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an understanding of the post-impact dynamics of ejecta clouds are crucial to the planning of a kinetic impact mission to an asteroid, and also has great implications for the history of planetary formation. the purpose of this article is to track the evolution of ejecta produced by aida mission, which targets for kinetic impact the secondary of near-earth binary asteroid (65803) didymos on 2022, and to feedback essential informations to aida's ongoing phase-a study. we present a detailed dynamic model for the simulation of an ejecta cloud from a binary asteroid that synthesizes all relevant forces based on a previous analysis of the mechanical environment. we apply our method to gain insight into the expected response of didymos to the aida impact, including the subsequent evolution of debris and dust. the crater scaling relations from laboratory experiments are employed to approximate the distributions of ejecta mass and launching speed. the size distribution of fragments is modeled with a power law fitted from observations of real asteroid surface. a full-scale demonstration is simulated using parameters specified by the mission. we report the results of the simulation, which include the computed spread of the ejecta cloud and the recorded history of ejecta accretion and escape. the violent period of the ejecta evolution is found to be short, and is followed by a stage where the remaining ejecta is gradually cleared. solar radiation pressure proves to be efficient in cleaning dust-size ejecta, and the simulation results after two weeks shows that large debris on polar orbits (perpendicular to the binary orbital plane) has a survival advantage over smaller ejecta and ejecta that keeps to low latitudes. | ejecta cloud from the aida space project kinetic impact on the secondary of a binary asteroid: i. mechanical environment and dynamical model |
methods to constrain the surface mineralogy of asteroids have seen considerable development during the last decade, with advancement in laboratory spectral calibrations and validation of interpretive methodologies by spacecraft rendezvous missions. this has enabled the accurate identification of several meteorite parent bodies in the main asteroid belt and helped constrain the mineral chemistries and abundances in ordinary chondrites and basaltic achondrites. with better quantification of spectral effects due to temperature, phase angle, and grain size, systematic discrepancies due to noncompositional factors can now be virtually eliminated for mafic silicate-bearing asteroids. interpretation of spectrally featureless asteroids remains a challenge. this chapter presents a review of all mineralogical interpretive tools currently in use and outlines procedures for their application. | mineralogy and surface composition of asteroids |
one of the most accurate models currently used to represent the gravity field of irregular bodies is the polyhedral approach. in this model, the mass of the body is assumed to be homogeneous, which may not be true for a real object. the main goal of the this paper is to study the dynamical effects induced by three different internal structures (uniform, three- and four-layered) of asteroid (21) lutetia, an object that recent results from space probe suggest being at least partially differentiated. the mascon gravity approach used in the this work consists of dividing each tetrahedron into eight parts to calculate the gravitational field around the asteroid. the zero-velocity curves show that the greatest displacement of the equilibrium points occurs in the position of the e4 point for the four-layered structure and the smallest one occurs in the position of the e3 point for the three-layered structure. moreover, stability against impact shows that the planar limit gets slightly closer to the body with the four-layered structure. we then investigated the stability of orbital motion in the equatorial plane of (21) lutetia and propose numerical stability criteria to map the region of stable motions. layered structures could stabilize orbits that were unstable in the homogeneous model. | the dynamical environment of asteroid 21 lutetia according to different internal models |
comets and small planetesimals are believed to contain primordial building blocks in the form of millimeter to centimeter sized pebbles. one of the viable growing mechanisms to form these small bodies is through the streaming instability (si) in which pebbles cluster and gravitationally collapse toward a planetesimal or comet in the presence of gas drag. however, most si simulations are global and lack the resolution to follow the final collapse stage of a pebble cloud within its hill radius. we aim to track the collapse of a gravitationally bound pebble cloud subject to mutual collisions and gas drag with the representative particle approach. we determine the radial pebble size distribution of the collapsed core and the impact of mutual pebble collisions on the pebble size distribution. we find that virial equilibrium is never reached during the cloud evolution and that, in general, pebbles with a given stokes number (st) collapse toward an optically thick core in a sequence from aerodynamically largest (st ~ 0.1) to aerodynamically smallest (st ~ 2 × 10−3). we show that at the location where the core becomes optically thick, the terminal velocity vt,* ~ 60 m s−1st2 is well below the fragmentation threshold velocity. while collisional processing is negligible during cloud evolution, the collisions that do occur are sticking. these results support the observations that comets and small planetary bodies are composed of primordial pebbles in the millimeter to centimeter size range. | the radial structure of planetary bodies formed by the streaming instability |
asteroid (3200) phaethon, a b-type asteroid, has been active during its perihelion passages. this asteroid is considered to be a source of the geminid meteor stream. it is reported that this asteroid is spinning at a rotation period of 3.60 hr and has a top shape (an oblate body with an equatorial ridge) with a mean equatorial diameter of 6.25 km. here, we report that phaethon's rotation state may be close to or above its critical rotation period when the bulk density is 0.5-1.5 g cm-3 (a typical bulk density of a b-type asteroid). we found that in this condition, the structure of phaethon is sensitive to failure unless the cohesive strength is ∼ 50 - ∼ 260 pa. this result implies that if there are some surface processes driven by, for example, thermal waves, large-scaled deformation may happen and cause mass shedding. from this interpretation, we propose the processes that produced the geminid meteor stream in the past and dust tails recently. phaethon initially rotated at a spin period shorter than the current period. the magnitude of structural deformation at this stage was higher than the present spin condition, and a large mass-shedding event, i.e., the geminid meteor stream, occurred. after this deformation process, the body became more oblate, and its spin slowed down. at this point, while the spin was high enough for the body to have mass-shedding events, the magnitude of these events became small. | mass-shedding activities of asteroid (3200) phaethon enhanced by its rotation |
a determination of the dynamical evolution of the asteroid belt is difficult because the asteroid belt has evolved since the time of asteroid formation through mechanisms that include: (1) catastrophic collisions, (2) rotational disruption, (3) chaotic orbital evolution, and (4) orbital evolution driven by yarkovsky radiation forces. the time-scales of these loss mechanisms are uncertain and there is a need for more observational constraints. in the inner main belt (imb), the mean size of the non-family asteroids increases with increasing inclination. here, we use that observation to show that all imb asteroids originate from either the known families or from ghost families, that is, old families with dispersed orbital elements. we estimate that the average age of the asteroids in the ghost families is a factor of 1/3 less than the yarkovsky orbital evolution time-scale. however, this orbital evolution time-scale is a long-term average that must allow for the collisional evolution of the asteroids and for stochastic changes in their spin directions. by applying these constraints on the orbital evolution time-scales to the evolution of the size-frequency distribution of the vesta asteroid family, we estimate that the age of this family is greater than 1.3 gyr and could be comparable with the age of the solar system. by estimating the number of ghost families, we calculate that the number of asteroids that are the root sources of the meteorites and the near-earth asteroids that originate from the imb is about 20. | dynamical evolution of the inner asteroid belt |
asteroid-mass primordial black holes (pbhs) can explain the observed dark matter abundance while being consistent with the current indirect detection constraints. these pbhs can produce gamma-ray signals from hawking radiation that are within the sensitivity of future measurements by the amego and e-astrogam experiments. pbhs which give rise to such observable gamma-ray signals have a cosmic origin from large primordial curvature fluctuations. there must then be a companion, stochastic gravitational wave (gw) background produced by the same curvature fluctuations. we demonstrate that the resulting gw signals will be well within the sensitivity of future detectors such as lisa, decigo, bbo, and the einstein telescope. the multimessenger signal from the observed gamma-rays and gws will allow a precise measurement of the primordial curvature perturbation that produces the pbh. indeed, we argue that the resulting correlation between the two types of observations can provide a smoking-gun signal of pbhs. | correlating gravitational wave and gamma-ray signals from primordial black holes |
context. large and publicly available astronomical archives open up new possibilities to search for and study solar system objects. however, advanced techniques are required to deal with the large amounts of data. these unbiased surveys can be used to constrain the size distribution of minor bodies, which represents a piece of the puzzle for the formation models of the solar system.aims: we aim to identify asteroids in archival images from the esa hubble space telescope (hst) science data archive using data mining.methods: we developed a citizen science project on the zooniverse platform, hubble asteroid hunter, and have asked members of the public to identify asteroid trails in archival hst images. we used the labels provided by the volunteers to train an automated deep learning model built with google cloud automl vision to explore the entire hst archive to detect asteroids crossing the field-of-view.results: we report the detection of 1701 new asteroid trails identified in archival hst data via our citizen science project and the subsequent machine learning exploration of the esa hst science data archive. we detect asteroids to a magnitude of 24.5, which are statistically fainter than the populations of asteroids identified from ground-based surveys. the majority of asteroids are distributed near the ecliptic plane, as expected, where we find an approximate density of 80 asteroids per square degree. we matched 670 trails (39% of the trails found) with 454 known solar system objects in the minor planet center database; however, no matches were found for 1031 (61%) trails. the unidentified asteroids are faint, on average 1.6 magnitudes fainter than the asteroids we succeeded in identifying. they probably correspond to previously unknown objects.conclusions: citizen science and machine learning are very useful techniques for the systematic search for solar system objects in existing astronomy science data archives. this work describes a method for finding new asteroids in astronomical archives that span decades; it could be effectively applied to other datasets, increasing the overall sample of well-characterised small bodies in the solar system and refining their ephemerides. full table a.1 is only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/661/a85 www.asteroidhunter.org | hubble asteroid hunter. i. identifying asteroid trails in hubble space telescope images |
mounting discoveries of debris discs orbiting newly formed stars and white dwarfs (wds) showcase the importance of modelling the long-term evolution of small bodies in exosystems. wd debris discs are, in particular, thought to form from very long-term (0.1-5.0 gyr) instability between planets and asteroids. however, the time-consuming nature of n-body integrators which accurately simulate motion over gyrs necessitates a judicious choice of initial conditions. the analytical tools known as periodic orbits can circumvent the guesswork. here, we begin a comprehensive analysis directly linking periodic orbits with n-body integration outcomes with an extensive exploration of the planar circular restricted three-body problem (crtbp) with an outer planet and inner asteroid near or inside of the 2:1 mean motion resonance. we run nearly 1000 focused simulations for the entire age of the universe (14 gyr) with initial conditions mapped to the phase space locations surrounding the unstable and stable periodic orbits for that commensurability. in none of our simulations did the planar crtbp architecture yield a long-time-scale (≳0.25 per cent of the age of the universe) asteroid-star collision. the pericentre distance of asteroids which survived beyond this time-scale (≈35 myr) varied by at most about 60 per cent. these results help affirm that collisions occur too quickly to explain wd pollution in the planar crtbp 2:1 regime, and highlight the need for further periodic orbit studies with the eccentric and inclined tbp architectures and other significant orbital period commensurabilities. | linking long-term planetary n-body simulations with periodic orbits: application to white dwarf pollution |
the focus of this paper is to connect the rotating mass dipole with natural elongated bodies. the dipole system is consisted with two point masses connected with a massless rod in a constant characteristic distance. a brief introduction on the dynamics near the rotating mass dipole is given with the distribution of its equilibrium points and zero-velocity curves. five parameters of the dipole model are required to approximate the potential distribution of an elongated body out of the body's surface, including the mass ratio, system mass, spinning period, characteristic distance and the ratio between the gravitational and centrifugal forces. the method to obtain the five parameters is presented along with its application to the asteroid 1620 geographos in detail. the accuracy of the dipole model is quantified with the relative tolerance of locations of the equilibrium points. six more elongated asteroids and comets, such as 25143 itokawa and 103p/hartley-2, are illustrated to provide a reference for further studies. model justification is evaluated through comparison between sample elongated bodies and their corresponding dipole models with regard to the external potential distribution, the stability and topological manifold structure of the equilibrium points. | study on the connection between the rotating mass dipole and natural elongated bodies |
the yarkovsky-o'keefe-radzievskii-paddack (yorp) effect is a small thermal-radiation torque experienced by small asteroids, and is considered to be crucial in their physical and dynamical evolution. it is important to understand this effect by providing measurements of yorp for a range of asteroid types to facilitate the development of a theoretical framework. we are conducting a long-term observational study on a selection of near-earth asteroids to support this. we focus here on (68346) 2001 kz66, for which we obtained both optical and radar observations spanning a decade. this allowed us to perform a comprehensive analysis of the asteroid's rotational evolution. furthermore, radar observations from the arecibo observatory enabled us to generate a detailed shape model. we determined that (68346) is a retrograde rotator with its pole near the southern ecliptic pole, within a 15○ radius of longitude 170○ and latitude -85○. by combining our radar-derived shape model with the optical light curves, we developed a refined solution to fit all available data, which required a yorp strength of $(8.43\pm 0.69)\times 10^{-8} \rm ~rad ~d^{-2}$. (68346) has a distinct bifurcated shape comprising a large ellipsoidal component joined by a sharp neckline to a smaller non-ellipsoidal component. this object likely formed either from the gentle merging of a binary system or from the deformation of a rubble pile due to yorp spin-up. the shape exists in a stable configuration close to its minimum in topographic variation, where regolith is unlikely to migrate from areas of higher potential. | detection of the yorp effect on the contact binary (68346) 2001 kz66 from combined radar and optical observations |
the extraordinary weather conditions available between february and march 2022 over spain have allowed us to analyse the brightest fireballs recorded by the monitoring stations of the spanish meteor network (spmn). we study the atmospheric flight of 15 large meteoroids to determine if they are meteorite dropper events to prepare campaigns to search for freshly fallen extraterrestrial material. we investigate their origins in the solar system and their dynamic association with parent bodies and meteoroid streams. employing our python pipeline 3d-firetoc, we reconstruct the atmospheric trajectory utilizing ground-based multistation observations and compute the heliocentric orbit. in addition, we apply an ablation model to estimate the initial and terminal mass of each event. using a dissimilarity criterion and propagating backward in time, we check the connection of these meteoroids with known complexes and near-earth objects. we also calculate if the orbits are compatible with recent meteoroid ejections. we find that ~27 per cent of these fireballs are dynamically associated with minor meteoroid streams and exhibit physical properties of cometary bodies, as well as one associated with a near-earth asteroid. we identify two meteorite-producing events; however, the on-site search was unsuccessful. by considering that these fireballs are mostly produced by cm-sized rocks that might be the fragmentation product of much larger meteoroids, our findings emphasize the idea that the population of near-earth objects is a source of near-term impact hazards, existing large earth-colliding meteoroids in the known complexes. | identifying meteorite droppers among the population of bright 'sporadic' bolides imaged by the spanish meteor network during the spring of 2022 |
dynamical models and observational evidence indicate that water-rich asteroids and comets deliver water to objects throughout the solar system, but the mechanisms by which this water is captured have been unclear. new experiments reveal that impact melts and breccias capture up to 30% of the water carried by carbonaceous chondrite-like projectiles under impact conditions typical of the main asteroid belt impact and the early phases of planet formation. this impactor-derived water resides in two distinct reservoirs: in impact melts and projectile survivors. impact melt hosts the bulk of the delivered water. entrapment of water within impact glasses and melt-bearing breccias is therefore a plausible source of hydration features associated with craters on the moon and elsewhere in the solar system and likely contributed to the early accretion of water during planet formation. | the delivery of water by impacts from planetary accretion to present |
previous efforts have modeled the didymos system as two irregularly shaped rigid bodies, although it is likely that one or both components are in fact rubble piles. here, we relax the rigid-body assumption to quantify how this affects the spin and orbital dynamics of the system following the dart impact. given the known fundamental differences between our simulation codes, we find that faster rigid-body simulations produce nearly the same result as rubble-pile models in scenarios with a moderate value for the momentum enhancement factor, β (β ~ 3) and an ellipsoidal secondary. this indicates that the rigid-body approach is likely adequate for propagating the post-impact dynamics necessary to meet the dart mission requirements. although, if dimorphos has a highly irregular shape or structure, or if β is unexpectedly large, then rubble-pile effects may become important. if dimorphos's orbit and spin state are sufficiently excited, then surface particle motion is also possible. however, these simulations are limited in their resolution and range of material parameters, so they serve as a demonstration of principle, and future work is required to fully understand the likelihood and magnitude of surface motion. | dynamical evolution of the didymos-dimorphos binary asteroid as rubble piles following the dart impact |
in 2018, the near-earth object (155140) 2005 ud (hereafter ud) experienced a close fly by of the earth. we present results from an observational campaign involving photometric, spectroscopic, and polarimetric observations carried out across a wide range of phase angles (0°7-88°). we also analyze archival neowise observations. we report an absolute magnitude of hv = 17.51 ± 0.02 mag and an albedo of pv = 0.10 ± 0.02. ud has been dynamically linked to phaethon due their similar orbital configurations. assuming similar surface properties, we derived new estimates for the diameters of phaethon and ud of d = 5.4 ± 0.5 km and d = 1.3 ± 0.1 km, respectively. thermophysical modeling of neowise data suggests a surface thermal inertia of ${\rm{\gamma }}={300}_{-110}^{+120}$ and regolith grain size in the range of 0.9-10 mm for ud and grain sizes of 3-30 mm for phaethon. the light curve of ud displays a symmetric shape with a reduced amplitude of am(0) = 0.29 mag and increasing at a linear rate of 0.017 mag/° between phase angles of 0° and ∼25°. little variation in light-curve morphology was observed throughout the apparition. using light-curve inversion techniques, we obtained a sidereal rotation period p = 5.235 ± 0.005 hr. a search for rotational variation in spectroscopic and polarimetric properties yielded negative results within observational uncertainties of ∼10% μm-1 and ∼16%, respectively. in this work, we present new evidence that phaethon and ud are similar in composition and surface properties, strengthening the arguments for a genetic relationship between these two objects. * partially based on data collected with 2 m rcc telescope at rozhen national astronomical observatory. | new evidence for a physical link between asteroids (155140) 2005 ud and (3200) phaethon |
elephant moraine (eet) 96029 is a cm carbonaceous chondrite regolith breccia with evidence for unusually mild aqueous alteration, a later phase of heating and terrestrial weathering. the presence of phyllosilicates and carbonates within chondrules and the fine-grained matrix indicates that this meteorite was aqueously altered in its parent body. features showing that water-mediated processing was arrested at a very early stage include a matrix with a low magnesium/iron ratio, chondrules whose mesostasis contains glass and/or quench crystallites, and a gehlenite-bearing calcium- and aluminium-rich inclusion. eet 96029 is also rich in fe,ni metal relative to other cm chondrites, and more was present prior to its partial replacement by goethite during antarctic weathering. in combination, these properties indicate that eet 96029 is one of the least aqueously altered cms yet described (cm2.7) and so provides new insights into the original composition of its parent body. following aqueous alteration, and whilst still in the parent body regolith, the meteorite was heated to ∼400-600 °c by impacts or solar radiation. heating led to the amorphisation and dehydroxylation of serpentine, replacement of tochilinite by magnetite, loss of sulphur from the matrix, and modification to the structure of organic matter that includes organic nanoglobules. significant differences between samples in oxygen isotope compositions, and water/hydroxyl contents, suggests that the meteorite contains lithologies that have undergone different intensities of heating. eet 96029 may be more representative of the true nature of parent body regoliths than many other cm meteorites, and as such can help interpret results from the forthcoming missions to study and return samples from c-complex asteroids. | elephant moraine 96029, a very mildly aqueously altered and heated cm carbonaceous chondrite: implications for the drivers of parent body processing |
dawn conducted an extensive exploration of dwarf planet ceres, the largest object between the sun and pluto that had not previously been visited by a spacecraft. following its arrival at ceres in march 2015, dawn acquired all the planned data from four circular polar orbits ranging in altitude from 13,600 km to 385 km. after the successful conclusion of the prime mission in june 2016, dawn's mission was extended, and new investigations, not previously considered, were conducted from four new orbits ranging as low as 35 km. in 2017 the project was approved for a second and final extended mission at ceres. starting in april 2018, dawn used its ion propulsion system to maneuver to two new orbits. these highly elliptical orbits enabled the acquisition of valuable new data, including significant improvements in the spatial resolution. mission operations concluded in october 2018 upon depletion of hydrazine for attitude control. the mission provided a uniquely detailed view of the first dwarf planet discovered. this paper describes ceres operations as well as some of the major findings there. | dawn at ceres: the first exploration of the first dwarf planet discovered |
recent remote measurements and in-situ observations confirm the idea that asteroids up to few hundreds of meters in size might be aggregates of loosely consolidated material, or 'rubble piles'. the dynamics of these objects can be studied using n-body simulations of gravitational aggregation. we investigate the role of particle shape in n-body simulations of gravitational aggregation. we explore contact interaction mechanisms and study the effects of parameters such as surface friction, particle size distribution and number of particles in the aggregate. as a case study, we discuss the case of rubble pile reshaping under its own self-gravity, with no spin and no external force imposed. we implement the n-body gravitational aggregation problem with contact and collisions between particles of irregular, non-spherical shape. contact interactions are modeled using a soft-contact method, considering the visco-elastic behavior of particles' surface. we perform numerical simulations to compare the behavior of spherical bodies with that of irregular randomly-generated angular bodies. the simulations are performed starting from an initial aggregate in a non-equilibrium state. the dynamics are propagated forward allowing particles to settle through reshaping until they reach an equilibrium state. preliminary tests are studied to investigate the quantitative and qualitative behavior of the granular media. the shape of particles is found to play a relevant role in the settling process of the rubble pile aggregate, affecting both transient dynamics and global properties of the aggregate at equilibrium. in the long term, particle shape dominates over simulation parameters such as surface friction, particle size distribution and number of particles in the aggregate. spherical particles are not suitable to model accurately the physics of contact interactions between particles of n-body aggregation simulations. irregular particles are required for a more realistic and accurate representation of the contact interaction mechanisms. | the role of fragment shapes in the simulations of asteroids as gravitational aggregates |
asteroids are the "time capsules" of the solar system, storing the origin and evolution of the protoplanetary disk. in addition, they are the remaining "building blocks" of the earth and terrestrial planets, preserving the initial materials of the latter. to study the first 10 million years history of the solar system, a multisite and anti-cross-contamination brief touch sampler (bts) was designed for the asteroid sample return (asr) mission of the chinese academy of sciences (cas). the sampler provides a pair of counterrotating brush wheels to balance the angular momentum during the sampling processes. a combination of brushes with different shapes and stiffnesses are used to maximize the success of the sample acquisition and guide the sample into the sample canister through the anti-impact guide cover. the sample canister is designed with three sample storage containers with independently sealed doors. the canister can accommodate samples from three different sites without cross contamination to conveniently study the substance distribution of asteroids. because asteroids have typical microgravity characteristics, prototype verification in a simulated microgravity environment was also conducted. the experimental results show that the sample acquisition processes are effective and that a minimum of 2 g of simulated regolith particles can be sampled within 3 s. | a multisite and anti-cross-contamination brief touch sampler for asteroid sample return mission☆ |
the osiris-rex spacecraft collected a surface sample from hokioi crater (55.8° n, 42.3° e; diameter ~20 m) on the asteroid bennu in 2020 october. we explore the geology of the sample collection site, known as nightingale, by using digital terrain models, relative albedo maps, and images collected by the osiris-rex spacecraft. hokioi crater sits at the northwest edge of an older, larger (120 m diameter) crater between two north-south ridges respectively located at roughly 0° and 90° longitude, between which unconsolidated material generally migrates from the geopotential high at the north (+z) pole to the geopotential low at the equator. the impact that formed hokioi crater exposed relatively unweathered, fine-grained dark material that we observe within and ejected beyond the crater. the regional slope and steep crater walls to the north of the nightingale site have enabled a mix of the dark debris and brighter material (which may include carbonates and/or exogenic basalts) surrounding hokioi crater to migrate onto the crater floor, where the sample was collected; some of this material may be old ejecta excavated from up to 10 m depth when the 120 m diameter crater formed. we therefore expect the osiris-rex sample to include materials of varying brightnesses, compositions, and exposure ages, derived primarily from the 0°-90° longitude quadrant and from as deep as 10 m. the sample may also include material derived from the impactor that formed hokioi crater. we expect it to have low cohesion (≪0.6 pa) and a friction angle between 32° and 39°. | geologic context of the osiris-rex sample site from high-resolution topography and imaging |
dust emission was detected on main-belt asteroid 596 scheila in 2010 december and was attributed to the collision of a few-tens-of-meters projectile on the surface of the asteroid. in such an impact, the ejected material from the collided body is expected to mainly come from its fresh, unweathered subsurface. therefore, it is expected that the surface of 596 was partially or entirely refreshed during the 2010 impact. by combining spectra of 596 from the literature and our own observations, we show that the 2010 impact event resulted in a significant slope change in the near-infrared (0.8-2.5 μm) spectrum of the asteroid, from moderately red (t type) before the impact to red (d type) after the impact. this provides evidence that red carbonaceous asteroids become less red with time due to space weathering, in agreement with predictions derived from laboratory experiments on the primitive tagish lake meteorite, which is spectrally similar to 596. this discovery provides the very first telescopic confirmation of the expected weathering trend of asteroids spectrally analog to tagish lake and/or anhydrous chondritic porous interplanetary dust particles. our results also suggest that the population of implanted objects from the outer solar system is much larger than previously estimated in the main belt, but many of these objects are hidden below their space-weathered surfaces. | the appearance of a "fresh" surface on 596 scheila as a consequence of the 2010 impact event |
the chicxulub crater is the site of an asteroid impact linked with the cretaceous-paleogene (k-pg) mass extinction at ∼66 ma. this asteroid struck in shallow water and caused a large tsunami. here we present the first global simulation of the chicxulub impact tsunami from initial contact of the projectile to global propagation. we use a hydrocode to model the displacement of water, sediment, and crust over the first 10 min, and a shallow-water ocean model from that point onwards. the impact tsunami was up to 30,000 times more energetic than the 26 december 2004 indian ocean tsunami, one of the largest tsunamis in the modern record. flow velocities exceeded 20 cm/s along shorelines worldwide, as well as in open-ocean regions in the north atlantic, equatorial south atlantic, southern pacific and the central american seaway, and therefore likely scoured the seafloor and disturbed sediments over 10,000 km from the impact origin. the distribution of erosion and hiatuses in the uppermost cretaceous marine sediments are consistent with model results. | the chicxulub impact produced a powerful global tsunami |
maskelynite is a diaplectic glass that forms from plagioclase at shock pressures of ∼20-30 gpa, depending on the ca concentration. the proportion of maskelynite-rich samples in a basaltic meteorite group correlates with the parent-body escape velocity and serves as a shock indicator of launching conditions. for eucrites (basalts widely presumed to be from vesta; vesc = 0.36 km s-1), ∼5% of the samples are maskelynite rich. for the moon (vesc = 2.38 km s-1), ∼30% of basaltic meteorites are maskelynite rich. for mars (vesc = 5.03 km s-1), ∼93% of basaltic meteorites are maskelynite rich. in contrast, literature data show that maskelynite is rare (∼1%) among mare basalts and basaltic fragments in apollo 11, 12, 15 and 17 soils (which were never ejected from the moon). angrites are unbrecciated basaltic meteorites that are maskelynite free; they were ejected at low-to-moderate shock pressures from an asteroid smaller than vesta. because most impacts that eject materials from a large (⩾100 km) parent body are barely energetic enough to do that, a collision that has little more than the threshold energy required to eject a sample from vesta will not be able to eject identical samples from the moon or mars. there must have been relatively few impacts, if any, that launched eucrites off their parent body that also imparted shock pressures of ∼20-30 gpa in the ejected rocks. more-energetic impacts were required to launch basalts off the moon and mars. on average, vesta ejecta were subjected to lower shock pressures than lunar ejecta, and lunar ejecta were subjected to lower shock pressures than martian ejecta. h and ll ordinary chondrites have low percentages of shock-stage s5 maskelynite-bearing samples (∼1% and ∼4%, respectively), probably reflecting shock processes experienced by these rocks on their parent asteroids. in contrast, l chondrites have a relatively high proportion of samples containing maskelynite (∼11%), most likely a result of catastrophic parent-body disruption 470 ma ago. | maskelynite in asteroidal, lunar and planetary basaltic meteorites: an indicator of shock pressure during impact ejection from their parent bodies |
the original hydrogen isotope (d/h) ratios of different planetary bodies may indicate where each body formed in the solar system. however, geological and atmospheric processes can alter these ratios through time. over the past few decades, d/h ratios in meteorites from vesta and mars, as well as from s- and c-type asteroids, have been measured. the aim of this article is to bring together all previously published data from these bodies, as well as the earth, in order to determine the original d/h ratio for each of these inner solar system planetary bodies. once all secondary processes have been stripped away, the inner solar system appears to be relatively homogeneous in terms of water d/h, with the original water d/h ratios of vesta, mars, the earth, and s- and c-type asteroids all falling between δd values of -100‰ and -590‰. this homogeneity is in accord with the `grand tack' model of solar system formation, where giant planet migration causes the s- and c-type asteroids to be mixed within 1 au to eventually form the terrestrial planets. this article is part of the themed issue 'the origin, history and role of water in the evolution of the inner solar system'. | d/h ratios of the inner solar system |
regolith generation by thermal fatigue has been identified as a dominant mechanism for the breakdown of small (cm-sized) rocks on certain airless bodies. simple numerical models for thermal fatigue seemed to indicate that this breakdown occurs faster in the larger decimeter-sized rocks, which is in contrast to the predictions of disruption models through successive micrometeorite impacts. the observation is justified by the existence of larger temperature gradient in bigger rocks, but it is not clear that this conclusion can be extrapolated or scaled to meter-sized boulders. here we reveal a transition in the rock disaggregation rates by thermal fatigue when rock sizes rise above a critical length scale. a simple analytic model is formulated to predict the time to fracture of rocks on small airless bodies. we consider an uncoupled approach consisting of a one-dimensional thermal model, and a two-dimensional fracture model. the solution of the heat equation is used as input to the thermomechanical crack growth problem. this new understanding could provide bounds on the survival rates of asteroidal rocks, and may help in coupling thermal fatigue with a mechanical disruption model to obtain a multi-mechanism view of regolith evolution in the solar system. | the efficiency of thermal fatigue in regolith generation on small airless bodies |
asteroid families are a valuable source of information to many asteroid-related researches, assuming a reliable list of their members could be obtained. however, as the number of known asteroids increases fast it becomes more and more difficult to obtain a robust list of members of an asteroid family. here, we are proposing a new approach to deal with the problem, based on the well-known hierarchical clustering method. an additional step in the whole procedure is introduced in order to reduce a so-called chaining effect. the main idea is to prevent chaining through an already identified interloper. we show that in this way a number of potential interlopers among family members is significantly reduced. moreover, we developed an automatic online-based portal to apply this procedure, i.e. to generate a list of family members as well as a list of potential interlopers. the asteroid families portal is freely available to all interested researchers. | an automatic approach to exclude interlopers from asteroid families |
we conducted a geologic mapping investigation of dawn spacecraft data to determine the geologic history of the kerwan impact basin region of dwarf planet ceres, which is mostly located in the ac-7 kerwan quadrangle. geological mapping was applied to dawn framing camera images from the low altitude mapping orbit (lamo, 35 m/pixel) and supplemented by digital terrain models and color images from the high altitude mapping orbit (hamo, 135 m/pixel), as well as preliminary visible and infrared spectrometer (vir) and gravity data. the 284-km diameter kerwan impact basin is the oldest unequivocal impact crater on ceres, and has a highly discontinuous, polygonal, degraded rim and contains a 'smooth' unit that both fills the basin floor and surrounds the degraded rim to the west, south, and east. although there are some subtle topographic features in the kerwan basin that could be interpreted as flow boundaries, there is no indisputable evidence of cryovolcanic features in or around the basin (however if such features existed they could be buried). nevertheless, all data point to impact-induced melting of a cerean crust enriched in a volatile, likely water ice, to produce the kerwan smooth material. subsequent geologic activity in this region includes emplacement of impact craters such as dantu, which produced a variety of colorful deposits, and rayed craters such as rao and cacaguat. based on the crater size-frequency distribution absolute model ages of the kerwan smooth material in and around the basin, marking a minimum age for the kerwan basin, our mapping defines this as the oldest boundary within the cerean geologic timescale, separating the pre-kerwanan and kerwanan periods at > 1.3 ga (lunar-derived chronology model) or > 230-850 ma (asteroid-derived chronology model, depending on strength of target material). | the geology of the kerwan quadrangle of dwarf planet ceres: investigating ceres' oldest, largest impact basin |
digital biofeedback systems (dbss) are used in physical rehabilitation to improve outcomes by engaging and educating patients and have the potential to support patients while doing targeted exercises during home rehabilitation. the components of feedback (mode, content, frequency and timing) can influence motor learning and engagement in various ways. the feedback design used in dbss for targeted exercise home rehabilitation, as well as the evidence underpinning the feedback and how it is evaluated, is not clearly known. to explore these concepts, we conducted a scoping review where an electronic search of pubmed, pedro and acm digital libraries was conducted from january 2000 to july 2019. the main inclusion criteria included dbss for targeted exercises, in a home rehabilitation setting, which have been tested on a clinical population. nineteen papers were reviewed, detailing thirteen different dbss. feedback was mainly visual, concurrent and descriptive, frequently providing knowledge of results. three systems provided clear rationale for the use of feedback. four studies conducted specific evaluations of the feedback, and seven studies evaluated feedback in a less detailed or indirect manner. future studies should describe in detail the feedback design in dbss and consider a robust evaluation of the feedback element of the intervention to determine its efficacy. | feedback design in targeted exercise digital biofeedback systems for home rehabilitation: a scoping review |
context. the detection of earth-like planets, exocomets or kuiper belts show that the different components found in the solar system should also be present in other planetary systems. trojans are one of these components and can be considered fossils of the first stages in the life of planetary systems. their detection in extrasolar systems would open a new scientific window to investigate formation and migration processes.aims: in this context, the main goal of the troy project is to detect exotrojans for the first time and to measure their occurrence rate (η-trojan). in this first paper, we describe the goals and methodology of the project. additionally, we used archival radial velocity data of 46 planetary systems to place upper limits on the mass of possible trojans and investigate the presence of co-orbital planets down to several tens of earth masses.methods: we used archival radial velocity data of 46 close-in (p < 5 days) transiting planets (without detected companions) with information from high-precision radial velocity instruments. we took advantage of the time of mid-transit and secondary eclipses (when available) to constrain the possible presence of additional objects co-orbiting the star along with the planet. this, together with a good phase coverage, breaks the degeneracy between a trojan planet signature and signals coming from additional planets or underestimated eccentricity.results: we identify nine systems for which the archival data provide >1σ evidence for a mass imbalance between l4 and l5. two of these systems provide >2σ detection, but no significant detection is found among our sample. we also report upper limits to the masses at l4/l5 in all studied systems and discuss the results in the context of previous findings. radial velocity data are only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (http://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?j/a+a/609/a96 | the troy project: searching for co-orbital bodies to known planets. i. project goals and first results from archival radial velocity |
the discovery of the first interstellar asteroid, 1i/2017 u1 (‘oumuamua), has opened a new era for research on interstellar objects. in this paper, we study the rotational dynamics of interstellar asteroids (isas) of irregular shapes moving through the interstellar gas. we find that regular mechanical torques resulting from the bombardment of gas flow on the irregular body could be important for the dynamics and destruction of isas. mechanical torques can spin up the isa, resulting in the breakup of the original isa into small binary asteroids when the rotation rate exceeds the critical frequency. we find that the breakup timescale is short for isas of highly irregular shapes and low tensile strength. we apply our results to the first observed isa, ‘oumuamua, and suggest that its extreme elongated shape may originate from a reassembly of the binary fragments, due to gravity along its journey in the interstellar medium. the tumbling of ‘oumuamua could have been induced by rotational disruption due to mechanical torques. finally, we discuss the survival possibility of high-velocity asteroids presumably formed by tidal disruption of planetary systems by the black hole at the galactic center. | spinup and disruption of interstellar asteroids by mechanical torques, and implications for 1i/2017 u1 (‘oumuamua) |
in the frame of near-earth-object exploration and planetary defence, the two-part aida mission is currently studied by nasa and esa. being composed of a kinetic impactor, dart (nasa), and by an observing spacecraft, aim (esa), aida has been designed to deliver vital data to determine the momentum transfer efficiency of a kinetic impact onto a small body and the key physical properties of the target asteroid. this will enable derivation of the impact response of the object as a function of its physical properties, a crucial quantitative point besides the qualitative proof of the deflection. in the course of the aim mission definition, a lander has been studied as an essential element of the overall mission architecture. it was meant to be deployed on didymoon, the secondary body of the binary nea system 65803 didymos and it was supposed to significantly enhance the analysis of the body's dynamical state, mass, geophysical properties, surface and subsurface structure. the mission profile and the design of the 13 kg (current best estimate) nano-lander have been derived from the mascot lander flying aboard hayabusa2. differing from its predecessor by having an increased lifetime of more than three months, a surface mobility capability including directed movement, a sensor system for localization and attitude determination on the surface and a redesigned mechanical interface to the mother spacecraft. the mascot2 instrument suite consists of a bi-static, low frequency radar as main instrument, supported by an accelerometer, a camera, a radiometer and a magnetometer; the latter three already flying on mascot. besides the radar measurements, the camera is meant to provide high-resolution images of the landing area, and accelerometers to record the bouncing dynamics by which the top surface mechanical properties can be determined. during the dart impact, mascot2 was expected to be able to detect the seismic shock, providing valuable information on the internal structure of the body. mascot2 was supposed also to serve as a technology demonstrator for very small asteroid landing and extended operations powered by a solar generator. in this paper, we describe the science concept, mission analysis of the separation, descent and landing phase, the operational timeline, and the latest status of the lander's design. despite the fact that aim funding has not been fully confirmed during the esa ministerial conference in 2016, mascot2 is an instrument package of high maturity and major interest for planetary defence and neo science. with appropriate tailoring and optimization, it can be considered and studied for future missions. | mascot2 - a small body lander to investigate the interior of 65803 didymos‧ moon in the frame of the aida/aim mission |
this paper proposes the use of solar-sail technology currently under development at nasa langley research center for a cubesat rendezvous mission with asteroid 2016 ho3, a quasi-satellite of earth. time-optimal trajectories are sought for within a 2022-2023 launch window, starting from an assumed launcher ejection condition in the earth-moon system. the optimal control problem is solved through a particular implementation of a direct pseudo-spectral method for which initial guesses are generated through a relatively simple and straightforward genetic algorithm search on the optimal launch date and sail attitude. the results show that the trajectories take 2.16-4.21 years to complete, depending on the assumed solar-sail reflectance model and solar-sail technology. to assess the performance of solar-sail propulsion for this mission, the trajectory is also designed assuming the use of solar electric propulsion. the resulting fuel-optimal trajectories take longer to complete than the solar-sail trajectories and require a propellant consumption that exceeds the expected propellant capacity onboard the cubesat. this comparison demonstrates the superior performance of solar-sail technology for this mission. | trajectory design for a solar-sail mission to asteroid 2016 ho3 |
an engineering mission okeanos to explore a jupiter trojan asteroid, using a solar power sail is currently under study. after a decade-long cruise, it will rendezvous with the target asteroid, conduct global mapping of the asteroid from the spacecraft, and in situ measurements on the surface, using a lander. science goals and enabling instruments of the mission are introduced, as the results of the joint study between the scientists and engineers from japan and europe. | science exploration and instrumentation of the okeanos mission to a jupiter trojan asteroid using the solar power sail |
a set of high-fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. three varieties of simulant were developed based on ci1 chondrites (typified by orgueil), cm2 chondrites (typified by murchison), and cr2/3 chondrites (multiple samples). the simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. the simulants can be made in different physical forms ranging from larger cobbles to fine-grained regolith. we analyzed simulant prototypes using scanning electron microscopy, x-ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. most measured properties compare favorably to the reference meteorites and therefore to predicted volatile-rich asteroid surface materials, including boulders, cobbles, and fine-grained soils. however, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. the asteroid simulants are available to the community from the nonprofit exolith lab at ucf, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit. | simulated asteroid materials based on carbonaceous chondrite mineralogies |
previous full-lifetime simulations of single-star multi-planet systems across all phases of stellar evolution have predominately assumed coplanar or nearly coplanar orbits. here we assess the consequences of this assumption by removing it and exploring the effect of giant branch mass loss on the stability of two-planet systems with small to moderate non-kozai (<40°) relative inclinations. we run nearly 104 simulations over 14 gyr for f-star, a-star and b-star planet hosts, incorporating main-sequence stellar masses of 1.5, 2.0, 2.5, 3.0 and 5.0 solar masses, and initial planetary semimajor axis ratios that straddle their three-dimensional hill stability limits. we find that the near-coplanar assumption can approximate well the stability frequencies and critical separations found for higher inclinations, except around strong mean-motion commensurabilities. late instabilities - after the star has become a white dwarf - occur throughout the explored mutual inclination range. consequently, non-kozai mutual inclination should not be used as a predictive orbital proxy for determining which white dwarf multi-planet systems discovered by gaia should represent high-priority follow-up targets for the detection of metal pollution and planetary debris discs. | effects of non-kozai mutual inclinations on two-planet system stability through all phases of stellar evolution |
we describe systematic ranging, an orbit determination technique suitable to assess the near-term earth impact hazard posed by newly discovered asteroids. for these late warning cases, the time interval covered by the observations is generally short, perhaps a few hours or even less, which leads to severe degeneracies in the orbit estimation process. the systematic ranging approach gets around these degeneracies by performing a raster scan in the poorly-constrained space of topocentric range and range rate, while the plane of sky position and motion are directly tied to the recorded observations. this scan allows us to identify regions corresponding to collision solutions, as well as potential impact times and locations. from the probability distribution of the observation errors, we obtain a probability distribution in the orbital space and then estimate the probability of an earth impact. we show how this technique is effective for a number of examples, including 2008 tc3 and 2014 aa, the only two asteroids to date discovered prior to impact. | systematic ranging and late warning asteroid impacts |
how can we design mechanisms to promote efficient use of shared resources? here, we answer this question in relation to the well-studied class of atomic congestion games, used to model a variety of problems, including traffic routing. within this context, a methodology for designing tolling mechanisms that minimize the system inefficiency (price of anarchy) exploiting solely local information is so far missing in spite of the scientific interest. in this manuscript we resolve this problem through a tractable linear programming formulation that applies to and beyond polynomial congestion games. when specializing our approach to the polynomial case, we obtain tight values for the optimal price of anarchy and corresponding tolls, uncovering an unexpected link with load balancing games. we also derive optimal tolling mechanisms that are constant with the congestion level, generalizing the results of caragiannis et al. [acm transactions on algorithms, 2010] to polynomial congestion games and beyond. finally, we apply our techniques to compute the efficiency of the marginal cost mechanism. surprisingly, optimal tolling mechanism using only local information perform closely to existing mechanism that utilize global information [bilò and vinci, acm transactions on economics and computation, 2019], while the marginal cost mechanism, known to be optimal in the continuous-flow model, has lower efficiency than that encountered levying no toll. all results are tight for pure nash equilibria, and extend to coarse correlated equilibria. | optimal taxes in atomic congestion games |
a multicolour phase-polarization curve of asteroid (3200) phaethon has been obtained during the 2017 december apparition by merging measurements taken at the observing station of calern (france) and at the rozhen observatory (bulgaria). all the observations were obtained in the positive polarization branch, the phase angle ranging from 36° to 116°. the measured values of linear polarization are among the highest ever observed for a solar system body. the covered interval of phase angle was not sufficiently extended to derive a firm determination of the pmax parameter, but this appears to occur at a phase angle around 130° and reaches more than 45 per cent of linear polarization. phaethon is the parent body of the geminid meteor shower, and the real physical nature of this object (asteroid or comet) has been a long-debated subject. our polarimetric measurements seem to support the asteroid hypothesis with a phase-polarization curve similar to the asteroid (2) pallas, but further observations at smaller phase angles are needed to draw definitive conclusions. | the phase-polarization curve of asteroid (3200) phaethon† |
the design of low-thrust-based multitarget interplanetary missions requires a method to quickly and accurately evaluate the low-thrust transfer between any two visiting targets. complete evaluation of the low-thrust transfer includes not only the estimation of the optimal fuel consumption but also the judgment of transfer feasibility. in this paper, a deep neural network (dnn)-based method is proposed for quickly evaluating low-thrust transfer. an efficient database generation method is developed for obtaining both the infeasible and optimal transfers. a classification dnn and a regression dnn are trained based on the infeasible and optimal transfers to judge the transfer feasibility and estimate the optimal fuel consumption, respectively. the simulation results show that the well-trained dnns are capable of quickly determining the transfer feasibility with a correct rate of greater than 98% and approximating the optimal transfer fuel consumption with a relative estimation error of less than 0.4%. the tests on two asteroid chains further show the superiority of the dnn-based method for application to the design of low-thrust-based multitarget interplanetary missions | fast evaluation of low-thrust transfers via multilayer perceptions |
the full two-body problem (f2bp) is often used to model binary asteroid systems, representing the bodies as two finite mass distributions whose dynamics are influenced by their mutual gravity potential. the emergent behavior of the f2bp is highly coupled translational and rotational mutual motion of the mass distributions. a large fraction of characterized binary asteroids appear to be at, or near, the doubly synchronous equilibrium, which occurs when both bodies are tidally-locked and in a circular co-orbit. stable oscillations about this equilibrium can be shown, for the nonplanar system, to be combinations of seven fundamental frequencies of the system and the mutual orbit rate. the fundamental frequencies arise as the linear periods of center manifolds identified about the equilibrium which are heavily influenced by each body's mass parameters. we leverage these eight dynamical constraints to investigate the observability of binary asteroid mass parameters via dynamical observations. this is accomplished by deriving a relationship between the fundamental frequencies and mass parameters for doubly synchronous systems. this relationship allows us to show the sensitivity of the dynamics to changes in the mass parameters, first for the planar dynamics, and then for the nonplanar dynamics. in so doing we are able to predict the idealized estimation covariance of the mass parameters based on observation quality. we can also define idealized observation accuracies for desired mass parameter certainties. we apply these tools to 617 patroclus, a doubly synchronous trojan binary and flyby target of the lucy mission, as well as the pluto and charon system in order to predict mutual behaviors of these doubly synchronous systems and to provide observational requirements for their mass parameters. | doubly synchronous binary asteroid mass parameter observability |
we present an analysis of the accuracy of geometric albedos determined for asteroids through the modeling of observed thermal infrared radiation. we show that albedo uncertainty is dominated by the uncertainty on the measured hv absolute magnitude, and that any analysis using albedos in a statistical application will also be dominated by this source of uncertainty. for all but the small fraction of asteroids with a large amount of characterization data, improved knowledge of the hv magnitude will be fundamentally limited by incomplete phase-curve coverage, incomplete light-curve knowledge, and the necessary conversion from the observed band to the v band. switching the absolute magnitude standard to a different band such a $r^{\prime} $ would mitigate the uncertainty due to band conversion for many surveys, but this only represents a small component of the total uncertainty. therefore, techniques making use of these albedos must ensure that their uncertainties are properly accounted for. | uncertainties on asteroid albedos determined by thermal modeling |
we present an overview of the skymapper optical follow-up programme for gravitational-wave event triggers from the ligo/virgo observatories, which aims at identifying early gw170817-like kilonovae out to $∼200 mpc$ distance. we describe our robotic facility for rapid transient follow-up, which can target most of the sky at $δ<+10\deg $ to a depth of $i_ab≈ 20 mag$ . we have implemented a new software pipeline to receive ligo/virgo alerts, schedule observations and examine the incoming real-time data stream for transient candidates. we adopt a real-bogus classifier using ensemble-based machine learning techniques, attaining high completeness ( $∼98%$ ) and purity ( $∼91%$ ) over our whole magnitude range. applying further filtering to remove common image artefacts and known sources of transients, such as asteroids and variable stars, reduces the number of candidates by a factor of more than 10. we demonstrate the system performance with data obtained for gw190425, a binary neutron star merger detected during the ligo/virgo o3 observing campaign. in time for the ligo/virgo o4 run, we will have deeper reference images allowing transient detection to $i_ab≈ 21 mag$. | skymapper optical follow-up of gravitational wave triggers: alert science data pipeline and ligo/virgo o3 run |
we used the times of occultations and eclipses between the components of the 65803 didymos binary system observed in its light curves from 2003 to 2021 to estimate the orbital parameters of dimorphos relative to didymos. we employed a weighted least-squares approach and a modified keplerian orbit model in order to accommodate the effects from nongravitational forces such as binary yorp that could cause a linear change in mean motion over time. we estimate that the period of the mutual orbit at the epoch 2022 september 26.0 tdb, the day of the dart impact, is 11.921 487 ± 0.000028 hr (1σ) and that the mean motion of the orbit is changing at a rate of (5.0 ± 1.0) × 10-18 rad s-2 (1σ). the formal 3σ uncertainty in orbital phase of dimorphos during the planned double asteroid redirection test (dart) mission is 5.°4. observations from 2022 july to september, a few months to days prior to the dart impact, should provide modest improvements to the orbital phase uncertainty and reduce it to about 4.°2. these results, generated using a relatively simple model, are consistent with those generated using the more sophisticated model of scheirich & pravec, which demonstrates the reliability of our method and adds confidence to these mission-critical results. | anticipating the dart impact: orbit estimation of dimorphos using a simplified model |
we study the capture of interstellar objects (isos) by a planet-star binary with mass ratio q ≪ 1, semimajor axis ap, orbital speed vc, and eccentricity ep. very close (slingshot) and wide encounters with the planet are amenable to analytical treatment, while numerically obtained capture cross-sections σ closely follow the analytical results even in the intermediate regime. wide interactions can only generate energy changes $\delta e\lesssim q{v}_{\mathrm{c}}^2$, when $\sigma \propto v_\infty ^{-2} |\ln \delta e|^{2/3}$ (with v∞ the iso's incoming speed far away from the binary), which is slightly enhanced for ep > 0. energy changes $\delta e\gtrsim q{v}_{\mathrm{c}}^2$, on the other hand, require close interactions when σ ∝ (v∞δe)-2 hardly depending on ep. finally, at $\delta e\gtrsim {v}_{\mathrm{c}}^2$, the cross-section drops to zero, depending on the planet's radius rp through the safronov number θ = qap/rp. we also derive the cross-sections for collisions of isos with planets or moons. | capture of interstellar objects - i. the capture cross-section |
detached eclipsing binaries are the primary tool used to measure precise masses and radii of stars. in our previous paper estimating the parameters of more than 30 000 detached eclipsing binaries, we identified 766 eclipsing binaries with additional features in their all-sky automated survey for supernovae (asas-sn) and transiting exoplanet survey satellite light curves. here, we characterize these 'extra-physics' systems, identifying eclipsing binaries with spotted stars, pulsating components, and candidate triple/quadruple systems. we use the gaia, asteroid terrestrial-impact last alert system (atlas), zwicky transient facility (ztf), and asas-sn variable star catalogues to search for possible blends. we use mist (mesa isochrones and stellar tracks) isochrones and evolutionary tracks to identify systems with main-sequence, subgiant, and giant primaries and highlight systems in sparsely populated regions of the colour-magnitude diagram. we find that the orbital period distribution of spotted binaries is divided by evolutionary state and find 68 with x-ray detections. for the candidate triple/quadruples and pulsating systems, we calculate the extra orbital/pulsational period and identify systems with resonances. finally, we highlight a number of exotic systems, including eclipsing cataclysmic variables, subdwarfs, and binaries with discs. | the value-added catalogue of asas-sn eclipsing binaries - ii. properties of extra-physics systems |
in this paper, we present an open-source software (simulator of asteroid malformation under stress, samus) that simulates constant-density, constant-viscosity liquid bodies subject to tidal forces for a range of assumed viscosities and sizes. this software solves the navier-stokes equations on a finite-element mesh, incorporating the centrifugal, coriolis, self-gravitational, and tidal forces. the primary functionality is to simulate the deformation of minor bodies under the influence of tidal forces. it may therefore be used to constrain the composition and physical structure of bodies experiencing significant tidal forces, such as 99942 apophis and 1i/'oumuamua. we demonstrate that samus will be useful to constrain the material properties of apophis during its near-earth flyby in 2029. depending on the material properties, apophis may experience an area change of up to 0.5%, with similar effects on the photometric brightness. we also apply samus to constrain the material dynamic viscosity of 1i/'oumuamua, the first interstellar object discovered traversing the inner solar system. 'oumuamua experienced a close approach to the sun at perihelion (q ≃ 0.25 au) during which there were significant tidal forces that may have caused deformation of the body. this deformation could have lead to observable changes in the photometric light curve based on the material properties. the application of samus to produce synthetic observations which incorporate tidal deformation effects demonstrates that no deformation-an infinite dynamic viscosity-best reproduces the photometric data. while these results indicate that 'oumuamua did not experience significant tidal deformation, a sophisticated model incorporating nonprincipal axis rotation is necessary to conclusively analyze both 'oumuamua and apophis. | numerical simulations of tidal deformation and resulting light curves of small bodies: material constraints of 99942 apophis and 1i/'oumuamua |
the cryogenic wide-field infrared survey explorer (wise) mission in 2010 was extremely sensitive to asteroids and not biased against detecting dark objects. the albedos of 428 near earth asteroids (neas) observed by wise during its fully cryogenic mission can be fit quite well by a three parameter function that is the sum of two rayleigh distributions. the rayleigh distribution is zero for negative values, and follows f(x) =x\exp [-{x}2/(2{σ }2)]/{σ }2 for positive x. the peak value is at x = σ, so the position and width are tied together. the three parameters are the fraction of the objects in the dark population, the position of the dark peak, and the position of the brighter peak. we find that 25.3% of the neas observed by wise are in a very dark population peaking at pv= 0.030, while the other 74.7% of the neas seen by wise are in a moderately dark population peaking at pv= 0.168. a consequence of this bimodal distribution is that the congressional mandate to find 90% of all neas larger than 140 m diameter cannot be satisfied by surveying to h = 22 mag, since a 140 m diameter asteroid at the very dark peak has h = 23.7 mag, and more than 10% of neas are darker than pv= 0.03. | the albedo distribution of near earth asteroids |
context. according to the latest theoretical and isotopic evidence, earth's water content originates mainly from today's asteroid belt region, or at least from the same precursor material. this suggests that water was transported inwards to earth, and to similar planets in their habitable zone, via (giant) collisions of planetary embryos and planetesimals during the chaotic final phase of planet formation.aims: in current dynamical simulations water delivery to terrestrial planets is still studied almost exclusively by assuming oversimplified perfect merging, even though water and other volatiles are particularly prone to collisional transfer and loss. to close this gap we have developed a computational framework to model collisional water transport by direct combination of long-term n-body computations with dedicated 3d smooth particle hydrodynamics (sph) collision simulations of differentiated, self-gravitating bodies for each event.methods: post-collision water inventories are traced self-consistently in the further dynamical evolution, in accretionary or erosive as well as hit-and-run encounters with two large surviving bodies, where besides collisional losses, water transfer between the encountering bodies has to be considered. this hybrid approach enables us for the first time to trace the full dynamical and collisional evolution of a system of approximately 200 bodies throughout the whole late-stage accretion phase (several hundred myr). as a first application we choose a solar system-like architecture with already formed giant planets on either circular or eccentric orbits and a debris disk spanning the whole terrestrial planet region (0.5-4 au).results: including realistic collision treatment leads to considerably different results than simple perfect merging, with lower mass planets and water inventories reduced regularly by a factor of two or more. due to a combination of collisional losses and a considerably lengthened accretion phase, final water content, especially with giant planets on circular orbits, is strongly reduced to more earth-like values, and closer to results with eccentric giant planets. water delivery to potentially habitable planets is dominated by very few decisive collisions, mostly with embryo-sized or larger objects and only rarely with smaller bodies, at least if embryos have formed throughout the whole disk initially. the high frequency of hit-and-run collisions and the differences to predominantly accretionary encounters, such as generally low water (and mass) transfer efficiencies, are a crucial part of water delivery, and of system-wide evolution in general. | realistic collisional water transport during terrestrial planet formation. self-consistent modeling by an n-body-sph hybrid code |
the cm carbonaceous chondrites have all been aqueously altered, and some of them were subsequently heated in a parent body environment. here we have sought to understand the impact of short duration heating on a highly aqueously altered cm through laboratory experiments on allan hills (alh) 83100. unheated alh 83100 contains 83 volume per cent serpentine within the fine-grained matrix and altered chondrules. the matrix also hosts grains of calcite and dolomite, which are often intergrown with tochilinite, fe(ni) sulphides (pyrrhotite, pentlandite), magnetite and organic matter. some of the magnetite formed by replacement of fe(ni) sulphides that were accreted from the nebula. laboratory heating to 400 °c has caused partial dehydroxylation of serpentine and loss of isotopically light oxygen leading to an increase in bulk δ18o and fall in δ17o. tochilinite has decomposed to magnetite, whereas carbonates have remained unaltered. with regards to infrared spectroscopy (4000-400 cm-1; 2.5-25 μm), heating to 400 °c has resulted in decreased emissivity (increased reflectance), a sharper and more symmetric oh band at 3684 cm-1 (2.71 μm), a broadening of the sisbnd o stretching band together with movement of its minimum to longer wavenumbers, and a decreasing depth of the mgsbnd oh band (625 cm-1; 16 μm). the sisbnd o bending band is unmodified by mild heating. with heating to 800 °c the serpentine has fully dehydroxylated and recrystallized to ∼fo60/70 olivine. bulk δ18o has further increased and δ17o decreased. troilite and pyrrhotite have formed, and recrystallization of pentlandite has produced fe,ni metal. calcite and dolomite were calcined at ∼700 °c and in their place is an un-named ca-fe oxysulphide. heating changes the structural order of organic matter so that raman spectroscopy of carbon in the 800 °c sample shows an increased (d1 + d4) proportional area parameter. the infrared spectrum of the 800 °c sample confirms the abundance of fe-bearing olivine and is very similar to the spectrum of naturally heated stage iv cm pecora escarpment 02010. the temperature-related mineralogical, chemical, isotopic and spectroscopic signatures defined in alh 83100 will help to track the post-hydration thermal histories of carbonaceous chondrite meteorites, and samples returned from the primitive asteroids ryugu and bennu. | signatures of the post-hydration heating of highly aqueously altered cm carbonaceous chondrites and implications for interpreting asteroid sample returns |
relatively recent cometary impacts at the moon could leave unique traces of their origins: high impact velocities and volatile abundances, combined with the presence of a dust- and ice-laden coma, may thermally and mechanically process the lunar surface in ways distinct from the impact of an asteroid. here we analytically and numerically assess the consequences of a cometary impact at the moon by considering the combined effects of a collision by the nucleus and inner coma. our results show that cometary impacts entrain the finest fraction of lunar soil grains (<10 μm) over regional scales (∼100-1000 km), produce large masses of vaporized material, and likely generate transient magnetic fields that could exceed the earth's surface field strength by a factor of 104 . this combination of processes is consistent with a mechanism to generate lunar swirls: the diffuse, meandering disturbances in brightness and regolith texture that curl across much of the lunar far-side and are also commonly (but not exclusively) associated with magnetic anomalies. previous observations of swirl features indicate that bright regions also possess a peculiar, altered regolith structure, which can be produced by the removal of fine soil grains. regional scouring by an impacting comet explains both the structure and albedo variations: large dynamic pressures entrain the smallest grains within a near-surface flow of dusty plasma, disrupting the backscattering, "fairy-castle" structure of lunar soils in equilibrium with the airless environment. the resulting surface is brightened by compaction of the previously open, porous macrostructure. darker lanes observed within swirl regions are interpreted as possible melt and/or vapor deposits. finally, the intense magnetic fields generated during high-speed cometary impacts provide an explanation for correlations between swirl locations and magnetic anomalies. | cometary impact effects at the moon: implications for lunar swirl formation |
nasa's osiris-rex and jaxa's hayabusa2 sample-return missions are currently on their way to encounter primitive near-earth asteroids (101955) bennu and (162173) ryugu, respectively. spectral and dynamical evidence indicates that these near-earth asteroids originated in the inner part of the main belt. there are several primitive collisional families in this region, and both these asteroids are most likely to have originated in the polana-eulalia family complex. we present the expected spectral characteristics of both targets based on our studies of four primitive collisional families in the inner belt: polana-eulalia, erigone, sulamitis, and clarissa. observations were obtained in the framework of our primitive asteroids spectroscopic survey (primass). our results are especially relevant to the planning and interpretation of in situ images and spectra to be obtained by the two spacecraft during the encounters with their targets. | expected spectral characteristics of (101955) bennu and (162173) ryugu, targets of the osiris-rex and hayabusa2 missions |
erg chech (ec) 002 is a meteorite with andesitic composition, potentially recording the lava crystallization and crust formation of its parent body. nucleosynthetic cr isotope composition (ɛ54cr = -0.35 ± 0.06) for ec 002 suggests a non-carbonaceous region of the solar system, and possibly represents the crustal composition of the brachinite parent body. the 53mn-to-53cr decay system shows it crystallized at 4566.6 ± 0.6 ma, i.e. 0.7 ± 0.6 ma after solar system formation (only considering the cogenetic matrix fractions with similar ɛ54cr values). this age represents the earliest recorded evidence for planetary melting and volcanism in the solar system, suggesting that the planetary crust formation occurred very early, only within the first few hundred thousand years of solar system history. however, the 53mn-53cr age does not overlap with 26al-26mg dating results, which might indicate that non-carbonaceous achondrites have lower initial 26al/27al than the canonical value defined by refractory inclusions in carbonaceous chondrites. | radiogenic chromium isotope evidence for the earliest planetary volcanism and crust formation in the solar system |
images of asteroids (162173) ryugu and (101955) bennu acquired by the hayabusa2 and osiris-rex missions, respectively, reveal rocky worlds covered in rubble. these two asteroids do not have hydrostatic shapes, indicating that they possess some internal friction and/or cohesion even if they lack tensile strength. understanding the deviation of the surfaces of these bodies from those of idealized shapes helps constrain the mechanical properties of their interiors. here, we focus on the feedback between yorp-induced spin-up (in which asymmetric reflection and re-emission of solar radiation from the surface systematically change the rotation rate), long-wavelength topography (which provides a structure to control the orientation), and surface roughness on ryugu and bennu. by performing spherical harmonic analyses of the shapes of these two asteroids, we find that although they are superficially similar, they exhibit different long-wavelength topography that implies different internal structures and rotational histories. bennu's shape and rotation rate require a modest amount of internal strength through some combination of at least 17° of internal friction or a few pa of cohesion, whereas ryugu could be nearly strengthless. bennu's longitudinal ridges make it susceptible to yorp spin-up, consistent with the observed increase in rotation rate that is not seen on ryugu. these longitudinal ridges also suggest a heterogeneous density structure for bennu, consistent with gravity data. | rotational states and shapes of ryugu and bennu: implications for interior structure and strength |
the asteroid impact & deflection assessment (aida) targets binary near-earth asteroid (65803) didymos. as part of this mission, the nasa-led double asteroid redirection test (dart) will make a kinetic impactor collide with the smaller secondary of didymos to test kinetic impact asteroid deflection technology, while the esa-led hera mission will evaluate the efficiency of the deflection by conducting detailed on-site observations. research has shown that the larger primary of didymos is spinning close to its critical spin, and the dart-impact-driven ejecta would give kinetic energy to the primary. it has been hypothesized that such an energy input might cause structural deformation of the primary, affecting the mutual orbit period, a critical parameter for assessing the kinetic impact deflection by the dart impactor. a key issue in the previous work was that the secondary was assumed to be spherical, which may not be realistic. here, we use a second-order inertia-integral mutual dynamics model to analyze the effects of the shapes of the primary and the secondary on the mutual orbit period change of the system. we first compare the second-order model with three mutual dynamics models, including a high-order inertia-integral model that takes into account the detailed shapes of didymos. the comparison tests show that the second-order model may have an error of ∼ 10 % for computing the mutual orbit period change, compared to the high-order model. we next use the second-order model to analyze how the original shape and shape deformation change the mutual orbit period. the results show that when the secondary is elongated, the mutual orbit period becomes short. also, shape deformation of the secondary further changes the mutual orbit period. a better understanding of this mechanism allows for detailed assessment of dart's kinetic impact deflection capability for didymos. | assessing possible mutual orbit period change by shape deformation of didymos after a kinetic impact in the nasa-led double asteroid redirection test |
aims: we model thermal evolution and water-rock differentiation of small ice-rock objects that accreted at different heliocentric distances, while also considering migration into the asteroid belt for ceres. we investigate how water-rock separation and various cooling processes influence ceres' structure and its thermal conditions at present. we also draw conclusions about the presence of liquids and the possibility of cryovolcanism.methods: we calculated energy balance in bodies heated by radioactive decay and compaction-driven water-rock separation in a three-component dust-water/ice-empty pores mixture, while also taking into consideration second-order processes, such as accretional heating, hydrothermal circulation, and ocean or ice convection. calculations were performed for varying accretion duration, final size, surface temperature, and dust/ice ratio to survey the range of possible internal states for precursors of ceres. subsequently, the evolution of ceres was considered in five sets of simulated models, covering different accretion and evolution orbits and dust/ice ratios.results: we find that ceres' precursors in the inner solar system could have been both wet and dry, while in the kuiper belt, they retain the bulk of their water content. for plausible accretion scenarios, a thick primordial crust may be retained over several gyr, following a slow differentiation within a few hundreds of myr, assuming an absence of destabilizing impacts. the resulting thermal conditions at present allow for various salt solutions at depths of ≲10 km. the warmest present subsurface is obtained for an accretion in the kuiper belt and migration to the present orbit.conclusions: our results indicate that ceres' material could have been aqueously altered on small precursors. the modeled structure of ceres suggests that a liquid layer could still be present between the crust and the core, which is consistent with dawn observations and, thus, suggests accretion in the kuiper belt. while the crust stability calculations indicate crust retention, the convection analysis and interior evolution imply that the crust could still be evolving. | ceres' partial differentiation: undifferentiated crust mixing with a water-rich mantle |
ceres is the largest body in the main asteroid belt. it was recently explored by the dawn mission to uncover strong similarities with other icy bodies. the morphological features observed on the surface of ceres indicate a relatively wide range of water ice concentrations, leading us to investigate the magnitude and distribution of crustal density heterogeneities, and to consider whether they could have caused a reorientation of ceres. here, we present three independent and corroborating lines of evidence for the true polar wander of ceres. thanks to the global gravity inversion approach applied to the shape and gravity data of ceres, we find crustal density heterogeneities up to approximately ±0.3 g cm-3, with a prominent positive density anomaly aligned with the equator, in the region of ahuna mons. the topography shows the remnants of an equatorial ridge compatible with the position of the palaeo-equator, and indicates that ceres reoriented by approximately 36°, with the palaeo-pole following an indirect path to the current pole of ceres. the tectonic patterns generated by the true polar wander are in close agreement with the location and orientation of the samhain catenae and uhola catenae crustal fractures. these results highlight the complex interior structure and richness of processes taking place in ceres-scale icy bodies. | true polar wander of ceres due to heterogeneous crustal density |
surface morphologies of a regolith particle retrieved from asteroid 25143 itokawa were observed using field-emission scanning electron microscopy (fe-sem). the images were compared with the internal structures of the space-weathered rim of the same particle observed by transmission electron and scanning transmission electron microscopies (tem/stem) to investigate whether there is a direct link between the surface morphology and internal structure. fe-sem observation showed that most of the particle surface is covered by convex spots less than 100 nm in size. tem/stem observation revealed that this particle has a space-weathered rim composed of partially amorphous structures with nano-fe particles and vesicles. the vesicles swell the surface and form blisters that correspond to the spotted structures observed by fe-sem. these observations indicate that a space-weathered rim with blisters can be observed by fe-sem without using destructive methods. the observation of the space-weathered rim by fe-sem also enabled us to obtain the distribution of the space-weathered rim on the particle surfaces. the existence of space-weathered rims on the opposing surfaces of the particle shows that most of the surfaces were directly exposed to the space environment by movement on the itokawa surface. the depths of the blister locations and the chemical composition of the space-weathered rim indicate that the observed space-weathered rim with blisters was formed mainly by solar wind irradiation. the space-weathered rim analyzed in this study is thicker than those of itokawa particles previously examined, indicating that the rim may has experienced longer solar wind exposure than those previously observed. | surface and internal structures of a space-weathered rim of an itokawa regolith particle |
nasa's osiris-rex spacecraft arrived at its sampling target, asteroid (101955) bennu, in december 2018 and started a series of global observation campaigns. here we investigate the global photometric properties of bennu as observed by the osiris-rex visible and infrared spectrometer (ovirs) over the time period december 9, 2018, to september 26, 2019. in this study we used observations obtained over wavelengths ranging from 0.4 to 3.7 μm, with a solar phase angle range of 5.3° to 132.6°. our aim is to characterize the global average disk-resolved photometric properties of bennu with multiple models. the best-fit model is a mcewen model with an exponential phase function and an exponential polynomial partition function. we use this model to correct the ovirs spectra of bennu to a standard reference viewing and illumination geometry at visible to infrared wavelengths for the purposes of global spectral mapping. we derive a bolometric bond albedo map in which bennu's surface values range from 0.021 to 0.027. we find a phase reddening effect, and our model is effective at removing this phase reddening. our average model albedo shows a blueish spectrum with a > 10% absorption feature centered at 2.74 μm. of all comparisons with previously visited asteroids and comets, only 28p/neujmin, 2p/encke, and (162173) ryugu are darker than bennu. we find that bennu is a few percent brighter than ryugu in the wavelengths respectively observed by the osiris-rex and hayabusa2 missions (from 0.48 to 0.86 μm). we also compare our spectroscopic photometry of bennu with the osiris-rex imaging photometry and with ground-based predictions. | photometry of asteroid (101955) bennu with ovirs on osiris-rex |
collisional and dynamical models of the main asteroid belt allow us to glean insights into planetesimal- and planet-formation scenarios as well as how the main belt reached its current state. here we discuss many of the processes affecting asteroidal evolution and the constraints that can be used to test collisional model results. we argue the main belt's wavy size-frequency distribution for diameter d < 100-km asteroids is increasingly a byproduct of comminution as one goes to smaller sizes, with its shape a fossil-like remnant of a violent early epoch. most d > 100-km asteroids, however, are primordial, with their physical properties set by planetesimal formation and accretion processes. the main-belt size distribution as a whole has evolved into a collisional steady state, and it has possibly been in that state for billions of years. asteroid families provide a critical historical record of main-belt collisions. the heavily depleted and largely dispersed "ghost families," however, may hold the key to understanding what happened in the primordial days of the main belt. new asteroidal fragments are steadily created by both collisions and mass shedding events via yorp spinup processes. a fraction of this population, in the form of d < 30 km fragments, go on to escape the main belt via the yarkovsky/yorp effects and gravitational resonances, thereby creating a quasi-steady-state population of planet-crossing and near-earth asteroids. these populations go on to bombard all inner solar system worlds. by carefully interpreting the cratering records they produce, it is possible to constrain how portions of the main-belt population have evolved with time. | the collisional evolution of the main asteroid belt |
the surfaces of airless bodies such as lunar and s-type asteroids typically become spectrally redder in visible to near-infrared reflectance with longer exposures to space weathering. however, some carbonaceous asteroids instead become spectrally bluer. space weathering experiments on carbonaceous meteorites have provided some clues as to the space weathering products that could produce spectral bluing. we applied these experimental results to our hapke radiative transfer model, with which we modeled spectral data from the osiris-rex mission in order to determine whether these space weathering products—specifically, nanophase and microphase metallic iron, troilite, and magnetite—could explain the globally blue spectrum of the carbonaceous asteroid (101955) bennu. the model suggests that the surface of bennu has microphase iron, nanophase magnetite, and nanophase and microphase troilite. considering previous space weathering experiments together with our spectral modeling of bennu, we posit that the presence of nanophase magnetite is what causes a carbonaceous asteroid to become spectrally bluer with exposure time. nanophase magnetite can form on asteroids that have fe-bearing hydrated minerals (phyllosilicates). on anhydrous carbonaceous asteroids, nanophase iron forms instead of magnetite, leading to spectral reddening. we therefore predict that samples returned by the osiris-rex mission from bennu will have more nanophase magnetite than nanophase iron with nanophase and microphase sulfides, whereas samples returned by the hayabusa2 mission from the carbonaceous asteroid (162173) ryugu, which is spectrally red, will contain nanophase and microphase sulfides as well as more nanophase iron than nanophase magnetite. | the role of hydrated minerals and space weathering products in the bluing of carbonaceous asteroids |
with the flourishing number of small body missions that involve surface interactions, understanding the mechanics of spacecraft - surface interactions is crucial for improving our knowledge about the landing phases of space missions, for preparing spacecraft operations, and for interpreting the results of measurements made during the surface interactions. given their regolith-covered surfaces, the process of landing on a small body can be considered as an impact at low-velocity on to a granular material in reduced-gravity. in order to study the influence of the surface material, projectile shape, and gravity on the collision dynamics, we used two experimental configurations (one for terrestrial gravity experiments and one for reduced-gravity experiments) to perform low-velocity collisions into different types of granular materials: quartz sand, and two different sizes of glass beads (1.5 and 5 mm diameter). both a spherical and a cubic projectile (with varying impact orientation) were used. the experimental data support a drag model for the impact dynamics composed of both a hydrodynamic drag force and quasi-static resistance force. the hydrodynamic and quasi-static contributions are related to the material frictional properties, the projectile geometry, and the gravity. the transition from a quasi-static to a hydrodynamical regime is shown to occur at lower impact velocities in reduced-gravity trials than in terrestrial gravity trials, indicating that regolith has a more fluid-like behaviour in low-gravity. the reduced quasi-static regime of a granular material under low-gravity conditions leads to a reduction in the strength, resulting in a decreased resistance to penetration and larger penetration depths. | low-velocity impacts into granular material: application to small-body landing |
ceres is the largest asteroid belt object, and the dawn spacecraft observed ceres since 2015. dawn observed two morphologically distinct linear features on ceres's surface: secondary crater chains and pit chains. pit chains provide unique insights into ceres's interior evolution. we interpret pit chains called the samhain catenae as the surface expression of subsurface fractures. using the pit chains' spacings, we estimate that the localized thickness of ceres's fractured, outer layer is approximately ≥58 km, at least 14 km greater than the global average. we hypothesize that extensional stresses, induced by a region of upwelling material arising from convection/diapirism, formed the samhain catenae. we derive characteristics for this upwelling material, which can be used as constraints in future interior modeling studies. for example, its predicted location coincides with hanami planum, a high-elevation region with a negative residual gravity anomaly, which may be surficial evidence for this proposed region of upwelling material. | evidence for the interior evolution of ceres from geologic analysis of fractures |
northwest africa (nwa) 6704 is a unique achondrite characterized by a near-chondritic major element composition with a remarkably intact igneous texture. to investigate the origin of this unique achondrite, we have conducted a combined petrologic, chemical, and 187re-187os, o, and ti isotopic study. the meteorite consists of orthopyroxene megacrysts (en55-57wo3-4fs40-42; fe/mn = 1.4) up to 1.7 cm in length with finer interstices of olivine (fa50-53; fe/mn = 1.1-2.1), chromite (cr# ∼ 0.94), awaruite, sulfides, plagioclase (ab92an5or3) and merrillite. the results of morphology, lattice orientation analysis, and mineral chemistry indicate that orthopyroxene megacrysts were originally hollow dendrites that most likely crystallized under high super-saturation and super-cooling conditions (1-102 °c/h), whereas the other phases crystallized between branches of the dendrites in the order of awaruite, chromite → olivine → merrillite → plagioclase. in spite of the inferred high super-saturation, the remarkably large size of orthopyroxene can be explained as a result of crystallization from a melt containing a limited number of nuclei that are preserved as orthopyroxene megacryst cores having high mg# or including vermicular olivine. the re-os isotope data for bulk and metal fractions yield an isochron age of 4576 ± 250 ma, consistent with only limited open system behavior of highly siderophile elements (hse) since formation. the bulk chemical composition is characterized by broadly chondritic absolute abundances and only weakly fractionated chondrite-normalized patterns for hse and rare earth elements (ree), together with substantial depletion of highly volatile elements relative to chondrites. the hse and ree characteristics indicate that the parental melt and its protolith had not undergone significant segregation of metals, sulfides, or silicate minerals. these combined results suggest that a chondritic precursor to nwa 6704 was heated well above its liquidus temperature so that highly volatile elements were lost and the generated melt initially contained few nuclei of relict orthopyroxene, but the melting and subsequent crystallization took place on a timescale too short to allow magmatic differentiation. such rapid melting and crystallization might occur as a result of impact on an undifferentiated asteroid. the o-ti isotope systematics (δ17o = -1.052 ± 0.004, 2 sd; ε50ti = 2.28 ± 0.23, 2 sd) indicate that the nwa 6704 parent body sampled the same isotopic reservoirs in the solar nebula as the carbonaceous chondrite parent bodies. this is consistent with carbonaceous chondrite-like refractory element abundances and oxygen fugacity (fmq = -2.6) in nwa 6704. yet, the si/mg ratio of nwa 6704 is remarkably higher than those of carbonaceous chondrites, suggesting significant nebular fractionation of forsterite in its provenance. | the origin of the unique achondrite northwest africa 6704: constraints from petrology, chemistry and re-os, o and ti isotope systematics |
in the preparation for esa's euclid mission and the large amount of data it will produce, we train deep convolutional neural networks (cnns) on euclid simulations to classify solar system objects from other astronomical sources. using transfer learning we are able to achieve a good performance despite our tiny data set with as few as 7512 images. our best model correctly identifies objects with a top accuracy of 94 {{ per cent}} and improves to 96 {{ per cent}} when euclid's dither information is included. the neural network misses {∼ }50{{ per cent}} of the slowest moving asteroids (v < 10 arcsec h-1) but is otherwise able to correctly classify asteroids even down to 26 mag. we show that the same model also performs well at classifying stars, galaxies, and cosmic rays, and could potentially be applied to distinguish all types of objects in the euclid data and other large optical surveys. | detecting solar system objects with convolutional neural networks |
the osiris-rex mission will conduct a radio science investigation of the asteroid bennu with a primary goal of estimating the mass and gravity field of the asteroid. the spacecraft will conduct proximity operations around bennu for over 1 year, during which time radiometric tracking data, optical landmark tracking images, and altimetry data will be obtained that can be used to make these estimates. most significantly, the main radio science experiment will be a 9-day arc of quiescent operations in a 1-km nominally circular terminator orbit. the pristine data from this arc will allow the radio science team to determine the significant components of the gravity field up to the fourth spherical harmonic degree. the radio science team will also be responsible for estimating the surface accelerations, surface slopes, constraints on the internal density distribution of bennu, the rotational state of bennu to confirm yorp estimates, and the ephemeris of bennu that incorporates a detailed model of the yarkovsky effect. | the osiris-rex radio science experiment at bennu |
in september 2020, the u.s. national aeronautics and space administration (nasa) announced that it is seeking proposals from private companies to extract small amounts of regolith from the surface of the moon. according to nasa administrator jim bridenstine, the exercise will buttress an interpretation of international space law that is favored by the u.s. government: “what we're trying to do is make sure that there is a norm of behavior that says that resources can be extracted and that we're doing it in a way that is in compliance with the outer space treaty” (ost) (1). nasa's move is part of a larger u.s. diplomatic effort. in april 2020, president trump signed an executive order (eo) that affirmed a right of commercial space mining and directed the u.s. state department to secure the expressed support of u.s. allies. shortly after, nasa announced a plan for bilateral artemis accords, which, if accepted by many nations, could enable the u.s. interpretation of international space law to prevail and make the united states—as the licensing nation for most of the world's space companies—the de facto gatekeeper to the moon, asteroids, and other celestial bodies. because acquiescence is often treated as consent in international law, even nasa's purchase of regolith would, if not protested by other nations, strengthen the u.s. interpretation. other nations need to speak up, now. | u.s. policy puts the safe development of space at risk |
the textures and accretion ages of chondrites have been used to argue that their parent asteroids never differentiated. without a core, undifferentiated planetesimals could not have generated magnetic fields through dynamo activity, so chondrites are not expected to have experienced such fields. however, the magnetic remanence carried by the cv chondrites is consistent with dynamo-generated fields, hinting that partially differentiated asteroids consisting of an unmelted crust atop a differentiated interior may exist. here, we test this hypothesis by applying synchrotron x-ray microscopy to metallic veins in the slowly cooled h6 chondrite portales valley. the magnetic remanence carried by nanostructures in these veins indicates that this meteorite recorded a magnetic field over a period of tens to hundreds of years at ∼100 myr after solar system formation. these properties are inconsistent with external field sources such as the nebula, solar wind, or impacts, but are consistent with dynamo-generated fields, indicating that the h chondrite parent body contained an advecting metallic core and was therefore partially differentiated. we calculate the thermal evolution of the chondritic portions of partially differentiated asteroids that form through incremental accretion across 105 to 106 years, finding this can agree with the measured ages and cooling rates of multiple h chondrites. we also predict that the cores of these bodies could have been partially liquid and feasibly generating a dynamo at 100 myr after solar system formation. these observations contribute to a growing body of evidence supporting a spectrum of internal differentiation within some asteroids with primitive surfaces. | paleomagnetic evidence for a partially differentiated ordinary chondrite parent asteroid |
it is likely that multiple bodies with masses between those of mars and earth (“planetary embryos”) formed in the outer planetesimal disk of the solar system. some of these were likely scattered by the giant planets into orbits with semimajor axes of hundreds of au. mutual torques between these embryos may lift the perihelia of some of them beyond the orbit of neptune, where they are no longer perturbed by the giant planets, so their semimajor axes are frozen in place. we conduct n-body simulations of this process and its effect on smaller planetesimals in the region of the giant planets and the kuiper belt. we find that (i) there is a significant possibility that one sub-earth mass embryo, or possibly more, is still present in the outer solar system; (ii) the orbit of the surviving embryo(s) typically has perihelion of 40-70 au, semimajor axis less than 200 au, and inclination less than 30° (iii) it is likely that any surviving embryos could be detected by current or planned optical surveys or have a significant effect on solar system ephemerides; (iv) whether or not an embryo has survived to the present day, its dynamical influence earlier in the history of the solar system can explain the properties of the detached disk (defined in this paper as containing objects with perihelia >38 au and semimajor axes between 80 and 500 au). | producing distant planets by mutual scattering of planetary embryos |
context. dynamical and albedo properties suggest that asteroids in cometary orbits (acos) are dormant or extinct comets. their study provides new insights for understanding the end-states of comets and the size of the comet population.aims: we intend to study the visible and near-infrared (nir) spectral properties of different aco populations and compare them to the independently determined properties of comets.methods: we select our acos sample based on published dynamical criteria and present our own observational results obtained using the 10.4 m gran telescopio canarias (gtc), the 4.2 m william herschel telescope (wht), the 3.56 m telescopio nazionale galileo (tng), and the 2.5 m isaac newton telescope (int), all located at the el roque de los muchachos observatory (la palma, spain), and the 3.0 m nasa infrared telescope facility (irtf), located at the mauna kea observatory, in hawaii. we include in the analysis the spectra of acos obtained from the literature. we derive the spectral class and the visible and nir spectral slopes. we also study the presence of hydrated minerals by studying the 0.7 μm band and the uv-drop below 0.5 μm associated with phyllosilicates.results: we present new observations of 17 acos, 11 of them observed in the visible, 2 in the nir and 4 in the visible and nir. we also discuss the spectra of 12 acos obtained from the literature. all but two acos have a primitive-like class spectrum (x or d-type). almost 100% of the acos in long-period cometary orbits (damocloids) are d-types. those in jupiter family comet orbits (jfc-acos) are ∼60% d-types and ∼40% x-types. the mean spectral slope s' of jfc-acos is 9.7 ± 4.6%/1000 å and for the damocloids this is 12.2 ± 2.0%/1000 å. no evidence of hydration on the surface of acos is found from their visible spectra. the spectral slope and spectral class distribution of acos is similar to that of comets.conclusions: the spectral taxonomical classification and the spectral slope distribution of acos, and the lack of spectral features indicative of the presence of hydrated minerals on their surface, strongly suggest that acos are likely dormant or extinct comets. | the visible and near-infrared spectra of asteroids in cometary orbits |
non-magmatic iron meteorites, including the iie group, can provide important insights into the history of metal-silicate differentiation and collisions on planetesimals. to better constrain the evolution of metal segregation and impacts on the iie parent body, w isotopic data are reported for 10 iie iron meteorites and a metal vein from the portales valley h6 chondrite. in addition, pt isotopic data were obtained to quantify cosmic ray-induced neutron capture effects on w isotopes. after correction for these effects, the iie iron meteorites exhibit variable pre-exposure 182w compositions, translating into hf-w model age clusters of ∼4-5 million years (ma), ∼10 ma, ∼15 ma, and ∼27 ma after cai formation. these distinct 182w clusters likely represent samples from several discrete metallic melt pools on the iie parent asteroid. the earliest metal segregation event at ∼4-5 ma was likely facilitated by 26al decay as an internal heat source. by contrast, the younger hf-w model ages may not be chronologically meaningful, and probably reflect the effects of secondary mixing and re-equilibration of metal and silicates, likely facilitated by impacts on the iie parent body. thus, contrary to prior work, the hf-w systematics of iie iron meteorites do not require a protracted history of metal-silicate separation on the iie parent body. instead the results of this study are fully consistent with a single partial metal-silicate differentiation event driven by endogenic heating at ∼4-5 ma, followed by one or multiple impact events causing mixing and re-equilibration of metal and silicates at a later stage. the exact timing of these impact event(s) remains poorly constrained, but they most likely occurred in the first few tens of ma of solar system history. | age and origin of iie iron meteorites inferred from hf-w chronology |
we present a new analysis of spitzer observations of comet 29p/schwassmann-wachmann 1 taken on ut 2003 november 21, 23, and 24, similar to a previous investigation of the observations (stansberry et al., 2004), but using the most recent spitzer data pipeline products and intensive image processing techniques. analysis of images from the irac 5.8 and 8.0 μ m bands and the mips 24.0 and 70.0 μ m bands resulted in photometry measurements of the nucleus after a suite of coma modeling and removal processes were implemented. sw1 was not identified in the 5.8 μ m image from the previous work so its incorporation into this analysis is entirely new. using the near earth asteroid thermal model (harris, 1998) resulted in a nucleus radius measurement of r =30.2-2.9+3.7 km and an infrared beaming parameter value of η =0.99-0.19+0.26 . we also measured an infrared geometric albedo, p5.8 = 0.5 ± 0.5 . extrapolating a 0.04 v-band albedo and using a normalized reflectivity gradient s‧ = 14.94 ± 1.09 [% (1000 å)-1] (duffard, r., et al. [2014]. astron. astrophys. 564, a92) we recover an infrared albedo of p5.8 = 0.31 in the near infrared consistent with the value recovered from thermal modeling. the dust composition extracted from irs spectra are very comet-like, containing mainly amorphous ferromagnesian silicates (but with a minority of crystalline silicates as well), water ice, and metal sulfides. | a new analysis of spitzer observations of comet 29p/schwassmann-wachmann 1 |
context. asteroid (6478) gault was discovered to exhibit a comet-like tail in observations from december 2018, becoming a new member of the so-called active asteroid population in the main asteroid belt.aims: we seek to investigate the grain properties of the dust ejected from asteroid (6478) gault and to give insight into the activity mechanism(s).methods: we use a monte carlo dust tail brightness code to retrieve the dates of dust ejection, the physical properties of the grains, and the total dust mass losses during each event. the code takes into account the brightness contribution of the asteroid itself. the model is applied to a large data set of images spanning the period from 2019 january 11 to 2019 march 13. in addition, we carried out both short- and long-term photometric measurements of the asteroid.results: it is shown that, to date, asteroid (6478) gault has experienced two episodes of impulsive dust ejection, which took place around 2018 november 5 and 2019 january 2. these two episodes released at least 1.4 × 107 kg and 1.6 × 106 kg of dust, respectively, at escape speeds. the size distribution, consisting of particles in the 1 μm-1 cm radius range, follows a broken power law with bending points near 15 μm and 870 μm. on the other hand, the photometric series indicate a nearly constant magnitude over several 5-7.3 h periods, which is a possible effect of the masking of a rotational light curve by the dust.conclusions: the dust particles forming gault's tails were released from the asteroid at escape speeds, but the specific ejection mechanism is unclear until photometry of the dust-free asteroid are conducted to assess whether this was related to rotational disruption or to other possible causes. | dust properties of double-tailed active asteroid (6478) gault |
context. space weathering is a process that changes the surface of airless planetary bodies. prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. these processes alter planetary reflectance spectra and often modify their compositional diagnostic features.aims: in this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes.methods: we used olivine and pyroxene pellets as proxies for planetary materials. to simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 kev and fluences of up to 1018 particles cm−2. to simulate micrometeoroid bombardment we used individual femtosecond laser pulses. we analysed the corresponding evolution of different spectral parameters, which we determined by applying the modified gaussian model, and we also conducted principal component analysis.results: the original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. the spectral slope changes seen in olivine are consistent with observations of a-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) vesta. we also observed some differences in the spectral effects induced by the two weathering agents. ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. this is most likely due to the different penetration depths of ions and laser pulses. our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface. all measured spectra in raw format are only available at the cds via anonymous ftp to cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/654/a143 | comparison of space weathering spectral changes induced by solar wind and micrometeoroid impacts using ion- and femtosecond-laser-irradiated olivine and pyroxene |
two dedicated asteroid rotation-period surveys have been carried out in the r band with ∼20 minute cadence using the intermediate palomar transient factory (iptf) during 2014 january 6-9 and february 20-23. the total survey area covered 174 deg2 in the ecliptic plane. reliable rotation periods for 1438 asteroids are obtained from a larger data set of 6551 mostly main-belt asteroids, each with ≥slant 10 detections. analysis of 1751, ptf-based, reliable rotation periods clearly shows the spin barrier at ∼2 hr for rubble-pile asteroids. we found a new large super-fast rotator, 2005 uw163, and another five candidates as well. for asteroids of 3\lt d\lt 15 km, our spin-rate distribution shows a number decrease along with frequency after 5 rev day-1, which is consistent with the results of the asteroid light curve database. the discrepancy between our work and that of pravec et al. (update 2014 april 20) comes mainly from asteroids with {{δ }}m\lt 0.2 mag, which could be the result of different survey strategies. for asteroids with d\lt 3 km, we see a significant number drop at f = 6 rev day-1. the relatively short yorp effect timescale for small asteroids could have spun up those elongated objects to reach their spin-rate limit resulting in breakup to create such a number deficiency. we also see that the c-type asteroids show a smaller spin-rate limit than the s-type, which agrees with the general impression that c-type asteroids have a lower bulk density than s-type asteroids. | asteroid spin-rate study using the intermediate palomar transient factory |
the collision of an asteroid with earth can potentially have significant consequences for the human population. the european and united states space agencies (esa and nasa) maintain asteroid hazard lists that contain all known asteroids with a non-zero chance of colliding with the earth in the future. some software tools exist that are, either, capable of calculating the impact points of those asteroids, or that can estimate the impact effects of a given impact incident. however, no single tool is available that combines both aspects and enables a comprehensive risk analysis. the question is, thus, whether tools that can calculate impact location may be used to obtain a qualitative understanding of the asteroid impact risk distribution. to answer this question, two impact risk distributions that control for impact effect modelling were generated and compared. the asteroid risk mitigation optimisation and research (armor) tool, in conjunction with the freely available software orbfit, was used to project the impact probabilities of listed asteroids with a minimum diameter of 30 m onto the surface of the earth representing a random sample (15% of all objects) of the hazard list. the resulting 261 impact corridors were visualised on a global map. furthermore, the impact corridors were combined with earth population data to estimate the ;simplified; risk (without impact effects) and ;advanced; risk (with impact effects) associated with the direct asteroid impacts that each nation faces from present to 2100 based on this sample. the relationship between risk and population size was examined for the 40 most populous countries and it was apparent that population size is a good proxy for relative risk. the advanced and simplified risk distributions were compared and the alteration of the results based on the introduction of physical impact effects was discussed. population remained a valid proxy for relative impact risk, but the inclusion of impact effects resulted in significantly different risks, especially when considered at the national level. therefore, consideration of physical impact effects is essential in estimating the risk to specific nations of the asteroid threat. | on the influence of impact effect modelling for global asteroid impact risk distribution |
many asteroids are likely rubble-piles that are a collection of smaller objects held together by gravity and possibly cohesion. these asteroids are seismically shaken by impacts, which leads to excitation of their constituent particles. as a result it has been suggested that their surfaces and sub-surface interiors may be governed by a size sorting mechanism known as the brazil nut effect. we study the behavior of a model asteroid that is a spherical, self-gravitating aggregate with a binary size-distribution of particles under the action of applied seismic shaking. we find that above a seismic threshold, larger particles rise to the surface when friction is present, in agreement with previous studies that focussed on cylindrical and rectangular box configurations. unlike previous works we also find that size sorting takes place even with zero friction, though the presence of friction does aid the sorting process above the seismic threshold. additionally we find that while strong size sorting can take place near the surface, the innermost regions remain unsorted under even the most vigorous shaking. | the spherical brazil nut effect and its significance to asteroids |
the paper presents a numerical implementation of the gravitational n-body problem with contact interactions between non-spherically shaped bodies. the work builds up on a previous implementation of the code and extends its capabilities. the number of bodies handled is significantly increased through the use of a cuda/gpu-parallel octree structure. the implementation of the code is discussed and its performance is compared against direct n2 integration. the code features both smooth (force-based) and non-smooth (impulse-based) methods, as well as a visco-elastic non-smooth method, to handle contact interaction between bodies. the numerical problem of simulating `rubble-pile' asteroid gravitational aggregation processes is addressed. we discuss the features of the problem and derive criteria to set up the numerical simulation from the dynamical constraints of the combined gravitational-collisional problem. examples of asteroid aggregation scenarios that could benefit from such implementation are finally presented. | a parallel-gpu code for asteroid aggregation problems with angular particles |
context. the interplanetary dust complex is currently understood to be largely the result of dust production from jupiter-family comets, with contributions also from longer-period comets (halley- and oort-type) and collisionally produced asteroidal dust.aims: here we develop a dynamical model of the interplanetary dust cloud from these source populations in order to develop a risk and hazard assessment tool for interplanetary meteoroids in the inner solar system.methods: the long-duration (1 myr) integrations of dust grains from jupiter-family and halley-type comets and main belt asteroids were used to generate simulated distributions that were compared to cobe infrared data, meteor data, and the diameter distribution of lunar microcraters. this allowed the constraint of various model parameters.results: we present here the first attempt at generating a model that can simultaneously describe these sets of observations. extended collisional lifetimes are found to be necessary for larger (radius ≥ 150 μm) particles. the observations are best fit with a differential size distribution that is steep (slope = 5) for radii ≥ 150 μm, and shallower (slope = 2) for smaller particles. at the earth the model results in 90-98% jupiter-family comet meteoroids, and small contributions from asteroidal and halley-type comet particles. in cobe data we find an approximately 80% contribution from jupiter-family comet meteoroids and 20% from asteroidal particles. the resulting flux at the earth is mostly within a factor of about two to three of published measurements. | imem2: a meteoroid environment model for the inner solar system |
mathematical modelling has shown that activity of the geminid meteor shower should rise with time, and that was confirmed by analysis of visual observations 1985-2016. we do not expect any outburst activity of the geminid shower in 2017, even though the asteroid (3200) phaethon has a close approach to earth in december of 2017. a small probability to observe dust ejected at perihelia 2009-2016 still exists. | increasing geminid meteor shower activity |
the asteroid belt is characterized by an extreme low total mass of material on dynamically excited orbits. the nice model explains many peculiar qualities of the solar system, including the belt's excited state, by invoking an orbital instability between the outer planets. however, previous studies of the nice model's effect on the belt's structure struggle to reproduce the innermost asteroids' orbital inclination distribution. here, we show how the final phase of giant planet migration sculpts the asteroid belt, in particular its inclination distribution. as interactions with leftover planetesimals cause saturn to move away from jupiter, its rate of orbital precession slows as the two planets' mutual interactions weaken. when the planets approach their modern separation, where jupiter completes just short of five orbits for every two of saturn's, jupiter's eccentric forcing on saturn strengthens. we use numerical simulations to show that the absence of asteroids with orbits that precess between 24 and 28 arcsec yr-1 is related to the inclination problem. as saturn's precession speeds back up, high-inclination asteroids are excited on to planet crossing orbits and removed from the inner main belt. through this process, the asteroid belt's orbital structure is reshaped, leading to markedly improved simulation outcomes. | a record of the final phase of giant planet migration fossilized in the asteroid belt's orbital structure |
asteroid phase curves are used to derive fundamental physical properties through the determination of the absolute magnitude h. the upcoming visible legacy survey of space and time (lsst) and mid-infrared near-earth object surveillance mission (neosm) surveys rely on these absolute magnitudes to derive the colours and albedos of millions of asteroids. furthermore, the shape of the phase curves reflects their surface compositions, allowing for conclusions on their taxonomy. we derive asteroid phase curves from dual-band photometry acquired by the asteroid terrestrial-impact last alert system telescopes. using bayesian parameter inference, we retrieve the absolute magnitudes and slope parameters of 127,012 phase curves of 94,777 asteroids in the photometric h, g1, g2- and h, g12∗-systems. the taxonomic complexes of asteroids separate in the observed g1, g2-distributions, correlating with their mean visual albedo. this allows for differentiating the x-complex into the p-, m-, and e-complexes using the slope parameters as alternative to albedo measurements. further, taxonomic misclassifications from spectrophotometric datasets as well as interlopers in dynamical families of asteroids reveal themselves in g1, g2-space. the h, g12∗-model applied to the serendipitous observations is unable to resolve target taxonomy. the g1, g2 phase coefficients show wavelength-dependency for the majority of taxonomic complexes. their values allow for estimating the degree of phase reddening of the spectral slope. the uncertainty of the phase coefficients and the derived absolute magnitude is dominated by the observational coverage of the opposition effect rather than the magnitude dispersion induced by the asteroids' irregular shapes and orientations. serendipitous asteroid observations allow for reliable phase curve determination for a large number of asteroids. to ensure that the acquired absolute magnitudes are suited for colour computations, it is imperative that future surveys densely cover the opposition effects of the phase curves, minimizing the uncertainty on h. the phase curve slope parameters offer an accessible dimension for taxonomic classification, correlating with the albedo and complimentary to the spectral dimension. | asteroid phase curves from atlas dual-band photometry |
recent high precision meteoritic data improve constraints on the formation timescale and bulk composition of the terrestrial planets. high resolution n-body simulations allow direct comparison of embryo growth timescale and accretion zones to these constraints. in this paper, we present results of high resolution simulations for embryo formation from a disc of up to 41,000 fully-self gravitating planetesimals with the gpu-based n-body code genga. our results indicate that the growth of embryos are highly dependent on the initial conditions. more massive initial planetesimals, a shorter gas disc decay timescale and initially eccentric jupiter and saturn (ejs) all lead to faster growth of embryos. asteroid belt material can thereby be implanted into the terrestrial planet region via sweeping secular resonances. this could possibly explain the rapid growth of mars within 10 myr inferred from its hf-w chronology. the sweeping secular resonance almost completely clears the asteroid belt and deposits this material in the mercury-venus region, altering the composition of embryos there. this could result in embryos in the mercury-venus region accreting an unexpectedly high mass fraction from beyond 2 au. changing the initial orbits of jupiter and saturn to more circular (cjs) or assuming embryos formed in a gas free environment removes the sweeping secular resonance effect and thus greatly decreases material accreted from beyond 2 au for mercury-venus region embryos. we therefore propose that rock samples from mercury and venus could aid greatly in deducing the condition and lifetime of the initial protoplanetary gas disc during planetesimal and embryo formation, as well as the initial architecture of the giant planets. | growing mars fast: high-resolution gpu simulations of embryo formation |
in 2018 december, the main-belt asteroid (6478) gault was reported to display activity. gault is an asteroid belonging to the phocaea dynamical family and was not previously known to be active, nor was any other member of the phocaea family. in this work, we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. we obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. we find that gault has a rotation period of p = 2.4929 ± 0.0003 h with a light-curve amplitude of 0.06 magnitude. this short rotation period close to the spin barrier limit is consistent with gault having a density no smaller than ρ = 1.85 g cm-3 and its activity being triggered by the yorp (yarkovsky-o'keefe-radzievskii-paddack) spin-up mechanism. analysis of the gault phase curve over phase angles ranging from 0.4° to 23.6° provides an absolute magnitude of h = 14.81 ± 0.04, g1 = 0.25 ± 0.07, and g2 = 0.38 ± 0.04. model fits to the phase curve find the surface regolith grain size constrained between 100 and 500 $\rm {\mu }$m. using relations between the phase curve and albedo, we determine that the geometrical albedo of gault is pv = 0.26 ± 0.05 corresponding to an equivalent diameter of $d = 2.8^{+0.4}_{-0.2}$ km. our spectroscopic observations are all consistent with an ordinary chondrite-like composition (s, or q-type in the bus-demeo taxonomic classification). a search through archival photographic plate surveys found previously unidentified detections of gault dating back to 1957 and 1958. only the latter had been digitized, which we measured to nearly double the observation arc of gault. finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit. | (6478) gault: physical characterization of an active main-belt asteroid |
context. the cooling history of individual meteorites can be reconstructed if closure temperatures and closure ages of different radioisotopic chronometers are available for a couple of meteorites. if a close similarity in chemical and isotopic composition suggests a common origin from the same parent body, some basic properties of this body can be derived.aims: the radius of the l chondrite parent body, its formation time, and its evolution history are determined by fitting theoretical models to empirical data of radioisotopic chronometers for l chondrites.methods: a simplified evolution model for the l chondrite parent body was constructed considering sintering of the initially porous material, temperature dependent heat conductivity, and an insulating regolith layer. such models were fitted to thermochronological data of five meteorites for which precise data for the hf-w and u-pb-pb thermochronometers have been published.results: a set of parameters for the l chondrite parent body is found that yields excellent agreement (within error bounds) between a thermal evolution model and thermochonological data of five examined l chondrites. empirical cooling rate data also agree with the model results within error bounds such that there is no conflict between cooling rate data and the onion-shell model. two models are found to be compatible with the presently available empirical data: one model with a radius of 115 km and a formation time of 1.89 ma after cai formation, and another model with 160 km radius and formation time of 1.835 ma. the central temperature of the smaller body remains well below the ni,fe-fes eutectic melting temperature and is consistent with the apparent non-existence of primitive achondrites related to the l chondrites. for the bigger model, incipient melting in the central core region is predicted, which opens the possibility that primitive achondrites related to l chondrites could be found. | thermal history modelling of the l chondrite parent body |
the implication of small amounts of cohesion within relatively small rubble pile asteroids is investigated with regard to their evolution under the persistent presence of the yorp effect. we find that below a characteristic size, which is a function of cohesive strength, density and other properties, rubble pile asteroids can enter a "disaggregation phase" in which they are subject to repeated fissions after which the formation of a stabilizing binary system is not possible. once this threshold is passed rubble pile asteroids may be disaggregated into their constituent components within a finite time span. these constituent components will have their own spin limits - albeit potentially at a much higher spin rate due to the greater strength of a monolithic body. the implications of this prediction are discussed and include modification of size distributions, prevalence of monolithic bodies among meteoroids and the lifetime of small rubble pile bodies in the solar system. the theory is then used to place constraints on the strength of binary asteroids characterized as a function of their type. | disaggregation of small, cohesive rubble pile asteroids due to yorp |
themis is an old and statistically robust asteroid family populating the outer main belt, and resulting from a catastrophic collision that took place 2.5 ± 1.0 gyr ago. within the old themis family a young sub-family, beagle, formed less than 10 myr ago, has been identified. we present the results of a spectroscopic survey in the visible and near infrared range of 22 themis and 8 beagle families members. the themis members investigated exhibit a wide range of spectral behaviors, including asteroids with blue/neutral and moderately red spectra, while the younger beagle family members look spectrally bluer than the themis ones and they have a much smaller spectral slope variability. four themis members, including (24) themis, have absorption bands centered at 0.68-0.73 μm indicating the presence of aqueously altered minerals. the best meteorite spectral analogues found for both themis and beagle families members are carbonaceous chondrites having experienced different degrees of aqueous alteration, prevalently cm2 but also cv3 and ci, and some of them are chondrite samples being unusual or heated. the presence of aqueous altered materials on the asteroids surfaces and the meteorite matches indicate that the parent body of the themis family experienced mild thermal metamorphism in the past. we extended the spectral analysis including the data available in the literature on themis and beagle families members, and we looked for correlations between spectral behavior and physical parameters using the albedo and size values derived from the wise data. the analysis of this larger sample confirms the spectral diversity within the themis family and that beagle members tend to be bluer and to have an higher albedo. the differences between the two families may be partially explained by space weathering processes, which act on these primitive surfaces in a similar way than on s-type asteroids, i.e. producing reddening and darkening. however we see several themis members having albedos and spectral slopes similar to the young beagle members. alternative scenarios are proposed including heterogeneity in the parent body having a compositional gradient with depth, and/or the survival of projectile fragments having a different composition than the parent body. | spectral variability on primitive asteroids of the themis and beagle families: space weathering effects or parent body heterogeneity? |
non-cumulate eucrites represent basaltic crust that experienced a complex thermal history involving multistage metamorphism and metasomatism, probably on asteroid vesta. to better constrain the thermal history of these rocks and their parent body, we have integrated high-precision u-pb age and trace element data for zircon grains with sizes up to 80 μm in the eucrite agoult. all analyzed zircon grains yielded concordant u-pb dates that correspond to the precise 207pb/206pb age of 4554.5 ± 2.0 ma. the ti contents in these zircon grains indicate their crystallization at subsolidus temperatures of ca. 900 °c, which are similar to the inferred conditions of pyroxene exsolution in most basaltic eucrites that occurred during protracted thermal metamorphism. the zircon crystallization temperatures, together with the presence of baddeleyite needles and variable zr concentration in agoult ilmenite grains, indicate metamorphic origin of the agoult zircon through zr release from ilmenite followed by reaction with silica. we therefore consider the zircon 207pb/206pb age as the timing of the widespread thermal metamorphism in vesta's crust. the metamorphic age is coincident with the oldest mn-cr date for cumulate eucrites, supporting the view that the thermal metamorphism is a result of burial of basaltic crust and subsequent heating from the hot interior rather than collision of asteroids. the zircon rare earth element patterns with restricted ce positive anomalies suggest that the metamorphism occurred at an oxygen fugacity below the iron-wüstite buffer, implying the absence of oxidizing agents such as aqueous fluid within the crust at that time. | timing of global crustal metamorphism on vesta as revealed by high-precision u-pb dating and trace element chemistry of eucrite zircon |
the processes that controlled accretion of water and volatiles to the inner solar system remain enigmatic, because it is difficult to determine the absolute concentrations of volatile elements in planetary bodies. in this contribution we study rare unequilibrated eucrites derived from the asteroid 4 vesta, to determine the water and fluorine content of this asteroid by measuring the volatile content of pyroxene. common thermal metamorphism in most equilibrated eucrites would have diffusively reset magmatic volatile contents. the unequilibrated eucrites are, therefore, the most suitable samples to determine primary magmatic volatile contents of 4 vesta. we find h2o and f contents in pyroxenes of 4-11 μg/g and 0.12-0.23 μg/g. we also determine a h2o partition coefficient for clinopyroxene and melt equilibrated at 0.1 mpa of dh2o = 0.1, which is higher than values previously reported for higher pressures. the higher compatibility of h2o in this experiment could partially be due to high oh/h2o ratio at the low total water contents in this experimental charge, but only further more detailed experiments will fully delineate the reasons for the more compatible behavior for water at lower pressures. however, given the lack of h2o partitioning data at low pressures we conclude that our 0.1 mpa experiment is the most appropriate to calculate magmatic water contents for melt in equilibrium with eucrite pyroxene. after using appropriate partition coefficients we calculate melt concentrations of 50-70 μg/g h2o and 1.5-2.4 μg/g f. in turn, these are converted into bulk 4 vesta water and f contents of 10-70 μg/g h2o and 0.3-2 μg/g f by assuming eucrite formation via either mantle partial melting or extraction from a magma ocean. we also measure the d/h of the clinopyroxenes and show that these are identical to the results of previous studies that reported d/h in eucrite apatite. these values match those found in carbonaceous chondrites suggesting that water in 4 vesta accreted from carbonaceous chondrites and not from cometary material. | the water and fluorine content of 4 vesta |
proposed mineralogical linkages between cm/ci carbonaceous chondrites and outer main belt asteroids remain uncertain due to a dearth of diagnostic absorptions in visible and near-infrared (∼0.4-2.5 μm) spectra of the two sets of objects. absorptions near 3 μm in both sets hold promise for illuminating the potential linkages. spectral comparisons of meteorites and asteroids have been challenging because meteorite spectra have usually been acquired in ambient terrestrial environments, and hence were contaminated by atmospheric water. in this study, we compare near-infrared spectra of chondrites measured in the laboratory under asteroid-like conditions (takir, d. et al. [2013]. meteorit. planet. sci. 48, 1618-1637) and spectra of asteroids measured with the long-wavelength cross-dispersed (lxd: 1.9-4.2-μm) mode of the spex spectrograph/imager at the nasa infrared telescope facility (irtf) (takir, d., emery, j.p. [2012]. icarus 219, 641-654). using the 3-μm band shape, we find that spectral group 2 cm and ci (ivuna) chondrites are possible meteorite analogs for asteroids with the sharp 3-μm features, which are predominately located in the 2.5 < a < 3.3 au region. spectral group 2 cm chondrites contain phyllosilicate phases intermediate between endmembers fe-serpentine and mg-serpentine, with a petrological subtype ranging from 2.2 to 2.1 (takir, d. et al. [2013]. meteorit. planet. sci. 48, 1618-1637). no meteorite match was found for asteroids showing a rounded 3-μm feature, which tend to be located farther from the sun (3.0 < a < 4.0 au), or for asteroids with distinctive spectra like 1 ceres or 52 europa. the study of the 3-μm band in meteorites and asteroids has implications for the understanding of phyllosilicate mineralogy and its distribution in the outer main belt region. | toward an understanding of phyllosilicate mineralogy in the outer main asteroid belt |
using infrared (ir) spectroscopy of thin sections, we characterize the relative degree of aqueous alteration and subsequent heating of a suite of cm chondrites to document spectral indicators of these processes that can contextualize observations of carbonaceous asteroids. we find that the progressive aqueous alteration of cms manifests in two spectral regions. the low-wavenumber region (1200-400 cm-1; 8-25 μm) records the increasing proportion of mg-fe phyllosilicates relative to anhydrous silicates as aqueous alteration proceeds, with a highly correlated shift of the christiansen feature (cf) to lower wavenumber and the si-o bending band minimum to higher wavenumber, and an increase in depth of the mg-oh band (~625 cm-1). the strongest correlation (r2 = 0.90) with petrologic subtype is the distance between the cf and si-o stretching band minimum, which predicts the petrologic subtype of the sample to within 0.1. the high-wavenumber region (4000-2500 cm-1, ≤3.33 μm) probes the variation in abundance and composition of mg-fe serpentine and tochilinite among the altered cms. all moderately to highly altered cms (≤2.3) have an oh/h2o ('3 μm') band emission maximum of 3690 cm-1 (2.71 μm) indicative of mg-bearing serpentine, and mildly aqueously altered cms (≥ 2.5) have a wider band with a complex shape that results from contributions of fe-bearing serpentine and tochilinite. among weakly heated cms (stage ii; 300-500 °c), the low-wavenumber region exhibits spectral features resulting from the dehydration and dehydroxylation of phyllosilicates that include broadening of the si-o stretching band and a shift of its minimum to lower wavenumber, and the disappearance of the mg-oh band. the location of the si-o bending band minimum appears to be unaffected by mild heating. extensively heated cms (stage iii+; > 500 °c) have a low-wavenumber region dominated by the spectral features of secondary, fe-bearing olivine and low-ca pyroxene and thus are readily distinguished from unheated and mildly heated cms. the oh/h2o band of all heated cms is broad and rounded with an emission peak at lower wavenumbers (≤3636 cm-1; ≥2.75 μm) than in unheated cms. however, spectral and petrographic evidence suggests that our heated cms have been compromised by terrestrial rehydration. our study confirms that thermal metamorphism effects are concentrated within the matrix and suggests that the matrix of the cm wis 91600 had a ci-like mineralogy prior to heating. | distinguishing relative aqueous alteration and heating among cm chondrites with ir spectroscopy |
carbonaceous chondrites experienced varying degrees of aqueous alteration on their parent asteroids, which influenced their mineralogies, textures, and bulk chemical and isotopic compositions. although this alteration was a crucial event in the history of these meteorites, their various alteration pathways are not well understood. one phase that formed during this alteration was magnetite, and its morphology and abundance vary between and within chondrite groups, providing a means of investigating chondrite aqueous alteration. we measured bulk magnetic properties and first-order reversal curve (forc) diagrams of cm, ci, co, and ungrouped c2 chondrites to identify the morphology and size range of magnetite present in these meteorites. we identify two predominant pathways of aqueous alteration among these meteorites that can be distinguished by the resultant morphology of magnetite. in wis 91600, tagish lake, and ci chondrites, magnetite forms predominantly from fe-sulfides as framboids and stacked plaquettes. in cm and co chondrites, <0.1 μm single-domain (sd) magnetite and 0.1-5 μm vortex (v) state magnetite formed predominantly via the direct replacement of metal and fe-sulfides. after ruling out differences in temperature, water:rock ratios, terrestrial weathering effects, and starting mineralogy, we hypothesise that the primary factor controlling the pathway of aqueous alteration was the composition of the ice accreted into each chondrite group's parent body. nebula condensation sequences predict that the most feasible method of appreciably evolving ice concentrations was the condensation of ammonia, which will have formed a more alkaline hydrous fluid upon melting, leading to fundamentally different conditions that may have caused the formation of different magnetite morphologies. as such, we suggest that wis 91600, tagish lake, and the ci chondrites accreted past the ammonia ice line, supporting a more distal or younger accretion of their parent asteroids. | constraints on the ice composition of carbonaceous chondrites from their magnetic mineralogy |
the parent cores of iron meteorites belong to the earliest accreted bodies in the solar system. these cores formed in two isotopically distinct reservoirs: noncarbonaceous (nc) type and carbonaceous (cc) type in the inner and outer solar system, respectively. we measured elemental compositions of cc-iron groups and used fractional crystallization modeling to reconstruct the bulk compositions and crystallization processes of their parent asteroidal cores. we found generally lower s and higher p in cc-iron cores than in nc-iron cores and higher hse (highly siderophile element) abundances in some cc-iron cores than in nc-iron cores. we suggest that the different hse abundances among the cc-iron cores are related to the spatial distribution of refractory metal nugget–bearing calcium aluminum–rich inclusions (cais) in the protoplanetary disk. cais may have been transported to the outer solar system and distributed heterogeneously within the first million years of solar system history.higher siderophile abundances in outer solar system asteroidal cores indicate heterogeneity between compositional reservoirs. | compositions of carbonaceous-type asteroidal cores in the early solar system |
aims: asteroids have been exposed to impacts since their formation, and as a consequence their surfaces are covered by small particles, pebbles, and boulders. the japanese jaxa/isas hayabusa mission collected micron-sized particles from the regolith of asteroid 25143 itokawa. the study in terrestrial laboratories of these particles provides a scientific opportunity as their physical properties can be compared with those characteristic of chondritic meteorites that are often considered proxies of the building materials of potentially hazardous asteroids (phas).methods: here we present the results from a study of the mechanical properties of three of these particles using a precise technique called nanoindentation. the derived results are compared with those obtained via a methodology similar to that used for the chelyabinsk meteorite.results: the reduced young's modulus values obtained for the itokawa samples are higher than those measured for the chelyabinsk chondrite, so these specific particles of asteroid regolith are more compacted than the minerals forming the particular ll chondrite associated with phas. this might be a natural consequence of particles surviving long exposure times on the surface of a (near-earth asteroid) nea. the double asteroid redirection test (dart) mission plans to excavate a crater in the surface of the (65803) didymos satellite. our results suggest that excavating a crater with a kinetic impactor in an area of significant fine-grained regolith will increase the momentum transfer. as this will facilitate the release of particles carrying target mass in the opposite direction to the movement of the projectile, there is no need to grind up the target during the mechanical excavation phase. | mechanical properties of particles from the surface of asteroid 25143 itokawa |
we present classical and quantum algorithms for approximating partition functions of classical hamiltonians at a given temperature. our work has two main contributions: first, we modify the classical algorithm of stefankovic, vempala and vigoda (j. acm, 56(3), 2009) to improve its sample complexity; second, we quantize this new algorithm, improving upon the previously fastest quantum algorithm for this problem, due to harrow and wei (soda 2020). the conventional approach to estimating partition functions requires approximating the means of gibbs distributions at a set of inverse temperatures that form the so-called cooling schedule. the length of the cooling schedule directly affects the complexity of the algorithm. combining our improved version of the algorithm of stefankovic, vempala and vigoda with the paired-product estimator of huber (ann. appl. probab., 25(2), 2015), our new quantum algorithm uses a shorter cooling schedule than previously known. this length matches the optimal length conjectured by stefankovic, vempala and vigoda. the quantum algorithm also achieves a quadratic advantage in the number of required quantum samples compared to the number of random samples drawn by the best classical algorithm, and its computational complexity has quadratically better dependence on the spectral gap of the markov chains used to produce the quantum samples. | simpler (classical) and faster (quantum) algorithms for gibbs partition functions |
recent paleomagnetic studies of allende cv chondrite as well as thermal modeling suggest the existence of partially differentiated asteroids with outer unmelted and variably metamorphosed crusts overlying differentiated interiors. to further constrain the magnetic history of the cv parent body, we report here paleomagnetic results on kaba cv chondrite. this meteorite contains 11 wt% pseudo-single domain magnetite, making it a rock with an excellent paleomagnetic recording capacity. kaba appears to carry a stable natural remanent magnetization acquired on its parent body upon cooling in an internally generated magnetic field of about 3 μt from temperatures below 150 °c during thermal metamorphism about 10 to several tens of myr after solar system formation. this strengthens the case for the existence of a molten advecting core in the cv parent body. furthermore, we show that no significant magnetic field (i.e. lower than ∼ 0.3 μt) was present when aqueous alteration took place on the kaba parent body around 4 to 6 myr after solar system formation, suggesting a delay in the onset of the dynamo in the cv parent body and confirming that nebular fields had already decayed at that time. | new constraints on the magnetic history of the cv parent body and the solar nebula from the kaba meteorite |
the discovery of fast radio burst (frb) 200428 from galactic sgr j1935+2154 makes it possible to measure rotational changes accompanied by frbs and to test several frb models which may be simultaneously associated with glitches. inspired by this idea, we present order of magnitude calculations to the scenarios proposed. frb models such as global starquakes, crust fractures, and collisions between pulsars and asteroids/comets are discussed. for each mechanism, the maximum glitch sizes are constrained by the isotropic energy release during the x-ray burst and/or the sgr j1935+2154-like radio burst rate. brief calculations show that, the maximum glitch sizes for different mechanisms differ by order(s) of magnitude. if glitches are detected to be coincident with frbs from galactic magnetars in the future, glitch behaviours (such as glitch size, rise time-scale, the recovery coefficient, and spin-down rate offset) are promising to serve as criterions to distinguish glitch mechanisms and in turn to constrain frb models. | constraining mechanism associated with fast radio burst and glitch from sgr j1935 |
in this investigation, the integrated attitude and landing control scheme for quadruped robots in asteroid landing mission scenario is discussed. compared with the gravitational field environment of the earth, the gravitational field near most asteroids has a smaller gravitational acceleration, a non-negligible horizontal acceleration component, and obvious uneven distribution characteristics. in this study, an integrated control method is proposed which focuses on the challenging attitude and landing control schemes of quadruped robots near asteroids by using reinforcement learning in conjunction with an auto-tuned reward function. in the proposed method, attitude adjustment and landing control are trained as a whole. by relying on the trained controller, the quadruped robot can reorient automatically to the most suitable attitude for landing according to gravity and terrain information, thus only relying on the movement of mechanical legs (and not on any additional actuators like reaction wheels) during the entire process. to solve the problem of sparse reward in the process of multi-objective reinforcement learning, an autotuning method of a multi-objective reward function is proposed to improve the training speed. the effectiveness of the proposed landing control method of a quadruped robot is verified near irregular rod-shaped asteroid 216 kleopatra. the numerical simulation results show that the quadruped robot can adjust reliably its attitude and finally land on irregular terrain without floating and escaping again, even when the gravitational acceleration is unknown and subject to large horizontal components. | integrated attitude and landing control for quadruped robots in asteroid landing mission scenarios using reinforcement learning |
the importance of the iot is increasing in every field of life, and it especially has a significant role in improving the efficiency of the healthcare system. its demand further increased during covid-19 to facilitate the patient remotely from their home digitally. every time the covid-19 patient visited the doctor for minor complications, it increased the risk of spreading the virus and the cost for the patient. another alarming situation arose when a patient was in a critical position and may not claim an emergency service from the nearby healthcare system, increasing the death rate. the iot uses healthcare services to properly monitor covid-19 patients by using the interconnected network to overcome these issues. through the iot, the patient is facilitated by the health care system without spreading the virus, decreasing the death ratio during covid-19. this paper aims to discuss different applications, technologies, and challenges of the iot healthcare system, related to covid-19. different databases were searched using keywords in pubmed, researchgate, scopus, acm, springer, elsevier, google scholar, etc. this paper is trying to discuss, identify, and highlight the useful applications of the iot healthcare system to provide guidelines to the researchers, healthcare institutions, and scientists to overcomes the hazards of covid-19 pandemics. hence, iot is beneficial by identifying the symptoms of covid-19 patients and by providing better treatments that use the healthcare system efficiently. at the end of the paper, challenges and future work are discussed, along with useful suggestions through which scientists can benefit from the iot healthcare system during covid-19 and in a severe pandemic. the survey paper is not limited to the healthcare system and covid-19, but it can be beneficial for future pandemics or in a worse situation. | application and challenges of iot healthcare system in covid-19 |
the internal structure of asteroids is still poorly known and has never been analyzed directly by measurements. our knowledge relies entirely on inferences from remote sensing observations of the surface and theoretical modeling. direct measurements are crucial to characterize an asteroid's internal structure and heterogeneity from sub-metric to global scale. the radar package developed in the frame of the phase a/b1 of the asteroid impact mission (aim) as part of the larger asteroid impact & deflection assessment (aida) mission is a mature instrument suite to answer this question and to improve our ability to understand and model the mechanisms driving near earth asteroids (nea). it is of main interest for science, exploration and planetary defense. this instrument suite consists of a monostatic high frequency radar (hfr) to investigate the stratigraphy of surface regolith and a bistatic low frequency radar (lfr) to characterize the deep interior. the chosen platform to deliver the surface unit of the lfr and other instruments for a close-up study of the target asteroid is the mascot nanolander, which already flies on hayabusa2 (hy2) in a mineralogy scout configuration. in this paper, we present the chosen instrumentation for radar science, baseline mission requirements and the initial design for integration into the lander platform, including all peculiarities and constraints. | a radar package for asteroid subsurface investigations: implications of implementing and integration into the mascot nanoscale landing platform from science requirements to baseline design |
this paper tackles the problem of spacecraft relative navigation to support the reach and capture of a passively cooperative space target using a chaser platform equipped with a robotic arm in the frame of future operations such as on orbit servicing and active debris removal. specifically, it presents a pose determination architecture based on monocular cameras to deal with a space target in geo equipped with retro-reflective and black-and-white fiducial markers. the proposed architecture covers the entire processing pipeline, i.e., starting from markers' detection and identification up to pose estimation by solving the perspective-n-points problem with a customized implementation of the levenberg-marquardt algorithm. it is designed to obtain relative position and attitude measurements of the target's main body with respect to the chaser, as well as of the robotic arm's end effector with respect to the selected grasping point. the design of the configuration of fiducial markers to be installed on the target's approach face to support the pose determination task is also described. a performance assessment is carried out by means of numerical simulations using the planet and asteroid natural scene generation utility tool to produce realistic synthetic images of the target. the proposed approach robustness is evaluated against variable illumination scenarios and considering different uncertainty levels in the knowledge of initial conditions and camera intrinsic parameters. | monocular-based pose estimation based on fiducial markers for space robotic capture operations in geo |
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