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A review of the results on the migration of celestial bodies in the Solar System and in some exoplanetary systems is presented. Some problems of planet accumulation and migration of planetesimals, small bodies and dust in the forming and present Solar System are considered. It has been noted that the outer layers of the Earth and Venus could have accumulated similar planetesimals from different areas of the feeding zone of the terrestrial planets. In addition to the theory of coaccretion and the mega-impact and multi-impact models, the formation of the embryos of the Earth and the Moon from a common rarefied condensation with subsequent growth of the main mass of the embryo of the Moon near the Earth is also discussed. Along with the Nice model and the "grand tack" model, a model is considered in which the embryos of Uranus and Neptune increased the semimajor axes of their orbits from values of no more than 10 AU to present values only due to gravitational interactions with planetesimals (without the motions of Jupiter and Saturn entering into resonance). The influence of changes in the semimajor axis of Jupiter's orbit on the formation of the asteroid belt is discussed, as well as the influence of planetesimals from the feeding zone of the giant planets on the formation of bodies beyond the orbit of Neptune. The migration of bodies to the terrestrial planets from different distances from the Sun is considered. It is noted that bodies from the feeding zone of the giant planets and from the outer asteroid belt could deliver to the Earth a quantity of water comparable to the mass of water in the Earth's oceans. The migration of bodies ejected from the Earth is considered. It is noted that about 20% of the ejected bodies that left the Earth's sphere of influence eventually fell back to the Earth. The probabilities of collisions of dust particles with the Earth are usually an order of magnitude greater than the probabilities of collisions of their parent bodies with the Earth. The migration of planetesimals is considered in exoplanetary systems Proxima Centauri and TRAPPIST-1. The amount of water delivered to the inner planet Proxima Centauri b, may have been more than the amount delivered to the Earth. The outer layers of neighboring planets in the TRAPPIST-1 system may contain similar material if there were many planetesimals near their orbits during the late stages of planetary accumulation. [ABSTRACT FROM AUTHOR]

A local orbital frame is an important and often applied coordinate frame in attitude and orbit control. Usually, a navigation filter estimates the position and velocity vector, which are used to build up this reference frame. It is beneficial for many space applications, such as communication or Earth observation missions, or for conducting orbit control maneuvers to change the orbit plane. Furthermore, satellite formation flying can require an orbital frame to describe relative motion. This work investigates the feasibility of determining the local-vertical local horizontal (LVLH) frame without full knowledge of the orbit. This scenario often applies to non-characterized small bodies like asteroids or comets. A discrete search method is used to determine the complete LVLH frame in real-time, assuming that one axis, a line-of-sight vector to the body's center of mass, is known. By minimizing an objective function, the remaining axes can be determined. The estimated parameters are the inclination and the right ascension of the ascending node of the osculating orbit plane. This study investigates the feasibility of this concept and then applies it to perturbed orbits and sensor noise. The proposed method demonstrates that a discrete search can determine the LVLH frame. The approach can be seen as a step toward increasing the autonomy of a spacecraft near small bodies with unknown environments. • A local orbital frame for spacecraft near small bodies is constructed without any knowledge of the model. • The solution enables spacecraft guidance and control without complete orbit information. • The method is suitable for spacecraft near small bodies with an unknown environment. • The robustness of this method is studied numerically under various initial conditions, orbit perturbations, and sensor noise. • The semi-major axis of an orbit strongly correlates with the estimation error. [ABSTRACT FROM AUTHOR]

The 30,000+ known Near Earth Objects (NEOs) are some of the closest objects to Earth. A few dedicated missions such as NEAR, Hayabusa-1 and -2, OSIRIS-Rex, and DART have revealed a lot about their nature, with more to come from ESA's Hera mission, and others. Dedicated space missions to individual NEOs are relatively costly, however, so we seek to find a way to reduce costs so that the composition and structure of more NEOs can be fully characterized, and we can continue to explore how to change the trajectory of selected objects, as was done with DART. Here we describe a low-cost approach to NEO missions for small body science and planetary defense that makes use of existing or planned space vehicles. • Low-cost approach to fly by, rendezvous with, or impact Near Earth Objects. • Repurposes existing or planned space vehicles. • Case Study using the Artemis European Service Module. [ABSTRACT FROM AUTHOR]

Future exploration tasks of small bodies will need to sample or visit multiple points on the target to obtain more scientific returns, requiring rovers to have the ability to hop on a small body surface. This paper proposes an approach to generate a desensitized optimal trajectory for hopping rovers, aiming at reducing the sensitivity of hopping trajectory in the presence of uncertainties. Firstly, considering parameter uncertainties and initial state errors, analytical expressions of optimal initial states are derived on a planar scene, based on ballistic dynamics. Then, similar methods are developed in both uphill and downhill cases of inclined scenes. Subsequently, the desensitization performance of long-distance hopping trajectory is analyzed under single-hop, identical, and non-identical N-hop strategies. To facilitate the application of the proposed analytical solution to the simulated surface environment of small bodies, a prediction-correction procedure is presented. Finally, Monte Carlo simulations are carried out to verify the effectiveness of the proposed methods. The results indicate that the sensitivity of the hopping trajectory to uncertainties can be effectively diminished by employing the desensitized optimal trajectory and multiple hopping strategy. [ABSTRACT FROM AUTHOR]

Affected by the angle of illumination, the images of small bodies taken by the spacecraft are incomplete, and it is difficult to reconstruct them with existing algorithms. To solve this problem, a 3D reconstruction algorithm for small bodies based on incomplete contours was proposed. Firstly, the image was subjected to threshold segmentation using the Otsu algorithm, and the extraction of incomplete contours was performed using the EDPF (edge drawing parameter free) algorithm. Subsequently, leveraging the solar azimuth information and combining it with the incomplete contours, the influence of shadows was taken into account. This process involved retaining both the illuminated regions and potential areas, resulting in the computation of expanded contours. Next, through the utilization of a set of expanded contours and projection matrices, the computation of the 3D bounding box was transformed into a linear inequality problem. Finally, voxel partitioning was performed to accomplish the 3D reconstruction of the small body. The quality of reconstruction was evaluated by normalizing the Hausdorff distance between the reconstructed results and reference models using the average radius. The simulation results indicate that the distribution probability of reconstruction errors being less than 4% is over 95%, and the algorithm also shows a certain level of robustness against changes in the angle of illumination. [ABSTRACT FROM AUTHOR]

Comet 67P/Churyumov‐Gerasimenko displays a pronounced hemispherical dichotomy in surface morphology, where the southern hemisphere exhibits more erosional features than the northern hemisphere due to receiving much greater solar radiation. Consequently, it is generally assumed that particles are ejected from the southern hemisphere through sublimation and a significant fraction eventually descends as airfall, covering the northern terrains. To investigate this south‐to‐north material transfer during the comet's perihelion passage, we used photoclinometry to measure material redistribution within its most extensive smooth terrain deposit around the Imhotep region. However, our findings do not align with this expected trend. Instead, we show that local‐scale processes substantially impact the erosion and accumulation of material, with one area experiencing net erosion while another nearby region, just a few dozen meters away, sees sediment buildup. Our analysis underscores the complex interplay of processes shaping Comet 67P's surface and likely comets more generally. Plain Language Summary: Comets are composed of some of the most primitive materials in the solar system, having spent most of their lifetimes in the far reaches of the outer solar system, shielded from the Sun's radiation. Jupiter Family Comets (JFCs) are a class of comets that get pulled into the inner solar system due to Jupiter's gravity. While JFCs still preserve abundant primordial materials, their new orbits expose them to significantly higher solar insolation, resulting in sublimation‐driven surface activity. The processes driving this activity, however, need to be better constrained. Observations of comet 67P/Churyumov‐Gerasimenko's (a JFC) surface indicate that particles are ejected from its southern hemisphere through sublimation, and a significant fraction eventually descends as "airfall," covering its northern terrains. To investigate this south‐to‐north material transfer during the comet's perihelion passage, we measured material redistribution within its largest "airfall" deposit. However, our findings do not align with this expected trend. Instead, we show that local‐scale processes substantially impact the erosion and accumulation of material, with one area experiencing net erosion while another nearby region, just a few meters away, sees sediment buildup. Our analysis highlights the complex interplay of processes shaping Comet 67P's surface and likely comets more generally. Key Points: We provide a method for measuring erosion and deposition values across 67P's smooth terrains with cm‐scale accuracyWhile sediment mostly accumulates in the topographic lows of Imhotep, there is no clear trend indicating south‐to‐north transport of sedimentLocal‐scale processes have significant impacts on the overall re‐distribution of material [ABSTRACT FROM AUTHOR]

The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres' surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 µm. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.

The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres' surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 µm. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.

Abstract We created high-resolution shape models of Phobos and Deimos using stereophotoclinometry and united images from Viking Orbiter, Phobos 2, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter into a single coregistered collection. The best-fit ellipsoid to the Phobos model has radii of (12.95 ± 0.04) km × (11.30 ± 0.04) km × (9.16 ± 0.03) km, with an average radius of (11.08 ± 0.04) km. The best-fit ellipsoid to the Deimos model has radii of (8.04 ± 0.08) km × (5.89 ± 0.06) km × (5.11 ± 0.05) km with an average radius of (6.27 ± 0.07) km. The new shape models offer substantial improvements in resolution over existing shape models, while remaining globally consistent with them. The Phobos model resolves grooves, craters, and other surface features ~ 100 m in size across the entire surface. The Deimos model is the first to resolve geological surface features. These models, associated data products, and a searchable, coregistered collection of images across six spacecraft are publicly available in the Small Body Mapping Tool, and will be archived with the NASA Planetary Data System. These products enable an array of future studies to advance the understanding of Phobos and Deimos, facilitate coregistration of other past and future datasets, and set the stage for planning and operating future missions to the moons, including the upcoming Martian Moons eXploration (MMX) mission. Graphical Abstract

Missions to small celestial bodies rely heavily on optical feature tracking for characterization of and relative navigation around the target body. While deep learning has led to great advancements in feature detection and description, training and validating data-driven models for space applications is challenging due to the limited availability of large-scale, annotated datasets. This paper introduces AstroVision, a large-scale dataset comprised of 115,970 densely annotated, real images of 16 different small bodies captured during past and ongoing missions. We leverage AstroVision to develop a set of standardized benchmarks and conduct an exhaustive evaluation of both handcrafted and data-driven feature detection and description methods. Next, we employ AstroVision for end-to-end training of a state-of-the-art, deep feature detection and description network and demonstrate improved performance on multiple benchmarks. The full benchmarking pipeline and the dataset will be made publicly available to facilitate the advancement of computer vision algorithms for space applications. • Missions to small bodies rely heavily on humans for optical feature tracking. • Deep Learning has led to great advancements in feature detection and description. • We present AstroVision, a first-of-a-kind dataset for vision-based tasks near small bodies. • We conduct an extensive evaluation of feature detection and description methods. • We demonstrate increased performance by training a deep feature network on our data. [ABSTRACT FROM AUTHOR]

We created high-resolution shape models of Phobos and Deimos using stereophotoclinometry and united images from Viking Orbiter, Phobos 2, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter into a single coregistered collection. The best-fit ellipsoid to the Phobos model has radii of (12.95 ± 0.04) km × (11.30 ± 0.04) km × (9.16 ± 0.03) km, with an average radius of (11.08 ± 0.04) km. The best-fit ellipsoid to the Deimos model has radii of (8.04 ± 0.08) km × (5.89 ± 0.06) km × (5.11 ± 0.05) km with an average radius of (6.27 ± 0.07) km. The new shape models offer substantial improvements in resolution over existing shape models, while remaining globally consistent with them. The Phobos model resolves grooves, craters, and other surface features ~ 100 m in size across the entire surface. The Deimos model is the first to resolve geological surface features. These models, associated data products, and a searchable, coregistered collection of images across six spacecraft are publicly available in the Small Body Mapping Tool, and will be archived with the NASA Planetary Data System. These products enable an array of future studies to advance the understanding of Phobos and Deimos, facilitate coregistration of other past and future datasets, and set the stage for planning and operating future missions to the moons, including the upcoming Martian Moons eXploration (MMX) mission. [ABSTRACT FROM AUTHOR]

This work presents a mission concept for in-orbit particle collection for sampling and exploration missions towards Near-Earth asteroids. Ejecta is generated via a small kinetic impactor and two possible collection strategies are investigated: collecting the particle along the anti-solar direction, exploiting the dynamical features of the L 2 Lagrangian point or collecting them while the spacecraft orbits the asteroid and before they re-impact onto the asteroid surface. Combining the dynamics of the particles in the Circular Restricted Three-Body Problem perturbed by Solar Radiation Pressure with models for the ejecta generation, we identify possible target asteroids as a function of their physical properties, by evaluating the potential for particle collection. • Novel mission concept for in-orbit sample collection at asteroids. • Identification and analysis of two possible collection strategies. • Ranking of most suitable targets among Near-Earth Asteroids. • Preliminary mission risk assessment from particle impacts. [ABSTRACT FROM AUTHOR]

Near-Earth asteroids (NEAs) are a kind of small solar system bodies that may lead to potential hazard to the safety of the Earth. Currently, most of the NEAs are discovered with ground-based telescopes and the number is still growing. In order to provide references and experience to our future near-Earth asteroid discovery and monitoring, we perform a multi-dimensionally statistical analysis on the discovery data of NEAs with public database obtained from the website of Minor Planet Center (MPC). We find the constraint of observation ability can lead to selection effect on the discoveries, which causes a yearly dependence trend and a size-dependence characteristic of the relative proportion for different orbit types of discovered NEAs. Besides, combined with the orbits obtained from numerical simulations, we revisit the discovery scenarios of these objects. The position distribution of the objects under different celestial coordinate systems are obtained, and the dependence on seasons, observatory latitudes, and the diameters are analyzed. Finally, we quantify the impact of the Sun, the Moon, and the galactic plane on the discoveries by analyzing the observation data, and find that ground-based telescopes generally have difficulty in discovering NEAs within 90 ∘ from the Sun direction, and that this limitation generally has a greater impact on smaller-sized objects. The lunar position also has a significant effect on the discoveries, with the restriction on the nights before and after the full Moon resulting in 29% of NEAs being undiscovered, and analysis shows that objects found in the first half of the lunar calendar month are generally more difficult to be followed than those found in the second half. The galactic plane, especially the direction near the galactic center, also has an effect on the discoveries, resulting in a season-dependent "blind spot" for observations near the ecliptic. [ABSTRACT FROM AUTHOR]

Collisions are one of the key processes shaping planetary systems. Asteroid families are outcomes of such collision still identifiable across our solar system. The families provide a unique view of catastrophic disruption phenomena and have been in the focus of planetary scientists for more than a century. Most of them are located in the main belt, a ring of asteroids between Mars and Jupiter. Here we review the basic properties of the families, discuss some recent advances, and anticipate future challenges. This review pays more attention to dynamic aspects such as family identification, age determination, and long-term evolution. The text, however, goes beyond that. Especially, we cover the details of young families that see the major advances in the last years, and we anticipate it will develop even faster in the future. We also discuss the relevance of asteroid families for water-ice content in the asteroid belt and our current knowledge on links between families and main-belt comets. query Please check the edit made in the article title. [ABSTRACT FROM AUTHOR]

Dust particles leaving the comet nucleus surface are entrained by the gas within the first few nuclear radius distances and are subjected to a complex hydrodynamical environment. From distances of about 20 nuclear radii outwards, the particles decouple from the accelerating gas and are mainly affected by solar gravity and radiation pressure for small-sized nuclei. Their motion is then a function of their so-called β parameter, which is the ratio of the radiation pressure force to gravity force, and their velocity when the gas drag vanishes. At a given observation time, the position of those particles projected on the sky plane form the coma, tail and trail structures that can be observed from ground-based or space-borne instrumentation. Monte Carlo models, based on the computer simulation of the Keplerian trajectories of a large set of dust particles, provide the best possible approach to extract the dust environment parameters from the observed scattered solar light or thermal emission. In this paper, we describe the Monte Carlo code along with some successful applications of such technique to a number of targets. [ABSTRACT FROM AUTHOR]

Compared with planets and their moons, small bodies retain the characteristics of their early formation. Therefore small bodies, especially Near Earth Asteroids (NEA), have become one of the most valuable targets in space exploration. This paper presents a review of the current status of small body exploration, including the science objectives, main optical imaging instruments and the main scientific results obtained from the relevant exploration missions in the past two decades. Then, it outlines and discusses future missions to small bodies by different space agencies, including those already planned and under development. Finally, it discusses the trend of optical imaging instrument development for exploring small bodies.

Abstract Early evolution of Solar System small bodies proceeded through interactions of mineral and water. Melting of water ice accreted with mineral particles to the parent body results in the formation of secondary minerals, the so-called aqueous alteration. Formation of phyllosilicates from anhydrous silicates is a typical alteration effect recorded in primitive meteorites. In addition to mineral and water, organic matter could have been also a significant component in meteorite parent bodies. However, the role of organic matter in the alteration of silicates is not well understood. We conducted a heating experiment of anhydrous silicate (olivine) with a mixture of organic compounds which simulated primordial organic matter in the Solar System. Dissolution and precipitation features were confirmed on the olivine surface after heating at 300 °C for 10 days, and proto-phyllosilicates were formed in the precipitation area. Magnesite was also detected as concomitant mineral phase. These minerals could be the evidence of aqueous alteration and carbonation of olivine induced by water generated through decomposition of the organic compounds with hydroxy groups. Our result showed that the in situ formation of hydrated silicates through a mineral–organic interaction without the initial presence of water. It further implies that formation of phyllosilicates on the olivine surface in contact with organic matter can occur in meteorite parent bodies which formed inside the H2O snow line but accreted with organic matter, initially without water. Water formed through decomposition of organic matter could be one candidate for hydrous silicate formation, for example, in ordinary chondrites from S-type asteroids inside the H2O snow line. Although the origin of water in ordinary chondrites is under debate, water generation from organic matter may also explain the D-rich water in ordinary chondrites because primordial organic matter is known to be D rich.

The knowledge of the interior structure (e.g., homogeneous, porous, or fractured) of Martian moons will lead to a better understanding of their formation as well as the early solar system. One approach to inferring the interior structure is via geodetic characteristics, such as gravity field and libration. Geodetic parameters can be derived from radiometric tracking measurements. A feasible mothership-CubeSat mission is proposed in this study with following purposes, (1) performing inter-sat Doppler measurements, (2) improving the understanding of Phobos as well as the dynamic model, (3) securing the mothership as well as the primary mission, and (4) supporting autonomous navigation, given the long distance between the Earth and Mars. This study analyzes budgets of volume, mass, power, deployment Δ v , and link, and the Doppler measurement noise of the system, and gives a feasible design for the CubeSat. The accuracy of orbit determination and geodesy is revealed via the Monte-Carlo simulation of estimation considering all uncertainties. Under an ephemeris error of the Mars-Phobos system ranging from 0 to 2 km, the autonomous orbit determination delivers an accuracy ranging from 0.2 m to 21 m and 0.05 mm/s to 0.4 cm/s. The geodesy can return 2nd-degree gravity coefficients at an accuracy of 1‰, even in the presence of an ephemeris error of 2 km. The achieved covariance of gravity coefficients and libration amplitude indicates an excellent possibility to distinguish families of interior structures. [ABSTRACT FROM AUTHOR]

The paper discusses a model of the bombardment of the Earth and the Moon by small bodies when these planets were formed. It is shown that the total ice mass delivered with the bodies to the Earth from the feeding zone of the giant planets and the outer asteroid belt could have been comparable to the total mass of the Earth's oceans. Objects that initially crossed Jupiter's orbit could become Earth-crossers mainly within the first one million years. Most collisions of bodies originally located at a distance of 4 to 5 AU (astronomical units) from the Sun with the Earth occurred during the first ten million years. Some bodies from the Uranus and Neptune zones could fall onto the Earth in more than 20 million years. From their initial distances from the Sun of about 3 to 3.5 AU, some bodies could fall onto the Earth and Moon in a few billion years for the model that takes into account only the gravitational influence of the planets. The ratio of the number of bodies that collided with the Earth to the number of bodies that collided with the Moon varied mainly from 20 to 40 for planetesimals from the feeding zone of the terrestrial planets. For bodies originally located at a distance of more than 3 AU from the Sun, this ratio was mainly in the range between 16.4 and 17.4. The characteristic velocities of collisions of planetesimals from the feeding zones of the terrestrial planets with the Moon varied from 8 to 16 km/s, depending on the initial values of the semi-major axes and eccentricities of orbits of the planetesimals. The collision velocities of bodies that came from the feeding zones of Jupiter and Saturn with the Moon were mainly from 20 to 23 km/s. [ABSTRACT FROM AUTHOR]

Missions to asteroids have been the trend in space exploration for the last years. They provide information about the formation and evolution of the Solar System, contribute to direct planetary defense tasks, and could be potentially exploited for resource mining. Be their purpose as it may, the factor that all these mission types have in common is the challenging dynamical environment they have to deal with. The gravitational environment of a certain asteroid is most of the times not accurately known until very late mission phases when the spacecraft has already orbited the body for some time. Shape models help to estimate the gravitational potential with a density distribution assumption (usually constant value) and some optical measurements of the body. These measurements, unlike the ones needed for harmonic coefficient estimation, can be taken from well before arriving at the asteroid's sphere of influence, which allows to obtain a better approximation of the gravitational dynamics much sooner. The disadvantage they pose is that obtaining acceleration values from these models implies a heavy computational burden on the on-board processing unit, which is very often too time-consuming for the mission profile. In this paper, the technique developed on [1] is used to create a validated Python-based tool that obtains spherical harmonic coefficients from the shape model of an asteroid or comet, given a certain density for the body. This validated software suite, called AstroHarm, is used to analyse the accuracy of the models obtained and the improvements in computational efficiency in a simulated spacecraft orbiting a small body. The results obtained are shown offering a qualitative comparison between different order spherical harmonic models and the original shape model. Finally, the creation of a catalogue for harmonics is proposed together with some thoughts on complex modelling using this tool. [ABSTRACT FROM AUTHOR]

Hera represents the European Space Agency's inaugural planetary defense space mission and plays a pivotal role in the Asteroid Impact and Deflection Assessment international collaboration with NASA DART mission that performed the first asteroid deflection experiment using the kinetic impactor techniques. With the primary objective of conducting a detailed post-impact survey of the Didymos binary asteroid following the DART impact on its small moon called Dimorphos, Hera aims to comprehensively assess and characterize the feasibility of the kinetic impactor technique in asteroid deflection while conducting an in-depth investigation of the asteroid binary, including its physical and compositional properties as well as the effect of the impact on the surface and shape of Dimorphos. In this work, we describe the Hera radio science experiment, which will allow us to precisely estimate critical parameters, including the mass, which is required to determine the momentum enhancement resulting from the DART impact, mass distribution, rotational states, relative orbits, and dynamics of the asteroids Didymos and Dimorphos. Through a multi-arc covariance analysis, we present the achievable accuracy for these parameters, which consider the full expected asteroid phase and are based on ground radiometric, Hera optical images, and Hera to CubeSats InterSatellite Link radiometric measurements. The expected formal uncertainties for Didymos and Dimorphos GM are better than 0.01% and 0.1%, respectively, while their J 2 formal uncertainties are better than 0.1% and 10%, respectively. Regarding their rotational state, the absolute spin pole orientations of the bodies can be recovered to better than 1°, and Dimorphos' spin rate to better than 10−3%. Dimorphos reconstructed relative orbit can be estimated at the sub-m level. Preliminary results, using a higher-fidelity dynamical model of the coupled motion between rotational and orbital dynamics, show uncertainties in the main parameters of interest that are comparable to those in standard radio science models. A first-order estimate of the expected uncertainty in the momentum transfer efficiency from DART's impact, obtainable with Hera, yields a value of about 0.25. This represents a significant improvement compared to current estimates. Overall, the retrieved values meet the Hera radio science requirements and goals, and remain valid under the condition that the system is determined to be in an excited but non-chaotic (or tumbling) state. The Hera radio science experiment will play an integral role in the exploration of the Didymos binary asteroid system and will provide unique scientific measurements, which, when combined with other observables such as optical images, altimetry measurements, and satellite-to-satellite tracking of the CubeSats, will support the mission's overarching goals in planetary defense and the deep understanding of binary asteroids. • We present the ESA-Hera Radio Science Experiment (RSE) • The Hera RSE allows to study the Didymos system after the NASA-DART impact • We present the expected accuracies in the parameters of interest for the asteroids • We use ground- and intersatellite-based radio data, onboard imagery, and LIDAR data • Dimorphos mass can be constrained to better than 0.1% [ABSTRACT FROM AUTHOR]

Abstract 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.

Exploration of small body systems poses the problem of designing path planning strategies for possibly uncharted environments. Traditional methods aimed at developing rigorous trajectory baselines may suffer inefficiencies, or turn infeasible when confronted with unknown dynamics. In strongly non-linear dynamics, mapping point design solutions from one dynamical regime to another may be hindered by underlying chaotic behavior. Rather than relying on baseline driven approaches, more generalized strategies may be found by observing human pilots controlling spacecraft motion within varying dynamical environments; the resultant data can then be utilized to initialize machine learning agents to provide more autonomous solutions. A previous numerical experiment resulted in a technical dataset comprising of human-based path planning strategies across a range of binary asteroid systems. This dataset is now used to train various imitation learning agents, and initiate the creation of a framework that integrates human–machine cooperation into the early training phases of artificial intelligent agents; the current application is for spacecraft guidance in binary asteroid systems, as a prototype of complex, potentially unknown, orbit dynamics. An interactive training architecture, based on the DAgger algorithm, is designed and employed to train both original and interactively coached agents, the latter stemming from both corrective and evaluative feedback by a real time human interactor. All agents were interactively trained for a predefined time period. The results from this investigation may provide the first, empirical observations of behavioral cloning within multi-body dynamics with largely randomized parameters, with some notable contributions including early characterization of training time, initial evidence of an autonomous agent learning meaningful policy features via imitation, and early identification of challenges in training fully autonomous agents for a multi-body dynamics path planning problem of this complexity and high dimensional state space. [ABSTRACT FROM AUTHOR]

• Hayabusa2 plans its extended mission to rendezvous with 1998 KY26 in 2031. • We show science assessments to select the final two candidates, 1998 KY26 and 2001 AV43. • The mission will explore the origin and evolution of small bodies and planetary defense. Hayabusa2 is the Japanese Asteroid Return Mission and targeted the carbonaceous asteroid Ryugu, conducted by the Japan Aerospace Exploration Agency (JAXA). The goal of this mission was to conduct proximity operations including remote sensing observations, material sampling, and a Small Carry-On Impact experiment, as well as sample analyses. As of September 2020, the spacecraft is on the way back to Earth with samples from Ryugu with no critical issues after the successful departure in November 2019. Here, we propose an extended mission in which the spacecraft will rendezvous with a small asteroid with ~30 m - ~40 m in diameter that is rotating at a spin period of ~10 min after an additional ~10-year cruise phase. We introduce that two scenarios are suitable for the extended mission. In the first scenario, the spacecraft will perform swing-by maneuvers at Venus once and Earth twice to arrive at asteroid 2001 AV43. In the second scenario, it will perform swing-by maneuvers at Earth twice to reach asteroid 1998 KY26. In both scenarios, the mission will continue until the early 2030s. JAXA recently released the decision that the spacecraft will rendezvous with 1998 KY26. This paper focuses on our scientific assessments of the two scenarios but leaves the decision process to go to 1998 KY26 for future reports. Rendezvous operations will be planned to detail the physical properties and surrounding environments of the target, one of the smallest elements of small planetary bodies. By achieving the planned operations, the mission will provide critical hints on the violent histories of collisions and accumulations of small bodies in the solar system. Furthermore, the established scientific knowledge and techniques will advance key technologies for planetary defense. [ABSTRACT FROM AUTHOR]

Asteroid Explorer Hayabusa2 arrived at asteroid Ryugu in June of 2018. During its stay around Ryugu, Hayabusa2 will undertake several challenging missions such as collecting soil samples and deploying rovers, a lander, and an impactor. Before the spacecraft attempts these missions, our initial and most important work is to reveal the asteroid’s characteristics and properties. Science equipment is used to obtain data for use in making an asteroid model and for the landing site selection (LSS) of sample soil collection and rover/lander deployment. The LSS requires surface images taken from an altitude of around 5 km. Middle altitude observation was the operation needed to meet this requirement. This paper presents an overview of the operation, design, and study of hovering at a 5-km altitude from the surface, and specifically describes the RHC hovering method and Monte Carlo analysis of hovering trajectory and dV. It also describes the actual operation results. [ABSTRACT FROM AUTHOR]

Early evolution of Solar System small bodies proceeded through interactions of mineral and water. Melting of water ice accreted with mineral particles to the parent body results in the formation of secondary minerals, the so-called aqueous alteration. Formation of phyllosilicates from anhydrous silicates is a typical alteration effect recorded in primitive meteorites. In addition to mineral and water, organic matter could have been also a significant component in meteorite parent bodies. However, the role of organic matter in the alteration of silicates is not well understood. We conducted a heating experiment of anhydrous silicate (olivine) with a mixture of organic compounds which simulated primordial organic matter in the Solar System. Dissolution and precipitation features were confirmed on the olivine surface after heating at 300 °C for 10 days, and proto-phyllosilicates were formed in the precipitation area. Magnesite was also detected as concomitant mineral phase. These minerals could be the evidence of aqueous alteration and carbonation of olivine induced by water generated through decomposition of the organic compounds with hydroxy groups. Our result showed that the in situ formation of hydrated silicates through a mineral–organic interaction without the initial presence of water. It further implies that formation of phyllosilicates on the olivine surface in contact with organic matter can occur in meteorite parent bodies which formed inside the H2O snow line but accreted with organic matter, initially without water. Water formed through decomposition of organic matter could be one candidate for hydrous silicate formation, for example, in ordinary chondrites from S-type asteroids inside the H2O snow line. Although the origin of water in ordinary chondrites is under debate, water generation from organic matter may also explain the D-rich water in ordinary chondrites because primordial organic matter is known to be D rich. [ABSTRACT FROM AUTHOR]

Planetary radar has provided a growing number of data sets on the inner planets and near‐Earth and main belt asteroid populations in the solar system. Physical interpretation of radar data for inference of surface properties requires constraints on the constitutive parameters of the material making up a given surface. In this study, the complex permittivity of seven minerals as a function of frequency and porosity is measured using the coaxial transmission line method to determine the mixing equation that best describes the relationship between the real part of the complex permittivity of single mineral crystals and granular mineral powders. We find the Looyenga‐Landau‐Lifshitz and Bruggeman symmetric mixing equations to describe our experimental results with the highest accuracy. The variation in the real part of the permittivity of solid mineral crystals between different minerals is shown to depend on the grain density and the chemical composition of the minerals. These mixing relationships are incorporated into an asteroid radar model and used to calculate the porosity in the near‐surface of seven asteroids visited by robotic spacecraft using Earth‐based radar observations. The results of the asteroid radar model support the presence of significant porosity in the boulders on the surface of asteroid 101955 Bennu. This research highlights the ability of radar to measure the porosity on asteroid surfaces and provides theoretical and experimental justification for the inversion of permittivity to bulk density assumed by the asteroid radar model. Plain Language Summary: Radar observations of planets, the Moon, and asteroids provide information about the upper surface, within a few tens of centimeters to meters, such as the electrical properties of this material. In this study, these electrical properties are measured in the laboratory for seven mineral samples under environmental conditions expected for planetary surfaces. Several well‐known mixing equations are tested for their accuracy in modeling the change in the measured electrical properties with the change in the porosity, or amount of empty space, in the samples. We incorporate two of these mixing equations into an asteroid radar model that converts the measured electrical properties of radar‐observed asteroids to the density of the surface material. Our model predicts low surface density for seven asteroids observed by Earth‐based radar telescopes, such as Arecibo Observatory. Space missions such as the National Aeronautics and Space Administration's OSIRIS‐REx and the Japanese Aerospace Exploration Agency's Hayabusa2 missions visiting asteroids will provide ground‐truth observations of these asteroids' surface properties, such as density, for validating our models. The density of the surfaces of asteroids provides information about the possible structure and evolutionary history of asteroids, and the early solar system. Key Points: New permittivity measurements support the use of the Looyenga‐Landau‐Lifshitz mixing equation for modeling planetary radar dataWe provide new estimates of near‐surface porosity for seven spacecraft‐visited asteroids using Earth‐based radar observationsPorous boulders on the surface of 101955 Bennu are likely one of the reasons for the low CPR measured by Earth‐based radar [ABSTRACT FROM AUTHOR]

One of the biggest challenges of a mining endeavour lies in the judgement of its economic feasibility such as the estimation of costs and the prediction of the market value of the designated product. Whereas the complexity of the latter originates mainly from the supply and demand of the economic situation, the complexity of the first derives from the lack of heritage data, the high degree of innovation and the uncertainties that are connected to any long-term project. In this paper, the authors apply a cause-effect analysis technique called structural equation modelling (SEM) using partial least squares (PLS) to estimate the costs of an asteroid mining mission concept called KaNaRiA. For data ascertainment, two expert interview rounds have been conducted involving international space engineers and scientists from different professional levels and areas. First, a qualitative method called the Delphi technique is used to identify the main cost drivers and quantify their influence on the overall costs. Second, the cost drivers were formulated as questions to enable the classification on a Likert-scale. The collected data is the input for the development of the cost prognosis model by applying PLS-SEM. The cost model is given and its usage explained. The resulting cost model allows a user-individual estimation of the mission costs depending on the individual judgement of the influence of the final, relevant cost drivers. An application of the model using the judgment of the authors' is presented. • The paper successfully demonstrates an approach for cost assessment of space missions with no heritage data. • The main cost drivers of an asteroid mining mission were identified. • The importance and their effect on the overall mission costs have been estimated. • A final cost model for the estimation of an asteroid mining mission has been established. [ABSTRACT FROM AUTHOR]

The aim of this study is to explore one of the most elusive, yet significant, spectacles made possible by the colonial situation in Israel/Palestine. It occurs for an instant when the paths of Palestinian children and Israeli adults cross, the former begging for money, cleaning windshields and peddling wares, and the latter being passersby. The presence of these children, these tiny bodies, undermines the imaginary border separating Israeli and Palestinian societies. I explore the reactions of horror/fascination evoked by the spectacle – reactions that expose its diverse contexts, including class-related economic and political imbalances of power. As I will illustrate, the presence of these children also revalidates these power relations. I further analyse the spectacle of the children of the junctions in comparison with the freak shows put on in the colonial metropolises of Western Europe and North America from the nineteenth to the mid-twentieth century. [ABSTRACT FROM AUTHOR]

The NASA/Dawn mission has acquired unprecedented measurements of the surface of the dwarf planet Ceres, the composition of which is a mixture of ultra-carbonaceous material, phyllosilicates, carbonates, organics, Fe-oxides, and volatiles as determined by remote sensing instruments including the VIR imaging spectrometer. We performed a refined analysis merging visible and infrared observations of Ceres’ surface for the first time. The overall shape of the combined spectrum suggests another type of silicate not previously considered, and we confirmed a large abundance of carbon material. More importantly, by analyzing the local spectra of the organic-rich region of the Ernutet crater, we identified a reddening in the visible range, strongly correlated to the aliphatic signature at 3.4 µm. Similar reddening was found in the bright material making up Cerealia Facula in the Occator crater. This implies that organic material might be present in the source of the faculae, where brines and organics are mixed in an environment that may be favorable for prebiotic chemistry.

Abstract Centaurs, minor planets with a semi-major axis between the orbits of Jupiter and Neptune (5–30 AU), are thought to be among the most diverse small bodies in the solar system. These important targets for future missions may have recently been Kuiper Belt Objects (KBOs), which are thought to be chemically and physically primitive remnants of the early solar system. While the Kuiper Belt spans distances of 30–50 AU, making direct observations difficult, Centaurs' proximity to the Earth and Sun make them more accessible targets for robotic missions. Thus, we outline a mission concept designed to reconnoiter 10199 Chariklo, the largest Centaur and smallest ringed body yet discovered. Named for a legendary Centaur tamer, the conceptual Camilla mission is designed to fit under the cost cap of the National Aeronautics and Space Administration (NASA) New Frontiers program, leveraging a conservative payload to support a foundational scientific investigation to these primitive bodies. Specifically, the single flyby encounter utilizes a combined high-resolution camera/VIS-IR mapping spectrometer, a sub-mm point spectrometer, and a UV mapping spectrometer. In addition, the mission concept utilizes a kinetic impactor, which would provide the first opportunity to sample the composition of potentially primitive subsurface material beyond Saturn, thus providing key insights into solar system origins. Such a flyby of the Chariklo system would provide a linchpin in the understanding of small body composition, evolution, and transport of materials in the solar system. Graphical abstract Image 1 Highlights • Flyby concept for 10199 Chariklo, the largest Centaur and smallest ring system. • Opportunity to learn about Kuiper Belt Objects much closer to Earth. • Impactor would provide deepest yet subsurface sampling in the outer Solar System. • Mission concept fits well within NASA New Frontiers Program cost cap. • Mission concept may fit within NASA Discovery Program cost cap. [ABSTRACT FROM AUTHOR]

The OSIRIS‐REx Asteroid Sample Return Mission is the third mission in National Aeronautics and Space Administration (NASA)'s New Frontiers Program and is the first U.S. mission to return samples from an asteroid to Earth. The most important decision ahead of the OSIRIS‐REx team is the selection of a prime sample‐site on the surface of asteroid (101955) Bennu. Mission success hinges on identifying a site that is safe and has regolith that can readily be ingested by the spacecraft's sampling mechanism. To inform this mission‐critical decision, the surface of Bennu is mapped using the OSIRIS‐REx Camera Suite and the images are used to develop several foundational data products. Acquiring the necessary inputs to these data products requires observational strategies that are defined specifically to overcome the challenges associated with mapping a small irregular body. We present these strategies in the context of assessing candidate sample sites at Bennu according to a framework of decisions regarding the relative safety, sampleability, and scientific value across the asteroid's surface. To create data products that aid these assessments, we describe the best practices developed by the OSIRIS‐REx team for image‐based mapping of irregular small bodies. We emphasize the importance of using 3‐D shape models and the ability to work in body‐fixed rectangular coordinates when dealing with planetary surfaces that cannot be uniquely addressed by body‐fixed latitude and longitude. Plain Language Summary: The OSIRIS‐REx Asteroid Sample Return Mission must map asteroid (101955) Bennu using the OSIRIS‐REx Camera Suite. Here we present the techniques that are established to accomplish this goal. Mapping helps us find the best place on the surface of Bennu from which to gather a sample. Because asteroids are small bodies with weak gravitational fields, maneuvering a spacecraft around them can be challenging. Considering these complexities, we have found ways to gather images of Bennu needed for creating maps. Additionally, due to the irregular shape of many asteroids, producing 2‐D maps in terms of latitude and longitude may be insufficient for describing their surface geography. To that end, we have developed software that is capable of creating and displaying image maps in 3‐D. Key Points: The OSIRIS‐REx Asteroid Sample Return Mission performs image‐based mapping of (101955) Bennu to aid in the selection of a sample‐siteWe develop observational strategies to perform mapping to address the challenges associated with surveying a small bodyWe identify pitfalls and best practices for mapping images of small bodies with large concavities, elongated axes, or overhanging terrain [ABSTRACT FROM AUTHOR]

Abstract We carried out impact experiments using cylindrical gypsum targets with various radii and investigated the crater on the top (flat) surface. At a ratio of projectile and target radii ∼1/20, the crater size abruptly increases; the spallation extends to the side surface of the targets. The results are closely similar to the previous ones on the curved surfaces. A shock wave propagation model, introduced by Suzuki et al. (2018, Icarus 301, 1–8), can represent such results as the steep increase of the size of the spallation zone in both cases of spherical and cylindrical targets. Using this model, the maximum fragment size is evaluated and agrees well with the experimental results. We found that the enlargement of the spallation zone is crucial to the transition from cratering to catastrophic disruption. We also carried out numerical calculations with iSALE code capable of simulating impact processes in solid materials. The maximum pressure distribution shows that the most parts of the spallation zone are not metamorphosed by shock waves. Also, the crater depth is represented by iSALE without damage models, while the "spallation" seems not to be well reproduced by iSALE even with the damage models. Highlights • We carried out impact experiments using cylindrical gypsum targets and investigated the crater on the top (flat) surface. • At a ratio of projectile and target radii ~1/20, the spallation extends to the side surface of the targets. • The enlargement of spallation zone is represented by a simple shock propagation model. • The enlargement of spallation zone is crucial to the transition from cratering to catastrophic disruption. • iSALE represents crater depth but seems not to reproduce spallation. [ABSTRACT FROM AUTHOR]

Abstract While common Descent and Landing strategies involve extended periods of forced motion, significant fuel savings could be achieved by exploiting the natural dynamics in the vicinity of the target. However, small bodies are characterised by perturbed and poorly known dynamics environments, calling for robust autonomous guidance, navigation and control. Airbus Defence and Space and the University of Bristol have been contracted by the UK Space Agency to investigate the optimisation of landing trajectories, including novel approaches from the dynamical systems theory, and robust nonlinear control techniques, with an application to the case of a landing on the Martian moon Phobos. Highlights • Description of the dynamics environment in the vicinity of the Martian Moon Phobos. • Derivation of orbits and their manifolds as ballistic initial guesses for landing. • Optimisation of powered landing open-loop reference trajectories. • Survey and implementation of closed-loop guidance strategies. • Monte-Carlo campaign for performance assessment in perturbed environment. [ABSTRACT FROM AUTHOR]

Limitations on using chemical thermodynamics to describe small systems are formulated. These limitations follow from statistical mechanics for equilibrium and nonequilibrium processes and reflect (1) differences between characteristic relaxation times in momentum, energy and mass transfer in different aggregate states of investigated systems; (2) achievements of statistical mechanics that allow us to determine criteria for the size of smallest region in which thermodynamics can be applied and the scale of the emergence of a new phase, along with criteria for the conditions of violating a local equilibrium. Based on this analysis, the main thermodynamic results are clarified: the phase rule for distorted interfaces, the sense and area of applicability of Gibbs's concept of passive forces, and the artificiality of Kelvin's equation as a result of limitations on the thermodynamic approach to considering small bodies. The wrongness of introducing molecular parameters into thermodynamic derivations and the activity coefficient for an activated complex into the expression for a reaction rate constant, is demonstrated. [ABSTRACT FROM AUTHOR]