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the samples returned from near-earth asteroid (162173) ryugu provide a pristine record of the 4.6 billion years since the birth of the solar system. the hayabusa2 initial analysis team has integrated a range of analytical techniques to investigate ryugu's organic chemistry. here, we highlight their latest findings, the potential questions which may be answered, and provide an overview of new prospects in the decade to come. | ryugu asteroid sample return provides a natural laboratory for primordial chemical evolution |
knowledge of the surface thermal inertia of an asteroid can provide insight into its surface structure: porous material has a lower thermal inertia than rock. we develop a means to estimate thermal inertia values of asteroids and use it to show that thermal inertia appears to increase with spin period in the case of main-belt asteroids (mbas). similar behavior is found on the basis of thermophysical modeling for near-earth objects (neos). we interpret our results in terms of rapidly increasing material density and thermal conductivity with depth, and provide evidence that thermal inertia increases by factors of 10 (mbas) to 20 (neos) within a depth of just 10 cm. our results are consistent with a very general picture of rapidly changing material properties in the topmost regolith layers of asteroids and have important implications for calculations of the yarkovsky effect, including its perturbation of the orbits of potentially hazardous objects and those of asteroid family members after the break-up event. evidence of a rapid increase of thermal inertia with depth is also an important result for studies of the ejecta-enhanced momentum transfer of impacting vehicles (“kinetic impactors”) in planetary defense. | thermal tomography of asteroid surface structure |
the existence of asteroid pairs, two bodies on similar heliocentric orbits, reveals an ongoing process of rotational fission among asteroids. this newly found class of objects has not been studied in detail yet. here we choose asteroids (6070) rheinland and (54827) 2001 nq8, the most suitable pair for an in-depth analysis. first, we use available optical photometry to determine their rotational state and convex shapes. rotational pole of rheinland is very near the south ecliptic pole with a latitude uncertainty of about 10°. there are two equivalent solutions for the pole of 2001 nq8, either (72°, -49°) or (242°, -46°) (ecliptic longitude and latitude). in both cases, the longitude values have about 10° uncertainty and the latitude values have about 15° uncertainty (both 3σ uncertainties). the sidereal rotation period of 2001 nq8 is 5.877186 ± 0.000002 hr. second, we construct a precise numerical integrator to determine the past state vectors of the pair’s components, namely their heliocentric positions and velocities, and orientation of their spin vectors. using this new tool, we investigate the origin of the (6070) rheinland and (54827) 2001 nq8 pair. we find a formal age solution of 16.34 ± 0.04 kyr. this includes effects of the most massive objects in the asteroid belt (ceres, pallas, and vesta), but the unaccounted gravitational perturbations from other asteroids may imply that the realistic age uncertainty is slightly larger than its formal value. analyzing results from our numerical simulation to 250 kya, we argue against a possibility that this pair would allow an older age. initial spin vectors of the two asteroids, at the moment of their separation, were not collinear, but tilted by 38^\circ +/- 12^\circ . | detailed analysis of the asteroid pair (6070) rheinland and (54827) 2001 nq8 |
context. in meteor physics, the luminous efficiency τ is used to convert the meteor's magnitude to the corresponding meteoroid's mass. however, a lack of sufficiently accurate verification methods or adequate laboratory tests mean that discussions around this parameter are a subject of controversy.aims: in this work, we aim to use meteor data obtained by the fireball recovery and interplanetary observation to calculate the luminous efficiencies of the recorded meteors. we also show the limitations of the methods presented herein.methods: deceleration-based formulas were used to calculate the masses of the pre-atmospheric meteoroids. these can in turn be compared to the meteor brightnesses to assess the luminous efficiencies of the recorded objects. fragmentation of the meteoroids is not considered within this model. good measurements of the meteor deceleration are required.results: we find τ-values, as well as the shape change coefficients, of 294 meteors and fireballs with determined masses in the range of 10−6-100 kg. the derived τ-values have a median of τmedian = 2.17%. most of them are of the order of 0.1-10%. we present how our values are obtained, compare them with data reported in the literature, and discuss several methods. a dependence of τ on the pre-atmospheric velocity of the meteor, ve, is noticeable with a relation of τ = 0.0023⋅ve2.3. furthermore, a dependence of τ on the initial meteoroid mass, me, is found with negative linear behaviour in log-log space: τ = 0.48⋅me−0.47.conclusions: the higher luminous efficiency of fast meteors could be explained by the higher amount of energy released. fast meteoroids produce additional emission lines that radiate more efficiently in specific wavelengths due to the appearance of the so-called second component of higher temperature. furthermore, the negative dependence of τ on me implies that the radiation of smaller meteoroids is more efficient. the results of this study also show the limitations of the ablation-based model for the determination of the luminous efficiency. | luminous efficiency based on fripon meteors and limitations of ablation models |
near-earth asteroids are a great threat to the earth, especially potential rendezvous and collision asteroids. to protect the earth from an asteroid collision, it is necessary to investigate the asteroid defence problem. an asteroid terminal defence method based on multisatellite interception was designed in this study. for an asteroid intruding in the sphere of the gravitational influence of the earth, multiple interceptor satellites are used to apply a kinetic energy impulse to deflect the orbit of the asteroid. first, the effects of planned interception time and planned interception position on the required impulse velocity increment applied to the asteroid are assessed for interception opportunity selection. second, multiple interceptor satellites are selected to perform the defence task from the on-orbit available interceptor satellite formation. an improved contract net protocol algorithm considering the lambert orbital manoeuvre is designed to fulfil the task allocation and satellite orbit planning. finally, simulation experiments demonstrate the rationale and effectiveness of the proposed method, which provides support for asteroid terminal defence technology. | multisatellite task allocation and orbit planning for asteroid terminal defence |
iron meteorites are thought to be samples of metallic cores and pools that formed in diverse small planetary bodies. their great diversity offers remarkable insights into the formation of asteroids and the early history of the solar system. the chemical compositions of iron meteorites generally match those predicted from experimental and theoretical considerations of melting in small bodies. these bodies, called planetesimals, were composed of mixtures of grains of silicates, metallic iron-nickel, and iron sulfide with compositions and proportions like those in chondrite meteorites. melting in planetesimals caused dense metal to sink through silicate so that metallic cores formed. a typical iron meteorite contains 5-10% nickel, ~0.5% cobalt, 0.1-0.5% phosphorus, 0.1-1% sulfur and over 20 other elements in trace amounts. a few percent of iron meteorites also contain silicate inclusions, which should have readily separated from molten metal because of their buoyancy. they provide important evidence for impacts between molten or partly molten planetesimals. the major heat source for melting planetesimals was the radioactive isotope 26al, which has a half-life of 0.7 million years. however, a few iron meteorites probably formed by impact melting of chondritic material. impact processes were also important in the creation of many iron meteorites when planetesimals were molten. chemical analysis show that most iron meteorites can be divided into 14 groups: about 15% appear to come from another 50 or more poorly sampled parent bodies. chemical variations within all but three groups are consistent with fractional crystallization of molten cores of planetesimals. the other three groups are richer in silicates and probably come from pools of molten metal in chondritic bodies. isotopic analysis provides formation ages for iron meteorites and clues to their provenance. isotopic dating suggests that the parent bodies of iron meteorites formed before those of chondrites, and some irons appear to be the oldest known meteorites. their unexpected antiquity is consistent with 26al heating of planetesimals. bodies that accreted more than ~2 million years after the oldest known solids (refractory inclusions in chondrites) should not have contained enough 26al to melt. isotopic analysis also shows that iron meteorites, like other meteorite types, display small anomalies due to pre-solar grains that were not homogenized in the solar nebula (or protoplanetary disk). although iron meteorites are derived from asteroids, their isotopic anomalies provide the best clues that some come from planetesimals that did not form in the asteroid belt. some may have formed beyond jupiter; others show isotopic similarities to earth and may have formed in the neighborhood of the terrestrial planets. iron meteorites therefore contain important clues to the formation of planetesimals that melted and they also provide constraints on theories for the formation of planets and asteroids. | iron meteorites: composition, age, and origin |
osiris-rex began observing particle ejection events shortly after entering orbit around near-earth asteroid (101955) bennu in january 2019. for some of these events, the only observations of the ejected particles come from the first two images taken immediately after the event by osiris-rex's navcam 1 imager. without three or more observations of each particle, traditional orbit determination is not possible. however, by assuming that the particles all ejected at the same time and location for a given event, and approximating that their velocities remained constant after ejection (a reasonable approximation for fast-moving particles, i.e., with velocities on the order of 10 cm/s or greater, given bennu's weak gravity), we show that it is possible to estimate the particles' states from only two observations each. we applied this newly developed technique to reconstruct the particle ejection events observed by the osiris-rex spacecraft during orbit about bennu. particles were estimated to have ejected with inertial velocities ranging from 7 cm/s to 3.3 m/s, leading to a variety of trajectory types. most (>80%) of the analyzed events were estimated to have originated from midlatitude regions and to have occurred after noon (local solar time), between 12:44 and 18:52. comparison with higher-fidelity orbit determination solutions for the events with sufficient observations demonstrates the validity of our approach and also sheds light on its biases. our technique offers the capacity to meaningfully constrain the properties of particle ejection events from limited data. | reconstruction of bennu particle events from sparse data |
recent data processing showed the existence of a difference that can reach 25 per cent for the dimensions of asteroid (216) kleopatra between the radar observations and the light curves. we rebuild the shape of (216) kleopatra from these new data applying a correction's factor of the size of 1.15 and estimate certain physical features by using the polyhedral model method. in our computations, we use a code that avoids singularities from the line integrals of a homogeneous arbitrary shaped polyhedral source. then, we find the location of the equilibrium points through the pseudo-potential energy and zero-velocity curves. the behaviour of the zero-velocity curves differ substantially if we apply a scale size of 1.15 relative to the original shape of (216) kleopatra. taking the rotation of asteroid (216) kleopatra into consideration, the aim of this work is to analyse the stability against impact and the dynamics of numerical simulations of 3d initially equatorial and polar orbits near the body. as results, we show that the minimum radii are more suited for the stability against impact. we find also that the minimum radius for direct, equatorial circular orbits that cannot impact with (216) kleopatra surface is 300 km and the lower limit on radius for polar circular orbits is 240 km. stable orbits occur at 280 km for equatorial circular orbits despite significant perturbations of its orbit. moreover, as the orbits suffer less perturbations due to the irregular gravitational potential of (216) kleopatra in the elliptic case, the most significant result of the analysis is that stable orbits exist at a periapsis radius of 250 km for initial eccentricities ei = 0.2 in both cases. finally, the polar orbits with eccentricities ranging between 0.1 and 0.2 appear to be more stable. | 3d plausible orbital stability close to asteroid (216) kleopatra |
context. the fields instrument onboard parker solar probe (psp) observes dust impacts on the spacecraft. the derived dust flux rates suggest that the particles originate from the vicinities of the sun and are ejected by radiation pressure. radiation pressure typically ejects particles of several 100 nm and smaller, which are also affected by the electromagnetic force.aims: we aim to understand the influence of the electromagnetic force on the dust trajectories and to predict the dust fluxes along the orbit of psp, within 1 au and near earth.methods: we study the trajectories of dust particles influenced by gravity, radiation pressure, and the electromagnetic force assuming that pitch-angle scattering can be neglected (scatter-free approximation). we estimate the dust fluxes along the second orbit of psp and in the vicinity of the earth based on average dust velocities derived from the trajectory calculations and dust production rates derived from a fragmentation model.results: the calculated cumulative flux of dust particles larger than 100 nm is of the same order (within a factor of ~2) as implied by psp observations. in this size interval, the dynamics of most particles is dominated by the radiation pressure force. the lorentz force becomes more important for smaller particles and fluxes can vary with magnetic field conditions. the calculated flux of the 30 to 75 nm particles at the psp is negligible for most of the second orbit, except for an isolated peak at the perihelion. the 30-75 nm particles that were created inwards from 0.16 au from the sun are in trapped orbits if the radiation pressure force is weaker than gravity, which is the case for dust from asteroids and for cometary dust that was altered in space.conclusions: the inner solar system is the most likely source of dust smaller than 100 nm that enters earth's atmosphere and our results suggest the flux is time-variable. | dust observations from parker solar probe: dust ejection from the inner solar system |
we analysed 44 fine-grained and scoriaceous micrometeorites. a bulk mid-ir spectrum (8-13 μm) for each grain was collected and the entire micrometeorite population classified into 5 spectral groups, based on the positions of their absorption bands. corresponding carbonaceous raman spectra, textural observations from sem-bse and bulk geochemical data via empa were collected to aid in the interpretation of mid-ir spectra. the 5 spectral groups identified correspond to progressive thermal decomposition. unheated hydrated chondritic matrix, composed predominantly of phyllosilicates, exhibit smooth, asymmetric spectra with a peak at ∼10 μm. thermal decomposition of sheet silicates evolves through dehydration, dehydroxylation, annealing and finally by the onset of partial melting. both ci-like and cm-like micrometeorites are shown to pass through the same decomposition stages and produce similar mid-ir spectra. using known temperature thresholds for each decomposition stage it is possible to assign a peak temperature range to a given micrometeorite. since the temperature thresholds for decomposition reactions are defined by the phyllosilicate species and the cation composition and that these variables are markedly different between cm and ci classes, atmospheric entry should bias the dust flux to favour the survival of ci-like grains, whilst preferentially melting most cm-like dust. however, this hypothesis is inconsistent with empirical observations and instead requires that the source ratio of ci:cm dust is heavily skewed in favour of cm material. in addition, a small population of anomalous grains are identified whose carbonaceous and petrographic characteristics suggest in-space heating and dehydroxylation have occurred. these grains may therefore represent regolith micrometeorites derived from the surface of c-type asteroids. since the spectroscopic signatures of dehydroxylates are distinctive, i.e. characterised by a reflectance peak at 9.0-9.5 μm, and since the surfaces of c-type asteroids are expected to be heated via impact gardening, we suggest that future spectroscopic investigations should attempt to identify dehydroxylate signatures in the reflectance spectra of young carbonaceous asteroid families. | the thermal decomposition of fine-grained micrometeorites, observations from mid-ir spectroscopy |
the physical processes active during the crystallization of a low-pressure, low-gravity planetesimal core are poorly understood but have implications for asteroidal magnetic fields and large-scale asteroidal structure. we consider a core with only a thin silicate shell, which could be analogous to some m-type asteroids including psyche, and use a parameterized thermal model to predict a solidification timeline and the resulting chemical profile upon complete solidification. we then explore the potential strength and longevity of a dynamo in the planetesimal's early history. we find that cumulate inner core solidification would be capable of sustaining a dynamo during solidification, but less power would be available for a dynamo in an inward dendritic solidification scenario. we also model and suggest limits on crystal settling and compaction of a possible cumulate inner core. | core solidification and dynamo evolution in a mantle-stripped planetesimal |
context. radiative heat transfer occurs in a porous medium, such as regolith on planetary bodies. radiation enhances the efficiency of heat transport through the subsurface, effecting a strong temperature dependence of thermal conductivity. however, this effect has been omitted in many studies of comet 67p/churyumov-gerasimenko (67p).aims: we concisely review the method for characterizing radiative heat transfer and present a generic treatment in thermal modeling. in particular, we study the impact of radiative heat transfer on 67p subject to both diurnal and seasonal variations of insolation.methods: we adapted a numerical model based on the crank-nicolson scheme to estimate the subsurface temperatures and water production rate of 67p, where conductivity may vary with depth.results: radiative heat transfer is efficient during the day near the surface but it dicreases at night, which means that more energy is deposited underneath the diurnal thermal skin. the effect increases with pore size and accordingly, with the size of the constituent aggregates of the nucleus. it also intensifies with decreasing heliocentric distance. close to perihelion, within 2 au, for example, radiation may raise the temperature by more than 20 k at a depth of 5 cm, compared with a purely conductive nucleus. if the nucleus is desiccated and composed of centimeter-sized aggregates, the subsurface at 0.5 m may be warmed to above 180 k.conclusions: radiative heat transfer is not negligible if the nucleus of 67p consists of aggregates that measure millimeters or larger. to distinguish its role and ascertain the pore size of the subsurface, measurements of temperatures from a depth of 1 cm down to several decimeters are most diagnostic. the water production rate of the nucleus, on the other hand, does not provide a useful constraint. | effect of radiative heat transfer in porous comet nuclei: case study of 67p/churyumov-gerasimenko |
biopolymer networks contribute mechanical integrity as well as functional organization to living cells. one of their major constituents, the protein actin, is present in a large variety of different network architectures, ranging from extensive networks to densely packed bundles. the shape of the network is directly linked to its mechanical properties and essential physiological functions. however, a profound understanding of architecture-determining mechanisms and their physical constraints remains elusive. we use experimental bottom-up systems to study the formation of confined actin networks by entropic forces. experiments based on molecular crowding as well as counterion condensation reveal a generic tendency of homogeneous filament solutions to aggregate into regular actin bundle networks connected by aster-like centers. the network architecture is found to critically rely on network formation history. starting from identical biochemical compositions, we observe drastic changes in network architecture as a consequence of initially biased filament orientation or mixing-induced perturbations. our experiments suggest that the tendency to form regularly spaced bundle networks is a rather general feature of isotropic, homogeneous filament solutions subject to uniform attractive interactions. due to the fundamental nature of the considered interactions, we expect that the investigated type of network formation further implies severe physical constraints for cytoskeleton self-organization on the more complex level of living cells. | formation of regularly spaced networks as a general feature of actin bundle condensation by entropic forces |
we use the recently determined rotation state, shape, size and thermophysical model of apophis to predict the strength of the yarkovsky effect in its orbit. apophis does not rotate about the shortest principal axis of the inertia tensor, rather its rotational angular momentum vector wobbles at an average angle of ≃37° from the body axis. therefore, we pay special attention to the modeling of the yarkovsky effect for a body in such a tumbling state, a feature that has not been described in detail so far. our results confirm that the yarkovsky effect is not significantly weakened by the tumbling state. the previously stated rule that the yarkovsky effect for tumbling kilometer-size asteroids is well represented by a simple model assuming rotation about the shortest body axis in the direction of the rotational angular momentum and with rotation period close to the precession period is confirmed. taking into account uncertainties of the model parameters, as well as the expected density distribution for apophis' spectral class, we predict the secular change in the semimajor axis is (- 12.8 ± 3.6) ×10-4 au/myr (formal 1 σ uncertainty). the currently available astrometric data for apophis do not allow an unambiguous direct detection of the yarkovsky effect. however, the fitted secular change in semimajor axis of (- 23 ± 13) ×10-4 au/myr is compatible with the model prediction. we revise the apophis' impact probability information in the second half of this century by extending the orbital uncertainty derived from the current astrometric data and by taking into account the uncertainty in the dynamical model due to the thermal recoil accelerations. this is done by mapping the combined uncertainty to the close encounter in 2029 and by determining the statistical weight of the known keyholes leading to resonant impact orbits. whereas collision with the earth before 2060 is ruled out, impacts are still possible from 2060 with probabilities up to a few parts in a million. more definitive analysis will be available after the apophis apparition in 2020-2021. | the yarkovsky effect for 99942 apophis |
we mapped all boulders larger than 105 m on the surface of dwarf planet ceres using images of the dawn framing camera acquired in the low altitude mapping orbit. we find that boulders on ceres are more numerous toward high latitudes and have a maximum lifetime of 150 ± 50 ma, based on crater counts. these characteristics are distinctly different from those of boulders on asteroid (4) vesta, an earlier target of dawn, which implies that ceres' boulders are mechanically weaker. clues to their properties can be found in the composition of ceres' complex crust, which is rich in phyllosilicates and salts. as water ice is thought to be present only meters below the surface, we suggest that boulders also harbor ice. furthermore, the boulder size-frequency distribution is best fit by a weibull distribution rather than the customary power law, just like for vesta boulders. this finding is robust in light of possible types of size measurement error. | the brittle boulders of dwarf planet ceres |
actin filaments (f-actin) are polymerized from monomeric globular actin (g-actin) to form regional networks for various functions through interplays of actin nucleating and cross-linking proteins. cortical actin networks, for instance, are assembled underneath and anchored to the plasma membrane. cortexes of most cell types are mingled with dynamic linear fibers, aster-like radial arrays, and interconnected webs of f-actin. the ablim1 is an f-actin-cross-linking protein that ensures the formation of dense cortical actin meshwork for cells to resist mechanical tension-induced blebbing. here we show that it functions as a phase separation-dependent actin nucleator and cross-linker to self-construct radial arrays and highly interconnected meshwork of f-actin bundles. | self-construction of actin networks through phase separation-induced ablim1 condensates |
after 3.5 years of cruise, and about 3 months in the vicinity of its target, the mascot lander was deployed successfully on october 3, 2018 by the hayabusa2 spacecraft onto the c-type near-earth asteroid (162173) ryugu. after a free-fall of 5 min 51 s from an altitude of 41 m mascot experienced its first contact with the asteroid hitting a big boulder. the lander bounced for ~11 min 3 s before it came to rest. mascot was able to perform science measurements with its payload suite at 3 different locations on the surface of ryugu. it investigated the fine-scale structure, multispectral reflectance, thermal characteristics and magnetic properties. the surface consists of very rugged terrain littered with large surface boulders. the in-situ measurements confirmed the absence of fine particles and dust as already implied by the remote sensing instruments aboard the hayabusa2 spacecraft. after about 17 h of operations, the mascot mission terminated with the last communication contact as its primary batteries depleted. this paper summarizes the mascot mission covering its four years of in-flight operations, its preparation for the descent, landing and in-situ investigation on the asteroid ryugu until the end of its operation. | the mascot lander aboard hayabusa2: the in-situ exploration of nea (162173) ryugu |
the aster global digital elevation model version 3 (gdem v3) was evaluated over the conterminous united states in a manner similar to the validation conducted for the original gdem version 1 (v1) in 2009 and gdem version 2 (v2) in 2011. the absolute vertical accuracy of gdem v3 was calculated by comparison with more than 23,000 independent reference geodetic ground control points from the u.s. national geodetic survey. the root mean square error (rmse) measured for gdem v3 is 8.52 meters. this compares with the rmse of 8.68 meters for gdem v2. another important descriptor of vertical accuracy is the mean error, or bias, which indicates if a dem has an overall vertical offset from true ground level. the gdem v3 mean error of -1.20 meters reflects an overall negative bias in gdem v3. the absolute vertical accuracy assessment results, both mean error and rmse, were segmented by land cover type to provide insight into how gdem v3 performs in various land surface conditions. while the rmse varies little across cover types (6.92 to 9.25 meters), the mean error (bias) does appear to be affected by land cover type, ranging from -2.99 to +4.16 meters across 14 land cover classes. these results indicate that in areas where built or natural aboveground features are present, gdem v3 is measuring elevations above the ground level, a condition noted in assessments of previous gdem versions (v1 and v2) and an expected condition given the type of stereo-optical image data collected by aster. gdem v3 was also evaluated by differencing with the shuttle radar topography mission (srtm) dataset. in many forested areas, gdem v3 has elevations that are higher in the canopy than srtm. the overall validation effort also included an evaluation of the gdem v3 water mask. in general, the number of distinct water polygons in gdem v3 is much lower than the number in a reference land cover dataset, but the total areas compare much more closely. | validation of the aster global digital elevation model version 3 over the conterminous united states |
hazards resulting from asteroid ocean impacts were modelled using hydrocode simulations to examine the near-field effects including the initial formation and subsequent long range propagation of tsunami waves that can transport potentially damaging energy far from the impact site. three-dimensional simulations of oblique impacts into deep water, with trajectory angles ranging from 27° to 60° above the horizontal, were performed with the los alamos rage hydrocode. the simulations include atmospheric effects such as ablation and airbursts. these oblique impact simulations are performed in order to help determine whether there are additional dangers due to the obliquity of impact not covered by previous studies. the energy transferred to both the air blast wave and the water are calculated as well as the amount of sea water lofted into the upper atmosphere. water crater sizes and subsequent surface elevation profiles, surface pressures, and depth-averaged mass fluxes within the water are prepared for use in far-field propagation studies. like previous three-dimensional simulations, these simulations show that except at exceedingly shallow entry angles below those simulated here the resulting waves are roughly circular and that the initial waves and central jet oscillation are highly turbulent and dissipate a lot of the energy. two-dimensional axisymmetric simulations of long range propagation of impact tsunami were performed using the lawrence livermore ale3d hydrocode on the nasa pleiades supercomputer. these simulations showed that impacts under 1 gigaton tnt equivalent into the deep ocean basins will create deep-water waves that undergo dispersion, whereas impacts onto continental shelves will create shallow-water waves that do not suffer dispersion. the simulations also showed that on the order of 1% of the kinetic energy of the impact is converted into the tsunami wave. this is an order of magnitude less than previous semi-empirical estimates of ∼15% based on explosion test data and laboratory scale impacts. | near and far-field hazards of asteroid impacts in oceans |
we obtain the exact statistical distribution of expected detection rates that may be obtained from the detection of 'oumuamua, which currently belongs to a class of objects that is only observed once in our solar system. the derivation of the distribution of future detection rates starts from the assumption that the detection is a result of a poisson process, and uses bayes theorem along with information theory to get the result. we derive the probability for the next such observation along with the confidence limits of this prediction assuming that observations are done with the forthcoming vera c. rubin observatory. this probability depends on the estimates of detection rates that existed prior to the 'oumuamua observation. however, unless the constraints given by these model-based estimates are within an order of magnitude of the actual detection rate, they have a negligible effect on the probability of making a second observation. the results are generalized to the expected future case where more than one observation exists. | statistical implications of the n = 1 observation of 1i/'oumuamua |
the emergence of a shock from a medium with a free surface is an important process in various astrophysical phenomena. it generates the first light associated with explosions such as supernovae and gamma ray bursts. most previous works considered planar or spherical geometries, where the shock front is parallel to the surface and emerges simultaneously from all points. here, we study the hydrodynamics of an oblique planar shock breaking out from the planar surface of a uniform density ideal gas with adiabatic index γ. we obtain an analytic solution to the flow as a function of the angle between the plane of the shock and the surface β. we find steady state solutions (in a frame moving with the intersection point of the shock and the surface) up to some critical angle (βmax = 63.4° for γ = 5/3 and βmax = 69.3° for γ = 4/3). we show how this analytic solution can be used in more complicated geometries where the shock is not planar, giving the exact profile of the outermost breakout ejecta. we apply our analytical results to a few realistic problems, such as underwater explosions, detonation under the surface of an asteroid, or off center detonations in a uniform sphere. | oblique shock breakout from a uniform density medium |
we reanalyze the imaging photopolarimeter data from pioneer 10 to study the zodiacal light in the b and r bands beyond earth orbit, applying an improved method to subtract integrated star light (isl) and diffuse galactic light (dgl). we found that there exists a significant instrumental offset, making it difficult to examine the absolute sky brightness. instead, we analyzed the differential brightness, i.e., the difference in sky brightness from the average at high ecliptic latitude, and compared with that expected from the model zodiacal light. at a heliocentric distance of r < 2 au, we found a fairly good correlation between the j-band model zodiacal light and the residual sky brightness after subtracting the isl and dgl. the reflectances of the interplanetary dust derived from the correlation study are marginally consistent with previous works. the zodiacal light is not significantly detectable at r > 3 au, as previously reported. however, a clear discrepancy from the model is found at r = 2.94 au which indicates the existence of a local dust cloud produced by the collision of asteroids or dust trail from active asteroids (or main-belt comets). our result confirms that the main component of the zodiacal light (smooth cloud) is consistent with the model even beyond the earth orbit, which justifies the detection of the extragalactic background light after subtracting the zodiacal light based on the model. | zodiacal light beyond earth orbit observed with pioneer 10 |
asteroids populations are highly diverse, ranging from coherent monoliths to loosely bound rubble piles, with a broad range of material and compositional properties. these different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. we have previously developed a fragment-cloud model (fcm) for assessing the atmospheric breakup and energy deposition of asteroids striking earth. the approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. in this work, we have extended the fcm to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. we have used the extended fcm to model the chelyabinsk, benešov, košice, and tagish lake meteors, and have obtained excellent matches to energy deposition profiles derived from their light curves. these matches provide validation for the fcm approach, help guide further model refinements, and enable inferences about pre-entry structure and breakup behavior. results highlight differences in the amount of small debris vs. discrete fragments in matching the various flare characteristics of each meteor. the chelyabinsk flares were best represented using relatively high debris fractions, while košice and benešov cases were more notably driven by their discrete fragmentation characteristics, perhaps indicating more cohesive initial structures. tagish lake exhibited a combination of these characteristics, with lower-debris fragmentation at high altitudes followed by sudden disintegration into small debris in the lower flares. results from all cases also suggest that lower ablation coefficients and debris spread rates may be more appropriate for the way in which debris clouds are represented in fcm, offering an avenue for future model refinement. | atmospheric energy deposition modeling and inference for varied meteoroid structures |
the so far unique role of our solar system in the universe regarding its capacity for life raises fundamental questions about its formation history relative to exoplanetary systems. central in this research is the accretion of asteroids and planets from a gas-rich circumstellar disk and the final distribution of their mass around the sun. the key building blocks of the planets may be represented by chondrules, the main constituents of chondritic meteorites, which in turn are primitive fragments of planetary bodies. chondrule formation mechanisms, as well as their subsequent storage and transport in the disk, are still poorly understood, and their origin and evolution can be probed through their link (i.e., complementary or noncomplementary) to fine-grained dust (matrix) that accreted together with chondrules. here, we investigate the apparent chondrule-matrix complementarity by analyzing major, minor, and trace element compositions of chondrules and matrix in altered and relatively unaltered cv, cm, and cr (vigarano-type, mighei-type, and renazzo-type) chondrites. we show that matrices of the most unaltered cm and cv chondrites are overall ci-like (ivuna-type) (similar to solar composition) and do not reflect any volatile enrichment or elemental patterns complementary to chondrules, the exception being their fe/mg ratios. we propose to unify these contradictory data by invoking a chondrule formation model in which ci-like dust accreted to so-called armored chondrules, which are ubiquitous in many chondrites. metal rims expelled during chondrule formation, but still attached to their host chondrule, interacted with the accreted matrix, thereby enriching the matrix in siderophile elements and generating an apparent complementarity. | a unifying model for the accretion of chondrules and matrix |
the purpose of this work is to develop a simple control law to implement stable orbits about a small rotating celestial body to achieve global coverage as well as fixed-body hovering on the equatorial plane. the celestial body is assumed to be rotating about a principal axis, with constant rotational velocity along the largest moment of inertia. a simple three dimensional closed-loop guidance law function of position and velocity is defined and analyzed, enabling the determination of the guidance constants to assure convergence to any desired circular orbit about the irregular celestial body, controlling independently five orbital parameters: inclination, right ascension of the ascending node, orbital radius, orbital rate and equatorial longitude. representative numerical results are presented for an eros type asteroid. | closed-loop control for global coverage and equatorial hovering about an asteroid |
we have investigated the influence of thin thermally opaque dust layers on the thermal emission of rocks and regolith and determined the thermal response of these dust-covered surfaces to diurnal insolation cycles. results are computed for hayabusa2's target asteroid (162173) ryugu, which was observed by thermal infrared instruments on the orbiter and in situ. we show that even a very thin (10..100 μm) fine-grained porous dust layer with thermal inertia of 25 j m-2 k-1 s-1/2 can have a significant influence on surface temperatures and alter the apparent thermal inertia of the underlying material derived under the simplified assumption of a homogenous half space by more than 20%. the masking of the underlying material is complete at about 1 diurnal skin depth, corresponding to 10 mm on ryugu. between 0.1 and 1 diurnal skin depths, we find a thermal lag smaller than what would be predicted for a surface consisting of dust only. if a dust cover were present on ryugu, this should be clearly visible in the data returned by the orbiter's thermal infrared imager (tir) and the mascot lander's radiometer (mara), which observed a single boulder at the landing site. however, this appears not to be the case, and dust seems to play a minor role in the thermal emission from the asteroid. | effects of dust layers on thermal emission from airless bodies |
the vacuum and thermal environment of airless planetary surfaces, particularly those dominated by a particulate regolith such as the moon and asteroids, produces intense near-surface thermal gradients that can substantially alter their thermal emissivity spectra when compared with spectra collected at ambient terrestrial conditions. therefore, spectroscopic measurements acquired under conditions designed to simulate the radiation environment in which remote measurements of airless bodies are made should be used as the basis for interpreting those data. as a foundation for this goal, we report the radiometric calibration of thermal infrared emission data collected with a fourier transform infrared spectrometer integrated with the custom asteroid and lunar environment chamber (alec) at brown university. this chamber is designed to simulate the environment of airless planetary bodies by evacuating the atmospheric gasses to vacuum (<10-4 mbar), cooling the chamber with a flow of liquid nitrogen, heating the base and sides of samples with temperature-controlled sample cups, and heating the top of samples with an external light source. we present a new method for deriving sample emissivity based on the absolute radiometry properties of our system, focusing on the 400-2000 cm-1 wavenumber range. this method produces calibrated radiance spectra from calibration targets, and particulate samples and those spectra are used to derive emissivity spectra. we demonstrate that the alec system and data reduction methods successfully replicate independently determined spectral properties of particulate samples under both ambient and cold, vacuum conditions. the alec system is shown to be capable of supporting ongoing and future planetary exploration of airless surfaces by facilitating careful investigation of meteorites, lunar samples, and planetary materials at an array of environmental conditions. | radiometric calibration of thermal emission data from the asteroid and lunar environment chamber (alec) |
context. rotation properties (spin-axis direction and rotation period) and coarse shape models of asteroids can be reconstructed from their disk-integrated brightness when measured from various viewing geometries. these physical properties are essential for creating a global picture of structure and dynamical evolution of the main belt.aims: the number of shape and spin models can be increased not only when new data are available, but also by combining independent data sets and inverting them together. our aim was to derive new asteroid models by processing readily available photometry.methods: we used asteroid photometry compiled in the lowell observatory photometry database with photometry from the gaia data release 2. both data sources are available for about 5400 asteroids. in the framework of the asteroids@home distributed computing project, we applied the light curve inversion method to each asteroid to find its convex shape model and spin state that fits the observed photometry.results: due to the limited number of gaia dr2 data points and poor photometric accuracy of lowell data, we were able to derive unique models for only ∼1100 asteroids. nevertheless, 762 of these are new models that significantly enlarge the current database of about 1600 asteroid models.conclusions: our results demonstrate the importance of a combined approach to inversion of asteroid photometry. while our models in general agree with those obtained by separate inversion of lowell and gaia data, the combined inversion is more robust, model parameters are more constrained, and unique models can be reconstructed in many cases when individual data sets alone are not sufficient. table a.1 is only available at the cds via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/j/a+a/631/a2 | inversion of asteroid photometry from gaia dr2 and the lowell observatory photometric database |
centaurs are minor planets orbiting between jupiter and neptune that have or had crossing orbits with one or more giant planets. recent observations and reinterpretation of previous observations have revealed the existence of ring systems around 10199 chariklo and 2060 chiron. however, the origin of the ring systems around such a minor planet is still an open question. here, we propose that the tidal disruption of a differentiated object that experiences a close encounter with a giant planet could naturally form diverse ring-satellite systems around the centaurs. during the close encounter, the icy mantle of the passing object is preferentially ripped off by the planet's tidal force and the debris is distributed mostly within the roche limit of the largest remnant body. assuming the existence of a 20-50 wt% silicate core below the icy mantle, a disk of particles is formed when the objects pass within 0.4-0.8 of the planet's roche limit with the relative velocity at infinity 3-6 km s-1 and 8 hr initial spin period of the body. the resultant ring mass is 0.1%-10% of the central object's mass. such particle disks are expected to spread radially, and materials spreading beyond the roche limit would accrete into satellites. our numerical results suggest that ring formation would be a natural outcome of such extreme close encounters, and centaurs can naturally have such ring systems because they cross the orbits of the giant planets. | formation of centaurs’ rings through their partial tidal disruption during planetary encounters |
rotation periods of 53 small (diameters 2 km < d < 40 km) jupiter trojans (jts) were derived using the high-cadence lightcurves obtained by the fossil phase i survey, a subaru/hyper suprime-cam intensive program. these are the first reported periods measured for jts with d < 10 km. we found a lower limit of the rotation period near 4 hr, instead of the previously published result of 5 hr found for larger jts. assuming a rubble-pile structure for jts, a bulk density of ≈0.9 g cm-3 is required to withstand this spin rate limit, consistent with the value ~0.8-1.0 g cm-3 derived from the binary jt system, (617) patroclus-menoetius system. | fossil. i. the spin rate limit of jupiter trojans |
this study investigates the origin of interplanetary dust particles (idps) through the optical properties, albedo and spectral gradient, of zodiacal light. the optical properties were compared with those of potential parent bodies in the solar system, which include d-type (as analogs of cometary nuclei), c-type, s-type, x-type, and b-type asteroids. we applied bayesian inference to the mixture model composed of the distribution of these sources, and found that >90% of the idps originate from comets (or their spectral analogs, d-type asteroids). although some classes of asteroids (c-type, x-type, and b-type) may make a moderate contribution, ordinary chondrite-like particles from s-type asteroids occupy a negligible fraction of the interplanetary dust cloud complex. the overall optical properties of the zodiacal light were similar to those of chondritic porous idps, supporting the dominance of cometary particles in the zodiacal cloud. | origin of interplanetary dust through optical properties of zodiacal light |
nearly all known extreme trans-neptunian objects (etnos) have argument of perihelion close to 0°. an existing observational bias strongly favours the detection of etnos with arguments of perihelion close to 0° and 180° yet no objects have been found at 180°. no plausible explanation has been offered so far to account for this unusual pattern. here, we study the dynamical evolution of comet 96p/machholz 1, a bizarre near-earth object (neo) that may provide the key to explain the puzzling clustering of orbits around argument of perihelion close to 0° recently found for the population of etnos. comet 96p/machholz 1 is currently locked in a kozai resonance with jupiter such that the value of its argument of perihelion is always close to 0° at its shortest possible perihelion (highest eccentricity and lowest inclination) and about 180° near its shortest aphelion (longest perihelion distance, lowest eccentricity and highest inclination). if this object is a dynamical analogue (albeit limited) of the known etnos, this implies that massive perturbers must keep them confined in orbital parameter space. besides, its future dynamical evolution displays orbital flips when its eccentricity is excited to a high value and its orbit turns over by nearly 180°, rolling over its major axis. this unusual behaviour, that is preserved when post-newtonian terms are included in the numerical integrations, may also help understand the production of neos on retrograde orbits. | flipping minor bodies: what comet 96p/machholz 1 can tell us about the orbital evolution of extreme trans-neptunian objects and the production of near-earth objects on retrograde orbits |
the present-day orbit distribution of the neptune trojans is a powerful probe of the dynamical environment of the outer solar system during the late stages of planet migration. in this work, i conservatively debias the inclination, eccentricity, and libration amplitude distributions of the neptune trojans by reducing a priori unknown discovery and follow-up survey properties to nuisance parameters and using a likelihood-free bayesian rejection sampler for parameter estimation. using this survey-agnostic approach, i confirm that the neptune trojans are a dynamically excited population: at >95% confidence, the neptune trojans' inclination width must be σi > 11 ° . for comparison and motivation purposes, i also model the jupiter trojan orbit distributions in the same basis and produce new estimates of their parameters (jupiter trojan σi = 14.4 ° ± 0.5 ° , σl11 = 11.8 ° ± 0.5 ° , and σe = 0.061 ± 0.002). the debiased inclination, libration amplitude, and eccentricity distributions of the neptune trojans are nominally very similar to those of the jupiter trojans. i use these new constraints to inform a suite of simulations of neptune trojan capture by an eccentric, rapidly-migrating neptune from an initially dynamically-hot disk. these simulations demonstrate that if migration and eccentricity-damping timescales were short (τa ≲ 10 myr, τe ≲ 1 myr), the disk that neptune migrated into must have been pre-heated (prior to neptune's appearance) to a width comparable to the neptune trojans' extant width to produce a captured population with an inclination distribution width consistent with that of the observed population. | the intrinsic neptune trojan orbit distribution: implications for the primordial disk and planet migration |
we present atacama large millimeter/submillimeter array (alma) 1.3 mm continuum images of the asteroid 3 juno obtained with an angular resolution of 0\buildrel{\prime\prime}\over{.} 042 (60 km at 1.97 au). the data were obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. a sequence of 10 consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the database of asteroid models from inversion techniques. we measure a geometric mean diameter of 259 ± 4 km, in good agreement with past estimates from a variety of techniques and wavelengths. due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. the median peak brightness temperature is 215 ± 13 k, while the median over the whole surface is 197 ± 15 k. with the unprecedented resolution of alma, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas and lower values beyond the evening terminator. the dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. these results demonstrate alma's potential to resolve thermal emission from the surface of main belt asteroids and to measure accurately their position, geometric shape, rotational period, and soil characteristics. . | the 2014 alma long baseline campaign: observations of asteroid 3 juno at 60 kilometer resolution |
cosmology experiments at millimeter wavelengths can detect planet nine if it is the size of neptune, has an effective temperature of 40 k, and is 700 au from the sun. it would appear as a ∼30 mjy source at 1 mm with an annual parallax of ∼5 arcmin. the challenge is to distinguish it from the approximately 4000 foreground asteroids brighter than 30 mjy. fortunately, these asteroids are known to the minor planet center and can be identified because they move across a resolution element in a matter of hours, orders of magnitude faster than planet nine. if planet nine is smaller, colder, and/or more distant than expected, then it could be as faint as 1 mjy at 1 mm. there are roughly 106 asteroids this bright and many are unknown, making current cosmology experiments confusion limited for moving sources. nonetheless, it may still be possible to find the proverbial needle in the haystack using a matched filter. this would require millimeter telescopes with high angular resolution and high sensitivity in order to alleviate confusion and to enable the identification of moving sources with relatively short time baselines. regardless of its millimeter flux density, searching for planet nine would require frequent radio measurements for large swaths of the sky, including the ecliptic and galactic plane. even if planet nine had already been detected by other means, measuring its millimeter flux would constrain its internal energy budget, and therefore help resolve the mystery of uranus and neptune, which have vastly different internal heat. | cosmologists in search of planet nine: the case for cmb experiments |
the centaur (2060) chiron exhibits outgassing behaviour and possibly hosts a ring system. on 2011 november 29, chiron occulted a fairly bright star (r ∼ 15 mag) as observed from the 3-m nasa infrared telescope facility (irtf) on mauna kea and the 2-m faulkes telescope north (ftn) at haleakala. data were taken as visible wavelength images and simultaneous, low-resolution, near-infrared (nir) spectra. here, we present a detailed examination of the light-curve features in the optical data and an analysis of the nir spectra. we place a lower limit on the spherical diameter of chiron's nucleus of 160.2 ± 1.3 km. sharp, narrow dips were observed between 280 and 360 km from the centre (depending on event geometry). for a central chord and assumed ring plane, the separated features are 298.5-302 and 308-310.5 km from the nucleus, with normal optical depth ∼0.5-0.9, and a gap of 9.1 ± 1.3 km. these features are similar in equivalent depth to chariklo's inner ring. the absence of absorbing/scattering material near the nucleus suggests that these sharp dips are more likely to be planar rings than a shell of material. the region of relatively increased transmission is within the 1:2 spin-orbit resonance, consistent with the proposed clearing pattern for a non-axisymmetric nucleus. characteristics of possible azimuthally incomplete features are presented, which could be transient, as well as a possible shell from ∼900-1500 km: future observations are needed for confirmation. there are no significant features in the nir light curves, nor any correlation between optical features and nir spectral slope. | characterization of material around the centaur (2060) chiron from a visible and near-infrared stellar occultation in 2011 |
we describe active asteroid 331p/gibbs (2012 f5) using archival hubble space telescope (hst) data taken between 2015 and 2018. 331p is an outer main belt active asteroid with a long-lived debris trail that formed in 2011. embedded in the debris trail we identify 19 fragments with radii between 0.04 and 0.11 km (albedo 0.05 assumed) containing about 1% of the mass of the primary nucleus. the largest shows a photometric range (~1.5 mag), a v-shaped minimum, and a two-peaked lightcurve period near 9 hr, consistent with a symmetric contact binary. less convincing explanations are that 331p-a is a monolithic, elongated splinter or that its surface shows hemispheric 4:1 albedo variations. the debris trail is composed of centimeter-sized and larger particles ejected with characteristic 10 cm s-1 speeds following a size distribution with index q = 3.7 ± 0.1 to 4.1 ± 0.2. the hst data show that earlier, ground-based measurements of the nucleus were contaminated by near-nucleus debris, which cleared by 2015. we find that the primary nucleus has effective radius 0.8 ± 0.1 km and is in rapid rotation (3.26 ± 0.01 hr), with a lightcurve range of 0.25 mag and a minimum density of 1600 kg m-3 if strengthless. the properties of 331p are consistent with (1) formation about 1.5 myr ago by impact shattering of a precursor body, (2) spin-up by radiation torques to critical rotation, (3) ejection of about 1% of the nucleus mass in mid 2011 by rotational instability, and (4) subsequent evolution of the fragments and dispersal of the debris by radiation pressure. | fragmenting active asteroid 331p/gibbs |
the goal of this work is to determine if the dynamics of individual taurid complex (tc) objects are consistent with the formation of the complex via fragmentation of a larger body, or if the current orbital affinities between the tc members result from other dynamical processes. to this end, the orbital similarity through the time of comet 2p/encke, 51 near-earth asteroids (neas), and 16 taurid fireballs was explored. clones of each body were numerically simulated backwards in time, and epochs when significant fractions of the clones of any two bodies approached each other with both a low minimum orbit intersection distance and small relative velocity were identified. only 12 pairs of bodies in our sample show such an association in the past 20 000 yr, primarily circa 3200 bce. these include 2p/encke and neas 2004 tg10, 2005 tf50, 2005 ur, 2015 tx24, and several southern taurid fireballs. we find this orbital convergence to be compatible with the fragmentation of a large parent body 5000-6000 yr ago, resulting in the separation of 2p/encke and several neas associated with the tc, as well as some larger meteoroids now recorded in the taurid stream. however, the influence of purely dynamical processes may offer an alternative explanation for this orbital rapprochement without requiring a common origin between these objects. in order to discriminate between these two hypotheses, future spectral surveys of the tc asteroids are required. | a dynamical analysis of the taurid complex: evidence for past orbital convergences |
artificial neural networks (anns) have been successfully used in the last years to identify patterns in astronomical images. the use of ann in the field of asteroid dynamics has been, however, so far somewhat limited. in this work, we used for the first time ann for the purpose of automatically identifying the behaviour of asteroid orbits affected by the m1:2 mean-motion resonance with mars. our model was able to perform well above 85 per cent levels for identifying images of asteroid resonant arguments in term of standard metrics like accuracy, precision, and recall, allowing to identify the orbital type of all numbered asteroids in the region. using supervised machine learning methods, optimized through the use of genetic algorithms, we also predicted the orbital status of all multi-opposition asteroids in the area. we confirm that the m1:2 resonance mainly affects the orbits of the massalia, nysa, and vesta asteroid families. | artificial neural network classification of asteroids in the m1:2 mean-motion resonance with mars |
the relationship between the near-earth objects (3200) phaethon and (155140) 2005 ud is unclear. while both are parents to meteor showers (the geminids and daytime sextantids, respectively) and have similar visible-wavelength reflectance spectra and orbits, dynamical investigations have failed to find any likely method to link the two objects in the recent past. here we present the first near-infrared reflectance spectrum of 2005 ud, which shows it to be consistently linear and red-sloped, unlike phaethon's very blue and concave spectrum. searching for a process that could alter some common starting material to both of these end states, we hypothesized that the two objects had been heated to different extents, motivated by their near-sun orbits, the composition of geminid meteoroids, and previous models of phaethon's surface. we thus set about building a new laboratory apparatus to acquire reflectance spectra of meteoritic samples after heating to higher temperatures than available in the literature to test this hypothesis and were loaned a sample of the ci chondrite orgueil from the vatican meteorite collection for testing. we find that while phaethon's spectrum shares many similarities with different ci chondrites, 2005 ud's does not. we thus conclude that the most likely relationship between the two objects is that their similar properties are only by coincidence as opposed to a parent-fragment scenario, though the ultimate test will be when jaxa's destiny+ mission visits one or both of the objects later this decade. we also discuss possible paths forward to understanding phaethon's properties from dynamical and compositional grounds. | investigating the relationship between (3200) phaethon and (155140) 2005 ud through telescopic and laboratory studies |
the investigation of asteroids near the sun is important for understanding the final evolutionary stage of primitive solar system objects. a near-sun asteroid (nsa), (155140) 2005 ud, has orbital elements similar to those of (3200) phaethon (the target asteroid for the jaxa's destiny+ mission). we conducted photometric and polarimetric observations of 2005 ud and found that this asteroid exhibits a polarization phase curve similar to that of phaethon over a wide range of observed solar phase angles (α = 20-105°) but different from those of (101955) bennu and (162173) ryugu (asteroids composed of hydrated carbonaceous materials). at a low phase angle (α ≲ 30°), the polarimetric properties of these nsas (2005 ud and phaethon) are consistent with anhydrous carbonaceous chondrites, while the properties of bennu are consistent with hydrous carbonaceous chondrites. we derived the geometric albedo, pv ~ 0.1 (in the range of 0.088-0.109); mean v-band absolute magnitude, hv = 17.54 ± 0.02; synodic rotational period, $t_\mathrm{rot} = 5.2388 \pm 0.0022 \, \mathrm{h}$ (the two-peaked solution is assumed); and effective mean diameter, $d_\mathrm{eff} = 1.32 \pm 0.06 \, \mathrm{km}$. at large phase angles (α ≳ 80°), the polarization phase curve are likely explained by the dominance of large grains and the paucity of small micron-sized grains. we conclude that the polarimetric similarity of these nsas can be attributed to the intense solar heating of carbonaceous materials around their perihelia, where large anhydrous particles with small porosity could be produced by sintering. | polarimetric properties of the near-sun asteroid (155140) 2005 ud in comparison with other asteroids and meteoritic samples |
this paper summarizes the evidence for the optical effects of space weathering, as well as the properties of the surface that control optical changes, on asteroid (101955) bennu. first, we set the stage by briefly reviewing what was known about space weathering of low-albedo materials from telescopic surveys, laboratory simulations, and sample return analysis. we then look at the evidence for the nature of space weathering on bennu from recent spacecraft imaging and spectroscopy observations, including the visible to near-infrared and thermal infrared wavelengths, followed by other measurements such as normal albedo measurements from lidar scans. we synthesize these different lines of evidence in an effort to describe a general model of space weathering processes and resulting color effects on dark c-complex asteroids, with hypotheses that can be tested by analyzing samples returned by the mission. a working hypothesis that synthesizes findings thus far is that the optical effects of maturation in the space environment depend on the level of hydration of the silicate/phyllosilicate substrate. subsequent variations in color depend on surface processes and exposure age. on strongly hydrated bennu, in color imaging data, very young craters are darker and redder than their surroundings (more positive spectral slope in the wavelength range 0.4-0.7 μm) as a result of their smaller particle sizes and/or fresh exposures of organics by impacts. solar wind, dehydration, or migration of fines may cause intermediate-age surfaces to appear bluer than the very young craters. exposed surfaces evolve toward bennu's moderately blue global average spectral slope. however, in spectroscopic and lidar data, the equator, the oldest surface on bennu, is darker and redder (wavelength range 0.55-2.0 μm) than average and has shallower absorption bands, possibly due to dehydration and/or nanophase and/or microphase opaque production. bennu is a rubble pile with an active surface, making age relationships, which are critical for determining space weathering signals, difficult to locate and quantify. hence, the full story ultimately awaits analyses of the bennu samples that will soon be delivered to earth. | overview of the search for signs of space weathering on the low-albedo asteroid (101955) bennu |
machine learning has become widely used in astronomy. gaussian process (gp) regression in particular has been employed a number of times to fit or resample supernova (sn) light curves, however by their nature typical gp models are not suited to fit sn photometric data and they will be prone to overfitting. recently gp resampling was used in the context of studying the morphologies of type ii and iib sne and they were found to be clearly distinct with respect to four parameters: the rise time (trise), the magnitude difference between 40 and 30 d post-explosion (δm40-30), the earliest maximum (post-peak) of the first derivative (dm1), and minimum of the second derivative (dm2). here we take a close look at gp regression and its limitations in the context of sn light curves in general, and we also discuss the uncertainties on these specific parameters, finding that dm1 and dm2 cannot give reliable astrophysical information. we do reproduce the clustering in trise-δm40-30 space, although it is not as clear cut as previously presented. the best strategy to accurately populate the trise-δm40-30 space will be to use an expanded sample of high-quality light curves [such as those in the asteroid terrestrial-impact last alert system (atlas) transient survey] and analytical fitting methods. finally, using the bpass fiducial models, we predict that future photometric studies will reveal clear clustering of the type iib and ii light curve morphologies with a distinct continuum of transitional events. | what can gaussian processes really tell us about supernova light curves? consequences for type ii(b) morphologies and genealogies |
asteroid photometry has three major applications: providing clues about asteroid surface physical properties and compositions, facilitating photometric corrections, and helping design and plan groundbased and spacecraft observations. the most significant advances in asteroid photometry in the past decade were driven by spacecraft observations that collected spatially resolved imaging and spectroscopy data. in the meantime, laboratory measurements and theoretical developments are revealing controversies regarding the physical interpretations of models and model parameter values. we will review the new developments in asteroid photometry that have occurred over the past decade in the three complementary areas of observations, laboratory work, and theory. finally, we will summarize and discuss the implications of recent findings. | asteroid photometry |
asteroid 2016 ho3 is a fast-rotating near-earth asteroid (nea), and a potential target for future exploration. studying the surface of this asteroid and whether it retains any regolith are primary science objectives, which can provide key clues to the formation and evolution of this small body. in order to support such future explorations, the stability condition for and distribution of regolith on a non-spherical fast-spinning small body are explored in this paper using derived models of 2016 ho3. first, a tri-axial ellipsoid shape model of 2016 ho3 is established based on light curve data. the possible shape configurations are presented. then, the ambient environment accelerations are analyzed and compared. the stability conditions to retain regolith on the surface of the ellipsoid model is derived and evaluated numerically. the influence of shape, density, cohesion and the angle of friction on the distribution is discussed. finally, the motion of failed regolith is investigated. the results show that 2016 ho3 is likely an elongated asteroid, which has a length to width ratio smaller than 0.48. a layer of millimeter-sized to centimeter-sized grains can exist on the surface of asteroid 2016 ho3, preferentially kept near the polar and the short axis regions. the required cohesion to bind such particles to the surface is less than 0.2 pa. meanwhile, any regolith disturbed from the surface will undergo periods of sliding and bouncing before escaping. this research can provide a reference for preliminary mission design for future missions to asteroid 2016 ho3. | the shape and surface environment of 2016 ho3 |
observations of the magnetization state of asteroids indicate diverse properties. values between 1.9 × 10-6 am2/kg (eros) and 10-2 am2/kg (braille) have been reported. a more detailed understanding of asteroidal magnetic properties allows far-reaching conclusions of the magnetization mechanism as well as the strength of the magnetic field of the solar system regions the asteroid formed in. the hayabusa2 mission with its lander mobile asteroid surface scout is equipped with a magnetometer experiment, masmag. masmag is a state-of-the-art three-axis fluxgate magnetometer, successfully operated also on philae, the rosetta mission lander. masmag has enabled, after eros for the second time ever, to determine the magnetic field of an asteroid during descent and on-surface operations. the new observations show that ryugu, a low-albedo c-type asteroid, has no detectable global magnetization, and any local magnetization is either small (<10-6 am2/kg) or on very small (subcentimeter) scales. this implies, for example, that energetic solar wind particles could reach and alter the surface unimpeded by strong asteroidal magnetic fields, such as minimagnetospheres in case of the moon. | magnetic properties of asteroid (162173) ryugu |
of the several near-earth and main belt asteroids visited by spacecraft to date, three display a paucity of small craters and an enhanced number of smoothed and degraded craters: 433 eros, which has a deficit of craters ≲ 100 m in diameter; 2867 šteins, which has a deficit of craters ≲ 500 m in diameter; and 25143 itokawa, which has a deficit of craters ≲ 100 m in diameter. the purpose of this work was to investigate and model topographic modification and crater erasure due to impact-induced seismic shaking, as well as impact-driven regolith production and loss, on these asteroid surfaces. to perform this study, we utilized the numerical, three-dimensional, cratered terrain evolution model (ctem) initially presented in j. e. richardson, icarus 204 (2009), which received a small-body (sb) specific update for this work. sbctem simulations of the surface of 433 eros correctly reproduce its observed cratering record (for craters up to ∼ 3 km in diameter) at a minimum main belt exposure age of 225 ± 75 myr using a 'very weak rock' target strength of 0.5-5.0 mpa, and producing a mean regolith depth of 80 ± 20 m, which agrees with published estimates of an actual regolith layer "tens of meters" in depth. sbctem simulations of the surface of 2867 šteins correctly reproduce its heavily softened cratering record at a minimum main belt exposure age of 175 ± 25 myr using a 'weak rock' target strength of 2.5-5.0 mpa. extending this simulation produces a mean regolith depth of 155 ± 5 m at a minimum main belt exposure age of 475 ± 25 myr, in good agreement with the 145 ± 35 m actual mean regolith depth estimated from two chains of drainage-pit craters on the surface, with both crater density and regolith depth in an equilibrium state. sbctem simulations of the surface of 25143 itokawa correctly reproduce its extremely sparse cratering record at a minimum main belt exposure age of 20 ± 5 myr, using a 'soft soil' target strength of 10-20 kpa, and producing a mean regolith overturn depth of 5 . 0 ± 1 . 0 m, given that itokawa is composed entirely of regolith and boulders. these simulations demonstrate the efficacy of impact-induced seismic shaking to erase small craters on the surface of asteroids ≲ 25 km mean diameter, correctly reproducing their observed cratering records while using a main belt impactor population and standard crater scaling relationships. these simulations also show that the observed regolith layer on asteroids in the 5-50 km size range can be generated entirely through impact cratering processes, and indicate that regolith depth can be used as a additional constraint on the surface age of a given asteroid. | impact-produced seismic shaking and regolith growth on asteroids 433 eros, 2867 šteins, and 25143 itokawa |
we apply three spherical-harmonic-based techniques to deliver external gravitational field models of the asteroid (101955) bennu within its circumscribing sphere. this region is known to be peculiar for external spherical harmonic expansions, because it may lead to a divergent series. the studied approaches are (i) spectral gravity forward modelling via external spherical harmonics, (ii) the least-squares estimation from surface gravitational data using external spherical harmonics and (iii) the combination of internal and external series expansions. while the first method diverges beyond any reasonable doubts, we show that the other two methods may ensure relative accuracy from ∼10-6 to 10-8 in the vicinity of bennu. this is possible even with the second method, despite the fact that it relies on a single series of external spherical harmonics. our main motivation was to study conceptual differences between spherical harmonic coefficients from satellite data (analogy to the first method) and from surface gravitational data (the second method). such coefficients are available through the popular spherical-harmonic-based models of the earth's gravitational field and often are combined together. we show that the coefficients from terrestrial data may lead to a divergence effect of partial sums, though excellent accuracy can be achieved when such model is used in full. under (presently) extreme but realistic conditions, the divergence effect of partial sums may affect many near-surface geoscientific applications, such as the geoid/quasigeoid computation or residual terrain modelling. computer codes (fortran, matlab) and data produced within the study are made freely available at http://edisk.cvt.stuba.sk/~xbuchab/. | gravitational field modelling near irregularly shaped bodies using spherical harmonics: a case study for the asteroid (101955) bennu |
an in-depth analysis and systematic comparison of asteroid redirection methods are performed within a resource exploitation framework using different assessment mechanisms. through this framework, mission objectives and constraints are specified for the redirection of an asteroid from a near-earth orbit to a stable orbit in the earth-moon system. the paper provides a detailed investigation of five redirection methods, i.e., ion beam, tugboat, gravity tractor, laser sublimation, and mass ejector, with respect to their capabilities for a redirection mission. a set of mission level criteria are utilized to assess the performance of each redirection method, and the means of assigning attributes to each criterion is discussed in detail. in addition, the uncertainty in physical characteristics of the asteroid population is quantified through the use of monte carlo analysis. the monte carlo simulation provides insight into the performance robustness of the redirection methods with respect to the targeted asteroid range. lastly, the attributes for each redirection method are aggregated using three different multicriteria assessment approaches, i.e., the analytical hierarchy process, a utility-based approach, and a fuzzy aggregation mechanism. the results of each assessment approach as well as recommendations for further studies are discussed in detail. | comparative analysis of redirection methods for asteroid resource exploitation |
nasa's double asteroid redirection test (dart) is designed to be the first demonstration of a kinetic impactor for planetary defense against a small-body impact hazard. the target is the smaller component of the binary asteroid 65,803 didymos. we have conducted high-fidelity rigid full two-body simulations of the mutual dynamics of this system in a broad benchmarking exercise to find the best simulation methodologies, and to understand the sensitivity of the system to initial conditions. due to the non-spherical shapes of the components and their close proximity, the components cannot be treated as point masses and so the dynamics differ significantly from a simple keplerian orbit, necessitating the use of numerical simulations to fully capture the system's dynamics. we find that the orbit phase (angular position or true anomaly) of the secondary is highly sensitive to the initial rotation phase of the primary, making prediction of the secondary's location from numerical simulation challenging. finally, we show that the dart impact should induce significant free and forced librations on the secondary. if this libration can be measured by esa's recently approved follow-up spacecraft, hera, it may be possible to constrain properties of the secondary's interior structure. | a benchmarking and sensitivity study of the full two-body gravitational dynamics of the dart mission target, binary asteroid 65803 didymos |
we analyze a sample of 58 jupiter family comets (jfcs) in near-earth orbits, defined as those whose perihelion distances at the time of discovery were qdisc < 1.3 au. in our definition jfcs have tisserand parameters 2 < t < 3 and orbital periods p < 20 yr. we integrated the orbits of these objects, plus 50 clones for each one of them, for 104 yr in the past and in the future. we find that most of them move on highly unstable orbits, having fallen in their current near-earth orbits in the recent past, going from less than one hundred years to a few thousands years. they experience frequent close encounters with jupiter down to distances ≲ 0.1 au. this is the expected behavior for comets whose limited physical lifetimes in the near-earth region make them unlikely to survive there for more than about a few hundred revolutions. in this sense the orbits of most jfcs are typically "cometary", and they should be regarded as newcomers in the near-earth region. yet, a minor fraction of jfcs (less than about one third) are found to move on stable orbits for the past ∼ 104 yr, and in some cases are found to continue to be stable at 5 × 104 yr in the past. they also avoid very close encounters with jupiter. their orbital behavior is very similar to that of neas in cometary orbits. while "typical" jfcs in unstable orbits probably come from the trans-neptunian region, the minor group of jfcs in asteroidal orbits may come from the main asteroid belt, like the neas. the asteroidal jfcs may have a more consolidated structure and a higher mineral content than that of comets coming from the trans-neptunian belt or the oort cloud, which could explain their much longer physical lifetimes in the near-earth region. in particular, we mention comets 66p/du toit, 162p/siding spring, 169p/neat, 182p/loneos, 189p/neat, 249p/linear, 300p/catalina, and p/2003 t12 (soho) as the most likely candidates to have an origin in the main asteroid belt. another interesting case is 207p/neat, which stays near the 3:2 inner mean motion resonance with jupiter, possibly evolving from the hilda asteroid zone. | jupiter family comets in near-earth orbits: are some of them interlopers from the asteroid belt? |
the bombardment of impactors (leftover planetesimals, asteroids and comets) created numerous impact craters on the moon. the giant planets in the outer solar system are believed to have experienced a dynamical instability, in which the migration of giant planets delivers impactors to the inner solar system bodies1,2. the difference between the population of large (diameter more than ~5 km) impact craters observed on heavily cratered lunar highlands and that on the lunar maria3 was thought to support the lunar late heavy bombardment, which started ~0.6 billion years after planet formation and could have been caused by the late instability of giant planets4-6. however, large craters on various-aged lunar surfaces have similar size-frequency distributions when considering the preferential erasure of small craters7,8. in addition, dynamical and geochemical evidence favour an early instability of giant planets at ~4.5 gyr ago2,5,9. here, we report the evolution at geological scales of regolith thickness on the moon, which is a proxy for the change of the size-frequency distribution slope for earth-moon impactors with diameters less than ~50 m (which generate craters with diameters less than ~1 km (ref. 10)). we found an abnormally slow growth of regolith thickness per unit of impact flux before 3 .5-0.6+0.3 ? gyr ago (3σ uncertainty), which can best be explained by a population of craters of less than ~1 km whose size-frequency distribution had a shallower power-law slope (-2.5 7-0.16+0.30 ?) than that afterward (-3.2 4-0.06+0.03 ?). the transition time at ~3.5 gyr ago supports the early instability of giant planets, in which dominant earth-moon impactors changed from leftover planetesimals to asteroids5. the value of -3.24 is consistent with the preferential delivery of small asteroids via yarkovsky-yorp effects11. | change in the earth-moon impactor population at about 3.5 billion years ago |
we consider the impact of electromagnetic induction and ohmic heating on a conducting planetary object that orbits a magnetic star. power dissipated as heat saps orbital energy. if this heat is trapped by an insulating crust or mantle, interior temperatures increase substantially. we provide a quantitative description of this behavior and discuss the astrophysical scenarios in which it might occur. magnetic fields around some main-sequence stars and white dwarfs are strong enough to cause the decay of close-in orbits of asteroids and dwarf planets, drawing them through the roche limit on megayear timescales. we confirm that ohmic heating around neutron stars is driven by the rotation of the stellar magnetic dipole, not orbital dynamics. in any case, heating can raise interior temperatures of asteroids or dwarf planets on close-in orbits to well above liquidus. hot material escaping to the surface may lead to volcanic ejections that can obscure the host star (as in the light curve of kic 8462852) and pollute its atmosphere (as observed with metal-rich white dwarfs). we speculate that mixing of a volatile-rich mantle or crust with material from an induction-heated core may lead to an explosion that could destroy the asteroid prior to tidal breakup. | ohmic heating of asteroids around magnetic stars |
our solar system is filled with meteoric particles, or cosmic dust, which is either interplanetary or interstellar in origin. interstellar dust (isd) enters the heliosphere due to the relative motion of the sun and the interstellar flow. interplanetary dust (ipd) comes primarily from asteroid collisions or comet sublimation, and comprises the bulk of material entering earth's atmosphere. this study examines variations in isd and the ipd flux at earth using observations from three different satellite techniques. first are size-resolved in situ meteoroid detections by the ulysses spacecraft, and second are in situ indirect dust observations by wind. third are measurements of meteoric smoke in the mesosphere by the solar occultation for ice experiment (sofie). wind and ulysses observations are sorted into the interstellar and interplanetary components. wind isd show the anticipated correlation to the 22-year solar magnetic cycle, and are consistent with model predictions of isd. because wind does not discriminate particle size, the ipd measurements were interpreted using meteoric mass distributions from ulysses observations and from different models. wind observations during 2007-2020 indicate a total meteoric influx at earth of 22 metric tons per day (t d−1), in reasonable agreement with long-term averages from sofie (25 t d−1) and ulysses (32 t d−1). the sofie and wind influx time series both show an unexpected correlation to the 22-year solar cycle. this relationship could be an artifact, or may indicate that ipd responds to changes in the solar magnetic field. | decadal and annual variations in meteoric flux from ulysses, wind, and sofie observations |
context. space weathering (sw) is crucial to improve the understanding of the evolution of optical characteristics on airless bodies. the classical view based on research of the moon suggests that sw decreases albedo (darkening) and steepens spectral slope (reddening) in visible to near-infrared (vis-nir) wavelengths, producing nanophase iron (npfe0). however, this conclusion is not perfectly applicable to asteroids.aims: in this study, we focus on investigating the space weathering spectral alteration effects (swsae) and the causes of spectral alteration on various types of asteroids after long-term continuous micrometeoroid bombardments.methods: we used a pulsed laser to irradiate eight meteorites at the same energy, namely, of 28 mj, in ten shots, including ordinary chondrites (ocs), aubrite (aub), enstatite chondrites (ecs), co, cv, and cm carbonaceous chondrites. then we measured and compared the virgin and irradiated vis-nir reflectance spectra of these meteorites. we further surveyed the causes of spectral alteration through a scanning electron microscope and transmission electron microscope.results: three different swsae are shown: (1) darkening and reddening on ocs, aub, co, and cv chondrites; (2) brightening and reddening on ecs; (3) brightening and bluing on cm chondrite. after irradiation, npfe0 and nanophase iron-nickel particles were respectively found in cv and co chondrites; thick amorphous layers without any nanophase particles were found in aub; melting and sputtering of metal were observed in ecs; a great deal of vesicles or bubbles without any nanophase particles were found in cm chondrite.conclusions: the long-term sw via micrometeoroid bombardments can spectrally remodel asteroid surfaces in different ways: darken and redden anhydrous silicate asteroids (e.g., s-, e-, and k-types); brighten and redden metal-rich m-type objects. the swsae of volatiles-rich carbonaceous asteroids (e.g., ch-, cgh-, and d-types) is related to sw degree: darkening and bluing at low degree then brightening and continue bluing as the sw degree increases. the various spectral units on ryugu, bennu, and phobos can be created by the heterogeneity of the degree of sw. | diverse space weathering effects on asteroid surfaces as inferred via laser irradiation of meteorites |
asteroids were likely a major source of volatiles and water to early earth. quantifying the hydration of asteroids is necessary to constrain models of the formation and evolution of the solar system and the origin of life on earth. the osiris-rex (origins, spectral interpretation, resource identification, and security-regolith explorer) mission showed that near-earth asteroid (101955) bennu contains widespread, abundant hydrated phyllosilicates, indicated by a ubiquitous absorption at ~ 2.7 μm. the objective of this work is to quantify the hydration-that is, the hydrogen content-of phyllosilicates on bennu's surface and investigate how this hydration varies spatially. we analyse spectral parameters (normalized optical path length, nopl; effective single-scattering albedo, espat; and gaussian modeling) computed from the hydrated phyllosilicate absorption band of spatially resolved visible-near-infrared spectra acquired by ovirs (the osiris-rex visible and infrared spectrometer). we also computed the same spectral parameters using laboratory-measured spectra of meteorites including cms, cis, and the ungrouped c2 tagish lake. we estimate the mean hydrogen content of water and hydroxyl groups in hydrated phyllosilicates on bennu's surface to be 0.71 ± 0.16 wt%. this value is consistent with the hydration range of some aqueously altered meteorites (cms, c2 tagish lake), but not the most aqueously altered group (cis). the sample collection site of the osiris-rex mission has slightly higher hydrogen content than average. spatial variations in hydrogen content on bennu's surface are linked to geomorphology, and may have been partially inherited from its parent body. | hydrogen abundance estimation and distribution on (101955) bennu |
the spectral properties of s and q-type asteroids can change over time due to interaction with the solar wind and micrometeorite impacts in a process known as 'space weathering.' space weathering raises the spectral slope and decreases the 1 μm absorption band depth in the spectra of s and q-type asteroids. over time, q-type asteroids, which have very similar spectra to ordinary chondrite meteorites, will change into s-type asteroids. because there are a significant number of q-type asteroids, there must be some process which is resurfacing s-type asteroids into q-types. in this study, we use asteroid data from the sloan digital sky survey to show a trend between the slope through the g‧, r‧, and i‧ filters, called the gri-slope, and size that holds for all populations of s and q-type asteroids in the inner solar system, regardless of orbit. we model the evolution of a suite of asteroids in a monte carlo yorp rotational evolution and space weathering model. we show that spin-up and failure from yorp is one of the key resurfacing mechanisms that creates the observed weathering trends with size. by varying the non-dimensional yorp coefficient and running time of the present model over the range 475-1425 myr, we find a range of values for the space weathering timescale, τsw ≈ 19-80 myr at 2.2 au. we also estimate the time to weather a newly resurfaced q-type asteroid into an s-complex asteroid at 1 au, τq → s(1au) ≈ 2-7 myr. | resurfacing asteroids from yorp spin-up and failure |
proper elements are quasi-invariants of a hamiltonian system, obtained through a normalization procedure. proper elements have been successfully used to identify families of asteroids, sharing the same dynamical properties. we show that proper elements can also be used within space debris dynamics to identify groups of fragments associated to the same break-up event. the proposed method allows to reconstruct the evolutionary history and possibly to associate the fragments to a parent body. the procedure relies on different steps: (i) the development of a model for an approximate, though accurate, description of the dynamics of the space debris; (ii) the construction of a normalization procedure to determine the proper elements; (iii) the production of fragments through a simulated break-up event. we consider a model that includes the keplerian part, an approximation of the geopotential, and the gravitational influence of sun and moon. we also evaluate the contribution of solar radiation pressure and the effect of noise on the orbital elements. we implement a lie series normalization procedure to compute the proper elements associated to semi-major axis, eccentricity and inclination. based upon a wide range of samples, we conclude that the distribution of the proper elements in simulated break-up events (either collisions and explosions) shows an impressive connection with the dynamics observed immediately after the catastrophic event. the results are corroborated by a statistical data analysis based on the check of the kolmogorov-smirnov test and the computation of the pearson correlation coefficient. | proper elements for space debris |
bennu, the target of the osiris-rex mission, is an asteroid with compositions analogous to low petrologic type ci, cm, cr, and/or ungrouped carbonaceous chondrites. asteroids like bennu provide information about the building blocks of the early solar system. analysis of the mid-infrared remote sensing data informs mineral quantification. we apply a phyllosilicate specific model, developed by breitenfeld et al. (2021, https://doi.org/10.1029/2021je007035) that distinguishes between mg and fe serpentines, to baseball diamond 1 (bbd1), equatorial station 3 (eq3), and touch-and-go osiris-rex thermal emission spectrometer data. the average total phyllosilicate predictions are 73 (bbd1) and 72 vol% (eq3). we observe higher fe-cronstedtite and lower mg-rich serpentine content in the equatorial region of bennu than average. mid-infrared spectral variability may be explained by sorting effects through mass movement. | mapping phyllosilicates on the asteroid bennu using thermal emission spectra and machine learning model applications |
taurids are an extensive stream of particles produced by comet 2p/encke, which can be observed mainly in october and november as a series of meteor showers rich in bright fireballs. several near-earth asteroids have also been linked with the meteoroid complex, and recently the orbits of two carbonaceous meteorites were proposed to be related to the stream, raising interesting questions about the origin of the complex and the composition of 2p/encke. our aim is to investigate the nature and diversity of taurid meteoroids by studying their spectral, orbital, and physical properties determined from video meteor observations. here we analyze 33 taurid meteor spectra captured during the predicted outburst in november 2015 by stations in slovakia and chile, including 14 multi-station observations for which the orbital elements, material strength parameters, dynamic pressures, and mineralogical densities were determined. it was found that while orbits of the 2015 taurids show similarities with several associated asteroids, the obtained spectral and physical characteristics point towards cometary origin with highly heterogeneous content. observed spectra exhibited large dispersion of iron content and significant na intensity in all cases. the determined material strengths are typically cometary in the kb classification, while pe criterion is on average close to values characteristic for carbonaceous bodies. the studied meteoroids were found to break up under low dynamic pressures of 0.02-0.10 mpa, and were characterized by low mineralogical densities of 1.3-2.5 g cm-3. the widest spectral classification of taurid meteors to date is presented. | spectra and physical properties of taurid meteoroids |
prior to its close encounter with the kuiper belt object (kbo) (486958) 2014 mu69 on 2019 january 1, nasa’s new horizons spacecraft observed other kbos from distances greater than 0.1 au at solar phase angles far larger than those attainable from earth. the expanded range in phase angle afforded by these distant kbo (dkbo) observations enables comparisons between their phase functions and those of other solar system objects. here we present extended new horizons phase angle coverage of plutino (15810) arawn (1994 jr1) to 131°, resonant kbo 2012 he85 to 64°, scattered disk kbo 2011 hk103 to 124°, hot classical (515977) 2012 hz84 to 73°, and cold classical kbos 2011 hj103 and 2011 jy31 to 27° and 122°, respectively. in general, dkbo solar phase curves have slopes (i.e., phase coefficients) and shapes (with corresponding phase integrals q) similar to those of other dark, small solar system objects including comet nuclei, asteroids, and satellites. until stellar occultations by these dkbos provide information about their size, geometric albedos p (and bond albedos a = pq) must be inferred from the median albedos measured by thermal radiometry for each dynamical class. bond albedos for these dkbos range from 0.01 to 0.04. cold classical jy31 has a slightly lower slope and higher phase integral than the other dkbos, and its slope and phase integral come closest to matching those of cold classical mu69, suggesting that cold classical kbos share surface scattering characteristics that are distinct from those of other kbos. | phase curves from the kuiper belt: photometric properties of distant kuiper belt objects observed by new horizons |
the surface of a living cell provides a platform for receptor signaling, protein sorting, transport, and endocytosis, whose regulation requires the local control of membrane organization. previous work has revealed a role for dynamic actomyosin in membrane protein and lipid organization, suggesting that the cell surface behaves as an active composite composed of a fluid bilayer and a thin film of active actomyosin. we reconstitute an analogous system in vitro that consists of a fluid lipid bilayer coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors. upon complete consumption of atp, this system settles into distinct phases of actin organization, namely bundled filaments, linked apolar asters, and a lattice of polar asters. these depend on actin concentration, filament length, and actin/myosin ratio. during formation of the polar aster phase, advection of the self-organizing actomyosin network drives transient clustering of actin-associated membrane components. regeneration of atp supports a constitutively remodeling actomyosin state, which in turn drives active fluctuations of coupled membrane components, resembling those observed at the cell surface. in a multicomponent membrane bilayer, this remodeling actomyosin layer contributes to changes in the extent and dynamics of phase-segregating domains. these results show how local membrane composition can be driven by active processes arising from actomyosin, highlighting the fundamental basis of the active composite model of the cell surface, and indicate its relevance to the study of membrane organization. | actomyosin dynamics drive local membrane component organization in an in vitro active composite layer |
ferrous oxide (feo)-rich asteroid achondrites can be defined as asteroid-derived samples that experienced incipient partial melting processes in the early solar system (>4.5 ga) leading to melt-residues and cumulate and melt rocks that have high feo in silicate grains (molar mg/[mg + fe] < 80), implying relatively oxidative conditions (fo2 of iw +1 to +3). these achondrites include olivine-dominated brachinite and brachinite-like achondrite meteorites, ungrouped meteorites including lewis cliff 88763, northwest africa (nwa) 6693 and nwa 6704, tafassasset, nwa 011/1296, and the oligoclase-rich meteorites graves nunataks (gra) 06128 and gra 06129. ferrous oxide-rich asteroidal achondrites differ from other partially-melted achondrites, including ureilites and acapulcoite-lodranites in that the latter have higher molar mg/ (mg + fe) in silicate grains, and lower fo2 (iw 0 to -2). new mineral chemical, whole-rock major- and trace-element and highly siderophile element (hse: re, os, ir, ru, rh, pt, pd, au) abundance data, and o and os isotope data are presented for feo-rich achondrite meteorites allan hills 84025 (brachinite), miller range (mil) 090206 and mil 090405 (brachinite-like achondrites), and nwa 6693 (ungrouped). these results, combined with available data for feo-rich asteroidal achondrites, reveal that these rocks include nearly-pure residues after partial melting, to samples formed by melt-rock reaction and as cumulates, requiring variable to extensive fe-ni-s partial melting, and between 1 and 20% silicate partial melting. the feo-rich asteroidal achondrites originate from at least four distinct parent bodies, based on o-cr-ti isotope systematics, and occur for both carbonaceous and non-carbonaceous chondrite precursor sources. the initial water and volatile contents of feo-rich asteroid achondrites were similar to carbonaceous chondrite groups, implying both carbonaceous and non-carbonaceous precursor materials generated water-rich partially-melted asteroidal bodies. the existence and recognition of feo-rich asteroid achondrites explains the otherwise enigmatic nature of some iron meteorite groups (e.g., iva, ivb) that require segregation from an oxidized asteroid parent body. the internal structure of some asteroid parent bodies was likely to be complex, reflecting early differentiation processes of nascent core formation, fe-ni-s melt pooling, variable silicate partial melting, igneous differentiation and the important role of melt-rock reaction, melt refertilization and late-stage c- (reduced bodies) or s-rich (oxidized bodies) fluid and vapor reactions. | ferrous oxide-rich asteroid achondrites |
in this paper, the global mapping of an irregular asteroid is studied referring to the ground track properties of a frozen orbit (at constant eccentricity and argument of pericentre on average). in fact, when the size of the asteroid is in the order of hundreds of kilometres or more, an appropriate design of the ground track becomes an important element to optimise the coverage and guarantee regular cycles of observation. to this end, the methodology used to design the ground track in missions for the observation of regular bodies, like planets, is extended to the case of irregular bodies, such as asteroids. moreover, to manage the irregular shape of the asteroid, the classical spherical coordinates (geographical longitude and latitude) are replaced by cylindrical coordinates, whereas the regions that are not reached by the ground track are modelled by using appropriate tetrahedra, useful to plan the coverage. in this context, the case of asteroid 216 kleopatra has been investigated. | global mapping of asteroids by frozen orbits: the case of 216 kleopatra |
spectral parameters of ceres measured by the dawn/vir imaging spectrometer are studied as a function of illumination angles, by applying a semi-empirical method based on a statistical analysis of the vir dataset acquired up to september 2016. the study also focuses on the photometry of the occator faculae, i.e. the brightest spots of the ceres surface, showing an albedo up to eight times the ceres average. the considered semi-empirical approach takes into account the small extension (and hence small dataset) of this region and lays the groundwork to apply scattering models even on such a limited area. the behavior of ceres visible and infrared reflectance with phase angle is similar to other asteroids belonging to its same spectral class, i.e. c-type. the depth of the bands at 2.7 μm (phyllosilicates), 3.1 μm (ammonium), 3.4 μm (magnesium carbonates) and the infrared spectral slope linearly increase with phase angle, showing analogies with other asteroids and occurrence of phase reddening. the different behavior of the 3.9 μm band depth (also due to mg carbonates), independent of illumination angles, could indicate that other carriers contribute to the 3.4 μm band and play a more important role in photometry outside the carbonate deposits. the phase function of the occator faculae is much steeper than expected from its high albedo. mixture of bright and dark material and larger roughness can be at the basis of this result. the phyllosilicate bands show a steeper increase with phase angle with respect to the ceres average, due to the lower presence of dark materials, and/or again larger roughness. the absence of trends with phase angles of the two carbonate bands and of the spectral slope suggests that carbonates do not produce phase reddening. | photometry of ceres and occator faculae as inferred from vir/dawn data |
we evaluated the planetary radar capabilities at arecibo, the goldstone 70 m dss-14 and 34 m dss-13 antennas, the 70 m dss-43 antenna at canberra, the green bank telescope (gbt), and the parkes radio telescope in terms of their relative sensitivities and the number of known near-earth asteroids (neas) detectable per year in monostatic and bistatic configurations. in the 2015 calendar year, monostatic observations with arecibo and dss-14 were capable of detecting 253 and 131 neas respectively, with signal-to-noise ratios (snrs) greater than 30/track. combined, the two observatories were capable of detecting 276 neas. of these, arecibo detected 77 and goldstone detected 32, or 30% and 24% of the numbers that were possible. the two observatories detected an additional 18 and 7 neas respectively, with snrs of less than 30/track. this indicates that a substantial number of potential targets are not being observed. the bistatic configuration with dss-14 transmitting and the gbt receiving was capable of detecting about 195 neas, or ∼50% more than with monostatic observations at dss-14. most of the detectable asteroids were targets of opportunity that were discovered less than 15 days before the end of their observing windows. about 50% of the detectable asteroids have absolute magnitudes \gt 25, which corresponds to diameters \lt ∼ 30 m. | capabilities of earth-based radar facilities for near-earth asteroid observations |
the cores of some small planetesimals, such as asteroid (16) psyche, are thought to have been exposed through collisions during the early solar system that removed their mantles. these small bodies likely solidified from the top down representing a fundamentally different solidification regime to that of earth's core. here we derive simplified models of the downward solidification of the metallic crust and consider thermal convection and the potential for viscous delamination of the weak, warm base of the crust to provide a buoyancy flux sufficient to drive a dynamo. thermal buoyancy is very short lived (∼1,000 years) and therefore cannot be the source of measured paleomagnetic remanence. in contrast, viscous delamination is found to provide a long-lasting buoyancy flux sufficient to generate an intense, multipolar magnetic field, while not greatly affecting the crustal solidification time. our results suggest that a psyche-sized (150-km radius) body solidified in roughly 6.7-20 myr and that delamination produced a strong magnetic field over much of this time. finally, including light, insoluble impurities, such as sulfur, results in a partially solid mushy zone at the base of the crust. this further weakens the base of the crust and results in smaller-scale delamination events. despite a significant change in the dynamics of delamination, the time to total solidification and the predicted properties of the magnetic field are broadly comparable to the sulfur-free case, though we argue this may result in observable compositional stratification of the body. | the top-down solidification of iron asteroids driving dynamo evolution |
a wide range of meteors were simulated impacting earth's atmosphere using the ale3d hydrocode. the size, density, strength curve, entry angle, and velocity of the meteors were varied to cover the parameter space of airbursts of interest to planetary defense in general which encompasses the tunguska event in particular. the hydrocode simulations were used to calibrate a simple analytical model that can be used to quickly estimate the burst height of an incoming asteroid or comet. the hydrocode simulations show both rocky asteroids and icy comets are plausible tunguska meteors, over a wide range of sizes, speeds, entry angles, at least in terms of the energy delivered and height of burst required to produce the tree-fall, and the lack of an obvious impact crater on the ground. this agrees with previous analytical estimates and hydrocode simulations of hypothetical tunguska meteors, and provides a complete range of possibilities. modelling of the tree wind resistance predicts windspeeds of 40-50 m/s are required to fell most of the trees. this is slower than previous estimates from nuclear test data, but faster than lower bound estimates from a 3 mt blast. it suggests an energy of 10 mt is most likely for tunguska, but requires missing tree size distribution and wind response data to better narrow the probability distribution of potential tunguska impactors. | hydrocode simulations of asteroid airbursts and constraints for tunguska |
the geology of the outstanding crater occator on ceres has been studied by combining highest resolution color images and other information from the dawn mission. thus, surface and sub-surface layers and geologic processes can be understood and interpreted in a consistent manner. in order to achieve this, morphometry, absolute surface unit ages, color, and the distribution of foci of activity were the key data. these data show that the ascent of brine from reservoir(s) at depth and deposition of its salts on the surface persisted much longer than initially thought possible as an immediate result of the primary impact. the youngest depositional processes of bright material occurred less than 2 ma ago. also, the bright cerealia and vinalia faculae are not the only traces of this activity; updoming is present on the southwestern crater floor. faculae coincide with fractures and vents and indicate complex mechanisms of the deposition of bright carbonate-rich material. due to the large age difference between the occator impact itself, modeled cooling times of heated crater material, and the recent activity at the faculae we conclude that endogenic forces were lately acting. the distribution and thickness of surface and sub-surface brine layers are far from homogeneous in the upper crust beneath occator. further evidence regarding the distribution of materials has been derived from the distribution of the ejecta and the transition of ejecta to background material outside the crater. | occator crater in color at highest spatial resolution |
electron- or x-ray-induced characteristic x-ray analysis has been widely used to determine chemical compositions of materials in vast research fields. in recent years, analysis of characteristic x-rays from muonic atoms, in which a muon is captured, has attracted attention because both a muon beam and a muon-induced characteristic x-ray have high transmission abilities. here we report the first non-destructive elemental analysis of a carbonaceous chondrite using one of the world-leading intense direct current muon beam source (music; muon science innovative channel). we successfully detected characteristic muonic x-rays of mg, si, fe, o, s and c from jbilet winselwan cm chondrite, of which carbon content is about 2 wt%, and the obtained elemental abundance pattern was consistent with that of cm chondrites. because of its high sensitivity to carbon, non-destructive elemental analysis with a muon beam can be a novel powerful tool to characterize future retuned samples from carbonaceous asteroids. | non-destructive elemental analysis of a carbonaceous chondrite with direct current muon beam at music |
collisions and attendant shock compaction must have been important for the accretion and lithification of planetesimals, including the parent bodies of chondrites, but the conditions under which these occurred are not well constrained. a simple model for the compaction of chondrites predicts that shock intensity as recorded by shock stage should be related to porosity and grain fabric. to test this model, we studied sixteen ordinary chondrites of different groups (h, l, ll) using x-ray computed microtomography (μct) to measure porosity and metal fabric, ideal gas pycnometry and 3d laser scanning to determine porosity, and optical microscopy (om) to determine shock stage. these included a subsample of six chondrites previously studied using transmission electron microscopy (tem) to characterize microstructures in olivine. combining with previous data, results support the simple model in general, but not for chondrites with low shock-porosity-foliation (low-spf chondrites). these include kernouvé (h6), portales valley (h6/7), butsura (h6), park (l6), gro 85209 (l6), estacado (h6), mil 99301 (ll6), spade (h6), and queen's mercy (h6), among others. the data for these meteorites are best explained by high ambient heat during or after shock. low-spf chondrites tend to have older 40ar/39ar ages (∼4435-4526 ma) than other, non-low-spf type 6 chondrites in this study. we conclude that the h, l, and ll asteroids all were shock-compacted at an early stage while warm, with collisions occurring during metamorphic heating of the parent bodies. results ultimately bear on whether chondrite parent bodies have internal structures more akin to a metamorphosed onion shell or metamorphosed rubble pile, and on the nature of accretion and lithification processes for planetesimals. | relationships among physical properties as indicators of high temperature deformation or post-shock thermal annealing in ordinary chondrites |
images from the optical navigation camera system (onc) onboard the hayabusa2 spacecraft show the mascot lander during its descent to the surface of asteroid (162173) ryugu. we used results from a previous stereo-photogrammetric analysis that provided precise onc image orientation data (camera position and pointing), onc orthoimages, and an onc-based 3d surface model to combine them with the visibilities of mascot itself and its shadow on-ground within the onc images. we integrated additional information from instruments onboard mascot (masmag, mara, mascam) and derived mascot's release position and modeled its free-fall descent path and its velocity over 350 s from its release at ∼41 m altitude above ground until its first contact with the surface of ryugu. after first contact, mascot bounced over the surface of ryugu for 663 s and came to rest at its first settlement point after four intermediate surface contacts. we again used onc images that show mascot and partly its shadow and reconstructed the bouncing path and the respective velocities of mascot. the achieved accuracy for the entire descent and bouncing path is ∼0.1 m (1σ). | the descent and bouncing path of the hayabusa2 lander mascot at asteroid (162173) ryugu |
capture in mean motion resonance has been observed in the solar system for small objects with prograde as well as retrograde orbits of moderate inclinations. however, no example of an object with a nearly polar orbit was known to be in resonance with a planet. in this letter, we report that the nearly-polar trans-neptunian object (471325), nicknamed niku, is in a 7:9 resonance with neptune, with a mean lifetime in resonance of 16 ± 11 million years. while entrance and exit in the 7:9 resonance is caused by close encounters with neptune, the resonant configuration provides a temporary protection mechanism against disruptive close encounters with this planet. the other nearly polar trans-neptunian objects do not seem to be in resonance with the planets with the possible exception of 2008 kv42, also known as drac, that has a small chance of being in the 8:13 resonance with neptune. | first trans-neptunian object in polar resonance with neptune |
jupiter trojans are a resonant asteroidal population characterised by photometric colours that are compatible with trans-neptunian objects, high inclinations, and an asymmetric distribution of the number of asteroids between the two swarms. different models have been proposed to explain the high inclination of the trojans and to interpret their relation with the trans-neptunian objects, but none of these models can also satisfactorily explain the asymmetry ratio between the number of asteroids in the two swarms. it has recently been found that the asymmetry ratio can arise if jupiter has migrated inwards through the protoplanetary disc by at least a few astronomical units during its growth. the more numerous population of the leading swarm and the dark photometric colours of the trojans are natural outcomes of this new model, but simulations with massless unperturbed disc particles led to a flat distribution of the trojan inclinations and a final total mass of the trojans that was 3-4 orders of magnitude larger than the current mass. we here investigate the possible origin of the peculiar inclination distribution of the trojans in the scenario where jupiter migrates inwards. we analyse different possibilities: (a) the secular evolution of an initially flat trojan population, (b) the presence of planetary embryos among the trojans, and (c) capture of the trojans from a pre-stirred planetesimal population in which jupiter grows and migrates. we find that the secular evolution of the trojans and secular perturbations from saturn do not affect the inclination distribution of the trojans appreciably, nor is there any significant mass depletion over the age of the solar system. embryos embedded in the trojan swarms, in contrast, can stir the trojans to their current degree of excitation and can also deplete the swarms efficiently, but it is very difficult to remove all of the massive bodies in 4.5 gyr of evolution. we propose that the disc where jupiter's core was forming was already stirred to high inclination values by other planetary embryos competing in the feeding zone of jupiter's core. we show that the trapped trojans preserve their high inclination through the gas phase of the protoplanetary disc and that saturn's perturbations are more effective on highly inclined trojans, leading to a lower capture efficiency and to a substantial depletion of the swarms during 4.5 gyr of evolution. | on the inclinations of the jupiter trojans |
white dwarfs that exhibit transit signatures of planetary debris and accreted planetary material provide exceptional opportunities to probe the material composition and dynamical structure of planetary systems. although previous theoretical work investigating the role of minor body disruption around white dwarfs has focused on spherical bodies, solar system asteroids can be more accurately modelled as triaxial ellipsoids. here, we present an analytical framework to identify the type of disruption (tidal fragmentation, total sublimation, or direct impact) experienced by triaxial asteroids approaching white dwarfs on extremely eccentric (e ~ 1) orbits. this framework is then used to identify the outcomes for simplified main belt analogues of 100 bodies across five different white dwarf temperatures. we also present an empirical relationship between cooling age and effective temperature for both da and db white dwarfs to identify the age of the white dwarfs considered here. we find that using a purely spherical shape model can underestimate the physical size and radial distance at which an asteroid is subjected to complete sublimation, and these differences increase with greater elongation of the body. contrastingly, fragmentation always occurs in the largest semi-axis of a body and so can be modelled by a sphere of that radius. both fragmentation and sublimation are greatly affected by the body's material composition, and hence by the composition of their progenitor asteroid belts. the white dwarf temperature, and hence cooling age, can affect the expected debris distribution: higher temperatures sublimate large elongated asteroids, and cooler temperatures accommodate more direct impacts. | white dwarf planetary debris dependence on physical structure distributions within asteroid belts |
the oort cloud is usually thought of as a collection of icy comets inhabiting the outer reaches of the solar system, but this picture is incomplete. we use simulations of the formation of the oort cloud to show that ∼4 per cent of the small bodies in the oort cloud should have formed within 2.5 au of the sun, and hence be ice-free rock-iron bodies. if we assume that these oort cloud asteroids have the same size distribution as their cometary counterparts, the large synoptic survey telescope should find roughly a dozen oort cloud asteroids during 10 years of operations. measurement of the asteroid fraction within the oort cloud can serve as an excellent test of the solar system's formation and dynamical history. oort cloud asteroids could be of particular concern as impact hazards as their high mass density, high impact velocity, and low visibility make them both hard to detect and hard to divert or destroy. however, they should be a rare class of object, and we estimate globally catastrophic collisions should only occur about once per billion years. | eight billion asteroids in the oort cloud |
asteroid surveys are the backbone of asteroid science, and with this in mind we begin with a broad review of the impact of asteroid surveys on our field. we then provide a brief history of asteroid discoveries so as to place contemporary and future surveys in perspective. surveys in the united states (u.s.) have discovered the vast majority of the asteroids, and this dominance has been consolidated since the publication of asteroids iii. our descriptions of the asteroid surveys that have been operational since that time are focused on those that have contributed the vast majority of asteroid observations and discoveries. we also provide some insight into upcoming next-generation surveys that are sure to alter our understanding of the small bodies in the inner solar system and provide evidence to untangle their complicated dynamical and physical histories. the minor planet center, the nerve center of the asteroid discovery effort, has improved its operations significantly in the past decade so that it can manage the increasing discovery rate, and ensure that it is well-placed to handle the data rates expected in the next decade. we also consider the difficulties associated with astrometric follow-up of newly identified objects. it seems clear that both of these efforts must operate in new modes in order to keep pace with expected discovery rates of next-generation ground- and spacebased surveys. | surveys, astrometric follow-up, and population statistics |
we are conducting a survey for distant solar system objects beyond the kuiper belt edge (∼50 au) with new wide-field cameras on the subaru and ctio telescopes. we are interested in the orbits of objects that are decoupled from the giant planet region to understand the structure of the outer solar system, including whether a massive planet exists beyond a few hundred astronomical units as first reported in 2014 by trujillo & sheppard. in addition to discovering extreme trans-neptunian objects detailed elsewhere, we found several objects with high perihelia (q > 40 au) that differ from the extreme and inner oort cloud objects due to their moderate semimajor axes (50 < a < 100 au) and eccentricities (e ≲ 0.3). newly discovered objects 2014 fz71 and 2015 fj345 have the third and fourth highest perihelia known after sedna and 2012 vp113, yet their orbits are not nearly as eccentric or distant. we found several of these high-perihelion but moderate orbit objects and observe that they are mostly near neptune mean motion resonances (mmrs) and have significant inclinations (i > 20°). these moderate objects likely obtained their unusual orbits through combined interactions with neptune’s mmrs and the kozai resonance, similar to the origin scenarios for 2004 xr190. we also find the distant 2008 st291 has likely been modified by the mmr+kr mechanism through the 6:1 neptune resonance. we discuss these moderately eccentric distant objects along with some other interesting low inclination outer classical belt objects like 2012 fh84 discovered in our ongoing survey. | beyond the kuiper belt edge: new high perihelion trans-neptunian objects with moderate semimajor axes and eccentricities |
the planet nine hypothesis has now enough constraints to deserve further attention in the form of detailed numerical experiments. the results of such studies can help us improve our understanding of the dynamical effects of such a hypothetical object on the extreme trans-neptunian objects or etnos and perhaps provide additional constraints on the orbit of planet nine itself. here, we present the results of direct n-body calculations including the latest data available on the planet nine conjecture. the present-day orbits of the six etnos originally linked to the hypothesis are evolved backwards in time and into the future under some plausible incarnations of the hypothesis to investigate if the values of several orbital elements, including the argument of perihelion, remain confined to relatively narrow ranges. we find that a nominal planet nine can keep the orbits of (90377) sedna and 2012 vp113 relatively well confined in orbital parameter space for hundreds of myr, but it may make the orbits of 2004 vn112, 2007 tg422 and 2013 rf98 very unstable on time-scales of dozens of myr, turning them retrograde and eventually triggering their ejection from the solar system. far more stable orbital evolution is found with slightly modified orbits for planet nine. | dynamical impact of the planet nine scenario: n-body experiments |
we present here the c-o colors for identified flora, vesta, nysa-polana, themis, and koronis family members within the historic data set (2015-2018) of the asteroid terrestrial-impact last alert system (atlas). the themis and koronis families are known to be relatively pure c- and s-type bus-demeo taxonomic families, respectively, and the extracted color data from the atlas broadband c- and o-filters of these two families are used to demonstrate that the atlas c-o color is a sufficient parameter to distinguish between the c- and s-type taxonomies. the vesta and nysa-polana families are known to display a mixture of taxonomies possibly due to vesta's differentiated parent body origin and nysa-polana actually consisting of two nested families with differing taxonomies. our data show that the flora family also displays a large degree of taxonomic mixing and the data reveal a substantial h-magnitude dependence on color. we propose and exclude several interpretations for the observed taxonomic mix. additionally, we extract rotation periods of all of the targets reported here and find good agreement with targets that have previously reported periods. | investigating taxonomic diversity within asteroid families through atlas dual-band photometry |
the asteroid (16) psyche is of scientific interest because it contains ∼1% of the total mass of the asteroid belt and is thought to be the remnant metallic core of a protoplanet. radar observations have indicated the significant presence of metal on the surface with a small percentage of silicates. prior ground-based observations showed rotational variations in the near-infrared (nir) spectra and radar albedo of this asteroid. however, no comprehensive study that combines multi-wavelength data has been conducted so far. here we present rotationally resolved nir spectra (0.7-2.5 μm) of (16) psyche obtained with the nasa infrared telescope facility. these data have been combined with shape models of the asteroid for each rotation phase. spectral band parameters extracted from the nir spectra show that the pyroxene band center varies from ∼0.92 to 0.94 μm. band center values were used to calculate the pyroxene chemistry of the asteroid, whose average value was found to be fs30en65wo5. variations in the band depth (bd) were also observed, with values ranging from 1.0% to 1.5%. using a new laboratory spectral calibration method, we estimated an average orthopyroxene content of 6% ± 1%. the mass-deficit region of psyche, which exhibits the highest radar albedo, also shows the highest value for the spectral slope and the minimum bd. the spectral characteristics of psyche suggest that its parent body did not have the typical structure expected for a differentiated body or that the sequence of events that led to its current state was more complex than previously thought. | detection of rotational spectral variation on the m-type asteroid (16) psyche |
we have conducted a detailed simulation of the ability of the large synoptic survey telescope (lsst) to link near-earth and main belt asteroid detections into orbits. the key elements of the study were a high-fidelity detection model and the presence of false detections in the form of both statistical noise and difference image artifacts. we employed the moving object processing system (mops) to generate tracklets, tracks, and orbits with a realistic detection density for one month of the lsst survey. the main goals of the study were to understand whether (a) the linking of near-earth objects (neos) into orbits can succeed in a realistic survey, (b) the number of false tracks and orbits will be manageable, and (c) the accuracy of linked orbits would be sufficient for automated processing of discoveries and attributions. we found that the overall density of asteroids was more than 5000 per lsst field near opposition on the ecliptic, plus up to 3000 false detections per field in good seeing. we achieved 93.6% neo linking efficiency for h< 22 on tracks composed of tracklets from at least three distinct nights within a 12 day interval. the derived neo catalog was comprised of 96% correct linkages. less than 0.1% of orbits included false detections, and the remainder of false linkages stemmed from main belt confusion, which was an artifact of the short time span of the simulation. the mops linking efficiency can be improved by refined attribution of detections to known objects and by improved tuning of the internal kd-tree linking algorithms. | near-earth object orbit linking with the large synoptic survey telescope |
satellites of asteroids have been discovered in nearly every known small-body population, and a remarkable aspect of the known satellites is the diversity of their properties. they tell a story of vast differences in formation and evolution mechanisms that act as a function of size, distance from the sun, and the properties of their nebular environment at the beginning of solar system history and their dynamical environment over the next 4.5 g.y. the mere existence of these systems provides a laboratory to study numerous types of physical processes acting on asteroids, and their dynamics provide a valuable probe of their physical properties otherwise possible only with spacecraft. advances in understanding the formation and evolution of binary systems have been assisted by (1) the growing catalog of known systems, increasing from 33 to ~250 between the merline et al. (2002) chapter in asteroids iii and now; (2) the detailed study and long-term monitoring of individual systems such as 1999 kw4 and 1996 fg3, (3) the discovery of new binary system morphologies and triple systems, (4) and the discovery of unbound systems that appear to be end-states of binary dynamical evolutionary paths. specifically for small bodies (diameter smaller than 10 km), these observations and discoveries have motivated theoretical work finding that thermal forces can efficiently drive the rotational disruption of small asteroids. long-term monitoring has allowed studies to constrain the system's dynamical evolution by the combination of tides, thermal forces, and rigid-body physics. the outliers and split pairs have pushed the theoretical work to explore a wide range of evolutionary end-states. | formation and evolution of binary asteroids |
we study the dynamics of pattern formation in a minimal model for active mixtures made of microtubules and molecular motors. we monitor the evolution of the (conserved) microtubule density and of the (non-conserved) nematic order parameter, focusing on the effects of an "anchoring" term that provides a direct coupling between the preferred microtubule direction and their density gradient. the key control parameter is the ratio between activity and elasticity. when elasticity dominates, the interplay between activity and anchoring leads to formation of banded structures that can undergo additional bending or rotational instabilities. when activity dominates, the nature of anchoring instead gives rise to a range of active cellular solids, including aster-like networks, disordered foams and spindle-like patterns. we speculate that the introduced "active model c" with anchoring is a minimal model to describe pattern formation in a biomimetic analogue of the microtubule cytoskeleton. | pattern formation in active model c with anchoring: bands, aster networks, and foams |
thermal infrared emission and thermophysical modeling techniques are powerful tools in deciphering the surface properties of asteroids. the near-earth asteroid (3200) phaethon is an active asteroid with a very small perihelion distance and is likely the source of the geminid meteor shower. using a thermophysical model with a non-convex shape of phaethon we interpret thermal infrared observations that span ten distinct sightings. the results yield an effective diameter of 5 . 4 ± 0 . 1 km and independent thermal inertia estimates for each sighting. we find that the thermal inertia varies across each of these sightings in a way that is stronger than the theoretical temperature-dependent expectation from radiative heat transfer within the regolith. thus, we test whether the variation in thermal inertia can be explained by the presence of a regolith layer over bedrock, or by a spatially heterogeneous scenario. we find that a model in which phaethon's hemispheres have distinctly different thermophysical properties can sufficiently explain the thermal inertias determined herein. in particular, we find that a boundary is located between latitudes - 30∘ and + 10∘ that separates two regions: a fine-grained southern latitudes and a northern hemisphere that is dominated by coarse-grained regolith and/or a high coverage of porous boulders. we discuss the implications related to phaethon's activity, potential association with 2005 ud, and the upcoming destiny+ mission. | evidence of surface heterogeneity on active asteroid (3200) phaethon |
for studies of the long-term evolution of small solar system objects, it is fundamental to add the yarkovsky and yarkovsky-o'keefe-radzievskii-paddack (yorp) effects in the dynamical model. still, implementations of these effects in publicly available n-body codes is either lacking, or the effects are implemented using significantly simplified models. in this paper, we present an implementation of the coupled yarkovsky/yorp effects in the mercury and orbfit n-body codes. along with these two effects, we also included the effects of non-destructive collisions and rotationally induced breakups to model the asteroid spin state properly. given the stochastic nature of many incorporated effects, the software is suitable for statistical dynamical studies. here we primarily explained the scientific aspect of the implementation, while technical details will be made freely available along with the source codes. | mercury and orbfit packages for numerical integration of planetary systems: implementation of the yarkovsky and yorp effects |
nutritional symbionts in sap-feeding insects are characterized by highly degenerate genomes. it is poorly understood how hosts evolve to maintain these symbionts, particularly when hosts rely on more than one symbiont that requires distinct support for basic cell functions. we show that the aster leafhopper (macrosteles quadrilineatus), which depends on two symbionts with tiny genomes (sulcia and nasuia), has differentially reprogramed gene-expression patterns in symbiont-associated cells. the host has acquired novel genetic traits and likely recruited preexisting mitochondrial support mechanisms to meet the specific needs of each symbiont. broad comparisons across anciently diverged sap-feeding hosts reveal that the evolution of symbiont support mechanisms is largely unique to each host lineage. important parallels are further observed with organelle evolution. | evolution of host support for two ancient bacterial symbionts with differentially degraded genomes in a leafhopper host |
electrostatic dust lofting may play an important role in surface evolution of airless bodies as indicated from a number of unexplained observations, including the lunar horizon glow and dust ponding on asteroids, for example. the initial launch velocity of a charged dust particle determines its range of motion, hence it is a critical quantity to assess the dynamics of electrostatic dust transport. here we report on laboratory measurements of the launch velocity of electrostatically lofted dust and its relationship with the dust size. for irregularly-shaped dust, similar-sized particles show a large velocity dispersion, indicating a large variation in the inter-particle cohesive force. the maximum launch velocity is shown to decrease with the increase in the dust radius and it is on the order of ~0.7 m/s for 15 μm radius particles. derived from the patched charge model (wang et al., 2016a. geophys. res. lett. 43, 6103-6110), the theoretical expectation of an inverse velocity-size relationship of lofted dust is shown to be consistent with the maximum launch velocity measurements. the dust shape is found to have a significant effect on the lofting process, showing that irregularly-shaped particles are lofted with much larger velocities than spherical particles. the initial launch angle relative to the surface shows a broad distribution. | laboratory measurements of initial launch velocities of electrostatically lofted dust on airless planetary bodies |
we present a new fluid plasma solver with adaptive cartesian mesh (acm) based on a full-newton (nonlinear, implicit) scheme for non-equilibrium gas discharge plasma. the electrons and ions are described using drift-diffusion approximation coupled to poisson equation for the electric field. the electron-energy transport equation is solved to account for electron thermal conductivity, joule heating, and energy loss of electrons in collisions with neutral species. the rate of electron-induced ionization is a function of electron temperature and could also depend on electron density (important for plasma stratification). the ion and gas temperature are kept constant. the transport equations are discretized using a non-isothermal scharfetter-gummel scheme to resolve possible large temperature gradients in the sheaths. we demonstrate the new solver for simulations of direct current (dc) and radiofrequency (rf) discharges. the implicit treatment of the coupled equations allows using large time steps. the full-newton method (fnm) enables fast nonlinear convergence at each time step, offering significantly improved simulation efficiency. we discuss the selection of time steps for solving different plasma problems. the new solver enables solving several problems we could not solve before with existing software: two- and three-dimensional structures of the entire dc discharges including cathode and anode regions, electric field reversals and double-layer formation, the normal cathode spot and an anode ring, moving striations in diffuse and constricted dc discharges, and standing striations in rf discharges. the developed fnm-acm technique offers many benefits for tackling the disparity of gas discharge plasma systems' time scales and nonlinearity. | implicit and coupled fluid plasma solver with adaptive cartesian mesh and its applications to non-equilibrium gas discharges |
this paper is an extension of our previously published acm multimedia 2022 paper, which was ranked 3rd in the macro-expressions (maes) and micro-expressions (mes) spotting task of the fme challenge 2021. in our earlier work, a deep learning framework based on facial action units (aus) was proposed to emphasize both local and global features to deal with the maes and mes spotting tasks. in this paper, an advanced concat-cnn model is proposed to not only utilize facial action units (au) features, which our previous work proved were more effective in detecting maes, but also to fuse the optical flow features to improve the detection performance of mes. the advanced concat-cnn proposed in this paper not only considers the intra-features correlation of a single frame but also the inter-features correlation between frames. further, we devise a new adaptive re-labeling method by labeling the emotional frames with distinctive scores. this method takes into account the dynamic changes in expressions to further improve the overall detection performance. compared with our earlier work and several existing works, the newly proposed deep learning pipeline is able to achieve a better performance in terms of the overall f1-scores: 0.2623 on cas(me)2, 0.2839 on cas(me)2-cropped, and 0.3241 on samm-lv, respectively. | deep learning pipeline for spotting macro- and micro-expressions in long video sequences based on action units and optical flow |
parent body thermal metamorphism is an important process that alters the structure of organic matter in the parent asteroid of meteorites. increasing and progressing thermal metamorphism results in carbonization and graphitization of carbonaceous matter in the parent body. such modifications in the carbon structures can be studied by raman microspectroscopy, thanks to its high sensitivity to structure and bonding within carbonaceous molecules. we have characterized polyaromatic carbonaceous matter in a total of 24 antarctic cv3 and co3 chondrites using micro-raman imaging spectroscopy in an effort to better understand parent body thermal metamorphism and assess its effects on the carbon structures. raman spectral parameters of the first-order carbon peaks (d and g) were extracted from at least 200 spectra for each meteorite and were compared to deduce relationships that yield information regarding the thermal metamorphism conditions. we also show, for the first time, spectral trends and relations of the second-order carbon peaks (2d and d+g) within the 2500-3200 cm−1 with thermal metamorphic history. the second-order peaks appear to contain information that is lacking in the first-order peaks. based on the second-order carbon peak parameters, we tentatively classify four cv3 chondrites into subtypes, and reclassify another. peak metamorphic temperatures of the investigated meteorites have been estimated based on the width of the d band as well as the calculated raman spectral curvature. estimated temperatures appear to correlate well with the assigned petrologic types. we have calculated higher peak metamorphic temperatures for the cv3 chondrites than for the considered co3 chondrites and further showed that the peak metamorphic temperatures of cv3oxa chondrites are higher than those of cv3oxb, indicating possibly different metamorphic conditions for the two oxidized subtypes. we observe that there is a relatively larger temperature increase going from co3.2 to co3.4 (150 °c increase) compared to co3.4-co3.6 (20 °c), which may indicate that the graphitization and structural ordering of carbon reach a critical temperature regime around petrologic type co3.3. | thermal metamorphic history of antarctic cv3 and co3 chondrites inferred from the first- and second-order raman peaks of polyaromatic organic carbon |
solar wind interactions with the surfaces of asteroids and small moons eject atoms and molecules from the uppermost several nanometers of regolith grains through a process called sputtering. a small fraction of the sputtered species, called secondary ions, leave the surface in an ionized state, and these are diagnostic of the surface composition. detection of secondary ions using ion mass spectrometry (ims) provides a powerful method of analysis due to low backgrounds and high instrument sensitivities. however, the sputtered secondary ion yield and the atomic composition of the surface are not 1-to-1 correlated. thus, relative yield fractions based on experimental measurements are needed to convert measured spectra to surface composition. here available experimental results are combined with computationally derived solar wind sputtering yields to estimate secondary ion fluxes from asteroid-sized bodies in the solar system. the monte carlo simulation code sdtrimsp is used to estimate the total sputtering yield due to solar wind ion bombardment for a diverse suite of meteorite and lunar soil compositions. experimentally measured relative secondary ion yields are analyzed to determine the abundance of refractory species (mg+, al+, ca+, and fe+) relative to si+, and it is shown that relative abundances indicate whether a body is primitive or has undergone significant geologic reprocessing. finally, estimates of the sputtered secondary ion fluxes are used to determine the ims sensitivity required to adequately resolve major element ratios for nominal orbital geometries. | solar wind sputtering rates of small bodies and ion mass spectrometry detection of secondary ions |
in this work, we investigate the bifurcations of relative equilibria in the gravitational potential of asteroids. a theorem concerning a conserved quantity, which is about the eigenvalues and number of relative equilibria, is presented and proved. the conserved quantity can restrict the number of non-degenerate equilibria in the gravitational potential of an asteroid. it is concluded that the number of non-degenerate equilibria in the gravitational field of an asteroid varies in pairs and is an odd number. in addition, the conserved quantity can also restrict the kinds of bifurcations of relative equilibria in the gravitational potential of an asteroid when the parameter varies. furthermore, studies have shown that there exist transcritical bifurcations, quasi-transcritical bifurcations, saddle-node bifurcations, saddle-saddle bifurcations, binary saddle-node bifurcations, supercritical pitchfork bifurcations, and subcritical pitchfork bifurcations for the relative equilibria in the gravitational potential of asteroids. it is found that for the asteroid 216 kleopatra, when the rotation period varies as a parameter, the number of relative equilibria changes from 7 to 5 to 3 to 1, and the bifurcations for the relative equilibria are saddle-node bifurcations and saddle-saddle bifurcations. | collision and annihilation of relative equilibrium points around asteroids with a changing parameter |
the double asteroid redirection test (dart) spacecraft will impact the moon dimorphos of the [65803] didymos binary in order to demonstrate asteroid deflection by a kinetic impactor. dart will measure the deflection by using ground-based telescopic observations of the orbital period change of didymos and will carry the light italian cubesat for imaging of asteroids (liciacube) cubesat, which will perform a flyby of didymos about 167 s after the dart impact, obtaining images of the dart impact ejecta plume. liciacube images showing the ejecta plume spatial structure and temporal evolution will help determine the vector momentum transfer from the dart impact. a model is developed for the impact ejecta plume optical depth, using a point-source scaling model of the dart impact. the model is applied to expected liciacube plume images and shows how plume images enable characterization of the ejecta mass versus velocity distribution. the ejecta plume structure, as it evolves over time, is determined by the amount of ejecta that has reached a given altitude at a given time. the evolution of the plume optical depth profiles determined from liciacube images can distinguish between strength-controlled and gravity-controlled impacts, by distinguishing the respective mass versus velocity distributions. liciacube plume images discriminate the differences in plume structure and evolution that result from different target physical properties, mainly the strength and porosity, thereby allowing inference of these properties to improve the determination of dart impact momentum transfer. | model of double asteroid redirection test impact ejecta plume observations |
solar system bodies like comets, asteroids, meteorites and dust particles contain organic matter with different abundances, structures and chemical composition. this chapter compares the similarities and differences of the organic composition in these planetary bodies. furthermore, these links are explored in the context of detecting the most pristine organic material, either by on-site analysis or sample return missions. finally, we discuss the targets of potential future sample return missions, as well as the contamination controls that should be in place in order to successfully study pristine organic matter. | organic matter in the solar system—implications for future on-site and sample return missions |
analysis of organic matter has been one of the major motivations behind solar system exploration missions. it addresses questions related to the organic inventory of our solar system and its implication for the origin of life on earth. sample return missions aim at returning scientifically valuable samples from target celestial bodies to earth. by analysing the samples with the use of state-of-the-art analytical techniques in laboratories here on earth, researchers can address extremely complicated aspects of extra-terrestrial organic matter. this level of detailed sample characterisation provides the range and depth in organic analysis that are restricted in spacecraft-based exploration missions, due to the limitations of the on-board in-situ instrumentation capabilities. so far, there are four completed and in-process sample return missions with an explicit mandate to collect organic matter: stardust and osiris-rex missions of nasa, and hayabusa and hayabusa2 missions of jaxa. regardless of the target body, all sample return missions dedicate to minimise terrestrial organic contamination of the returned samples, by applying various degrees or strategies of organic contamination mitigation methods. despite the dedicated efforts in the design and execution of contamination control, it is impossible to completely eliminate sources of organic contamination. this paper aims at providing an overview of the successes and lessons learned with regards to the identification of indigenous organic matter of the returned samples vs terrestrial contamination. | concerns of organic contamination for sample return space missions |
context. the jaxa asteroid sample return mission hayabusa2 reached its target (162173) ryugu in june 2018 and released the european (cnes-dlr) lander mascot in october 2018. mascot successfully landed on the surface, and the hayabusa2 optical navigation camera system has been able to image parts of the mascot trajectory.aims: this work builds on our previous study of interactions between a landing package and a granular material in the context of mascot on ryugu. the purpose is to expand our knowledge on this topic and to help constrain physical properties of surfaces by considering the actual trajectory of mascot and observations of ryugu from hayabusa2.methods: we ran a new campaign of numerical simulations using the n-body code pkdgrav with the soft-sphere discrete element method by expanding the parameter space to characterize the actual landing scenario of mascot on ryugu. the surface was modeled as a granular medium, but we also considered a large boulder in the bed at various depths and a rigid wall representing a cliff. mascot was faithfully modeled as the actual lander, and we considered different impact angles, speeds, and surface slopes. we were particularly interested in the outgoing-to-incoming speed ratio of mascot during the landing process.results: we found that a boulder in the bed generally increases both the stochasticity of the outcomes and the speed ratio, with larger increases when the boulder sits closer to the surface. we also found that the surface slope does not affect our previous results and that the impact speed does not affect the speed ratio for moderate-friction granular material. finally, we found that a speed ratio as low as 0.3, as estimated in the actual scenario, can occur with a solid-rock surface, not only with a soft surface, because the geometry of the lander is nonspherical. this means that we must infer the physical properties of the surface from outcomes such as the speed ratio with caution: it depends on the lander geometry. | numerical modeling of lander interaction with a low-gravity asteroid regolith surface. ii. interpreting the successful landing of hayabusa2 mascot |
due to the rapid growth in the use of smartphones, the digital traces (e.g., mobile phone data, call detail records) left by the use of these devices have been widely employed to assess and predict human communication behaviors and mobility patterns in various disciplines and domains, such as urban sensing, epidemiology, public transportation, data protection, and criminology. these digital traces provide significant spatiotemporal (geospatial and time-related) data, revealing people's mobility patterns as well as communication (incoming and outgoing calls) data, revealing people's social networks and interactions. thus, service providers collect smartphone data by recording the details of every user activity or interaction (e.g., making a phone call, sending a text message, or accessing the internet) done using a smartphone and storing these details on their databases. this paper surveys different methods and approaches for assessing and predicting human communication behaviors and mobility patterns from mobile phone data and differentiates them in terms of their strengths and weaknesses. it also gives information about spatial, temporal, and call characteristics that have been extracted from mobile phone data and used to model how people communicate and move. we survey mobile phone data research published between 2013 and 2021 from eight main databases, namely, the acm digital library, ieee xplore, mdpi, sage, science direct, scopus, springerlink, and web of science. based on our inclusion and exclusion criteria, 148 studies were selected. | mobile phone data: a survey of techniques, features, and applications |
we present results of a stellar occultation by the jupiter trojan asteroid patroclus and its nearly equal size moon, menoetius. the geocentric mid-time of the event was 2013 october 21 06:43:02 ut. eleven sites out of 36 successfully recorded an occultation. seven chords across patroclus yielded an elliptical limb fit of 124.6 by 98.2 km. there were six chords across menoetius that yielded an elliptical limb fit of 117.2 by 93.0 km. there were three sites that got chords on both objects. at the time of the occultation we measured a separation of 664.6 km (0.247 arcsec) and a position angle for menoetius of 265.°7 measured eastward from j2000 north. combining this occultation data with previous light curve data, the axial ratios of both objects are 1.3 : 1.21 : 1, indicative of a mostly oblate ellipsoid with a slight asymmetry in its equatorial projection. the oblate shape is not an equilibrium shape for the current rotation period, but would be if it were rotating with an ∼8 h period. this faster period is consistent with a pre-evolved state of the system with an orbital separation that is 50% smaller. our best estimate of the system density is 0.88 g cm-3. | size and shape from stellar occultation observations of the double jupiter trojan patroclus and menoetius |
the mobile asteroid surface scout (mascot), an asteroid lander carried by the hayabusa2 spacecraft, successfully landed on the near-earth asteroid (162173) ryugu on october 03, 2018. thereby accomplishing the first-ever landing of a european spacecraft on the surface of this type of celestial body. mascot was a prototype design of a new class of nano-size surface science packages for the exploration of small solar system bodies. the very low gravity (thus, very low escape velocity) of the target body required the design of a miniaturized deployment mechanism with a relatively small, well-reproducible separation velocity. in addition, the mechanism also had to safely restrain the lander to the mother spacecraft during the launch and its 3.5-year cruise phase. in this paper, we describe in detail the design, numerical analysis and test of this newly developed separation mechanism. furthermore, we compare the mechanism to other existing deployment systems and verify its performance with two independent analysis methods using actual flight data taken during the ultimate flight activation event, which initiated the successful delivery and surface operation of the mascot asteroid lander. | the mascot separation mechanism |
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