance measurements. a list of parameters including the spacecraft initial conditions and the global asteroid gm are solved using a weighted least-squares fit. the simulation results indicate that the gm solution is very sensitive to the ephemeris error. we need an accuracy within 2 km on the ephemeris of the asteroid to achieve a reliable estimate of gm. | a simulated global gm estimate of the asteroid 469219 kamo`oalewa for china's future asteroid mission |
contact. the nasa new frontiers asteroid sample return mission origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) has provided a large amount of data on the asteroid (101955) bennu, including high-quality spectra obtained by the osiris-rex visible and infrared spectrometer (ovirs).aims: to better constrain the surface properties and compositional variations of bennu, we studied the visible and near-infrared spectral behavior across the asteroid surface by means of a statistical analysis aiming to distinguish spectrally distinct groups, if present.methods: we applied the g-mode multivariate statistical analysis to the near-infrared ovirs spectra to obtain an automatic statistical clustering at different confidence levels.results: the statistical analysis highlights spectral variations on the surface of bennu. five distinct spectral groups are identified at a 2σ confidence level. at a higher confidence level of 3σ, no grouping is observed.conclusions: the results at a 2σ confidence level distinguish a dominant spectral behavior group (group 1, background) and four small groups showing spectral slope variations, associated with areas with different surface properties. the background group contains most of the analyzed data, which implies a globally homogeneous surface at the spectral and spatial resolution of the data. the small groups with redder spectra are concentrated around the equatorial ridge and are associated with morphological surface features such as specific craters and boulders. no significant variation is detected in the band area or depth of the 2.74 μm band, which is associated with hydrated phyllosilicate content. the spectral slope variations are interpreted as a consequence of different regolith particle sizes, and/or porosity, and/or space weathering, that is, the presence of more or less fresh material. the osiris-rex mission primary sampling site, nightingale, and a boulder known as the roc, are redder than the background surface. | osiris-rex spectral analysis of (101955) bennu by multivariate statistics |
near-earth asteroids (neas) are organized into five main classes: amor, apollo, aten, atira and 'ayló'chaxnim. asteroids belonging to the 'ayló'chaxnim class are located entirely within the orbit of venus making them difficult to detect by ground-based observatories. the first-known asteroid of this class, (594913) 'ayló'chaxnim, was discovered by the zwicky transient facility (ztf) in 2020 january during a twilight search for asteroids at small solar elongations that ran between september 2019 and january 2020. due to its large diameter of ∼2 km, the discovery of (594913) 'ayló'chaxnim is surprising because contemporary nea population models predict a scarcity of asteroids of this size located inside the orbit of venus. to compare the discovery of (594913) 'ayló'chaxnim by ztf with the predictions of nea population models, we estimated the ztf survey completeness at detecting 'ayló'chaxnim asteroids and the number of 'ayló'chaxnim asteroids expected to have been discovered by simulating observations of synthetic 'ayló'chaxnim asteroids. we find that the 'ayló'chaxnim population completeness of the survey is ∼18% and there is only a 5% probability that a single 'ayló'chaxnim asteroid would have been discovered. given the small chance for (594913) 'ayló'chaxnim to have been discovered, its presence is either a statistical fluke or it implies that asteroid population models may need to be revised. | preliminary estimates of the zwicky transient facility 'ayló'chaxnim asteroid population completeness |
in order to determine the controls on the reflectance spectra of hydrated carbonaceous chondrites, reflectance spectra were measured for a series of samples with well-determined mineralogy, water-content, and thermal history. this includes 5 cr chondrites, 11 cm chondrites, and 7 thermally metamorphosed cm chondrites. these samples were characterized over the 0.35-150 μm range by reflectance spectroscopy in order to cover the full spectral range accessible from ground based observation, and that will be determined in the near-future by the hayabusa-2 and osiris-rex missions. while spectra show absorption features shortward of 35 μm, no strong absorption bands were identified in this suite of samples longward of 35 μm. this work shows that the 0.7-μm band observed in hydrated carbonaceous chondrites is correlated with the total water content as well as with the band depth at 2.7 μm, confirming the suggestion that they are related to mg-rich, fe-bearing phyllosilicates. a feature at 2.3 μm, diagnostic of such phyllosilicates was found for all samples with a detectable 0.7-μm band, also indicative of mg-rich phyllosilicates. a strong variability is found in the shape of the 3-μm band among cm chondrites, and between cm, cr and thermally metamorphosed cm chondrites. heavily altered cm chondrites show a single strong band around 2.72 μm while more thermally metamorphosed cm samples show an absorption band at higher wavelength. the cr chondrite gro 95577 has a 3-μm feature very similar to those of extensively altered cm chondrites while other cr chondrite rather shows goethite-like signatures (possibly due to terrestrial weathering of metals). thermally metamorphosed cm chondrites all have 3-μm features, which are not purely due to terrestrial adsorbed water. the band shape ranges from heavily altered cm-like to goethite-like. the overall reflectance was found to be significantly higher for cr chondrites than for cm chondrites. this is also true for the hydrated cr chondrite gro 95577 whose reflectance spectrum is almost identical to spectra obtained for cm chondrites except that it is brighter by about 40% in the visible. another possibility to distinguish hydrated cm from hydrated cr chondrites is to use the combination of band depths at 0.7 and 2.3 μm. when comparing the spectra obtained with cg and cgh spectral end member, it is found that the band depth determined for hydrated chondrites (0.7 and 2.3 μm) are always higher than calculated for these spectral endmembers. if one considers only asteroids with unambiguous hydration detection, band depth at 0.7 μm is of similar value to those measured for hydrated carbonaceous chondrites. | what is controlling the reflectance spectra (0.35-150 μm) of hydrated (and dehydrated) carbonaceous chondrites? |
the thermophysical properties of small solar system bodies are essential to be determined, on which the thermal evolution of small bodies largely depends. the carbonaceous asteroid ryugu is one of the small undifferentiated bodies formed in the early solar system. hayabusa2 explored the asteroid ryugu and returned the surface samples in 2020 for detailed on-ground investigation, including measurements of thermal properties. because the available sample amount was limited, this study developed a novel method to measure the thermal diffusivity of small and irregularly shaped samples of about 1 mm in diameter by combining lock-in thermography and periodic heating methods on the microscale. this method enables us to measure the thermal diffusivity of both flat-plate and granular shape samples by selecting the suitable detecting direction of the temperature response. especially, when the sample has a flat-plate shape, the anisotropic distribution of the in-plane thermal diffusivity can be evaluated. this method was applied to six ryugu samples, and the detailed anisotropic distribution of the thermal diffusivity was obtained. the measurement results showed that the samples show local thermal anisotropy caused by cracks and voids. the average thermal diffusivity among all samples was (2.8 to 5.8) × 10-7 m2.s. based on the density and specific heat of the samples obtained independently, the thermal effusivity was estimated to be 791 j.(s1/2.m2.k) to 1253 j.(s1/2.m2.k), which is defined as the resistance of surface temperature to the change of thermal input. the determined thermal effusivity, often called thermal inertia in planetary science, is larger than the observed value of 225 ± 45 j. (s1/2.m2.k) of the asteroid ryugu's surface, obtained from the diurnal temperature change of the rotating asteroid by a thermal infrared camera onboard hayabuas2. this difference is likely to be attributed to the difference in the analytical scale between the sample and the surface boulders compared with the thermal diffusion length. consequently, it was found that the present result is more representative of the thermal diffusivity and thermal inertia of local part of individual ryugu particles. | measurement of microscopic thermal diffusivity distribution for ryugu sample by infrared lock-in periodic heating method |
polluted white dwarfs (wds) offer a unique way to study the bulk compositions of exoplanetary material, but it is not always clear if this material originates from comets, asteroids, moons, or planets. we combine n-body simulations with an analytical model to assess the prevalence of extrasolar moons as wd polluters. using a sample of observed polluted wds, we find that the extrapolated parent body masses of the polluters are often more consistent with those of many solar system moons, rather than solar-like asteroids. we provide a framework for estimating the fraction of wds currently undergoing observable moon accretion based on results from simulated wd planetary and moon systems. focusing on a three-planet wd system of super-earth to neptune-mass bodies, we find that we could expect about one percent of such systems to be currently undergoing moon accretions as opposed to asteroid accretion. | exomoons as sources of white dwarf pollution |
biological communities on the abyssal plain are largely dependent on detritus from the surface ocean as their main source of energy. seasonal fluctuations in the deposition of that detritus cause temporal variations in the quantity and quality of food available to these communities, altering their structure and the activity of the taxa present. however, direct observations of energy acquisition in relation to detritus availability across megafaunal taxa in abyssal communities are few. we used time-lapse photography and coincident measurement of organic matter flux from water column sediment traps to examine the impact of seasonal detrital inputs on resource acquisition by the deposit feeding megafauna assemblages at two sites: station m (northeast pacific, 4000 m water depth) and the porcupine abyssal plain sustained observatory (pap-so, northeast atlantic 4850 m water depth). at station m, studied over 18-months, the seasonal particle flux was followed by a salp deposition event. at that site, diversity in types of deposit feeding was related to seabed cover by detritus. at pap-so, studied over 30 months, the seasonal particle flux consisted of two peaks annually. while the two study sites were similar in mean flux (~8.0 mgc m-2 d-1), the seasonality in the flux was greater at pap-so. the mean overall tracking at pap-so was five times that of station m (1.9 and 0.4 cm2 h-1, respectively); both are likely underestimated because tracking by some common taxa at both sites could not be quantified. at both sites, responses of deposit-feeding megafauna to the input of detritus were not consistent across the taxa studied. the numerically-dominant megafauna (e.g. echinoids, large holothurians and asteroids) did not alter their deposit feeding in relation to the seasonality in detrital supply. taxa for which deposit feeding occurrence or rate were correlated to seasonality in particle flux were relatively uncommon (e.g. enteropneusta), known to cache food (e.g. echiurans), or to be highly selective for fresh detritus (e.g. the holothurian oneirophanta mutabilis). thus, the degree of seasonality in deposit feeding appeared to be taxon-specific and related to natural history characteristics such as feeding and foraging modes. | response of deep-sea deposit-feeders to detrital inputs: a comparison of two abyssal time-series sites |
all asteroids are currently classified as either family, originating from the disruption of known bodies1, or non-family. an outstanding question is the origin of these non-family asteroids. were they formed individually, or as members of known families but with chaotically evolving orbits, or are they members of old ghost families, that is, asteroids with a common parent body but with orbits that no longer cluster in orbital element space? here, we show that the sizes of the non-family asteroids in the inner belt are correlated with their orbital eccentricities and anticorrelated with their inclinations, suggesting that both non-family and family asteroids originate from a small number of large primordial planetesimals. we estimate that 85% of the asteroids in the inner main belt originate from the flora, vesta, nysa, polana and eulalia families, with the remaining 15% originating from either the same families or, more likely, a few ghost families. these new results imply that we must seek explanations for the differing characteristics of the various meteorite groups in the evolutionary histories of a few, large, precursor bodies2. our findings also support the model that asteroids formed big through the gravitational collapse of material in a protoplanetary disk3. | the common origin of family and non-family asteroids |
the microwave power absorption efficiency of the μ10 ecr ion thruster, utilized in the japanese asteroid explorers hayabusa and hayabusa2, is investigated in order to allow performance measurement and provide information for its improvement. a model detailing the local electron behavior in a real ecr plasma discharge, based the magnetic field characteristics, is presented. three methods to evaluate the microwave power absorption efficiency are proposed: an estimation based on the chamber geometry and magnetic field characteristics, a measuremen based on performance parameters and a measurement performed with langmuir probes. the equations used for each method are analytically derived. the local electron behavior model is confirmed with a langmuir probe experiment. measurement of the microwave power absorption efficiency is performed with the two independent methods proposed. results from the two experiments show good agreement with each other and with the theory. finally, a diffusion model explaining the different electron temperature distributions observed in the chamber is proposed. the model and experiments clarify the physics behind previously observed performance variations and give valuable hints for future chamber improvement. | microwave power absorption to high energy electrons in the ecr ion thruster |
context. information about the spin state of asteroids is important for our understanding of the dynamical processes affecting them. however, spin properties of asteroids are known for only a small fraction of the whole population.aims: to enlarge the sample of asteroids with a known rotation state and basic shape properties, we combined sparse-in-time photometry from the lowell observatory database with flux measurements from nasa's wise satellite.methods: we applied the light curve inversion method to the combined data. the thermal infrared data from wise were treated as reflected light because the shapes of thermal and visual light curves are similar enough for our purposes. while sparse data cover a wide range of geometries over many years, wise data typically cover an interval of tens of hours, which is comparable to the typical rotation period of asteroids. the search for best-fitting models was done in the framework of the asteroids@home distributed computing project.results: by processing the data for almost 75 000 asteroids, we derived unique shape models for about 900 of them. some of them were already available in the damit database and served us as a consistency check of our approach. in total, we derived new models for 662 asteroids, which significantly increased the total number of asteroids for which their rotation state and shape are known. for another 789 asteroids, we were able to determine their sidereal rotation period and estimate the ecliptic latitude of the spin axis direction. we studied the distribution of spins in the asteroid population. apart from updating the statistics for the dependence of the distribution on asteroid size, we revealed a significant discrepancy between the number of prograde and retrograde rotators for asteroids smaller than about 10 km.conclusions: combining optical photometry with thermal infrared light curves is an efficient approach to obtaining new physical models of asteroids. the amount of asteroid photometry is continuously growing and joint inversion of data from different surveys could lead to thousands of new models in the near future. tables a.1 and a.2 are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/617/a57 | asteroid models reconstructed from the lowell photometric database and wise data |
in 2018, the mother spacecraft of the hayabusa2 mission will release the lander mascot above the surface of the asteroid (162173) ryugu. the lander will impact the regolith layer of the asteroid at low speed. while the descent trajectory of mascot is well determined before its release, its behavior once it touches the surface of ryugu remains a great unknown. predictions of the contact properties as a function of the assumed regolith properties and landing geometry (e.g., energy after bounce if not zero, collision duration…) are extremely valuable in terms of landing site selection and interpretation of the data acquired during and after landing. in this study, we use the n-body code pkdgrav to perform more than 480 numerical simulations of the first contact between the lander mascot and a granular medium representing the regolith layer. we explore the influence of several input parameters on the outcomes of the contact. these parameters are related to the lander, the grains of the regolith and the layer thickness. we identify a certain number of trends for the lander's behavior, depending on the configuration of the contact, and perform a statistical analysis of the most critical output parameters. we also investigate the ejected material and show that, in addition to the data acquired from the lander itself, a post-impact visualization of the contact site(s) may help to infer non-observable properties of the regolith layer. our results provide some insights on several input parameters that are implemented in the study of mascot's whole trajectory. this work is a starting point of a much broader study, aiming to explore as widely as possible the parameter space associated with a low-speed impact of a lander onto a regolith layer. | numerical simulations of the contact between the lander mascot and a regolith-covered surface |
the orbital structure of the asteroid belt holds a record of the solar system’s dynamical history. the current belt only contains ∼10-3 earth masses yet the asteroids’ orbits are dynamically excited, with a large spread in eccentricity and inclination. in the context of models of terrestrial planet formation, the belt may have been excited by jupiter’s orbital migration. the terrestrial planets can also be reproduced without invoking a migrating jupiter; however, as it requires a severe mass deficit beyond earth’s orbit, this model systematically under-excites the asteroid belt. here we show that the orbits of the asteroids may have been excited to their current state if jupiter’s and saturn’s early orbits were chaotic. stochastic variations in the gas giants’ orbits cause resonances to continually jump across the main belt and excite the asteroids’ orbits on a timescale of tens of millions of years. while hydrodynamical simulations show that the gas giants were likely in mean motion resonance at the end of the gaseous disk phase, small perturbations could have driven them into a chaotic but stable state. the gas giants’ current orbits were achieved later, during an instability in the outer solar system. although it is well known that the present-day solar system exhibits chaotic behavior, our results suggest that the early solar system may also have been chaotic. | the asteroid belt as a relic from a chaotic early solar system |
with approximately one ninth of earth's mass, mars is widely considered to be a stranded planetary embryo that never became a fully-grown planet. a currently popular planet formation theory predicts that mars formed near earth and venus and was subsequently scattered outwards to its present location. in such a scenario, the compositions of the three planets are expected to be similar to each other. however, bulk elemental and isotopic data for martian meteorites demonstrate that key aspects of mars' composition are markedly different from that of earth. this suggests that mars formed outside of the terrestrial feeding zone during primary accretion. it is therefore probable that mars always remained significantly farther from the sun than earth; its growth was stunted early and its mass remained relatively low. here we identify a potential dynamical pathway that forms mars in the asteroid belt and keeps it outside of earth's accretion zone while at the same time accounting for strict age and compositional constraints, as well as mass differences. our uncommon pathway (approximately 2% probability) is based on the grand tack scenario of terrestrial planet formation, in which the radial migration by jupiter gravitationally sculpts the planetesimal disc at mars' current location. we conclude that mars' formation requires a specific dynamical pathway, while this is less valid for earth and venus. we further predict that mars' volatile budget is most likely different from earth's and that venus formed close enough to our planet that it is expected to have a nearly identical composition from common building blocks. | the cool and distant formation of mars |
context. in the core accretion scenario of planet formation, rocky cores grow by first accreting solids until they are massive enough to accrete gas. for giant planet formation, this means that a massive core must form within the lifetime of the gas disk. inspired by observations of solar system features such as the asteroid and kuiper belts, the accretion of roughly kilometre-sized planetesimals is traditionally considered as the main accretion mechanism of solids but such models often result in longer planet formation timescales. the accretion of millimetre- to centimetre-sized pebbles, on the other hand, allows for rapid core growth within the disk lifetime. the two accretion mechanisms are typically discussed separately.aims: we investigate the interplay between the two accretion processes in a disk containing both pebbles and planetesimals for planet formation in general and in the context of giant planet formation specifically. the goal is to disentangle and understand the fundamental interactions that arise in such hybrid pebble-planetesimal models laying the groundwork for informed analysis of future, more complex, simulations.methods: we combined a simple model of pebble formation and accretion with a global model of planet formation which considers the accretion of planetesimals. we compared synthetic populations of planets formed in disks composed of different amounts of pebbles and 600 metre-sized planetesimals to identify the impact of the combined accretion scenario. on a system level, we studied the formation pathway of giant planets in these disks.results: we find that, in hybrid disks containing both pebbles and planetesimals, the formation of giant planets is strongly suppressed, whereas, in a pebbles-only or planetesimals-only scenario, giant planets can form. we identify the heating associated with the accretion of up to 100 kilometre-sized planetesimals after the pebble accretion period to delay the runaway gas accretion of massive cores. coupled with strong inward type-i migration acting on these planets, this results in close-in icy sub-neptunes originating from the outer disk.conclusions: we conclude that, in hybrid pebble-planetesimal scenarios, the late accretion of planetesimals is a critical factor in the giant planet formation process and that inward migration is more efficient for planets in increasingly pebble-dominated disks. we expect a reduced occurrence rate of giant planets in planet formation models that take the accretion of pebbles and planetesimals into account. | the interplay between pebble and planetesimal accretion in population synthesis models and its role in giant planet formation |
context. asteroids orbiting into the highly magnetized and highly relativistic wind of a pulsar offer a favorable configuration for repeating fast radio bursts (frb). the body in direct contact with the wind develops a trail formed of a stationary alfvén wave, called an alfvén wing. when an element of wind crosses the alfvén wing, it sees a rotation of the ambient magnetic field that can cause radio-wave instabilities. in the observer's reference frame, the waves are collimated in a very narrow range of directions, and they have an extremely high intensity. a previous work, published in 2014, showed that planets orbiting a pulsar can cause frbs when they pass in our line of sight. we predicted periodic frbs. since then, random frb repeaters have been discovered.aims: we present an upgrade of this theory with which repeaters can be explained by the interaction of smaller bodies with a pulsar wind.methods: considering the properties of relativistic alfvén wings attached to a body in the pulsar wind, and taking thermal consideration into account, we conducted a parametric study.results: we find that frbs, including the lorimer burst (30 jy), can be explained by small-size pulsar companions (1 to 10 km) between 0.03 and 1 au from a highly magnetized millisecond pulsar. some parameter sets are also compatible with a magnetar. our model is compatible with the high rotation measure of frb 121102. the bunched timing of the frbs is the consequence of a moderate wind turbulence. an asteroid belt composed of fewer than 200 bodies would suffice for the frb occurrence rate measured with frb 121102.conclusions: after this upgrade, this model is compatible with the properties discovered since its first publication in 2014, when repeating frbs were still unknown. it is based on standard physics and on common astrophysical objects that can be found in any type of galaxy. it requires 1010 times less power than (common) isotropic-emission frb models. | repeating fast radio bursts caused by small bodies orbiting a pulsar or a magnetar |
context. dynamical models of solar system evolution have suggested that the so-called p- and d-type volatile-rich asteroids formed in the outer solar system beyond neptune's orbit and may be genetically related to the jupiter trojans, comets, and small kuiper belt objects (kbos). indeed, the spectral properties of p- and d-type asteroids resemble that of anhydrous cometary dust.aims: we aim to gain insights into the above classes of bodies by characterizing the internal structure of a large p- and d-type asteroid.methods: we report high-angular-resolution imaging observations of the p-type asteroid (87) sylvia with the very large telescope spectro-polarimetric high-contrast exoplanet research (sphere) instrument. these images were used to reconstruct the 3d shape of sylvia. our images together with those obtained in the past with large ground-based telescopes were used to study the dynamics of its two satellites. we also modeled sylvia's thermal evolution.results: the shape of sylvia appears flattened and elongated (a/b ~1.45; a/c ~1.84). we derive a volume-equivalent diameter of 271 ± 5 km and a low density of 1378 ± 45 kg m−3. the two satellites orbit sylvia on circular, equatorial orbits. the oblateness of sylvia should imply a detectable nodal precession which contrasts with the fully-keplerian dynamics of its two satellites. this reveals an inhomogeneous internal structure, suggesting that sylvia is differentiated.conclusions: sylvia's low density and differentiated interior can be explained by partial melting and mass redistribution through water percolation. the outer shell should be composed of material similar to interplanetary dust particles (idps) and the core should be similar to aqueously altered idps or carbonaceous chondrite meteorites such as the tagish lake meteorite. numerical simulations of the thermal evolution of sylvia show that for a body of such a size, partial melting was unavoidable due to the decay of long-lived radionuclides. in addition, we show that bodies as small as 130-150 km in diameter should have followed a similar thermal evolution, while smaller objects, such as comets and the kbo arrokoth, must have remained pristine, which is in agreement with in situ observations of these bodies. nasa lucy mission target (617) patroclus (diameter ≈140 km) may, however, be differentiated. tables a.1, b.1, c.1 and c.2 and the reduced and deconvolved sphere images are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/650/a129 based on observations made with eso telescopes at the la silla paranal observatory under program 073.c-0851 (pi merline), 073.c-0062 (pi marchis), 085.c-0480 (pi nitschelm), 088.c-0528 (pi rojo), 199.c-0074 (pi vernazza). | evidence for differentiation of the most primitive small bodies |
in this work we present the design of the atlas unit (asteroid terrestrial-impact last alert system) that will be installed at teide observatory in tenerife island (spain). atlas-teide will be built by the instituto de astrofisica de canarias (iac) and will be operated as part of the atlas network in the framework of an operation and science exploitation agreement between the iac and the atlas team at university of hawaii. atlas-teide will be the first atlas unit based on commercial on the shelf (cots) components. its design is modular, each module (building block) consist of four celestron rasa 11 telescopes that point to the same sky field, equipped with qhy600pro cmos cameras on an equatorial direct drive mount. each module is equivalent to a 56cm effective diameter telescope and provides a 7.3 deg^2 field of view and a 1.26 arcsec/pix plate scale. atlas-teide will consist of four atlas modules in a roll-off roof building. this configuration allows to cover the same sky area of the actual atlas telescopes. the first atlas module was installed in november 2022 in an existing clamshell at the to. this module (atlas-p) is being used as a prototype to test the system capabilities, develop the needed software (control, image processing, etc.) and complete the fully integration of atlas-teide in the atlas network. the preliminary results of the tests are presented here, and the benefits of the new atlas design are discussed. | atlas-teide: the next generations of atlas units for the teide observatory |
we report the methods of and initial scientific inferences from the extraction of precision photometric information for the >800 trans-neptunian objects (tnos) discovered in the images of the dark energy survey (des). scene-modeling photometry is used to obtain shot-noise-limited flux measures for each exposure of each tno, with background sources subtracted. comparison of double-source fits to the pixel data with single-source fits are used to identify and characterize two binary tno systems. a markov chain monte carlo method samples the joint likelihood of the intrinsic colors of each source as well as the amplitude of its flux variation, given the time series of multiband flux measurements and their uncertainties. a catalog of these colors and light-curve amplitudes a is included with this publication. we show how to assign a likelihood to the distribution q(a) of light-curve amplitudes in any subpopulation. using this method, we find decisive evidence (i.e., evidence ratio <0.01) that cold classical (cc) tnos with absolute magnitude 6 < hr< 8.2 are more variable than the hot classical (hc) population of the same hr , reinforcing theories that the former form in situ and the latter arise from a different physical population. resonant and scattering tnos in this hrrange have variability consistent with either the hcs or ccs. des tnos with hr< 6 are seen to be decisively less variable than higher-hrmembers of any dynamical group, as expected. more surprising is that detached tnos are decisively less variable than scattering tnos, which requires them to have distinct source regions or some subsequent differential processing. | photometry of outer solar system objects from the dark energy survey. i. photometric methods, light-curve distributions, and trans-neptunian binaries |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.