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a new (improved) model of inflation and primordial black hole (pbh) formation is proposed by combining the starobinsky model of inflation, appleby–battye–starobinsky (abs) model of dark energy, and a quantum correction in the modified f(r) gravity. the energy scale parameter in the abs model is taken to be close to the inflationary scale, in order to describe double inflation instead of dark energy. the quantum correction is given by the term quartic in the spacetime scalar curvature r with a negative coefficient (−δ) in the f(r) function. it is demonstrated that very good agreement (within 1σ) with current measurements of the cosmic microwave background (cmb) radiation can be achieved by choosing the proper value of δ, thus solving the problem of low values of the tilt of cmb scalar perturbations in the earlier proposed model in arxiv:2205.00603. a large (by a factor of 107 against cmb) enhancement in the power spectrum of scalar perturbations is achieved by fine tuning the parameters of the model. it is found by numerical analysis that it can lead to formation of asteroid-size pbhs with masses up to 1020 g, which may form dark matter in the current universe. | improved model of primordial black hole formation after starobinsky inflation |
it is well known that the near-earth objects population is sustained by bodies that migrate inwards from the main asteroid belt and outer regions of the solar system. in this work, we aim to revisit the dynamic evolution of the neo population inside the solar system using a known debiased population of large objects. therefore, we separate the phase space into five different regions: near-earth objects (neo), main asteroid belt (mab), jupiter family comets (jfc), centaurs (cen), and trans-neptunian objects. we performed numerical simulations for 985 neos for 100 myrs and tracked their transferences between regions to determine the most common routes and fates for this population. the results show that solar thermal disruption is the most efficient mechanism to remove neos because 70% of the studied objects are led to this fate. also, 13% of the objects are ejected from the solar system, representing a significant contribution of interstellar minor bodies from the neo population. we find that, during their dynamical evolution, more than half of the objects are first transferred to the jfc region and an even larger percentage of them make their way out from the solar system through it. there is also a significant frequent exchange of bodies between neo and mab regions. almost 30% of the bodies move to the mab region, but less than 1% of them end their lives inside it, so it seems that for this sample of objects, mab is a transitional region where escaped neos briefly pass through. we also found that only about 14% of the bodies never leave the neo region. from those, about half of them collide with the terrestrial planets, while the remaining either survive for the whole integration of 100 myrs or move to a low pericenter orbit. additionally, we show that almost 10% of the studied sample can reach the cen region and remain there for a substantial amount of time, telling a different side of the story for the neo population. | the known large near-earth objects' highways: dynamical evolution, fates, and lifetimes |
our knowledge of the internal structure of asteroids is, so far, indirect - relying entirely on inferences from remote sensing observations of the surface, and theoretical modeling of formation and evolution. what are the bulk properties of the regolith and deep interior? and what are the physical processes that shape asteroid internal structures? is the composition and size distribution observed on the surface representative of the bulk? these questions are crucial to understand small bodies' history from accretion in the early solar system to the present, and direct measurements are needed to answer these questions for the benefit of science as well as for planetary defense or exploration. radar is one of the main instruments capable of sounding asteroids to characterize internal structure from sub-meter to global scale. in this paper, we review the science case for direct observation of the deep internal structure and regolith of a rocky asteroid of kilometer size or smaller. we establish the requirements and model dielectric properties of asteroids to outline a possible instrument suite, and highlight the capabilities of radar instrumentation to achieve these observations. we then review the expected science return including secondary objectives contributing to the determination of the gravitational field, the shape model, and the dynamical state. this work is largely inherited from marcopolo-r and aida/aim studies. | direct observations of asteroid interior and regolith structure: science measurement requirements |
aims: we present a study of the spectrophotometric properties of dwarf planet ceres in the visual-to-infrared (vis-ir) spectral range by means of hyper-spectral images acquired by the vir imaging spectrometer on board the nasa dawn mission.methods: disk-resolved observations with a phase angle within the 7° <α < 132° interval were used to characterize ceres' phase curve in the 0.465-4.05 μm spectral range. hapke's model was applied to perform the photometric correction of the dataset to standard observation geometry at vis-ir wavelength, allowing us to produce albedo and color maps of the surface. the v-band magnitude phase function of ceres has been computed from disk-resolved images and fitted with both the classical linear model and h-g formalism.results: the single-scattering albedo and the asymmetry parameter at 0.55 μm are w = 0.14 ± 0.02 and ξ = -0.11 ± 0.08, respectively (two-lobe henyey-greenstein phase function); at the same wavelength, ceres' geometric albedo as derived from our modeling is 0.094 ± 0.007; the roughness parameter is bar{θ=29° ± 6°}. albedo maps indicate small variability on a global scale with an average reflectance at standard geometry of 0.034 ± 0.003. nonetheless, isolated areas such as the occator bright spots, haulani, and oxo show an albedo much higher than average. we measure a significant spectral phase reddening, and the average spectral slope of ceres' surface after photometric correction is 1.1% kå-1 and 0.85% kå-1 at vis and ir wavelengths, respectively. broadband color indices are v-r = 0.38 ± 0.01 and r-i = 0.33 ± 0.02. color maps show that the brightest features typically exhibit smaller slopes. the h-g modeling of the v-band magnitude phase curve for α < 30° gives h = 3.14 ± 0.04 and g = 0.10 ± 0.04, while the classical linear model provides v(1,1,0°) = 3.48 ± 0.03 and β = 0.036 ± 0.002. the comparison of our results with spectrophotometric properties of other minor bodies indicates that ceres has a less back-scattering phase function and a slightly higher albedo than comets and c-type objects. however, the latter represents the closest match in the usual asteroid taxonomy. | spectrophotometric properties of dwarf planet ceres from the vir spectrometer on board the dawn mission |
asteroid 2008 tc3 (approximately 4 m diameter) was tracked and studied in space for approximately 19 h before it impacted earth's atmosphere, shattering at 44-36 km altitude. the recovered samples (>680 individual rocks) comprise the meteorite almahata sitta (ahs). approximately 50-70% of these are ureilites (ultramafic achondrites). the rest are chondrites, mainly enstatite, ordinary, and rumuruti types. the goal of this work is to understand how fragments of so many different types of parent bodies became mixed in the same asteroid. almahata sitta has been classified as a polymict ureilite with an anomalously high component of foreign clasts. however, we calculate that the mass of fallen material was ≤0.1% of the pre-atmospheric mass of the asteroid. based on published data for the reflectance spectrum of the asteroid and laboratory spectra of the samples, we infer that the lost material was mostly ureilitic. therefore, 2008 tc3 probably contained only a few percent nonureilitic materials, similar to other polymict ureilites except less well consolidated. from available data for the ahs meteorite fragments, we conclude that 2008 tc3 samples essentially the same range of types of ureilitic and nonureilitic materials as other polymict ureilites. we therefore suggest that the immediate parent of 2008 tc3 was the immediate parent of all ureilitic material sampled on earth. we trace critical stages in the evolution of that material through solar system history. based on various types of new modeling and re-evaluation of published data, we propose the following scenario. (1) the ureilite parent body (upb) accreted 0.5-0.6 ma after formation of calcium-aluminum-rich inclusions (cai), beyond the ice line (outer asteroid belt). differentiation began approximately 1 ma after cai. (2) the upb was catastrophically disrupted by a major impact approximately 5 ma after cai, with selective subsets of the fragments reassembling into daughter bodies. (3) either the upb (before breakup), or one of its daughters (after breakup), migrated to the inner belt due to scattering by massive embryos. (4) one daughter (after forming in or migrating to the inner belt) became the parent of 2008 tc3. it developed a regolith, mostly ≥3.8 ga ago. clasts of enstatite, ordinary, and rumuruti-type chondrites were implanted by low-velocity collisions. (5) recently, the daughter was disrupted. fragments were injected or drifted into earth-crossing orbits. 2008 tc3 comes from outer layers of regolith, other polymict ureilites from deeper regolith, and main group ureilites from the interior of this body. in contrast to other models that have been proposed, this model invokes a stochastic history to explain the unique diversity of foreign materials in 2008 tc3 and other polymict ureilites. | origin and history of ureilitic material in the solar system: the view from asteroid 2008 tc3 and the almahata sitta meteorite |
the june 2, 2018 impact of asteroid 2018 la over botswana is only the second asteroid detected in space prior to impacting over land. here, we report on the successful recovery of meteorites. additional astrometric data refine the approach orbit and define the spin period and shape of the asteroid. video observations of the fireball constrain the asteroid's position in its orbit and were used to triangulate the location of the fireball's main flare over the central kalahari game reserve. twenty three meteorites were recovered. a consortium study of eight of these classifies motopi pan as an hed polymict breccia derived from howardite, cumulate and basaltic eucrite, and diogenite lithologies. before impact, 2018 la was a solid rock of ~156 cm diameter with high bulk density ~2.85 g cm−3, a relatively low albedo pv ~ 0.25, no significant opposition effect on the asteroid brightness, and an impact kinetic energy of ~0.2 kt. the orbit of 2018 la is consistent with an origin at vesta (or its vestoids) and delivery into an earth impacting orbit via the ν6 resonance. the impact that ejected 2018 la in an orbit toward earth occurred 22.8 ± 3.8 ma ago. zircons record a concordant u pb age of 4563 ± 11 ma and a consistent 207pb/206pb age of 4563 ± 6 ma. a much younger pb pb phosphate resetting age of 4234 ± 41 ma was found. from this impact chronology, we discuss what is the possible source crater of motopi pan and the age of vesta's veneneia impact basin. | the impact and recovery of asteroid 2018 la |
this paper investigates the laser polarization error in the optical rotation detection system (ords) of an atomic comagnetometer (acm), which will seriously degrade the long-term performance of the ords. we first establish an optical transmission model of the ords by using jones matrix concerning the optical imperfection of polarizers. then, we analyze the polarization error based on this model and propose a novel error suppression method. finally, we experimentally test the long-term performance of the ords and the acm before and after the polarization error suppression to verify the effectiveness of the proposed method. the experimental results show that the long-term performance of the ords and the acm can be improved by approximately 3.4 times with the proposed polarization error suppression method. | analysis and suppression of the polarization error for the optical rotation detection system in an atomic comagnetometer |
the origins, spectral-interpretation, resource-identification, security and regolith-explorer (osiris-rex) spacecraft supports all aspects of the mission science objectives, from extensive remote sensing at the asteroid bennu, to sample collection and return to earth. in general, the success of planetary missions requires the collection, return, and analysis of data, which in turn depends on the successful operation of instruments and the host spacecraft. in the case of osiris-rex, a sample-return mission, the spacecraft must also support the acquisition, safe stowage, and return of the sample. the target asteroid is bennu, a b-class near-earth asteroid roughly 500 m diameter. the lockheed martin-designed and developed osiris-rex spacecraft draws significant heritage from previous missions and features the touch-and-go-sample-acquisition-mechanism, or tagsam, to collect sample from the surface of bennu. lockheed martin developed tagsam as a novel, simple way to collect samples on planetary bodies. during short contact with the asteroid surface, tagsam releases curation-grade nitrogen gas, mobilizing the surface regolith into a collection chamber. the contact surface of tagsam includes "contact pads", which are present to collect surface grains that have been subject to space weathering. extensive 1-g laboratory testing, "reduced-gravity" testing (via parabolic flights on an airplane), and analysis demonstrate that tagsam will collect asteroid material in nominal conditions, and a variety of off-nominal conditions, such as the presence of large obstacles under the tagsam sampling head, or failure in the sampling gas firing. tagsam, and the spacecraft support of the instruments, are central to the success of the mission. | the osiris-rex spacecraft and the touch-and-go sample acquisition mechanism (tagsam) |
a distinct set of broad emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 μm, is often detected in protoplanetary disks (ppds). these features are commonly attributed to polycyclic aromatic hydrocarbons (pahs). we model these emission features in the infrared spectra of 69 ppds around 14 t tauri and 55 herbig ae/be stars in terms of astronomical pahs. for each ppd, we derive the size distribution and the charge state of the pahs. we then examine the correlations of the pah properties (i.e., sizes and ionization fractions) with the stellar properties (e.g., stellar effective temperature, luminosity, and mass). we find that the characteristic size of the pahs tends to correlate with the stellar effective temperature ({t}{eff}) and interpret this as the preferential photodissociation of small pahs in systems with higher {t}{eff} of which the stellar photons are more energetic. in addition, the pah size shows a moderate correlation with the red-ward wavelength shift of the 7.7 μm pah feature that is commonly observed in disks around cool stars. the ionization fraction of pahs does not seem to correlate with any stellar parameters. this is because the charging of pahs depends on not only the stellar properties (e.g., {t}{eff}, luminosity) but also their spatial distribution in the disks. the marginally negative correlation between pah size and stellar age suggests that continuous replenishment of pahs via the outgassing of cometary bodies and/or the collisional grinding of planetesimals and asteroids is required to maintain the abundance of small pahs against complete destruction by photodissociation. | polycyclic aromatic hydrocarbons in protoplanetary disks around herbig ae/be and t tauri stars |
we show that ‘oumuamua’s excited spin could be in a high-energy long axis mode (lam) state, which implies that its shape could be far from the highly elongated shape found in previous studies. clean and anova algorithms are used to analyze ‘oumuamua’s lightcurve using 818 observations over 29.3 days. two fundamental periodicities are found at frequencies (2.77 ± 0.11) and (6.42 ± 0.18) cycles/day, corresponding to (8.67 ± 0.34) hr and (3.74 ± 0.11) hr, respectively. the phased data show that the lightcurve does not repeat in a simple manner, but approximately shows a double minimum at 2.77 cycles/day and a single minimum at 6.42 cycles/day. ‘oumuamua could be spinning in either the lam or short axis mode (sam). for both, the long axis precesses around the total angular momentum vector with an average period of (8.67 ± 0.34) hr. for the three lams we have found, the possible rotation periods around the long axis are 6.58, 13.15, or 54.48 hr, with 54.48 hr being the most likely. ‘oumuamua may also be nutating with respective periods of half of these values. we have also found two possible sam states where ‘oumuamua oscillates around the long axis with possible periods at 13.15 and 54.48 hr. in this case any nutation occurs with the same periods. determination of the spin state, the amplitude of the nutation, the direction of the total angular momentum vector (tamv), and the average total spin period may be possible with a direct model fit to the lightcurve. we find that ‘oumuamua is “cigar-shaped,” if close to its lowest rotational energy, and an extremely oblate spheroid if close to its highest energy state. | the excited spin state of 1i/2017 u1 ‘oumuamua |
sn 2016gkg is a nearby sn iib discovered shortly after explosion. like several other type iib events with early-time data, sn 2016gkg displays a double-peaked light curve, with the first peak associated with the cooling of a low-mass extended progenitor envelope. we present unprecedented intranight-cadence multi-band photometric coverage of the first light curve peak of sn 2016gkg obtained from the las cumbres observatory global telescope network, the asteroid terrestrial-impact last alert system, the swift satellite, and various amateur-operated telescopes. fitting these data to analytical shock-cooling models gives a progenitor radius of ∼40-150 {r}⊙with ∼2-40 × 10-2 {m}⊙of material in the extended envelope (depending on the model and the assumed host-galaxy extinction). our radius estimates are broadly consistent with values derived independently (in other works) from hst imaging of the progenitor star. however, the shock-cooling model radii are on the lower end of the values indicated by pre-explosion imaging. hydrodynamical simulations could refine the progenitor parameters deduced from the shock-cooling emission and test the analytical models. | constraints on the progenitor of sn 2016gkg from its shock-cooling light curve |
occultations of stars by asteroids have been observed since 1961, increasing from a very small number to now over 500 annually. we have created and regularly maintain a growing data set of more than 5000 observed asteroidal occultations. the data set includes the raw observations, astrometry at the 1 mas level based on centre of mass or figure (not illumination), where possible the asteroid's diameter to 5 km or better, and fits to shape models, the separation and diameters of asteroidal satellites, and double star discoveries with typical separations being in the tens of mas or less. the data set is published at nasa's planetary data system and is regularly updated. we provide here an overview of the data set, discuss the issues associated with determining the astrometry and diameters, and give examples of what can be derived from the data set. we also compare the occultation diameters of asteroids with the diameters measured by the satellites neowise, akari acua, and iras, and show that the best satellite-determined diameter is a combination of the diameters from all three satellites. | precise astrometry and diameters of asteroids from occultations - a data set of observations and their interpretation |
the nature and origin of the asteroids orbiting in near-earth space, including those on a potentially hazardous trajectory, is of both scientific interest and practical importance. we aim here at determining the taxonomy of a large sample of near-earth and mars-crosser asteroids and analyze the distribution of these classes with orbit. we use this distribution to identify the source regions of near-earth objects and to study the strength of planetary encounters to refresh asteroid surfaces. we measure the photometry of these asteroids over four filters at visible wavelengths on images taken by the sloan digital sky survey (sdss). these colors are used to classify the asteroids into a taxonomy consistent with the widely used bus-demeo taxonomy (demeo et al. [2009]. icarus 202, 160-180) based on visible and near-infrared spectroscopy. we report here on the taxonomic classification of 206 near-earth and 776 mars-crosser asteroids determined from sdss photometry, representing an increase of 40% and 663% of known taxonomy classifications in these populations. using the source region mapper by greenstreet et al. (greenstreet, s., ngo, h., gladman, b. [2012]. icarus, 217, 355-366), we compare for the first time the taxonomic distribution among near-earth and main-belt asteroids of similar diameters. both distributions agree at the few percent level for the inner part of the main belt and we confirm this region as a main source of near-earth objects. the effect of planetary encounters on asteroid surfaces are also studied by developing a simple model of forces acting on a surface grain during planetary encounter, which provides the minimum distance at which a close approach should occur to trigger resurfacing events. by integrating numerically the orbit of the 519 s-type and 46 q-type asteroids in our sample back in time for 500,000 years and monitoring their encounter distance with venus, earth, mars, and jupiter, we seek to understand the conditions for resurfacing events. the population of q-type is found to present statistically more encounters with venus and the earth than s-types, although both s- and q-types present the same amount of encounters with mars. | spectral properties of near-earth and mars-crossing asteroids using sloan photometry |
carbon impurities in gan form both acceptors and donors. donor-to-acceptor ratios (dars) determine the semi-insulating behavior of carbon-doped gan (gan:c) layers and are still debated. two models are discussed; both can theoretically achieve semi-insulating behavior: the dominant acceptor model (dam, dar < 1 ) and the auto-compensation model (acm, dar = 1 ). we perform a capacitance-voltage analysis on metal/gan:c/ngan (n-doped gan) structures, exhibiting fermi-level pinning in gan:c, 0.7 ev above the valence band maximum. this observation coupled with further interpretation clearly supports the dam and contradicts the acm. furthermore, we reveal a finite depletion width of a transition region in gan:c next to ngan, where carbon acceptors drop below the fermi level becoming fully ionized. calculation of the potential drop in this region exhibits dar values of 0.5-0.67 for gan:c with total carbon concentrations of 10 18 cm − 3 and 10 19 cm − 3. based on those results, we re-evaluate formerly published density functional theory (dft)-calculated formation energies of point defects in gan. unexpectedly, growth in thermodynamic equilibrium with the bulk carbon phase contradicts our experimental analysis. therefore, we propose the consideration of extreme carbon-rich growth conditions. as bulk carbon and carbon cluster formation are not reported to date, we consider a metastable gan:c solid solution with the competing carbon bulk phase being kinetically hindered. dft and experimental results agree, confirming the role of carbon at nitrogen sites as dominant acceptors. under n-rich conditions, carbon at gallium sites is the dominant donor, whereas additional nitrogen vacancies are generated under ga-rich conditions. | mechanism leading to semi-insulating property of carbon-doped gan: analysis of donor acceptor ratio and method for its determination |
observations of the first interstellar minor object 1i/2017 ’oumuamua did not reveal direct signs of outgassing that would have been natural if it had a volatile-rich composition. however, a recent measurement by micheli et al. of a substantial non-gravitational acceleration affecting the orbit of this object has been interpreted as resulting from its cometary activity, which must be rather vigorous. here we critically reassess this interpretation by exploring the implications of measured non-gravitational acceleration for ’oumuamua’s rotational state. we show that outgassing torques should drive the rapid evolution of ’oumuamua’s spin (on a timescale of a few days), assuming torque asymmetry that is typical for solar system comets. however, given the highly elongated shape of the object, its torque asymmetry is likely higher, implying an even faster evolution. this would have resulted in rapid rotational fission of ’oumuamua during its journey through the solar system, and is clearly incompatible with the relative stability of its rotational state inferred from photometric variability. based on these arguments, as well as the lack of direct signs of outgassing, we conclude that the classification of ’oumuamua as a comet (invoked to explain its claimed anomalous acceleration) is questionable. | spin evolution and cometary interpretation of the interstellar minor object 1i/2017 ’oumuamua |
as differentiated planetesimals cool, their cores can solidify from the outside in1, as evidenced by palaeomagnetic measurements and cooling-rate estimates of iron meteorites2,3. the details of outside-in solidification and fate of residual core melt are poorly understood. for a core primarily composed of iron and nickel alloyed with lighter constituent elements such as sulfur, this inward core growth would probably be achieved by growth of solid iron-nickel dendrites4. growth of iron-nickel dendrites results in interconnected pockets of residual melt that become progressively enriched in sulfur up to a eutectic composition of 31 wt% sulfur as iron-nickel continues to solidify4. here, we show that regions of residual sulfur-enriched iron-nickel melt in the core attain sufficient excess pressures to propagate via dykes into the mantle. thus, core material will intrude into the overlying rocky mantle or possibly even erupt onto the planetesimal's surface. we refer to these processes collectively as ferrovolcanism. our calculations show that ferrovolcanic surface eruptions are more likely on bodies with mantles less than 50 km thick. we show that intrusive ferromagmatism can produce pallasites, an enigmatic class of meteorites composed of olivine crystals entrained in a matrix of iron-nickel metal4. ferrovolcanic eruptions may explain the observations that asteroid 16 psyche has a bulk density inconsistent with iron meteorites5 yet shows evidence of a metallic surface composition6. | ferrovolcanism on metal worlds and the origin of pallasites |
on 2019 january 5 a streamer associated with the 4-10 km main belt asteroid (6478) gault was detected by the atlas sky survey, a rare discovery of activity around a main belt asteroid. archival data from atlas and pan-starrs1 show the trail in early 2018 december, but not between 2010 and 2018 january. the feature has significantly changed over one month, perfectly matching predictions of pure dust dynamical evolution and changes in the observing geometry for a short release of dust around 2018 october 28. follow-up observations with the hubble space telescope (hst) show a second narrow trail corresponding to a brief release of dust on 2018 december 30. both releases occurred with negligible velocity. we find the dust grains to be fairly large, with power-law size distributions in the 10-5-10-3 m range and power-law indices of ∼-1.5. three runs of ground-based data find a signature of ∼2 hr rotation, close to the rotational limit, suggesting that the activity is the result of landslides or reconfigurations after yarkovsky-o’keefe-radzievskii-paddack (yorp) spin-up. | the sporadic activity of (6478) gault: a yorp-driven event? |
1i/’oumuamua is the first interstellar interloper to be detected, and it shows a non-gravitational acceleration that cannot be accounted for by outgassing, given the strict upper limits of outgassing evident from spitzer observations, unless the relative abundances of the common volatiles are very different to those in comets. as an alternative, it has been suggested that its peculiar acceleration is due to radiation pressure, requiring a planar-sheet geometry of an unknown natural or artificial origin. here we assess whether or not the internal structure of 1i/’oumuamua, rather than its geometry, could support a radiation-pressure-driven scenario. we adopt a mass fractal structure and find that the type of aggregate that could yield the required area-to-mass ratio would have to be extraordinarily porous, with a density ∼10-5 g cm-3. such porous aggregates can naturally arise from the collisional grow of icy dust particles beyond the snowline of a protoplanetary disk, and we propose that 1i/’oumuamua might be a member of this population. this is a hypothesis worth investigating because, if this were the case, 1i/’oumuamua would have opened a new observation window on to the study of the building blocks of planets around other stars. this could set unprecedented constraints on planet formation models. | could 1i/’oumuamua be an icy fractal aggregate? |
we perform n-body simulations of the early phases of open cluster evolution including a large population of planetesimals, initially arranged in kuiper-belt like discs around each star. using a new, fourth-order, and time-reversible n-body code on graphics processing units (gpus), we evolve the whole system under the stellar gravity, i.e. treating planetesimals as test particles, and consider two types of initial cluster models, similar to ic348 and the hyades, respectively. in both cases, planetesimals can be dynamically excited, transferred between stars, or liberated to become free-floating (such as a/2017 u1 or 'oumuamua) during the early cluster evolution. we find that planetesimals captured from another star are not necessarily dynamically distinct from those native to a star. after an encounter, both native and captured planetesimals can exhibit aligned periastrons, qualitatively similar to that seen in the solar system and commonly thought to be the signature of planet 9. we discuss the implications of our results for both our solar system and exoplanetary systems. | the fate of planetesimal discs in young open clusters: implications for 1i/'oumuamua, the kuiper belt, the oort cloud, and more |
containing only a few percentages of the mass of the moon, the current asteroid belt is around three to four orders of magnitude smaller than its primordial mass inferred from disk models. yet dynamical studies have shown that the asteroid belt could not have been depleted by more than about an order of magnitude over the past ∼4 gyr. the remainder of the mass loss must have taken place during an earlier phase of the solar system’s evolution. an orbital instability in the outer solar system occurring during the process of terrestrial planet formation can reproduce the broad characteristics of the inner solar system. here, we test the viability of this model within the constraints of the main belt’s low present-day mass and orbital structure. although previous studies modeled asteroids as massless test particles because of limited computing power, our work uses graphics processing unit acceleration to model a fully self-gravitating asteroid belt. we find that depletion in the main belt is related to the giant planets’ exact evolution within the orbital instability. simulations that produce the closest matches to the giant planets’ current orbits deplete the main belt by two to three orders of magnitude. these simulated asteroid belts are also good matches to the actual asteroid belt in terms of their radial mixing and broad orbital structure. | excitation and depletion of the asteroid belt in the early instability scenario |
monolayers of anisotropic cells exhibit long-ranged orientational order and topological defects. during the development of organisms, orientational order often influences morphogenetic events. however, the linkage between the mechanics of cell monolayers and topological defects remains largely unexplored. this holds specifically at the timescales relevant for tissue morphogenesis. here, we build on the physics of liquid crystals to determine material parameters of cell monolayers. in particular, we use a hydrodynamical description of an active polar fluid to study the steady-state mechanical patterns at integer topological defects. our description includes three distinct sources of activity: traction forces accounting for cell-substrate interactions as well as anisotropic and isotropic active nematic stresses accounting for cell-cell interactions. we apply our approach to c2c12 cell monolayers in small circular confinements, which form isolated aster or spiral topological defects. by analyzing the velocity and orientational order fields in spirals as well as the forces and cell number density fields in asters, we determine mechanical parameters of c2c12 cell monolayers. our work shows how topological defects can be used to fully characterize the mechanical properties of biological active matter. | integer topological defects of cell monolayers: mechanics and flows |
as asteroids break up during atmospheric entry, they deposit energy that can be seen in flares of light and, if substantial enough, can produce damaging blast waves. analytic models of asteroid breakup and energy deposition processes are needed in order to assess potential airburst hazards, and to enable inferences about asteroid properties or breakup physics to be made from comparisons with observed meteors. this paper presents a fragment-cloud model (fcm) that is able to represent a broad range of breakup behaviors and the resulting variations in energy deposition in ways that make it a useful tool for both applications. sensitivity studies are performed to investigate how variations the model's fragmentation parameters affect the energy deposition results for asteroids 20-500 m in diameter. the model is also used to match observational data from the chelyabinsk meteor and infer potential asteroid properties and representative modeling parameter ranges. results illustrate how the model's fragmentation parameters can introduce different energy deposition features, and how much they affect the overall energy deposition rates, magnitudes, and altitudes that would drive ground damage for risk assessment applications. | a fragment-cloud model for asteroid breakup and atmospheric energy deposition |
after accretion of meteorite parent bodies, larger and smaller collisions have led to significant modifications of these bodies. involved processes include excavation of material, thermal metamorphism, melting, mixing of different materials, re-accretion, and re-lithification. all these processes can be repeated several times. in this study polished thin sections (pts) of 2280 chondrites (1193 h, 947 l, and 140 ll chondrites) were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites. in addition, we have determined the abundance and characteristics of shock vein-bearing h, l, and ll chondrites and of impact melt rock clasts. we also recognized xenolithic components based on o-isotope studies. noble gas data were considered in order to detect regolith breccias and to discuss late impact histories. the investigation of 2280 samples shows that 23% (276 of 1193) of the h chondrites, 23% (220 of 947) of the l chondrites, and 79 % (110 of 140) of the ll chondrites are brecciated. considering the heavily-brecciated ll chondrites in 63 of the 140 chondrites (45%) shock veins were clearly detected. 57 of these 63 chondrites are brecciated rocks. the investigation of the h and l chondrites has shown that about 26% (310 of 1193) of the h chondrites and 40% (379 of 947) of the l chondrites contain shock veins. in our data-set 20% of the h chondrites and 8.3% of the ll chondrites, but only 3.0% of the l chondrites contain solar noble gases. remarkably, about 62% of all brecciated h chondrites (with noble gases analyzed) contain solar noble gases compared to only around 11% and 10% of the brecciated l and ll chondrites, respectively. the identification of xenolithic clasts (e.g., ci-, cm-, and ureilite-like lithologies) in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules. these clasts must have been formed early within the first 2 ma on subsequently-destroyed precursor, first generation parent bodies. the formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage. although the onion-shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint (petrologic types 3-6) subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble-pile structure are required to explain certain features discussed in this work. however, distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 ma were responsible to deliver the majority of the ordinary chondritic meteoroids to earth. yet, this certainly does not tell anything about the number of "last-generation" parent bodies that exist in the asteroid belt, since s-type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites. | brecciation among 2280 ordinary chondrites - constraints on the evolution of their parent bodies |
whole rock δ17o and nucleosynthetic isotopic variations for chromium, titanium, nickel, and molybdenum in meteorites define two isotopically distinct populations: carbonaceous chondrites (ccs) and some achondrites, pallasites, and irons in one and all other chondrites and differentiated meteorites in the other. since differentiated bodies accreted 1-3 myr before the chondrites, the isotopic dichotomy cannot be attributed to temporal variations in the disk. instead, the two populations were most likely separated in space, plausibly by proto-jupiter. formation of ccs outside jupiter could account for their characteristic chemical and isotopic composition. the abundance of refractory inclusions in ccs can be explained if they were ejected by disk winds from near the sun to the disk periphery where they spiraled inward due to gas drag. once proto-jupiter reached 10-20 m ⊕, its external pressure bump could have prevented millimeter- and centimeter-sized particles from reaching the inner disk. this scenario would account for the enrichment in ccs of refractory inclusions, refractory elements, and water. chondrules in ccs show wide ranges in δ17o as they formed in the presence of abundant 16o-rich refractory grains and 16o-poor ice particles. chondrules in other chondrites (ordinary, e, r, and k groups) show relatively uniform, near-zero δ17o values as refractory inclusions and ice were much less abundant in the inner solar system. the two populations were plausibly mixed together by the grand tack when jupiter and saturn migrated inward emptying and then repopulating the asteroid belt with roughly equal masses of planetesimals from inside and outside jupiter’s orbit (s- and c-type asteroids). | isotopic dichotomy among meteorites and its bearing on the protoplanetary disk |
the japan aerospace exploration agency launched the asteroid sample return spacecraft ;hayabusa2; on december 3, 2014. hayabusa2 will reach the c-type asteroid 1999 ju3 in 2018, and return back to the earth in 2020. sample collections from three sites, four surface rovers deployment and a 4 mj-class kinetic impact crater generation are planned in the 1.5 years of the asteroid-proximity operation. the mission objective of hayabusa2 has three aspects, science, engineering and exploration, all of which would be expanded by the successful round-trip journey. this paper describes the outline of the hayabusa2 mission and the current flight status after the seven month of the interplanetary cruise. | flight status of robotic asteroid sample return mission hayabusa2 |
many small bodies in the solar system have bulk density well below the solid density of the constituent mineral grains in their meteorite counterparts. those low-density bodies undoubtedly have significant porosity, which is a key factor that affects the formation of impact craters. this paper summarizes the results of lab experiments in which materials with porosity ranging from 43% to 96% were impacted at ∼1800 m/s. the experiments were performed on a geotechnical centrifuge, in order to reproduce the lithostatic overburden stress and ejecta ballistics that occur in large-scale cratering events on asteroids or planetary satellites. experiments performed at various accelerations, up to 514g, simulate the outcomes of impacts at size scales up to several tens of km in diameter. our experiments show that an impact into a highly porous cohesionless material generates a large ovoid-shaped cavity, due to crushing by the outgoing shock. the cavity opens up to form a transient crater that grows until the material flow is arrested by gravity. the cavity then collapses to form the final crater. during collapse, finely crushed material that lines the cavity wall is carried down and collected in a localized region below the final crater floor. at large simulated sizes (high accelerations), most of the crater volume is formed by compaction, because growth of the transient crater is quickly arrested. nearly all ejected material falls back into the crater, leaving the crater without an ejecta blanket. we find that such compaction cratering and suppression of the ejecta blankets occur for large craters on porous bodies when the ratio of the lithostatic stress at one crater depth to the crush strength of the target exceeds ∼0.005. the results are used to identify small solar system bodies on which compaction cratering likely occurs. a model is developed that gives the crater size and ejecta mass that would result for a specified impact into a porous object. | impacts into porous asteroids |
one of the most enigmatic and hitherto unexplained properties of jupiter trojans is their bimodal color distribution. this bimodality is indicative of two sub-populations within the trojans, which have distinct size distributions. in this paper, we present a simple, plausible hypothesis for the origin and evolution of the two trojan color sub-populations. in the framework of dynamical instability models of early solar system evolution, which suggest a common primordial progenitor population for both trojans and kuiper belt objects, we use observational constraints to assert that the color bimodalities evident in both minor body populations developed within the primordial population prior to the onset of instability. we show that, beginning with an initial composition of rock and ices, location-dependent volatile loss through sublimation in this primordial population could have led to sharp changes in the surface composition with heliocentric distance. we propose that the depletion or retention of h2s ice on the surface of these objects was the key factor in creating an initial color bimodality. objects that retained h2s on their surfaces developed characteristically redder colors upon irradiation than those that did not. after the bodies from the primordial population were scattered and emplaced into their current positions, they preserved this primordial color bimodality to the present day. we explore predictions of the volatile loss model—in particular, the effect of collisions within the trojan population on the size distributions of the two sub-populations—and propose further experimental and observational tests of our hypothesis. | a hypothesis for the color bimodality of jupiter trojans |
although the two moons of mars, phobos and deimos, have long been thought to be captured asteroids, recent observations of their compositions and orbits suggest that they may have formed from debris generated by one or more giant impacts of bodies with ∼0.01× target mass. recent studies have both analytically estimated debris produced by giant impacts on mars and numerically examined the evolution of circum-mars debris disks. we perform a numerical study (smoothed particle hydrodynamics simulation) of debris retention from giant impacts onto mars, particularly in relation to a borealis-scale giant impact (e ∼ 3 ×1029 j) capable of producing the borealis basin. we find that a borealis-scale impact is capable of producing a disk of mass ∼ 5 ×1020 kg (∼1-4% of the impactor mass), sufficient debris to form at least one of the martian moons according to recent numerical studies of martian debris disk evolution. while a borealis-scale impact may generate sufficient debris to form both phobos and deimos, further studies of the debris disk evolution are necessary. our results can serve as inputs for future studies of martian debris disk evolution. | formation of phobos and deimos via a giant impact |
the orbital evolution of the giant planets after nebular gas was eliminated from the solar system but before the planets reached their final configuration was driven by interactions with a vast sea of leftover planetesimals. several variants of planetary migration with this kind of system architecture have been proposed. here, we focus on a highly successful case, which assumes that there were once five planets in the outer solar system in a stable configuration: jupiter, saturn, uranus, neptune, and a neptune-like body. beyond these planets existed a primordial disk containing thousands of pluto-sized bodies, ∼50 million d > 100 km bodies, and a multitude of smaller bodies. this system eventually went through a dynamical instability that scattered the planetesimals and allowed the planets to encounter one another. the extra neptune-like body was ejected via a jupiter encounter, but not before it helped to populate stable niches with disk planetesimals across the solar system. here, we investigate how interactions between the fifth giant planet, jupiter, and disk planetesimals helped to capture disk planetesimals into both the asteroid belt and first-order mean-motion resonances with jupiter. using numerical simulations, we find that our model produces the right proportion of p- and d-type asteroids in the inner, central, and outer main belt, while also populating the hilda and thule regions in jupiter’s 3/2 and 4/3 resonances. moreover, the largest observed p/d types in each sub-population are an excellent fit to our captured population results (within uncertainties). the model produces a factor of ∼10 overabundance of diameter d > 10 km p/d types in the main belt, but this mismatch can likely be explained by various removal mechanisms (e.g., collision evolution over 4 gyr, dynamical losses via yarkovsky thermal forces over 4 gyr, thermal destruction of the planetesimals en route to the inner solar system). overall, our instability model provides a more satisfying match to constraints than that of levison et al., and it provides us with strong supporting evidence that the five giant planet instability model is reasonable. our results lead us to predict that d-type asteroids found in the near-earth object population on low delta-v orbits with earth are the surviving relics from the same source population that now make up the kuiper belt, the irregular satellites, and the jupiter trojans. the singular tagish lake meteorite, a primitive sample unlike other carbonaceous chondrite meteorites, is likely a fragment from a d-type asteroid implanted into the inner main belt. this would effectively make it the first known hand sample with the same composition as kuiper belt objects. | capture of trans-neptunian planetesimals in the main asteroid belt |
stereophotoclinometry (spc) makes it possible to extract the shapes of surfaces by combining information from images, namely stereo parallax data and surface shading from slopes, with knowledge of the location of a spacecraft. this technique has been used extensively in the past few decades to describe the shapes of planets and small bodies, such as asteroids and comets. it has also been used to carefully navigate spacecraft around very small bodies, as in the case of the osiris-rex mission to the ~500 m diameter asteroid (101955) bennu. this paper describes the mathematical foundation of spc, with examples from the osiris-rex mission. | stereophotoclinometry on the osiris-rex mission: mathematics and methods |
the effect of protoplanetary differentiation on the fate of life-essential volatiles such as nitrogen and carbon and its subsequent effect on the dynamics of planetary growth is unknown. because the dissolution of nitrogen in magma oceans depends on its partial pressure and oxygen fugacity, it is an ideal proxy to track volatile redistribution in protoplanets as a function of their sizes and growth zones. using high-pressure/temperature experiments in graphite-undersaturated conditions, here we show that the siderophilic (iron-loving) character of nitrogen is an order of magnitude higher than previous estimates across a wide range of oxygen fugacity. the experimental data combined with metal-silicate-atmosphere fractionation models suggest that asteroid-sized protoplanets, and planetary embryos that grew from them, were nitrogen depleted. however, protoplanets that grew to planetary embryo size before undergoing differentiation had nitrogen-rich cores and nitrogen-poor silicate reservoirs. bulk silicate reservoirs of large earth-like planets obtained nitrogen from the cores of the latter type of planetary embryos. therefore, to satisfy the volatile budgets of earth-like planets during the main stage of their growth, the timescales of planetary embryo accretion had to be shorter than their differentiation timescales; that is, moon- to mars-sized planetary embryos grew rapidly within ~1-2 myrs of the solar system's formation. | rates of protoplanetary accretion and differentiation set nitrogen budget of rocky planets |
we report that object 282p/(323137) 2003 bm80 is undergoing a sustained activity outburst, lasting over 15 months thus far. these findings stem in part from our nasa partner citizen science project active asteroids (http://activeasteroids.net), which we introduce here. we acquired new observations of 282p via our observing campaign (vatican advanced technology telescope (vatt), lowell discovery telescope (ldt), and the gemini south telescope), confirming 282p was active on ut 2022 june 7, some 15 months after 2021 march images showed activity in the 2021-2022 epoch. we classify 282p as a member of the quasi-hilda objects (qhos), a group of dynamically unstable objects found in an orbital region similar to, but distinct in their dynamical characteristics to, the hilda asteroids (objects in 3:2 resonance with jupiter). our dynamical simulations show 282p has undergone at least five close encounters with jupiter and one with saturn over the last 180 yr. 282p was most likely a centaur or jupiter-family comet (jfc) 250 yr ago. in 350 yr, following some 15 strong jovian interactions, 282p will most likely migrate to become a jfc or, less likely, an outer main-belt asteroid orbit. these migrations highlight a dynamical pathway connecting centaurs and jfcs with quasi-hildas and, potentially, active asteroids. synthesizing these results with our thermodynamical modeling and new activity observations, we find volatile sublimation is the primary activity mechanism. observations of a quiescent 282p, which we anticipate will be possible in 2023, will help confirm our hypothesis by measuring a rotation period and ascertaining the spectral type. * based on observations obtained at the international gemini observatory, a program of nsf's noirlab, which is managed by the association of universities for research in astronomy (aura) under a cooperative agreement with the national science foundation on behalf of the gemini observatory partnership: the national science foundation (united states), national research council (canada), agencia nacional de investigación y desarrollo (chile), ministerio de ciencia, tecnología e innovación (argentina), ministério da ciência, tecnologia, inovações e comunicações (brazil), and korea astronomy and space science institute (republic of korea). ** magellan telescope time was granted by nsf's noirlab, through the telescope system instrumentation program (tsip). tsip was funded by the national science foundation (nsf). | migratory outbursting quasi-hilda object 282p/(323137) 2003 bm80 |
context. the recent close approach of the near-earth asteroid (3200) phaethon offered a rare opportunity to obtain high-quality observational data of various types.aims: we used the newly obtained optical light curves to improve the spin and shape model of phaethon and to determine its surface physical properties derived by thermophysical modeling. we also used the available astrometric observations of phaethon, including those obtained by the arecibo radar and the gaia spacecraft, to constrain the secular drift of the orbital semimajor axis. this constraint allowed us to estimate the bulk density by assuming that the drift is dominated by the yarkovsky effect.methods: we used the convex inversion model to derive the spin orientation and 3d shape model of phaethon, and a detailed numerical approach for an accurate analysis of the yarkovsky effect.results: we obtained a unique solution for phaethon's pole orientation at (318 ° , - 47 ° ) ecliptic longitude and latitude (both with an uncertainty of 5°), and confirm the previously reported thermophysical properties (d = 5.1 ± 0.2 km, γ = 600 ± 200j m-2 s-0.5 k-1). phaethon has a top-like shape with possible north-south asymmetry. the characteristic size of the regolith grains is 1 - 2 cm. the orbit analysis reveals a secular drift of the semimajor axis of -(6.9 ± 1.9)×10-4 au myr-1. with the derived volume-equivalent size of 5.1 km, the bulk density is 1.67 ± 0.47 g cm-3. if the size is slightly larger ∼5.7 - 5.8 km, as suggested by radar data, the bulk density would decrease to 1.48 ± 0.42 g cm-3. we further investigated the suggestion that phaethon may be in a cluster with asteroids (155140) 2005 ud and (225416) 1999 yc that was formed by rotational fission of a critically spinning parent body.conclusions: phaethon's bulk density is consistent with typical values for large (> 100 km) c-complex asteroids and supports its association with asteroid (2) pallas, as first suggested by dynamical modeling. these findings render a cometary origin unlikely for phaethon. | (3200) phaethon: bulk density from yarkovsky drift detection |
we present an updated set of near-earth asteroids with a yarkovsky-related semimajor axis drift detected from the orbital fit to the astrometry. we find 87 reliable detections after filtering for the signal-to-noise ratio of the yarkovsky drift estimate and making sure the estimate is compatible with the physical properties of the analysed object. furthermore, we find a list of 24 marginally significant detections for which future astrometry could result in a yarkovsky detection. a further outcome of the filtering procedure is a list of detections that we consider spurious because they are either unrealistic or not explicable by the yarkovsky effect. among the smallest asteroids of our sample, we determined four detections of solar radiation pressure in addition to the yarkovsky effect. as the data volume increases in the near future, our goal is to develop methods to generate very long lists of asteroids that have a yarkovsky effect that is reliably detected and have limited amounts of case by case specific adjustments. furthermore, we discuss the improvements this work could bring to impact monitoring. in particular, we exhibit two asteroids for which the adoption of a non-gravitational model is needed to make reliable impact predictions. | detecting the yarkovsky effect among near-earth asteroids from astrometric data |
collisions are one of the key processes shaping planetary systems. asteroid families are outcomes of such collision still identifiable across our solar system. the families provide a unique view of catastrophic disruption phenomena and have been in the focus of planetary scientists for more than a century. most of them are located in the main belt, a ring of asteroids between mars and jupiter. here we review the basic properties of the families, discuss some recent advances, and anticipate future challenges. this review pays more attention to dynamic aspects such as family identification, age determination, and long-term evolution. the text, however, goes beyond that. especially, we cover the details of young families that see the major advances in the last years, and we anticipate it will develop even faster in the future. we also discuss the relevance of asteroid families for water-ice content in the asteroid belt and our current knowledge on links between families and main-belt comets. query please check the edit made in the article title. | asteroid families: properties, recent advances, and future opportunities |
hayabusa2 was launched on 3 december 2014 on an h-iia launch vehicle from the tanegashima space center, and is, at the time of writing, cruising toward asteroid 162137 ryugu (1999ju3). after reaching the asteroid, it will stay for about 1.5 years to observe the asteroid and collect surface material samples. | development of the laser altimeter (lidar) for hayabusa2 |
current observations allow primordial black holes (pbhs) in asteroid mass range 1017- 1022 g to constitute the entire dark matter energy density (barring a small mass range constrained by 21-cm observations). in this work, we explore the possibility of probing pbhs with masses 1017- 1019 g via the upcoming x/gamma ray imaging spectrometer (xgis) telescope array on board the transient high-energy sky and early universe surveyor (theseus) mission. while our projected limits are comparable with those proposed in the literature for 1016 g <mpbh<1017 g , we show that the xgis-theseus mission can potentially provide the strongest bound for 1017 g <mpbh≲3 ×1018 g for nonrotating pbhs. the bounds become more stringent by nearly an order of magnitude for maximally rotating pbhs in the mass range 5 ×1015 g <mpbh≲1019 g . | future constraints on primordial black holes from xgis-theseus |
the planets of our solar system formed from a gas-dust disk. however, there are some properties of the solar system that are peculiar in this context. first, the cumulative mass of all objects beyond neptune (trans-neptunian objects [tnos]) is only a fraction of what one would expect. second, unlike the planets themselves, the tnos do not orbit on coplanar, circular orbits around the sun, but move mostly on inclined, eccentric orbits and are distributed in a complex way. this implies that some process restructured the outer solar system after its formation. however, some of the tnos, referred to as sednoids, move outside the zone of influence of the planets. thus, external forces must have played an important part in the restructuring of the outer solar system. the study presented here shows that a close fly-by of a neighboring star can simultaneously lead to the observed lower mass density outside 30 au and excite the tnos onto eccentric, inclined orbits, including the family of sednoids. in the past it was estimated that such close fly-bys are rare during the relevant development stage. however, our numerical simulations show that such a scenario is much more likely than previously anticipated. a fly-by also naturally explains the puzzling fact that neptune has a higher mass than uranus. our simulations suggest that many additional sednoids at high inclinations still await discovery, perhaps including bodies like the postulated planet x. | outer solar system possibly shaped by a stellar fly-by |
hydrocarbon exploration in the last decade has yielded sufficient data to evaluate the gulf of mexico basin response to the chicxulub asteroid impact. given its passive marine setting and proximity to the impact structure on the yucatán peninsula, the gulf is the premier locale in which to study the near-field geologic effect of a bolide impact. we mapped a thick (decimeter- to hectometer-scale) deposit of carbonate debris at the cretaceous-paleogene boundary that is ubiquitous in the gulf and readily identifiable on borehole and seismic data. we interpret deposits seen in seismic and borehole data in the deepwater gulf to be predominately muddy debrites with minor turbidites based on cores in the southeastern gulf. mapping of the deposit in the northern gulf of mexico reveals that the impact redistributed roughly 1.05 × 105 km3 of sediment therein and over 1.98 × 105 km3 gulfwide. deposit distribution suggests that the majority of sediment derived from coastal and shallow-water environments throughout the gulf via seismic and megatsunamic processes initiated by the impact. the texas shelf and northern margin of the florida platform were significant sources of sediment, while the central and southern florida platform underwent more localized platform collapse. the crustal structure of the ancestral gulf influenced postimpact deposition both directly and indirectly through its control on salt distribution in the louann salt basin. nevertheless, impact-generated deposition overwhelmed virtually all topography and depositional systems at the start of the cenozoic, blanketing the gulf with carbonate debris within days. | the cretaceous-paleogene boundary deposit in the gulf of mexico: large-scale oceanic basin response to the chicxulub impact |
the near-earth object wide-field infrared survey explorer (neowise) mission continues to detect, track, and characterize minor planets. we present diameters and albedos calculated from observations taken during the second year since the spacecraft was reactivated in late 2013. these include 207 near-earth asteroids (neas) and 8885 other asteroids. of the neas, 84% neas did not have previously measured diameters and albedos by the neowise mission. comparison of sizes and albedos calculated from neowise measurements with those measured by occultations, spacecraft, and radar-derived shapes shows accuracy consistent with previous neowise publications. diameters and albedos fall within ±∼20% and ±∼40%, 1-sigma, respectively, of those measured by these alternate techniques. neowise continues to preferentially discover near-earth objects which are large (>100 m), and have low albedos. | neowise reactivation mission year two: asteroid diameters and albedos |
high-metallicity pollution is common in white dwarf (wd) stars hosting remnant planetary systems. however, they rarely have detectable debris accretion discs, possibly because much of the influx is fast steeply infalling debris in star-grazing orbits, producing a more tenuous signature than a slowly accreting disc. processes governing such deposition between the roche radius and photosphere have so far received little attention and we model them here analytically by extending recent work on sun-grazing comets to wd systems. we find that the evolution of cm-to-km size (a0) infallers most strongly depends on two combinations of parameters, which effectively measure sublimation rate and binding strength. we then provide an algorithm to determine the fate of infallers for any wd, and apply the algorithm to four limiting combinations of hot versus cool (young/old) wds with snowy (weak, volatile) versus rocky (strong, refractory) infallers. we find: (i) total sublimation above the photosphere befalls all small infallers across the entire wd temperature (twd) range, the threshold size rising with twd and 100× larger for rock than snow. (ii) all very large objects fragment tidally regardless of twd: for rock, a0 ≽ 105 cm; for snow, a0 ≽ 103-3 × 104 cm across all wd cooling ages. (iii) a considerable range of a0 avoids fragmentation and total sublimation, yielding impacts or grazes with cold wds. this range rapidly narrows with increasing twd, especially for snowy bodies. finally, we briefly discuss how the various forms of deposited debris may finally reach the photosphere surface itself. | deposition of steeply infalling debris around white dwarf stars |
recent dynamical models of solar system evolution and isotope studies of rock-forming elements in meteorites have suggested that volatile-rich asteroids formed in the outer solar system beyond jupiter's orbit, despite being currently located in the main asteroid belt1-4. the ambient temperature under which asteroids formed is a crucial diagnostic to pinpoint the original location of asteroids and is potentially determined by the abundance of volatiles they contain. in particular, abundances and 13c/12c ratios of carbonates in meteorites record the abundances of carbon-bearing volatile species in their parent asteroids. however, the sources of carbon for these carbonates remain poorly understood5-8. here we show that the tagish lake meteorite contains abundant carbonates with consistently high 13c/12c ratios. the high abundance of 13c-rich carbonates in tagish lake excludes organic matter as their main carbon source5,9. therefore, the tagish lake parent body, presumably a d-type asteroid10, must have accreted a large amount of 13c-rich co2 ice. the estimated 13c/12c and co2/h2o ratios of ice in tagish lake are similar to those of cometary ice11,12. thus, we infer that at least some d-type asteroids formed in the cold outer solar system and were subsequently transported into the inner solar system owing to an orbital instability of the giant planets1,3. | migration of d-type asteroids from the outer solar system inferred from carbonate in meteorites |
we investigate the production of primordial black holes (pbhs) in a mixed inflaton-curvaton scenario with a quadratic curvaton potential, assuming the curvaton is in de sitter equilibrium during inflation with <χ> = 0. in this setup, the curvature perturbation sourced by the curvaton is strongly non-gaussian, containing no leading gaussian term. we show that for m 2/h 2 ≳ 0.3, the curvaton contribution to the spectrum of primordial perturbations on cmb scales can be kept negligible but on small scales the curvaton can source pbhs. in particular, pbhs in the asteroid mass range 10-16 m ⊙ ≲ m ≲ 10-10 m ⊙ with an abundance reaching f pbh = 1 can be produced when the inflationary hubble scale h ≳ 1012 gev and the curvaton decay occurs in the window from slightly before the electroweak transition to around the qcd transition. | primordial black holes from a curvaton scenario with strongly non-gaussian perturbations |
we present a study of the active asteroid (3200) phaethon in the 2016 apparition using the solar and terrestrial relations observatory (stereo) spacecraft and compare the results with data from the previous two perihelia in 2009 and 2012. once again, phaethon brightened by ∼2 mag soon after its perihelion passage, contradicting expectations from the phase function of a macroscopic monolithic body. subsequently, a short antisolar tail of ∼0.°1 in length was formed within ∼1 day and quickly disappeared. no trail was seen. our syndyne-synchrone analysis indicates that the tail was comprised of submicron to micron particles and can be approximated by a synchrone coinciding with the outburst. we estimate that the outburst has released a mass of ∼104-105 kg, comparable to the two mass ejections in 2009 and 2012, and that the average mass-loss rate is ∼0.1-1 kg s-1. the forward-scattering effect hinted at low level activity of phaethon prior to the outburst, which increased the effective cross section by merely ≲1 km2. without the forward-scattering enhancement, detecting such activity at side-scattering phase angles is very difficult. the forward-scattering effect also reinforces the idea that the ejected dust grains rather than gas emissions were responsible for the activity of phaethon. despite phaethon's reactivation, it is highly unlikely that the geminid meteoroid stream can be sustained by similar perihelion mass-loss events. | resurrection of (3200) phaethon in 2016 |
the first interstellar object observed in our solar system, 1i/2017 u1 ('oumuamua), exhibited a number of peculiar properties, including extreme elongation and acceleration excess. recently, seligman & laughlin proposed that the object was made out of molecular hydrogen (h2) ice. the question is whether h2 objects could survive their travel from the birth sites to the solar system. here we study destruction processes of icy h2 objects through their journey from giant molecular clouds (gmcs) to the interstellar medium (ism) and the solar system, owing to interstellar radiation, gas and dust, and cosmic rays. we find that thermal sublimation due to heating by starlight can destroy 'oumuamua-size objects in less than 10 myr. thermal sublimation by collisional heating in gmcs could destroy h2 objects of 'oumuamua-size before their escape into the ism. most importantly, the formation of icy grains rich in h2 is unlikely to occur in dense environments because collisional heating raises the temperature of the icy grains, so that thermal sublimation rapidly destroys the h2 mantle before grain growth. | destruction of molecular hydrogen ice and implications for 1i/2017 u1 ('oumuamua) |
we present the discovery and extensive follow-up of a remarkable fast-evolving optical transient, at 2022aedm, detected by the asteroid terrestrial impact last alert survey (atlas). in the atlas o band, at 2022aedm exhibited a rise time of 9 ± 1 days, reaching a luminous peak with mg≈ -22 mag. it faded by 2 mag in the g band during the next 15 days. these timescales are consistent with other rapidly evolving transients, though the luminosity is extreme. most surprisingly, the host galaxy is a massive elliptical with negligible current star formation. radio and x-ray observations rule out a relativistic at 2018cow-like explosion. a spectrum in the first few days after explosion showed short-lived he ii emission resembling young core-collapse supernovae, but obvious broad supernova features never developed; later spectra showed only a fast-cooling continuum and narrow, blueshifted absorption lines, possibly arising in a wind with v ≈ 2700 km s-1. we identify two further transients in the literature (dougie in particular, as well as at 2020bot) that share similarities in their luminosities, timescales, color evolution, and largely featureless spectra and propose that these may constitute a new class of transients: luminous fast coolers. all three events occurred in passive galaxies at offsets of ~4-10 kpc from the nucleus, posing a challenge for progenitor models involving massive stars or black holes. the light curves and spectra appear to be consistent with shock breakout emission, though this mechanism is usually associated with core-collapse supernovae. the encounter of a star with a stellar-mass black hole may provide a promising alternative explanation. | at 2022aedm and a new class of luminous, fast-cooling transients in elliptical galaxies |
the tumultuous early era of outer solar system evolution culminated when neptune migrated across the primordial kuiper belt (pkb) and triggered a dynamical instability among the giant planets. this event led to the ejection of ~99.9% of the pkb (here called the destabilized population), heavy bombardment of the giant planet satellites, and the capture of jupiter's trojans. while this scenario has been widely tested using dynamical models, there have been fewer investigations into how the pkb, its destabilized population, and the trojans experienced collisional evolution. here we examined this issue for all three populations with the code boulder. our constraints included the size-frequency distributions (sfds) of the trojan asteroids and craters on the giant planet satellites. using this combination, we solved for the unknown disruption law affecting bodies in these populations. the weakest ones, from an impact energy per mass perspective, were diameter d ~ 20 m. overall, collisional evolution produces a power-law-like shape for multikilometer trojans and a wavy-shaped sfd in the pkb and destabilized populations. the latter can explain (i) the shapes of the ancient and younger crater sfds observed on the giant planet satellites, (ii) the shapes of the jupiter family and long-period comet sfds, which experienced different degrees of collision evolution, and (iii) the present-day impact frequency of superbolides on jupiter and smaller projectiles on saturn's rings. our model results also indicate that many observed comets, the majority which are d < 10 km, are likely to be gravitational aggregates formed by large-scale collision events. | the collisional evolution of the primordial kuiper belt, its destabilized population, and the trojan asteroids |
the study of structure, thermodynamic state, equation of state (eos) and transport properties of warm dense matter (wdm) has become one of the key aspects of laboratory astrophysics. this field has demonstrated its importance not only concerning the internal structure of planets, but also other astrophysical bodies such as brown dwarfs, crusts of old stars or white dwarf stars. there has been a rapid increase in interest and activity in this field over the last two decades owing to many technological advances including not only the commissioning of high energy optical laser systems, z-pinches and x-ray free electron lasers, but also short-pulse laser facilities capable of generation of novel particle and x-ray sources. many new diagnostic methods have been developed recently to study wdm in its full complexity. even ultrafast nonequilibrium dynamics has been accessed for the first time thanks to subpicosecond laser pulses achieved at new facilities. recent years saw a number of major discoveries with direct implications to astrophysics such as the formation of diamond at pressures relevant to interiors of frozen giant planets like neptune, metallic hydrogen under conditions such as those found inside jupiter's dynamo or formation of lonsdaleite crystals under extreme pressures during asteroid impacts on celestial bodies. this paper provides a broad review of the most recent experimental work carried out in this field with a special focus on the methods used. all typical schemes used to produce wdm are discussed in detail. most of the diagnostic techniques recently established to probe wdm are also described. this paper also provides an overview of the most prominent examples of these methods used in experiments. even though the main emphasis of the publication is experimental work focused on laboratory astrophysics primarily at laser facilities, a brief outline of other methods such as dynamic compression with z-pinches and static compression using diamond anvil cells (dac) is also included. some relevant theoretical and computational efforts related to wdm and astrophysics are mentioned in this review. | experimental methods for warm dense matter research |
many air-less planetary bodies, including the moon, asteroids, and comets, are covered by regolith. the thermal conductivity of the regolith is an essential parameter controlling the surface temperature variation. a thermal conductivity model applicable to natural soils as well as planetary surface regolith is required to analyze infrared remote sensing data. in this study, we investigated the temperature and compressional stress dependence of the thermal conductivity of the lunar regolith simulant jsc-1a, and the temperature dependence of sieved jsc-1a samples under vacuum conditions. we confirmed that a series of the experimental data for jsc-1a are fitted well by our analytical model of the thermal conductivity (sakatani et al., 2017). comparison with the calibration data of the sieved samples with those for original jsc-1a indicates that the thermal conductivity of natural samples with a wide grain size distribution can be modeled as mono-sized grains with a volumetric median size. the calibrated model can be used to estimate the volumetric median grain size from infrared remote sensing data. our experiments and the calibrated model indicates that uncompressed jsc-1a has similar thermal conductivity to lunar top-surface materials, but the lunar subsurface thermal conductivity cannot be explained only by the effects of the density and self-weighted compressional stress. we infer that the nature of the lunar subsurface regolith grains is much different from jsc-1a and lunar top-surface regolith, and/or the lunar subsurface regolith is over-consolidated and the compressional stress higher than the hydrostatic pressure is stored in the lunar regolith layer. | thermal conductivity of lunar regolith simulant jsc-1a under vacuum |
hayabusa2, the first sample return mission to a c-type asteroid was launched by the japan aerospace exploration agency (jaxa) on december 3, 2014 and will arrive at the asteroid in the middle of 2018 to collect samples from its surface, which may contain both hydrated minerals and organics. the optical navigation camera (onc) system on board the hayabusa2 consists of three individual framing ccd cameras, onc-t for a telescopic nadir view, onc-w1 for a wide-angle nadir view, and onc-w2 for a wide-angle slant view will be used to observe the surface of ryugu. the cameras will be used to measure the global asteroid shape, local morphologies, and visible spectroscopic properties. thus, image data obtained by onc will provide essential information to select landing (sampling) sites on the asteroid. this study reports the results of initial inflight calibration based on observations of earth, mars, moon, and stars to verify and characterize the optical performance of the onc, such as flat-field sensitivity, spectral sensitivity, point-spread function (psf), distortion, and stray light of onc-t, and distortion for onc-w1 and w2. we found some potential problems that may influence our science observations. this includes changes in sensitivity of flat fields for all bands from those that were measured in the pre-flight calibration and existence of a stray light that arises under certain conditions of spacecraft attitude with respect to the sun. the countermeasures for these problems were evaluated by using data obtained during initial in-flight calibration. the results of our inflight calibration indicate that the error of spectroscopic measurements around 0.7 μm using 0.55, 0.70, and 0.86 μm bands of the onc-t can be lower than 0.7% after these countermeasures and pixel binning. this result suggests that our onc-t would be able to detect typical strength (∼3%) of the serpentine absorption band often found on cm chondrites and low albedo asteroids with ≥ 4σ confidence. | initial inflight calibration for hayabusa2 optical navigation camera (onc) for science observations of asteroid ryugu |
the majority of stars both host planetary systems and evolve into a white dwarf (wd). to understand their post-main-sequence planetary system evolution, we present a search for transiting/eclipsing planets and other substellar bodies (sbs) around wds using a sample of 1148 wds observed by k2. using transit injections, we estimate the completeness of our search. we place constraints on the occurrence of planets and sbs around wds as a function of planet radius and orbital period. for short-period (p < 40 d) small objects, from asteroid-sized to 1.5 r⊕, these are the strongest constraints known to date. we further constrain the occurrence of hot jupiters ( < 1.5 per cent), habitable zone earth-sized planets ( < 28 per cent), and disintegrating short-period planets ( ∼ 12 per cent). we blindly recovered all previously known eclipsing objects, providing confidence in our analysis, and make all light curves publicly available. | the occurrence of planets and other substellar bodies around white dwarfs using k2 |
in this work, we investigate the evolution of a primordial belt of asteroids, represented by a large number of massless test particles, under the gravitational effect of migrating jovian planets in the framework of the jumping-jupiter model. we perform several simulations considering test particles distributed in the main belt, as well as in the hilda and trojan groups. the simulations start with jupiter and saturn locked in the mutual 3:2 mean motion resonance plus three neptune-mass planets in a compact orbital configuration. mutual planetary interactions during migration led one of the neptunes to be ejected in less than 10 myr of evolution, causing jupiter to jump by about 0.3 au in semimajor axis. this introduces a large-scale instability in the studied populations of small bodies. after the migration phase, the simulations are extended over 4 gyr, and we compare the final orbital structure of the simulated test particles to the current main belt of asteroids with absolute magnitude h < 9.7. the results indicate that, in order to reproduce the present main belt, the primordial belt should have had a distribution peaked at ∼10° in inclination and at ∼0.1 in eccentricity. we discuss the implications of this for the grand tack model. the results also indicate that neither primordial hildas, nor trojans, survive the instability, confirming the idea that such populations must have been implanted from other sources. in particular, we address the possibility of implantation of hildas and trojans from the main belt population, but find that this contribution should be minor. | the evolution of asteroids in the jumping-jupiter migration model |
taurid meteor shower produces prolonged but usually low activity every october and november. in some years, however, the activity is significantly enhanced. previous studies based on long-term activity statistics concluded that the enhancement is caused by a swarm of meteoroids locked in 7:2 resonance with jupiter. here we present precise data on 144 taurid fireballs observed by new digital cameras of the european fireball network in the enhanced activity year 2015. orbits of 113 fireballs show common characteristics and form together a well defined orbital structure, which we call new branch and which was evidently responsible for the enhanced activity. this new branch is part of southern taurids and was encountered by the earth between october 25 and november 17. we found that this branch is characterized by longitudes of perihelia lying between 155.9-160° and latitudes of perihelia between 4.2-5.7°. semimajor axes are between 2.23-2.28 au and indeed overlap with the 7:2 resonance. eccentricities are in wide range 0.80-0.90. the most eccentric orbits with lowest perihelion distances were encountered at the beginning of the activity period. the orbits form a concentric ring in the inner solar system. the masses of the observed meteoroids were in a wide range from 0.1 g to more than 1000 kg. we found that all meteoroids larger than 300 g were very fragile (type iiib), while those smaller than 30 g were much more compact (mostly of type ii and some of them even type i). based on orbital characteristics, we argue that asteroids 2015 tx24 and 2005 ur, both of diameters 200-300 m, are direct members of the new branch. it is therefore very likely that the new branch contains also numerous still not discovered objects of decameter or even larger size. since asteroids of sizes of tens to hundreds meters pose a threat to the ground even if they are intrinsically weak, impact hazard increases significantly when the earth encounters the taurid new branch every few years. further studies leading to better description of this real source of potentially hazardous objects, which can be large enough to cause significant regional or even continental damage on the earth, are therefore extremely important. | discovery of a new branch of the taurid meteoroid stream as a real source of potentially hazardous bodies |
we review recent studies of the cluster structure of light nuclei within the framework of the algebraic cluster model (acm) for nuclei composed of k α-particles and within the framework of the cluster shell model (csm) for nuclei composed of k α-particles plus x additional nucleons. the calculations, based on symmetry considerations and thus for the most part given in analytic form, are compared with experiments in light cluster nuclei. the comparison shows evidence for z2, d3h and td symmetry in the even-even nuclei 8be (k = 2), 12c (k = 3) and 16o (k = 4), respectively, and for the associated double groups z2‧ and d3h‧ in the odd nuclei 9be, 9b (k = 2 , x = 1) and 13c (k = 3 , x = 1), respectively. | cluster structure of light nuclei |
the asteroid (16) psyche is the largest of the m-type asteroids, which have been hypothesized to be the cores of disrupted planetesimals and the parent bodies of the iron meteorites. while recent evidence has collected against a pure metal composition for psyche, its spectrum and radar properties remain anomalous. we observed (16) psyche in thermal emission with the atacama large millimeter/submillimeter array at a resolution of 30 km over two-thirds of its rotation. the diurnal temperature variations are at the ~10 k level over most of the surface and are best fit by a smooth surface with a thermal inertia of 280 ± 100 j m-2 k-1 s-1/2. we measure a millimeter emissivity of 0.61 ± 0.02, which we interpret via a model that treats the surface as a porous mixture of silicates and metals, where the latter may take the form of iron sulfides/oxides or, alternatively, conducting metallic inclusions. the emissivity indicates a metal content of no less than 20% and potentially much higher, but the polarized emission that should be present for a surface with ≥20% metal content is almost completely absent. this requires a highly scattering surface, which may be due to the presence of reflective metallic inclusions. if such is the case, a consequence is that metal-rich asteroids may produce less polarized emission than metal-poor asteroids, exactly the opposite prediction from standard theory, arising from the dominance of scattering over the bulk material properties. | the surface of (16) psyche from thermal emission and polarization mapping |
bo cet is renowned cataclysmic variable having an orbital period above the period gap (0.139835 d) and showing both features of a z cam/iw and star and an su uma star. using the asteroid terrestrial-impact last alert system (atlas) forced photometry and the all-sky automated survey for supernovae (asas-sn) sky patrol data, i found that bo cet underwent a superoutburst in 2022 october-november after a series of short, normal outbursts with increasing amplitudes. this sequence of outbursts (supercycle) is what is seen in many su uma stars and this observation strengthened the suggestion that the accumulating mass and angular momentum in the disk during repeated normal outbursts caused a superoutburst even in the unusual system bo cet. the outburst just preceding the superoutburst bore characteristics of an iw and-type standstill. this phenomenon reinforces the suggestion that the terminal outburst in iw and stars occurs when the disk radius reaches a certain limit. i consider that this outburst was a failed superoutburst, during which the disk reached the radius of the 3:1 resonance but the outburst faded before superhumps developed. in bo cet with a mass ratio on the borderline of the stability of the 3:1 resonance, there may have been a competition between the effects of tidal truncation and the 3:1 resonance as the disk radius grew and the latter won in the current case. this finding in bo cet might suggest that iw and-type and su uma-type phenomena are more strongly physically related than have been thought. | su uma-type supercycle in the iw and-type dwarf nova bo cet above the period gap |
asassn-15cm had been identified as a dwarf nova with an orbital period of 5.0 hours and a hot, luminous secondary of of a spectral type around k2.5 in the previous study. using the zwicky transient facility (ztf) data, the asteroid terrestrial-impact last alert system (atlas) forced photometry and the all-sky automated survey for supernovae (asas-sn) sky patrol data, i found that this object underwent a superoutburst in 2019. i obtained a refined orbital period of 0.2084652(3) d and a superhump period of 0.2196(1) d, which gave a mass ratio q=0.22. modeling of quiescent ellipsoidal variations yielded an inclination of i=55 deg, consistent with the lack of eclipses during outbursts. the object adds another example of su uma stars above or in the period gap containing a secondary with an evolved core, and has the longest orbital period among the established ones. asassn-15cm showed relatively regular superoutbursts with a supercycle of 849(18) d between 2015 and 2022, and the next superoutburst is expected to occur in the early half of 2024. coordinated detailed observations during the next superoutburst are expected to better clarify the nature of this object. | asassn-15cm: an su uma star with an orbital period of 5.0 hours |
there is an unceasing incoming flux of extraterrestrial materials reaching the earth atmosphere. some of these objects produce luminous columns when they ablate during the hypersonic encounter with air molecules. a few fireballs occur each year bright enough to be detected from space. the source of these events is still a matter of debate, but it is generally accepted that they are of sporadic origin. we studied the nasa-jpl center for neos studies (cneos) fireball database to infer the dynamic origin of large bolides produced by meter-sized projectiles that impacted our planet. these likely meteorite-dropping events were recorded by the us government satellite sensors. we estimated the false-positive rate and analyzed the time evolution of multiple orbit dissimilarity criteria concerning potential associations with near-earth objects and meteoroid streams. we found that at least 16% of the large bolides could be associated with meteoroid streams, about 4% are likely associated with near-earth asteroids, and 4% may be linked to near-earth comets. this implies that a significant fraction of meter-sized impactors producing large bolides may have an asteroidal or cometary origin. in addition, we found at least three bolides having hyperbolic orbits with high tensile strength values. meter-sized meteoroids of interstellar origin could be more common than previously thought, representing about 1% of the flux of large bolides. the inferred bulk physical properties suggest that the interstellar medium could bias these projectiles toward high strength rocks with the ability to survive prolonged exposure to the harsh interstellar space conditions. | orbital characterization of superbolides observed from space: dynamical association with near-earth objects, meteoroid streams, and identification of hyperbolic meteoroids |
we studied the membership, size ratio and rotational properties of 13 asteroid clusters consisting of between 3 and 19 known members that are on similar heliocentric orbits. by backward integrations of their orbits, we confirmed their cluster membership and estimated times elapsed since separation of the secondaries (the smaller cluster members) from the primary (i.e., cluster age) that are between 105 and a few 106 years. we ran photometric observations for all the cluster primaries and a sample of secondaries and we derived their accurate absolute magnitudes and rotation periods. we found that 11 of the 13 clusters follow the same trend of primary rotation period vs mass ratio as asteroid pairs that was revealed by pravec et al. (2010). we generalized the model of the post-fission system for asteroid pairs by pravec et al. (2010) to a system of n components formed by rotational fission and we found excellent agreement between the data for the 11 asteroid clusters and the prediction from the theory of their formation by rotational fission. the two exceptions are the high-mass ratio (q > 0.7) clusters of (18777) hobson and (22280) mandragora for which a different formation mechanism is needed. two candidate mechanisms for formation of more than one secondary by rotational fission were published: the secondary fission process proposed by jacobson and scheeres (2011) and a cratering collision event onto a nearly critically rotating primary proposed by vokrouhlický et al. (2017). it will have to be revealed from future studies which of the clusters were formed by one or the other process. to that point, we found certain further interesting properties and features of the asteroid clusters that place constraints on the theories of their formation, among them the most intriguing being the possibility of a cascade disruption for some of the clusters. | asteroid clusters similar to asteroid pairs |
we present new results of polarimetric observations of 15 main belt asteroids of different composition. by merging new and published data we determined polarimetric parameters characterizing individual asteroids and mean values of the same parameters characterizing different taxonomic classes. the majority of asteroids show polarimetric phase curves close to the average curve of the corresponding class. we show that using polarimetric data it is possible to refine asteroid taxonomy and derive a polarimetric classification for 283 main belt asteroids. polarimetric observations of asteroid (21) lutetia are found to exhibit possible variations of the position angle of the polarization plane over the surface. | refining the asteroid taxonomy by polarimetric observations |
finding the basic mechanism governing the surface history of asteroids of various shapes is essential for understanding their origin and evolution. in particular, the asteroids (162173) ryugu1 and (101955) bennu2 currently being visited by hayabusa2 and osiris-rex appear to be top shaped. this distinctive shape, characterized by a raised equatorial bulge, is shared by other similarly sized asteroids, including didymos a3, 2008 ev54 and 1999 kw4 alpha5. however, the possibly common formation mechanism that causes the top-like shape is still under debate. one clue may lie in the boulders on their surfaces. the distribution of these boulders, which was precisely measured in unprecedented detail by the two spacecraft1,2, constitutes a record of the geological evolution of the surface regolith since the origin of these asteroids. here, we show that during the regolith migration driven by yarkovsky-o'keefe-radzievskii-paddack spin-up6-9 the surface boulders coevolve with the underlying regolith and exhibit diverse dynamical behaviours: they can remain undisturbed, sink into the regolith layer and become tilted, or be totally buried by the downslope deposition, depending on their latitudes. the predominant geological features commonly observed on top-shaped asteroids, including the boulder-rich region near the pole1,10, the deficiency of large boulders in the equatorial area10,11 and partially buried, oblique boulders exposed on the regolith surface12,13, are commensurate with this coevolution scenario. the surface regolith migration thus is the prevalent mechanism for the formation history of the top-shaped asteroids with stiffer cores. | reconstructing the formation history of top-shaped asteroids from the surface boulder distribution |
the hydrophilic nature of halogens makes these elements ideal for probing potential hydrous geologic processes. generally, in magmatic settings the stable isotopes of cl may fractionate when h is in low concentrations and little fractionation occurs when the h concentration is high. we determined the cl isotope composition and halogen content (f, cl, br, and i) of apatite and merrillite in seven basaltic eucrites, which are meteorites linked to the asteroid 4-vesta, by using secondary ion mass spectrometry. we compare our halogen results with h isotope data, existing bulk rock concentrations, and petrologic models. the inferred cl isotope composition of eucrites from this study, expressed in standard δ37 cl notation, which ranges from -3.8 to 7.7‰, correlates with the bulk major- and trace-element content, e.g., the cl isotope composition positively correlates with mg and sc, while cl isotope composition negatively correlates with k, v, and cr. here we suggest that eucrites preserve evidence of a degassing magma ocean as evidenced by the decreasing bulk rock k content with increasing δ37 cl . if the eucrite parent body, 4-vesta, accreted with a negative δ37 cl of - 3.8 ± 1.1 ‰, at least some parts of the solar nebula would have been isotopically light compared to most estimates of the earth, which on average is close to 0‰. | chlorine and hydrogen degassing in vesta's magma ocean |
in single-star systems like our own solar system, comets dominate the mass budget of bodies ejected into interstellar space, since they form further away and are less tightly bound. however, 1i/`oumuamua, the first interstellar object detected, appears asteroidal in its spectra and lack of detectable activity. we argue that the galactic budget of interstellar objects like 1i/`oumuamua should be dominated by planetesimal material ejected during planet formation in circumbinary systems, rather than in single-star systems or widely separated binaries. we further show that in circumbinary systems, rocky bodies should be ejected in comparable numbers to icy ones. this suggests that a substantial fraction of interstellar objects discovered in future should display an active coma. we find that the rocky population, of which 1i/`oumuamua seems to be a member, should be predominantly sourced from a-type and late b-star binaries. | ejection of rocky and icy material from binary star systems: implications for the origin and composition of 1i/`oumuamua |
during asteroid entry, energy is deposited in the atmosphere through thermal ablation and momentum-loss due to aerodynamic drag. analytic models of asteroid entry and breakup physics are used to compute the energy deposition, which can then be compared against measured light curves and used to estimate ground damage due to airburst events. this work assesses and compares energy deposition results from four existing approaches to asteroid breakup modeling, and presents a new model that combines key elements of those approaches. the existing approaches considered include a liquid drop or "pancake" model where the object is treated as a single deforming body, and a set of discrete fragment models where the object breaks progressively into individual fragments. the new model incorporates both independent fragments and aggregate debris clouds to represent a broader range of fragmentation behaviors and reproduce more detailed light curve features. all five models are used to estimate the energy deposition rate versus altitude for the chelyabinsk meteor impact, and results are compared with an observationally derived energy deposition curve. comparisons show that four of the five approaches are able to match the overall observed energy deposition profile, but the features of the combined model are needed to better replicate both the primary and secondary peaks of the chelyabinsk curve. | asteroid fragmentation approaches for modeling atmospheric energy deposition |
this paper describes asteroid, the pytorch-based audio source separation toolkit for researchers. inspired by the most successful neural source separation systems, it provides all neural building blocks required to build such a system. to improve reproducibility, kaldi-style recipes on common audio source separation datasets are also provided. this paper describes the software architecture of asteroid and its most important features. by showing experimental results obtained with asteroid's recipes, we show that our implementations are at least on par with most results reported in reference papers. the toolkit is publicly available at https://github.com/mpariente/asteroid . | asteroid: the pytorch-based audio source separation toolkit for researchers |
this document serves as a brief overview of the "safe and reliable machine learning" tutorial given at the 2019 acm conference on fairness, accountability, and transparency (fat* 2019). the talk slides can be found here: https://bit.ly/2gfsukp, while a video of the talk is available here: https://youtu.be/fglockc4kme, and a complete list of references for the tutorial here: https://bit.ly/2gdlpme. | tutorial: safe and reliable machine learning |
white dwarfs that have accreted planetary bodies are a powerful probe of the bulk composition of exoplanetary material. in this paper, we present a bayesian model to explain the abundances observed in the atmospheres of 202 dz white dwarfs by considering the heating, geochemical differentiation, and collisional processes experienced by the planetary bodies accreted, as well as gravitational sinking. the majority (>60 per cent) of systems are consistent with the accretion of primitive material. we attribute the small spread in refractory abundances observed to a similar spread in the initial planet-forming material, as seen in the compositions of nearby stars. a range in na abundances in the pollutant material is attributed to a range in formation temperatures from below 1000 k to higher than 1400 k, suggesting that pollutant material arrives in white dwarf atmospheres from a variety of radial locations. we also find that solar system-like differentiation is common place in exoplanetary systems. extreme siderophile (fe, ni, or cr) abundances in eight systems require the accretion of a core-rich fragment of a larger differentiated body to at least a 3σ significance, whilst one system shows evidence that it accreted a crust-rich fragment. in systems where the abundances suggest that accretion has finished (13/202), the total mass accreted can be calculated. the 13 systems are estimated to have accreted masses ranging from the mass of the moon to half that of vesta. our analysis suggests that accretion continues for 11 myrs on average. | bayesian constraints on the origin and geology of exoplanetary material using a population of externally polluted white dwarfs |
we are conducting a survey using twilight time on the dark energy camera with the blanco 4 m telescope in chile to look for objects interior to earth's and venus' orbits. to date we have discovered two rare atira/apohele asteroids, 2021 lj4 and 2021 ph27, which have orbits completely interior to earth's orbit. we also discovered one new apollo-type near earth object (neo) that crosses earth's orbit, 2022 ap7. two of the discoveries have diameters ≳1 km. 2022 ap7 is likely the largest potentially hazardous asteroid (pha) discovered in about eight years. to date we have covered 624 square degrees of sky near to and interior to the orbit of venus. the average images go to 21.3 mag in the r band, with the best images near 22nd mag. our new discovery 2021 ph27 has the smallest semimajor axis known for an asteroid, 0.4617 au, and the largest general relativistic effects (53 arcsec/century) known for any body in the solar system. the survey has detected ~15% of all known atira neos. we put strong constraints on any stable population of venus co-orbital resonance objects existing, as well as the atira and vatira asteroid classes. these interior asteroid populations are important to complete the census of asteroids near earth, including some of the most likely earth impactors that cannot easily be discovered in other surveys. comparing the actual population of asteroids found interior to earth and venus with those predicted to exist by extrapolating from the known population exterior to earth is important to better understand the origin, composition, and structure of the neo population. | a deep and wide twilight survey for asteroids interior to earth and venus |
preliminary mission design requires an efficient and accurate approximation to the low-thrust rendezvous trajectories, which might be generally three-dimensional and involve multiple revolutions. in this paper, a new shaping method using cubic spline functions is developed for the analytical approximation, which shows advantages in the optimality and computational efficiency. the rendezvous constraints on the boundary states and transfer time are all satisfied analytically, under the assumption that the boundary conditions and segment numbers of cubic spline functions are designated in advance. two specific shapes are then formulated according to whether they have free optimization parameters. the shape without free parameters provides an efficient and robust estimation, while the other one allows a subsequent optimization for the satisfaction of additional constraints such as the constraint on the thrust magnitude. applications of the proposed method in combination with the particle swarm optimization algorithm are discussed through two typical interplanetary rendezvous missions, that is, an inclined multi-revolution trajectory from the earth to asteroid dionysus and a multi-rendezvous trajectory of sample return. simulation examples show that the proposed method is superior to existing methods in terms of providing good estimation for the global search and generating suitable initial guess for the subsequent trajectory optimization. | analytical shaping method for low-thrust rendezvous trajectory using cubic spline functions |
water ice near the surface of main belt asteroids is gradually lost to space. a mantle of low thermal conductivity causes large surface temperature amplitudes, and thus increased cooling by thermal re-radiation, lowering temperatures well below the fast-rotator limit. a computational barrier for modeling this ice loss is the multi-scale character of the problem: accurate temperatures require many time steps within a solar day, but ice retreats slowly over billions of years. this barrier is overcome with asynchronous coupling: models of temperature, ice loss, and impact stirring each use their own time steps and are coupled with one another. the model is applied to 1 ceres and 7968 elst-pizarro. on ceres, ice can be expected in the top half meter poleward of 60° latitude on both hemispheres, even if excursions of the axis tilt took place, and even in the presence of impact gardening. at the poles, ice can be expected within a centimeter of the surface. the retreating ice crust leads to emission of water from the surface, mainly at the equator; the gradually retreating ice supplies a water exosphere less dense than has been observed by the herschel telescope. for main belt comet elst-pizarro, depths to ice depend on the properties of the surface mantle. for a dust mantle estimated depths are on the order of a decimeter; for a rocky surface the depth at the pole is on the order of one meter. hence, it could have been activated by a small impact that exposed buried ice. | predictions of depth-to-ice on asteroids based on an asynchronous model of temperature, impact stirring, and ice loss |
the cr chondrites carry one of the most pristine records of the solar nebula materials that accreted to form planetesimals. they have experienced very variable degrees of aqueous alteration, ranging from incipient alteration in their matrices to the complete hydration of all of their components. in order to constrain their chemical alteration pathways and the conditions of alteration, we have investigated the mineralogy and fe oxidation state of silicates in the matrices of 8 cr chondrites, from type 3 to type 1. fe-l edge x-ray absorption near edge structure (xanes) was performed on matrix fib sections using synchrotron-based scanning transmission x-ray microscopy (stxm). the fe3+ / ∑ fe ratio of submicron silicate particles was obtained and coordinated with tem observations. in all the least altered cr chondrites (que 99177, eet 87770, eet 92042, lap 02342, gra 95229 and renazzo), we find that the matrices consist of abundant submicron fe-rich hydrated amorphous silicate grains, mixed with nanometer-sized phyllosilicates. the fe3+ / ∑ fe ratios of both amorphous and nanocrystalline regions are very high with values ranging from 68 to 78%. in the most altered samples (al rais and gro 95577), fine-grained phyllosilicates also have a high fe3+ / ∑ fe ratio (around 70%), whereas the coarse, micrometer-sized phyllosilicates are less oxidized (down to 55%) and have a lower iron content. these observations suggest the following sequence: submicron fe2+-amorphous silicate particles were the building blocks of cr matrices; after accretion they were quickly hydrated and oxidized, leading to a metastable, amorphous gel-like phase. nucleation and growth of crystalline phyllosilicates was kinetically-limited in most type 3 and 2 crs, but increased as alteration became more extensive in al rais and gro 95577. the decreasing fe3+ / ∑ fe ratio is interpreted as a result of the transfer of fe3+ from silicates to oxides during growth, while aqueous alteration progressed (higher temperature, longer duration, change of fluid composition). in a fully closed system, equilibrium thermodynamics suggest that the water to rock ratios, typically assumed to be low (<1) for chondrites, should primarily control the iron valency of the silicates and predict a lower fe3+ / ∑ fe ratio. such a high fe3+ / ∑ fe value could be accounted for, however, if the system was partially open, at least with respect to h2 (and other gases as well). rapid degassing of the fluid would have favored more oxidizing fluid conditions. recently proposed scenarios involving some degree of water d/h increase through rayleigh isotopic fractionation are supported by these results. | widespread oxidized and hydrated amorphous silicates in cr chondrites matrices: implications for alteration conditions and h2 degassing of asteroids |
phosphorus (p) is critical to modern biochemical functions and can control ecosystem growth. it was presumably important as a reagent in prebiotic chemistry. however, on the early earth, p sources may have consisted primarily of poorly soluble calcium phosphates, which may have rendered phosphate as a minimally available nutrient or reagent if these minerals were the sole source. here, we review aqueous p availability on the early earth (>2.5 gyr ago), considering both mineral sources and geochemical sinks relevant to its solvation, and activation by abiotic and biological pathways. phosphorus on earth's early surface would have been present as a mixture of phosphate minerals, as a minor element in silicate minerals, and in reactive, reduced phases from accreted dust, meteorites and asteroids. these p sources would have weathered and plausibly furnished the prebiotic earth with abundant and potentially reactive p. after the origin of a biosphere, life evolved to draw on not just reactive available p sources, but also insoluble and unreactive sources. the rise of an ecosystem dependent on this element at some point forged a p-limited biosphere, with evolutionary stress forcing the efficient extraction and recycling of p from both abiotic and biotic sources and sinks. | phosphorus availability on the early earth and the impacts of life |
detecting celestial bodies while in deep-space travel is a critical task for the correct execution of space missions. major bodies such as planets are bright and therefore easy to observe, while small bodies can be faint and therefore difficult to observe. a critical task for both rendezvous and fly-by missions is to detect asteroid targets, either for relative navigation or for opportunistic observations. traditional, large spacecraft missions can detect small bodies from far away, owing to the large aperture of the onboard optical cameras. this is not the case for deep-space miniaturized satellites, whose small-aperture cameras pose new challenges in detecting and tracking the line-of-sight directions to small bodies. this paper investigates the celestial bodies far-range detection limits for deep-space cubesats, suggesting active measures for small bodies detection. the m–argo cubesat mission is considered as the study case for this activity. the analyses show that the detection of small asteroids (with absolute magnitude fainter than 24) is expected to be in the range of 30,000–50,000 km, exploiting typical miniaturized cameras for deep-space cubesats. given the limited detection range, this paper recommends to include a zero-phase-angle way point at close range in the mission design phase of asteroid rendezvous missions exploiting deep-space cubesats to allow detection. | celestial bodies far-range detection with deep-space cubesats |
the highly hydrated, petrologic type 1 cm and ci carbonaceous chondrites likely derived from primitive, water-rich asteroids, two of which are the targets for jaxa's hayabusa2 and nasa's osiris-rex missions. we have collected visible and near-infrared (vnir) and mid infrared (mir) reflectance spectra from well-characterized cm1/2, cm1, and ci1 chondrites and identified trends related to their mineralogy and degree of secondary processing. the spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately altered cm1/2 chondrites to near 2.73 μm in the highly altered cm1 chondrites. the christiansen features (cf) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more mg-rich, which occurs as aqueous alteration proceeds. spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. the observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. for example, (1) ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly altered cm1 mil 05137, suggesting abundant mg-rich phyllosilicates on the surface. notably, both osiris-rex and hayabusa2 have onboard instruments which cover the vnir and mir wavelength ranges, so the results presented here will help in corroborating initial results from bennu and ryugu. | linking mineralogy and spectroscopy of highly aqueously altered cm and ci carbonaceous chondrites in preparation for primitive asteroid sample return |
we report on the results of the analysis of spectral observations of the asteroid didymos at the time of impact of the dart mission probe, obtained a few minutes before, directly at the moment, and within a few minutes after the spacecraft hit the surface of the dimorphos. we found evidence of alkali metal emissions that appeared at the moment and continued for several minutes after the impact. the observation evidence of the appearance of na, li and k atoms as a result of the impact of the dart probe on the dimorphos in a relative amount close to the abundance of these elements in the solar system are reliably established. we conclude that the main contribution to alkaline emissions is atoms bound to the dust cloud ejected during the impact. this dust cloud is a steady source of alkaline metal atoms. we did not detect the presence of alkaline mater not bound to the dust cloud and moved independently. | observations of alkaline emissions nai, ki and lii during first minutes after dart probe impact on dimorphos |
the solar wind has been implicated as a source of water on airless bodies such as the moon, asteroids, and possibly mercury, yet a kinetic and mechanistic chemical model consistent with present-day observational data is still lacking. utilizing available data sets on temperature-driven water formation and desorption from metal oxides (e.g., sio2, tio2, and al2o3) with surface hydroxyl defects (-oh) and experimental data from a lunar mare regolith apollo sample (10084), the 2.8-μm optical signal on the moon is modeled. specifically, the presence and persistence of this band result from the balance of formation and loss mechanisms associated with solar wind production and thermal transformation of hydroxyls on and within the regolith. this cycle involves formation and release of molecular water via recombinative desorption of the chemically bound -oh. though this mechanism forms gas-phase h2o on the sunlit side, photodissociation and dissociative adsorption lead to rehydroxylation and very limited exospheric water over a lunation. | solar wind-induced water cycle on the moon |
asteroid exploration has a significant importance in promoting our understanding of the solar system and the origin of life on earth. a unique opportunity to study near-earth asteroid 99942 apophis will occur in 2029 because it will be at its perigee. in the current work, a drilling, sampling, and sample-handling system (dsshs) is proposed to penetrate the asteroid regolith, collect regolith samples at different depths, and distribute the samples to different scientific instruments for in situ analysis. in this system, a rotary-drilling method is employed for the penetration, and an inner sampling tube is utilized to collect and discharge the regolith samples. the sampling tube can deliver samples up to a maximum volume of 84 mm3 at a maximum penetration depth of 300 mm to 17 different ovens. to activate the release of volatile substances, the samples will be heated up to a temperature of 600 °c by the ovens, and these substances will be analyzed by scientific instruments such as a mass spectrometer, an isotopic analyzer, and micro-cameras, among other instruments. the dsshs is capable of penetrating rocks with a hardness value of six, and it can be used for china's asteroid exploration mission in the foreseeable future. | drilling, sampling, and sample-handling system for china's asteroid exploration mission |
previous studies indicate that more than a quarter of all white dwarf (wd) atmospheres are polluted by remnant planetary material, with some wds being observed to accrete the mass of pluto in 106 yr. the short sinking time-scale for the pollutants indicates that the material must be frequently replenished. moons may contribute decisively to this pollution process if they are liberated from their parent planets during the post-main-sequence evolution of the planetary systems. here, we demonstrate that gravitational scattering events amongst planets in wd systems easily trigger moon ejection. repeated close encounters within tenths of planetary hill radii are highly destructive to even the most massive, close-in moons. consequently, scattering increases both the frequency of perturbing agents in wd systems, as well as the available mass of polluting material in those systems, thereby enhancing opportunities for collision and fragmentation and providing more dynamical pathways for smaller bodies to reach the wd. moreover, during intense scattering, planets themselves have pericentres with respect to the wd of only a fraction of an astronomical unit, causing extreme hill-sphere contraction, and the liberation of moons into wd-grazing orbits. many of our results are directly applicable to exomoons orbiting planets around main-sequence stars. | liberating exomoons in white dwarf planetary systems |
localized contractile configurations or asters spontaneously appear and disappear as emergent structures in the collective stochastic dynamics of active polar actomyosin filaments. passive particles which (un)bind to the active filaments get advected into the asters, forming transient clusters. we study the phase segregation of such passive advective scalars in a medium of dynamic asters, as a function of the aster density and the ratio of the rates of aster remodeling to particle diffusion. the dynamics of coarsening shows a violation of porod behavior; the growing domains have diffuse interfaces and low interfacial tension. the phase-segregated steady state shows strong macroscopic fluctuations characterized by multiscaling and intermittency, signifying rapid reorganization of macroscopic structures. we expect these unique nonequilibrium features to manifest in the actin-dependent molecular clustering at the cell surface. | phase segregation of passive advective particles in an active medium |
the impact cratering record of the moon and the terrestrial planets provides important clues about the formation and evolution of the solar system. especially intriguing is the epoch ≃3.8-3.9 gyr ago (ga), known as the late heavy bombardment (lhb), when the youngest lunar basins such as imbrium and orientale formed. the lhb was suggested to originate from a slowly declining impactor flux or from a late dynamical instability. here, we develop a model for the historical flux of large asteroid impacts and discuss how it depends on various parameters, including the time and nature of the planetary migration/instability. we find that the asteroid impact flux dropped by 1-2 orders of magnitude during the first 1 gyr and remained relatively unchanged over the last 3 gyr. the early impacts were produced by asteroids whose orbits became excited during the planetary migration/instability, and by those originating from the inner extension of the main belt. the profiles obtained for the early and late versions of the planetary instability initially differ, but end up being similar after ∼3 ga. thus, the time of the instability can only be determined by considering the cratering and other constraints during the first ≃1.5 gyr of the solar system history. our absolute calibration of the impact flux indicates that asteroids were probably not responsible for the lhb, independently of whether the instability happened early or late, because the calibrated flux is not large enough to explain imbrium/orientale and a significant proportion of large lunar craters. | modeling the historical flux of planetary impactors |
in the past decade, the number of known binary near-earth asteroids has more than quadrupled and the number of known large main-belt asteroids with satellites has doubled. half a dozen triple asteroids have been discovered, and the previously unrecognized populations of asteroid pairs and small main-belt binaries have been identified. the current observational evidence confirms that small (≲20 km) binaries form by rotational fission and establishes that the yarkovsky-o'keefe-radzievskii-paddack (yorp) effect powers the spin-up process. a unifying paradigm based on rotational fission and post-fission dynamics can explain the formation of small binaries, triples, and pairs. large (>~20 km) binaries with small satellites are most likely created during large collisions. | asteroid systems: binaries, triples, and pairs |
future gamma-ray experiments, such as the e-astrogam and amego telescopes, can detect the hawking radiation of photons from primordial black holes (pbhs) if they make up a fraction or all of dark matter. pbhs can analogously also hawking radiate new particles, which is especially interesting if these particles are mostly secluded from the standard model sector, since they might therefore be less accessible otherwise. a well-motivated example of this type is axionlike particles (alps) with a tiny coupling to photons. we assume that the alps produced by pbhs decay into photons well before reaching the earth, so these will augment the photons directly radiated by the pbhs. remarkably, we find that the peaks in the energy distributions of alps produced from pbhs are different than the corresponding ones for hawking radiated photons due to the spin-dependent graybody factor. therefore, we demonstrate that this process will in fact distinctively modify the pbhs' gamma-ray spectrum relative to the standard model prediction. we use monochromatic asteroid-mass pbhs as an example to show that e-astrogam can observe the pbh-produced alp gamma-ray signal (for masses up to ∼60 mev ) and further distinguish it from hawking radiation without alps. by measuring the gamma-ray signals, e-astrogam can thereby probe yet unexplored parameters in the alp mass and photon coupling. | detecting axionlike particles with primordial black holes |
the closest perihelion pass of parker solar probe (psp), so far, occurred between 2021 november 16 and 26 and reached ~13.29 r ☉ from sun center. this pass resulted in very unique observations of the solar corona by the wide-field instrument for solar probe (wispr). wispr observed at least 10 coronal mass ejections (cmes), some of which were so close that the structures appear distorted. all of the cmes appeared to have a magnetic flux rope (mfr) structure, and most were oriented such that the view was along the axis orientation, revealing very complex interiors. two cmes had a small mfr develop in the interior, with a bright circular boundary surrounding a very dark interior. trailing the larger cmes were substantial outflows of small blobs and flux-rope-like structures within striated ribbons, lasting for many hours. when the heliospheric plasma sheet was inclined, as it was during the days around perihelion on 2021 november 21, the outflow was over a very wide latitude range. one cme was overtaken by a faster one, with a resultant compression of the rear of the leading cme and an unusual expansion in the trailing cme. the small thomson surface creates brightness variations of structures as they pass through the field of view. in addition to this dynamic activity, a brightness band from excess dust along the orbit of asteroid/comet 3200 phaethon is also seen for several days. | overview of the remote sensing observations from psp solar encounter 10 with perihelion at 13.3 r ⊙ |
on september 26th 2022, liciacube monitored double asteroid redirection test (dart) mission impact on asteroid dimorphos, which is the smaller component of a binary asteroid system. these close observations revealed the impact ejecta features of the first planetary defence test with a kinetic impactor. | impact observations of asteroid dimorphos via light italian cubesat for imaging of asteroids (liciacube) |
the application of a modern solving algorithm or method of resolving dynamical equations for small projectile of finite sizes orbiting to be captured in a trapped zigzaging oscillations on orbit around the another large asteroid and in a further inelastic colliding scenario with him (using a formulation of the elliptic restricted three-body problem, er3bp) is studied semi-analytically. herein, two primaries msun and mp (mp < msun) revolve around their barycenter on keplerian orbits with low eccentricities. a smaller body (projectile for attacking a large asteroid) is supposed to be a solid, almost symmetric ellipsoid, having the gravitational potential of the maccullagh type. our aim is to develop a previously introduced solving procedure and to investigate the updated dynamics of the projectile captured to a trapped dynamical resonance, thereby having the inelastic collision of a small projectile orbiting on quasi-stable elliptic orbits around the large asteroid, mp. | capture in regime of a trapped motion with further inelastic collision for finite-sized asteroid in er3bp |
a comprehensive asteroid threat assessment requires the quantification of both the impact likelihood and resulting consequence across the range of possible events. this paper presents a probabilistic asteroid impact risk (pair) assessment model developed for this purpose. the model incorporates published impact frequency rates with state-of-the-art consequence assessment tools, applied within a monte carlo framework that generates sets of impact scenarios from uncertain input parameter distributions. explicit treatment of atmospheric entry is included to produce energy deposition rates that account for the effects of thermal ablation and object fragmentation. these energy deposition rates are used to model the resulting ground damage, and affected populations are computed for the sampled impact locations. the results for each scenario are aggregated into a distribution of potential outcomes that reflect the range of uncertain impact parameters, population densities, and strike probabilities. as an illustration of the utility of the pair model, the results are used to address the question of what minimum size asteroid constitutes a threat to the population. to answer this question, complete distributions of results are combined with a hypothetical risk tolerance posture to provide the minimum size, given sets of initial assumptions for objects up to 300 m in diameter. model outputs demonstrate how such questions can be answered and provide a means for interpreting the effect that input assumptions and uncertainty can have on final risk-based decisions. model results can be used to prioritize investments to gain knowledge in critical areas or, conversely, to identify areas where additional data have little effect on the metrics of interest. | a probabilistic asteroid impact risk model: assessment of sub-300 m impacts |
when the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) spacecraft collected a sample of surface material from asteroid bennu in 2020 october, it was the first time that an autonomous optical navigation system relying on natural terrain features had been used to guide a spacecraft to a planetary surface. this system, called natural feature tracking (nft), works by rendering features from digital terrain models and then correlating them with the terrain in real-time navigation images to estimate the spacecraft's position and velocity with respect to the asteroid. here we describe how the osiris-rex mission built the catalog of features for nft and how those features performed during rehearsals for and execution of the touch-and-go (tag) sample collection event. feature performance (quality and accuracy of match) in the rendering and correlation process is the basis of the nft measurement. all features scored well above the minimum correlation threshold thanks to the effort invested in selecting and modeling them. residuals across the tag trajectory were small, indicating that features in the catalog were defined consistently relative to each other. nft delivered the spacecraft to within 1 m of the targeted location, with a difference of only 3.5 cm and 1.4 s from the predicted location and time of touch. this exceptional performance was crucial for spacecraft safety given bennu's rough and hazardous terrain. | autonomous navigation performance using natural feature tracking during the osiris-rex touch-and-go sample collection event |
the origins, spectral interpretation, resource identification, and security-regolith explorer (osiris-rex) mission rendezvoused with asteroid (101955) bennu in 2018 with the primary objective of collecting a sample of regolith from the surface. as the first nasa asteroid sample return mission, osiris-rex deployed several new technologies to achieve program objectives. here we present an overview of natural feature tracking (nft), a system developed to autonomously guide the spacecraft to the desired sampling site using optical navigation and the natural terrain on the surface of bennu. nft utilized a series of image-based digital terrain models (dtms) constructed by means of stereophotoclinometry to represent patches on the surface of the asteroid. these dtms were used to generate synthetic renderings of the terrain and identify features for use in navigating to the sampling location. in addition, high-resolution models of the sampling site constructed from scanning lidar data were used for predicting the time and location of contact with the surface. these models went through a series of validation tests to ensure the performance of the nft system. when the spacecraft executed the sampling trajectory in 2020 october, nft enabled real-time guidance updates that delivered it safely to the desired sampling location while also providing critical hazard avoidance capabilities in the rocky bennu environment. | the use of digital terrain models for natural feature tracking at asteroid bennu |
meteoroid bombardment of the earth-moon system must have caused catastrophic damage to the terrestrial ecosphere. however, ancient meteoroid impacts and their relations to environmental changes are not well understood because of erosion and/or resurfacing processes on earth. here, we investigate the formation ages of 59 lunar craters with fresh morphologies and diameters greater than approximately 20 km and first find that 8 of 59 craters were formed simultaneously. considering the radiometric ages of ejecta from copernicus crater and impact glass spherules from various apollo landing sites, we conclude that sporadic meteoroid bombardment occurred across the whole moon at approximately 800 ma. based on crater scaling laws and collision probabilities with the earth and moon, we suggest that at least (4-5) × 1016 kg of meteoroids, approximately 30-60 times more than the chicxulub impact, must have plunged into the earth-moon system immediately before the cryogenian, which was an era of great environmental changes. | asteroid shower on the earth-moon system immediately before the cryogenian period revealed by kaguya |
the asuka (a)-12236 meteorite has recently been classified as a cm carbonaceous chondrite of petrologic type 3.0/2.9 and is among the most primitive cm meteorites studied to date. here, we report the concentrations, relative distributions, and enantiomeric ratios of amino acids in water extracts of the a-12236 meteorite and another primitive cm chondrite elephant moraine (eet) 96029 (cm2.7) determined by ultra-high-performance liquid chromatography time-of-flight mass spectrometry. eet 96029 was highly depleted in amino acids and dominated by glycine, while a wide diversity of two- to six-carbon aliphatic primary amino acids were identified in a-12236, which had a total amino acid abundance of 360 ± 18 nmol g-1, with most amino acids present without hydrolysis (free). the amino acid concentrations of a-12236 were double those previously measured in the cm2.7 paris meteorite, consistent with a-12236 being a highly primitive and unheated cm chondrite. the high relative abundance of α-amino acids in a-12236 is consistent with formation by a strecker-cyanohydrin dominated synthesis during a limited early aqueous alteration phase on the cm meteorite parent body. the presence of predominantly free glycine, a near racemic mixture of alanine (d/l ~0.93-0.96), and elevated abundances of several terrestrially rare non-protein amino acids including α-aminoisobutyric acid (α-aib) and racemic isovaline indicate that these amino acids in a-12236 are extraterrestrial in origin. given a lack of evidence for biological amino acid contamination in a-12236, it is possible that some of the l-enantiomeric excesses (lee ~34-64%) of the protein amino acids, aspartic and glutamic acids and serine, are indigenous to the meteorite; however, isotopic measurements are needed for confirmation. in contrast to more aqueously altered cms of petrologic types ≤2.5, no l-isovaline excesses were detected in a-12236. this observation strengthens the hypothesis that extensive parent body aqueous activity is required to produce or amplify the large l-isovaline excesses that cannot be explained solely by exposure to circularly polarized radiation or other chiral symmetry breaking mechanisms prior to incorporation into the asteroid parent body. | abundant extraterrestrial amino acids in the primitive cm carbonaceous chondrite asuka 12236 |
the apollo-derived tenet of an anhydrous moon has been contested following measurement of water in several lunar samples that require water to be present in the lunar interior. however, significant uncertainties exist regarding the flux, sources and timing of water delivery to the moon. here we address those fundamental issues by constraining the mass of water accreted to the moon and modelling the relative proportions of asteroidal and cometary sources for water that are consistent with measured isotopic compositions of lunar samples. we determine that a combination of carbonaceous chondrite-type materials were responsible for the majority of water (and nitrogen) delivered to the earth-moon system. crucially, we conclude that comets containing water enriched in deuterium contributed significantly <20% of the water in the moon. therefore, our work places important constraints on the types of objects impacting the moon ~4.5-4.3 billion years ago and on the origin of water in the inner solar system. | an asteroidal origin for water in the moon |
we present spectral measurements of a suite of mineral mixtures and meteorites that are possible analogs for asteroid (101955) bennu, the target asteroid for nasa's origins, spectral interpretation, resource identification, security, regolith explorer (osiris-rex) mission. the sample suite, which includes anhydrous and hydrated mineral mixtures and a suite of chondritic meteorites (cm, ci, cv, cr, and l5), was chosen to characterize the spectral effects due to varying amounts of aqueous alteration and minor amounts of organic material. our results demonstrate the utility of mineral mixtures for understanding the mixing behavior of meteoritic materials and identifying spectrally dominant species across the visible to near-infrared (vnir) and thermal infrared (tir) spectral ranges. our measurements demonstrate that, even with subtle signatures in the spectra of chondritic meteorites, we can identify diagnostic features related to the minerals comprising each of the samples. also, the complementary nature of the two spectral ranges regarding their ability to detect different mixture and meteorite components can be used to characterize analog sample compositions better. however, we observe differences in the vnir and tir spectra between the mineral mixtures and the meteorites. these differences likely result from (1) differences in the types and physical disposition of constituents in the mixtures versus in meteorites, (2) missing phases observed in meteorites that we did not add to the mixtures, and (3) albedo differences among the samples. in addition to the initial characterization of the analog samples, we will use these spectral measurements to test phase detection and abundance determination algorithms in anticipation of mapping bennu's surface properties and selecting a sampling site. | spectral characterization of analog samples in anticipation of osiris-rex's arrival at bennu: a blind test study |
osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) is a nasa mission to return a sample of asteroid (101955) bennu. photometric modeling of bennu's surface is a key element of both sample site characterization and our broader scientific understanding of the asteroid. bennu's heterogeneous surface presents substantial variation in reflectance and produces a scattered dataset that poses a challenge to photometric modeling. we show that the resolution of the shape model with which we calculate photometric angles strongly affects the accuracy of the analysis, as well as the efficacy of subsequent photometric corrections. we use global imaging data to fit empirical photometric models of the surface. these models represent the average behavior of bennu's surface and can be used beyond this work to photometrically correct panchromatic and color basemaps of bennu and perform albedo analyses of individual features on bennu's surface. bennu's global photometry reveals a moderate opposition effect and detectable phase reddening, both of which suggest a macroscopically rough surface, which is confirmed by centimeter-scale images of the asteroid. | disk-resolved photometric modeling and properties of asteroid (101955) bennu |
remote sensing observations made by the spacecraft hayabusa provided the first direct evidence of a rubble-pile asteroid: 25143 itokawa. itokawa was found to have a surface structure very different from other explored asteroids; covered with coarse pebbles and boulders ranging at least from cm to meter size. the cumulative size distribution of small circular depressions on itokawa, most of which may be of impact origin, has a significantly shallower slope than that on the moon; small craters are highly depleted on itokawa compared to the moon. this deficiency of small circular depressions and other features, such as clustered fragments and pits on boulders, suggest that the boulders on itokawa might behave like armor, preventing crater formation: the ;armoring effect;. this might contribute to the low number density of small crater candidates. in this study, the cratering efficiency reduction due to coarse-grained targets was investigated based on impact experiments at velocities ranging from ∼ 70 m/s to ∼ 6 km/s using two vertical gas gun ranges. we propose a scaling law extended for cratering on coarse-grained targets (i.e., target grain size ≳ projectile size). we have found that the crater efficiency reduction is caused by energy dissipation at the collision site where momentum is transferred from the impactor to the first-contact target grain, and that the armoring effect can be classified into three regimes: (1) gravity scaled regime, (2) reduced size crater regime, or (3) no apparent crater regime, depending on the ratio of the impactor size to the target grain size and the ratio of the impactor kinetic energy to the disruption energy of a target grain. we found that the shallow slope of the circular depressions on itokawa cannot be accounted for by this new scaling law, suggesting that obliteration processes, such as regolith convection and migration, play a greater role in the depletion of circular depressions on itokawa. based on the new extended scaling law, we found that the crater retention age on itokawa is 3-33 myr in the main belt, which is in good agreement with the cosmic-ray-exposure ages for returned samples from itokawa which may reflect the age of material a few meters beneath the surface. these ages strongly suggest that the global resurfacing that reset the 1-10 m deep surface layer may have occurred in the main belt long after the possible catastrophic disruption of a rigid parent body of itokawa suggested by ar degassing age ( ∼ 1.3 gyr). | cratering efficiency on coarse-grain targets: implications for the dynamical evolution of asteroid 25143 itokawa |
impacting an asteroid with a spacecraft traveling at high speed delivers an impulsive change in velocity to the body. in certain circumstances, this strategy could be used to deflect a hazardous asteroid, moving its orbital path off of an earth-impacting course. however, the efficacy of momentum delivery to asteroids by hypervelocity impact is sensitive to both the impact conditions (particularly velocity) and specific characteristics of the target asteroid. here we numerically model asteroid response to kinetic impactors under a wide range of initial conditions, using an adaptive smoothed particle hydrodynamics code. impact velocities spanning 1-30 km/s were investigated, yielding, for a particular set of assumptions about the modeled target material, a power-law dependence consistent with a velocity-scaling exponent of μ = 0.44. target characteristics including equation of state, strength model, porosity, rotational state, and shape were varied, and corresponding changes in asteroid response were documented. the kinetic-impact momentum-multiplication factor, β, decreases with increasing asteroid cohesion and increasing porosity. although increased porosity lowers β, larger porosities result in greater deflection velocities, as a consequence of reduced target masses for asteroids of fixed size. porosity also lowers disruption risk for kinetic impacts near the threshold of disruption. including fast (p = 2.5 h) and very fast (p = 100 s) rotation did not significantly alter β but did affect the risk of disruption by the impact event. asteroid shape is found to influence the efficiency of momentum delivery, as local slope conditions can change the orientation of the crater ejecta momentum vector. these results emphasize the need for asteroid characterization studies to bracket the range of target conditions expected at near-earth asteroids while also highlighting some of the principal uncertainties associated with the kinetic-impact deflection strategy. | deflection by kinetic impact: sensitivity to asteroid properties |
the disruption of asteroids and comets produces cm-sized meteoroids that end up impacting the earth's atmosphere and producing bright fireballs that might have associated shock waves or, in geometrically favourable occasions excavate craters that put them into unexpected hazardous scenarios. the astrometric reduction of meteors and fireballs to infer their atmospheric trajectories and heliocentric orbits involves a complex and tedious process that generally requires many manual tasks. to streamline the process, we present a software package called spmn 3d fireball trajectory and orbit calculator (3d-firetoc), an automatic python code for detection, trajectory reconstruction of meteors, and heliocentric orbit computation from video recordings. the automatic 3d-firetoc package comprises of a user interface and a graphic engine that generates a realistic 3d representation model, which allows users to easily check the geometric consistency of the results and facilitates scientific content production for dissemination. the software automatically detects meteors from digital systems, completes the astrometric measurements, performs photometry, computes the meteor atmospheric trajectory, calculates the velocity curve, and obtains the radiant and the heliocentric orbit, all in all quantifying the error measurements in each step. the software applies corrections such as light aberration, refraction, zenith attraction, diurnal aberration, and atmospheric extinction. it also characterizes the atmospheric flight and consequently determines fireball fates by using the α - β criterion that analyses the ability of a fireball to penetrate deep into the atmosphere and produce meteorites. we demonstrate the performance of the software by analysing two bright fireballs recorded by the spanish fireball and meteorite network (spmn). | accurate 3d fireball trajectory and orbit calculation using the 3d-firetoc automatic python code |
the accretion of dark matter around the primordial black holes (pbhs) could lead to the formation of surrounding minihalos, whose mass can be several orders of magnitude higher than the central pbh mass. the gravitational microlensing produced by such dressed pbhs could be quite different from that of the bare pbhs, which may significantly affect the constraints on the pbh abundance. in this paper, we study the gravitational microlensing produced by dressed pbhs in detail. we find that all the microlensing effects by dressed pbhs have asymptotic behavior depending on the minihalo size, which can be used to predict the microlensing effects by comparing the halo size with the einstein radius. when the minihalo radius and the einstein radius are comparable, the effect of the density distribution of the halo is significant to the microlensing. applying the stellar microlensing by dressed pbhs to the data of the optical gravitational lensing experiment and subaru/hsc andromeda observations, we obtain the improved constraints on the pbh abundance. it shows that the existence of dark matter minihalos surrounding pbhs can strengthen the constraints on the pbh abundance from stellar microlensing by several orders, and can shift the constraints to the well-known asteroid mass window where pbhs can constitute all the dark matter. | gravitational microlensing by dressed primordial black holes |
the growing popularity of cloud-based machine learning raises a natural question about the privacy guarantees that can be provided in such a setting. our work tackles this problem in the context where a client wishes to classify private images using a convolutional neural network (cnn) trained by a server. our goal is to build efficient protocols whereby the client can acquire the classification result without revealing their input to the server, while guaranteeing the privacy of the server's neural network. to this end, we design gazelle, a scalable and low-latency system for secure neural network inference, using an intricate combination of homomorphic encryption and traditional two-party computation techniques (such as garbled circuits). gazelle makes three contributions. first, we design the gazelle homomorphic encryption library which provides fast algorithms for basic homomorphic operations such as simd (single instruction multiple data) addition, simd multiplication and ciphertext permutation. second, we implement the gazelle homomorphic linear algebra kernels which map neural network layers to optimized homomorphic matrix-vector multiplication and convolution routines. third, we design optimized encryption switching protocols which seamlessly convert between homomorphic and garbled circuit encodings to enable implementation of complete neural network inference. we evaluate our protocols on benchmark neural networks trained on the mnist and cifar-10 datasets and show that gazelle outperforms the best existing systems such as minionn (acm ccs 2017) by 20 times and chameleon (crypto eprint 2017/1164) by 30 times in online runtime. similarly when compared with fully homomorphic approaches like cryptonets (icml 2016) we demonstrate three orders of magnitude faster online run-time. | gazelle: a low latency framework for secure neural network inference |
the astorb database at lowell observatory is an actively curated catalog of all known asteroids in the solar system. astorb has heritage dating back to the 1970s and has been publicly accessible since the 1990s. work began in 2015 to modernize the underlying database infrastructure, operational software, and associated web applications. that effort involved the expansion of astorb to incorporate new data such as physical properties (e.g. albedo, colors, spectral types) from a variety of sources. the data in astorb are used to support a number of research tools hosted at https://asteroid.lowell.edu. here we present a full description of the software tools, computational foundation, and data products upon which the astorb ecosystem has been built. | the astorb database at lowell observatory |
the dart spacecraft will impact dimorphos (the secondary body of the didymos binary asteroid) to test the kinetic impactor deflection method against possibly hazardous near-earth asteroids. the dart impact ejecta plume, and possibly the impact crater, will be imaged by the liciacube spacecraft, hosted as a piggyback and released by dart just before the impact, and then, several years later, by the hera probe. to exploit the wealth of data obtained and understand the physics of the whole impact experiment, it is of paramount importance to properly model the dynamics of the binary system pre- and postimpact and the dynamics of the particles ejected from the impact crater. a model was developed to simulate the evolution of the ejecta particles created during the impact in order to first interpret the liciacube images and then test the survival of particles on long intervals of time that might be detected by the hera mission either as individual bodies or as parts of rings. the dynamical evolution of the particles is simulated over different timescales to highlight the most important perturbations and their relative importance. the ejecta dynamics turns out to be highly chaotic due to repeated close encounters with the two asteroids. however, we find that some ejecta survive in the binary orbital environment for timescales comparable to the hera arrival time. the effects of the particles reimpacting against either one of the components is also analyzed to estimate the amount of momentum transfer to the target bodies. | dynamical evolution of ejecta from the dart impact on dimorphos |
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