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One of the primary goals of Hayabusa2 is to land on the asteroid Ryugu to collect its surface materials. The key for a successful touchdown is to find a promising landing site that meets both scientific and engineering requirements. Due to the limited availability of pre-arrival information about Ryugu, the landing site selection (LSS) must be conducted based on proximity observations over a limited length of time. In addition, Ryugu was discovered to possess an unexpectedly high abundance of boulders with an absence of wide and flat areas, further complicating the LSS. To resolve these problems, we developed a systematic and stepwise LSS process with a focus on the surface topography of Ryugu and the associated touchdown safety. The proposed LSS scheme consists of two phases: Phase-I LSS, a comprehensive survey of potential landing areas at the 100-m scale based on the global mapping of Ryugu, and Phase-II LSS, a narrowing-down process of the candidate landing sites at the 10-m scale using high-resolution images and a local terrain model. To verify the feasibility of a precision landing at the target site, we also investigated the landing dispersion via a Monte Carlo simulation, which incorporates the effect of the irregular surface gravity field. One of the major characteristics of the Hayabusa2 LSS developed in this study is the iterative feedback between LSS analyses on the ground and actual spacecraft operations near the target asteroid. Using the newly developed method, we chose a landing site with a radius of 3 m, and Hayabusa2 successfully conducted its first touchdown on February 21, 2019. This paper reports the methodology and results of the stepwise iterative LSS for the first Hayabusa2 touchdown. The touchdown operation results reconstructed from flight data are also provided, demonstrating the validity of the adopted LSS strategy. [ABSTRACT FROM AUTHOR]

The Hayabusa2 mission journeys to C-type near-Earth asteroid (162173) Ryugu (1999 JU) to observe and explore the 900 m-sized object, as well as return samples collected from the surface layer. The Haybusa2 spacecraft developed by Japan Aerospace Exploration Agency (JAXA) was successfully launched on December 3, 2014 by an H-IIA launch vehicle and performed an Earth swing-by on December 3, 2015 to set it on a course toward its target Ryugu. Hayabusa2 aims at increasing our knowledge of the early history and transfer processes of the solar system through deciphering memories recorded on Ryugu, especially about the origin of water and organic materials transferred to the Earth's region. Hayabusa2 carries four remote-sensing instruments, a telescopic optical camera with seven colors (ONC-T), a laser altimeter (LIDAR), a near-infrared spectrometer covering the 3-μm absorption band (NIRS3), and a thermal infrared imager (TIR). It also has three small rovers of MINERVA-II and a small lander MASCOT (Mobile Asteroid Surface Scout) developed by German Aerospace Center (DLR) in cooperation with French space agency CNES. MASCOT has a wide angle imager (MasCam), a 6-band thermal radiator (MARA), a 3-axis magnetometer (MasMag), and a hyperspectral infrared microscope (MicrOmega). Further, Hayabusa2 has a sampling device (SMP), and impact experiment devices which consist of a small carry-on impactor (SCI) and a deployable camera (DCAM3). The interdisciplinary research using the data from these onboard and lander's instruments and the analyses of returned samples are the key to success of the mission. [ABSTRACT FROM AUTHOR]

The Japan Aerospace Exploration Agency launched an asteroid sample return spacecraft "Hayabusa2" on December 3, 2014 by the Japanese H2A launch vehicle. Hayabusa2 aims at the round trip mission to the asteroid 162173 Ryugu. Hayabusa2 successfully conducted the Earth gravity assist on December 3, 2015, and now the spacecraft is flying toward Ryugu with the microwave discharge ion engine as the means of propulsion. As of September 2016, 1346 h of the ion engine operation has been achieved as planned. Three touch downs/sample collections, one kinetic impact/crater generation, four surface rovers deployment and many other in-situ observations are planned in the asteroid proximity phase. The operation team will perform extensive operation practice/rehearsal using a hardware-in-the-loop simulator in the year 2017 to be ready for the asteroid arrival in the summer 2018. [ABSTRACT FROM AUTHOR]

Hayabusa2 took on the challenge of collecting fresh subsurface samples from asteroid (162173) Ryugu during its second touchdown operation. For this ambitious goal, the spacecraft conducted artificial cratering by using a small carry-on impactor (SCI), leading to the exposure of subsurface materials. The key to mission success lies in the target site selection for the SCI and landing operations, which is the focus of this paper. On the one hand, the science goal of collecting subsurface materials required us to land on one of the areas with a large amount of impact ejecta excavated by SCI, where boulder abundance is not necessarily low. On the other hand, spacecraft safety demanded that we avoid landing on hazardous areas with large boulders. These two conditions often conflicted with each other. In order to resolve this dilemma, we developed a scheme to select a target site that secures the chance of retrieving a significant amount of subsurface samples without posing serious safety risks. Although the basic selection scheme was similar to that for the first touchdown, the second landing site selection involved additional analyses of artificial cratering and subsurface sampling. Consequently, the site selection campaign, including various types of spacecraft operations, contributed to the successful retrieval of Ryugu samples, which presumably contain materials excavated from subsurface layers. The present study provides the framework to access internal asteroid materials, pushing the envelope of space exploration. • Hayabusa2 aimed to collect subsurface samples from Ryugu excavated by an impactor. • Hayabusa2 completed landing and sampling on a target site with a diameter of 3.5 ​m. • The estimated thickness of the impact ejecta at the landing site was 1–3 ​cm. • No hazardous boulders larger than 65 ​cm existed within the landing site. [ABSTRACT FROM AUTHOR]

Abstract: Dust particles exposed to the stellar radiation and wind drift radially inward by the Poynting–Robertson (P-R) drag and pile up at the zone where they begin to sublime substantially. The reason they pile up or form a ring is that their inward drifts due to the P-R drag are suppressed by stellar radiation pressure when the ratio of radiation pressure to stellar gravity on them increases during their sublimation phases. We present analytic solutions to the orbital and mass evolution of such subliming dust particles, and find their drift velocities at the pileup zone are almost independent of their initial semimajor axes and masses. We derive analytically an enhancement factor of the number density of the particles at the outer edge of the sublimation zone from the solutions. We show that the formula of the enhancement factor reproduces well numerical simulations in the previous studies. The enhancement factor for spherical dust particles of silicate and carbon extends from 3 to more than 20 at stellar luminosities , where is solar luminosity. Although the enhancement factor for fluffy dust particles is smaller than that for spherical particles, sublimating particles inevitably form a dust ring as long as their masses decrease faster than their surface areas during sublimation. The formulation is applicable to dust ring formation for arbitrary shape and material of dust in dust-debris disks as well as in the Solar System. [Copyright &y& Elsevier]

Abstract: In a disk with a low optical depth, dust particles drift radially inward by the Poynting–Robertson (P-R) drag rather than are blown out by stellar radiation pressure following destructive collisions. We investigate the radial distribution of icy dust composed of pure ice and refractory materials in dust-debris disks taking into account the P-R drag and ice sublimation. We find that icy dust particles form a dust ring by their pile-ups at the edge of their sublimation zone, where they sublime substantially at the temperature 100–110 K. The distance of the dust ring is 20–35 AU from the central star with its luminosity and for , where is the solar luminosity. The effective optical depth is enhanced by a factor of 2 for and more than 10 for . The optical depth of the outer icy dust disk exceeds that of the inner disk filled with refractory particles, namely, the residue of ice sublimation, which are further subjected to the P-R effect. As a result, an inner hole is formed inside the sublimation zone together with a dust ring along the outer edge of the hole. [Copyright &y& Elsevier]

Though the Moon is considered to have been formed by the so-called giant impact, the mass of the Earth immediately after the impact is still controversial. If the Moon was formed during the Earth''s accretion, a subsequent accretion of residual heliocentric planetesimals onto the protoearth and the protomoon must have occurred. In this co-accretion stage, a significant amount of lunar-impact-ejecta would be ejected to circumterrestrial orbits, since the mean impact velocity of the planetesimals with the protomoon is much larger than the escape velocity of the protomoon. Orbital calculations of test particles ejected from the protomoon, whose semimajor axis is smaller than that of the present Moon, reveal that most of the particles escaping from the protomoon also escape from the Hill sphere of the protoearth and reduce the planetocentric angular momentum of the primordial Earth–Moon system. Using the results of the ejecta simulations, we investigate the evolution of the mass ratio and the total angular momentum (Earth''s spin angular momentum + Moon''s orbital angular momentum) of the Earth–Moon system during the co-accretion. We find that the mass of the protomoon is almost constant or rather decreases and the total angular momentum decreases significantly, if the random velocity of planetesimals is as large as the escape velocity of the protoearth. On the other hand, if the random velocity is the half of the escape velocity of the protoearth, the mass ratio is kept to be almost as large as the present value and the decrease of the total angular momentum is not so significant. Comparing with the results of giant impact simulations, we find that the mass of the protoearth immediately after the Moon-forming impact was 0.7–0.8 times the present value if the impactor-to-target mass ratio was 3:7, whereas the giant impact occurred almost in the end of the Earth''s accretion if the impactor-to-target mass ratio was 1:9. [Copyright &y& Elsevier]

Parent bodies of carbonaceous chondrites that initially contained metallic iron potentially exert strong reduction power during aqueous alteration to generate molecular hydrogen in excess of hydrogen solubility in water-rich fluids. The surplus hydrogen escapes from the system, which is subsequently supplied to overlying regions in planetesimals. Based on this concept, we conducted chemical equilibrium modeling of the aqueous alteration and simulated gaseous H 2 migration within the icy planetesimal that has a melted mantle and an icy shell during the early stages of radiogenic heating. In the chemical equilibrium modeling, we simulated the aqueous alteration of chondritic rocks at 0–350 °C and a water/rock mass ratio of 0.2–10 with initial CO 2 contents of 0–10 mol% in the fluid. The results showed that the mineral assemblage and solution composition change with the temperature, water/rock mass ratio, and initial fluid composition. The reproduced mineral paragenesis and abundance well explain those of carbonaceous chondrites. Furthermore, it was revealed that the initial H 2 fugacity of the system influences not only the stability of minerals and solution compositions, but also the preservation potential of organic molecules. Indeed, within these parameter spaces, the modeling results account for the organic/inorganic carbon-rich alterations reported for the Tagish Lake meteorite, Ceres, and Ryugu. Simulations of gaseous H 2 migration in a planetesimal revealed that gaseous H 2 in the deep interior can be transported to the interface with an icy shell even if the permeability is low. Moreover, it is highly possible that an H 2 -rich layer would have been widely formed just below the icy shell. Therefore, it is expected that H 2 -rich regions beneath the ice layer in planetesimals have substantial potential for the synthesis and preservation of organic molecules. These results imply that the alteration of carbonaceous chondrite parent bodies and C-complex asteroids is characterized by not only the type of parent bodies (e.g., formation age and distance from the Sun) but also the locations within their parent bodies. [ABSTRACT FROM AUTHOR]

The near-Earth asteroid 1998 KY26 is a rendezvous target of the Hayabusa2 extended mission, with a diameter as small as 20 – 40 m and a spin period as short as 10. 7 min. This research aims to develop a plan for Hayabusa2 operations around this particular asteroid constrained by the remaining spacecraft resources. The main part of this paper begins with the characterization of the orbital and surface dynamics about 1998 KY26. The analysis demonstrates that the orbital motion of the spacecraft in the microgravity environment is dominated by solar radiation pressure, while the centrifugal force due to the high spin rate plays a prominent role at the surface. The dynamical environment significantly differs from that of the original target Ryugu, for which Hayabusa2 was specifically designed, posing technical challenges in close-proximity operations. In particular, this article highlights the feasibility of two primary operations: hovering for station-keeping and controlled descent for close-up observations. The discussion is further extended to more advanced operations, such as those using the projectile and target marker aboard the spacecraft. Our research pushes the envelope to explore one of the smallest members of the Solar System. • Hayabusa2 ♯ target asteroid 1998 KY26 is a fast rotator with a diameter of ∼ 30 m. • Low gravity and rapid rotation form distinctive orbital and surface environments. • Station-keeping can be achieved by hovering 1 – 3 km above the asteroid. • Controlled descent to lower altitudes shows minimal guidance error and fuel cost. • Advanced options include operations using the projectile and the target marker. [ABSTRACT FROM AUTHOR]

The thermophysical properties of small Solar System bodies are essential to be determined, on which the thermal evolution of small bodies largely depends. The carbonaceous asteroid Ryugu is one of the small undifferentiated bodies formed in the early Solar System. Hayabusa2 explored the asteroid Ryugu and returned the surface samples in 2020 for detailed on-ground investigation, including measurements of thermal properties. Because the available sample amount was limited, this study developed a novel method to measure the thermal diffusivity of small and irregularly shaped samples of about 1 mm in diameter by combining lock-in thermography and periodic heating methods on the microscale. This method enables us to measure the thermal diffusivity of both flat-plate and granular shape samples by selecting the suitable detecting direction of the temperature response. Especially, when the sample has a flat-plate shape, the anisotropic distribution of the in-plane thermal diffusivity can be evaluated. This method was applied to six Ryugu samples, and the detailed anisotropic distribution of the thermal diffusivity was obtained. The measurement results showed that the samples show local thermal anisotropy caused by cracks and voids. The average thermal diffusivity among all samples was (2.8 to 5.8) × 10−7 m2·s. Based on the density and specific heat of the samples obtained independently, the thermal effusivity was estimated to be 791 J·(s1/2·m2·K) to 1253 J·(s1/2·m2·K), which is defined as the resistance of surface temperature to the change of thermal input. The determined thermal effusivity, often called thermal inertia in planetary science, is larger than the observed value of 225 ± 45 J· (s1/2·m2·K) of the asteroid Ryugu's surface, obtained from the diurnal temperature change of the rotating asteroid by a thermal infrared camera onboard Hayabuas2. This difference is likely to be attributed to the difference in the analytical scale between the sample and the surface boulders compared with the thermal diffusion length. Consequently, it was found that the present result is more representative of the thermal diffusivity and thermal inertia of local part of individual Ryugu particles. [ABSTRACT FROM AUTHOR]

[Display omitted] • Deformation of a rotated granular heap was experimentally measured and modeled by a simple force-balance model. • Hysteresis of the deformation was observed. • Empirical relations between granular friction, centrifugal loading, and packing fraction were obtained. We experimentally examined the history dependence of the rotation-induced granular deformation. As an initial state, we prepared a quasi-two-dimensional granular pile whose apex is at the rotational axis and its initial inclination is at the angle of repose. The rotation rate was increased from 0 to 620 (rpm) and then decreased back to 0. During the rotation, deformation of the rotated granular pile was captured by a camera. From the acquired image data, granular friction coefficient μ was measured as a function of the ratio between centrifugal force and gravity, Γ. To systematically evaluate the variation of μ both in the increasing (spinning up) and decreasing (spinning down) rotation-rate regimes, surface profiles of the deformed granular piles were fitted to a model considering the force balance among gravity, friction, and centrifugal force at the surface. We found that μ value grows in the increasing Γ regime. However, when Γ was reduced, μ cannot recover its initial value. A part of the history-dependent behaviors of the rotated granular pile can be understood by the force balance model. [ABSTRACT FROM AUTHOR]

Asteroid 162173 Ryugu and asteroid 101955 Bennu, which were recently visited by spacecraft Hayabusa2 and OSIRIS-REx, respectively, are spinning top-shaped rubble piles. Other axisymmetric top-shaped near-Earth asteroids have been observed with ground-based radar, most of which rotate near breakup rotation periods of ∼ 3 h. This suggests that rotation-induced deformation of asteroids through rotational spinup produces top shapes. Although some previous simulations using the Discrete Element Method showed that spinup of rubble piles may produce oblate top shapes, it is still unclear what kinds of conditions such as friction angles of constituent materials and spinup timescales are required for top-shape formation. Here we show, through Smoothed Particle Hydrodynamics simulations of granular bodies spinning-up at different rates, that the rotation-induced deformation of spherical rubble piles before breakup can be classified into three modes according to the friction angle ϕ d : quasi-static and internal deformation for ϕ d ≤ 40 ° , dynamical and internal deformation for 50 ° ≤ ϕ d ≤ 60 ° , and a set of surface landslides for ϕ d ≥ 70 °. Note that these apparent large values of friction angle can be acceptable if we consider the effect of cohesion among blocks of a rubble pile under weak gravity. Bodies with ϕ d ≤ 60 ° evolve into oblate spheroids through internal deformation, but never form pronounced equators defining a top shape. In contrast, bodies with ϕ d ≥ 70 ° deform into axisymmetric top shapes through an axisymmetric set of surface landslides if spinup timescales are ≲ a few days. In addition, through slow spinups with timescales ≳ 1 month, bodies with ϕ d ≥ 70 ° deform into non-axisymmetric shapes via localized sets of landslides. We suggest that rapid spinup mechanisms are preferable for the formation of axisymmetric top shapes. • We simulated spinup deformation of rubble-pile asteroids using the SPH method. • We mainly investigated deformation modes for various friction angles ϕ d. • Internal deformation occurs for ϕ d < 60 ° , while surface landslides occur for ϕ d > 7 0 ° . • Axisymmetric surface landslides lead to the formation of axisymmetric top shapes. • However, slow spinup with timescale ¿ 1 month leads to non-axisymmetric landslides. [ABSTRACT FROM AUTHOR]

Hayabusa2 is a Japanese interplanetary probe launched on December 3, 2014, which arrived at asteroid Ryugu on June 27, 2018. During its stay around Ryugu, it completed several challenging operations, including deploying two rovers and a lander, conducting two sample collections, and performing a kinetic impact experiment. The kinetic impact experiment was one of the biggest challenges of the Hayabusa2 mission. Investigating the physical and chemical properties of asteroid internal materials and structures is an important scientific objective for small body exploration. We developed a small kinetic impactor called the SCI (Small Carry-on Impactor) to achieve this objective. The SCI is a compact kinetic impactor designed to remove a small region of Ryugu's uppermost surface regolith layer and create an artificial crater. The spacecraft deployed the SCI on April 5, 2019, successfully creating an artificial crater with a diameter of 15 m. This paper describes the operational planning of the kinetic impact experiment and summarizes the operation results. • Sub-surface exploration is a new challenge for Hayabusa2. • A small kinetic impactor was developed to create an artificial crater. • The impactor created a 15m-class artificial crater on April 5, 2019. • The crater formation process was observed by a deployable camera. • The sub-surface sampling was completed during the touchdown operation on July 11, 2019. [ABSTRACT FROM AUTHOR]

Hayabusa2 arrived at the C-type asteroid Ryugu in June 2018. During one and a half year of the Ryugu-proximity operation, we succeeded in two rovers landing, one lander landing, two spacecraft touchdown/sample collection, one kinetic impact operation and two tiny reflective balls and one rover orbiting. Among the two successful touchdowns, the second one succeeded in collecting subsurface material exposed by the kinetic impact operation. This paper describes the asteroid proximity operation activity of the Hayabusa2 mission, and gives an overview of the achievements done so far. Some important engineering and scientific activities, which have been done in synchronous with the spacecraft operations to tackle with unexpected Ryugu environment, are also described. • JAXA launched the world-second asteroid sample return mission Hayabusa2 in 2014. • Hayabusa2 completed 1.5 years of the asteroid proximity operation with full success. • Surface and subsurface landings, 1 crater forming, landers delivery were conducted. • Adoptive mission re-planning and spacecraft reconfigurations were key to the success. • Hayabusa2 is now on the way back to the Earth with the collected Ryugu sample. [ABSTRACT FROM AUTHOR]

Abstract The Japan Aerospace Exploration Agency launched the asteroid sample return spacecraft "Hayabusa2" on December 3, 2014. Hayabusa2 will reach the C-type asteroid 162173 Ryugu in 2018, and return back to the Earth in 2020. Sample collections from three sites, four surface rovers deployment and a 4 MJ-class kinetic impact crater forming are planned in the 1.5 years of the asteroid-proximity operation. The mission objective of Hayabusa2 has three aspects, science, engineering and exploration, all of which would be expanded by the successful round-trip journey. The objectives and technologies used in this mission is not a direct solution for the future planetary defense, but should contribute to this field by increasing general asteroid knowledge and enhancing human capabilities of small body-surface access/roving/sampling/impacting. This paper describes the outline of the Hayabusa2 mission, overviews the kinetic impact technology as an example of planetary defense-related technologies and the current flight status after the two and a half years of the interplanetary cruise. Highlights • JAXA successfully launched the world-second asteroid sample return mission Hayabusa2 in 2014. • Hayabusa2 is equipped with some key devices strongly related to planetary defense technologies. • The first 2.5 years of operation history are explained with major achievements. • The asteroid proximity operation plan is overviewed with preparation activities by the team. [ABSTRACT FROM AUTHOR]

Mare basalts provide insights into the composition and thermal history of the lunar mantle. The ages of mare basalts suggest a first peak of magma activity at 3.2-3.8 Ga and a second peak at ~2 Ga. In this study, we reassess the correlation between the titanium contents and the eruption ages of mare basalt units using the compositional and chronological data updated by SELENE (Kaguya). Using morphological and geological criteria, we calculated the titanium content of 261 mare units across a representative area of each mare unit. In the Procellarum KREEP Terrane, where the latest eruptions are located, an increase in the mean titanium content is observed during the Eratosthenian period, as reported by previous studies. We found that the increase in the mean titanium content occurred within a relatively short period near approximately 2.3 Ga, suggesting that the magma source of the mare basalts changed at this particular age. Moreover, the high-titanium basaltic eruptions are correlated with a second peak in volcanic activity near ~2 Ga. The high-titanium basaltic eruptions occurring during the last volcanic activity period can be explained by the three possible scenarios (1) the ilmenite-bearing cumulate rich layer in the core-mantle boundary formed after the mantle overturn, (2) the basaltic material layers beneath the lunar crust formed through upwelling magmas, and (3) ilmenite-bearing cumulate blocks remained in the upper mantle after the mantle overturn. [ABSTRACT FROM AUTHOR]

Asteroid 162,173 Ryugu is a rubble-pile asteroid, whose top-shape is compatible with models of deformation by spin up. Rims of major craters on Ryugu have an east–west asymmetric profile; their western crater rims are sharp and tall, while their eastern crater rims are rounded and low. Although there are various possible explanations, we theoretically assess the effect of asteroid rotation as the possible reason for this east–west asymmetry. It is known that the trajectories and fates of ejecta are affected by the rotation. The Coriolis force and the inertial speed of the rotating surface are the factors altering the ejecta trajectories. Consequently, we found that the east–west asymmetric crater rims might be formed as a result of rotation, when the inertial speed of the rotating surface is nearly equal to the first cosmic velocity of the body. In other words, it is possible that the observed east–west asymmetric rims of the Urashima, Cendrillon, and Kolobok craters were formed when Ryugu's rotation period was ~3.6 h. • Major craters on Ryugu have east–west asymmetric rims. • Effect of rotation assessed as the possible cause of the east–west asymmetry. • The effect creates the E -W asymmetry only if rotation period was less than 3.6 h. [ABSTRACT FROM AUTHOR]

Proximity observations by OSIRIS-REx and Hayabusa2 provided clues on the shape evolution processes of the target asteroids, (101955) Bennu and (162173) Ryugu. Their oblate shapes with equatorial ridges, or the so-called top shapes, may have evolved due to their rotational conditions at present and in the past. Different shape evolution scenarios were previously proposed; Bennu's top shape may have been driven by surface processing, while Ryugu's may have been developed due to large deformation. These two scenarios seem to be inconsistent. Here, we revisit the structural analyses in earlier works and fill a gap to connect these explanations. We also apply a semi-analytical technique for computing the cohesive strength distribution in a uniformly rotating triaxial ellipsoid to characterize the global failure of top-shaped bodies. Assuming that the structure is uniform, our semi-analytical approach describes the spatial variations in failed regions at different spin periods; surface regions are the most sensitive at longer spin periods, while interiors fail structurally at shorter spin periods. This finding suggests that the shape evolution of a top shape may vary due to rotation and internal structure, which can explain the different evolution scenarios of Bennu's and Ryugu's top shapes. We interpret our results as the indications of top shapes' various evolution processes. • We reanalyzed results from FEM analyses for asteroids Bennu and Ryugu, the targets of OSIRIS-REx and Hayabusa2, respectively. • We also applied a semi-analytical approach to quantify how the failure modes of top shapes vary with spin. • Top shapes may evolve by two deformation modes: surface processing at low spin and internal failure at high spin. [ABSTRACT FROM AUTHOR]

Precise information of spacecraft position with respect to target body is of importance in terms of scientific interpretation of remote sensing data. In case of Hayabusa2, a sample return mission from asteroid Ryugu, such information is also necessary for landing site selection activity. We propose a quick method to improve the spacecraft trajectory when laser altimeter range measurements and a shape model are provided together with crude initial trajectory, spacecraft attitude information, and asteroid spin information. We compared topographic features contained in the altimeter data with those expressed by the reference shape model, and estimated long-period trajectory correction so that discrepancy between the two topographic profiles was minimized. The improved spacecraft positions are consistent with those determined by image-based stereophotoclinometry method within a few tens of meters. With such improved trajectory, the altimeter ranges can be converted to Ryugu's topographic profiles that are appropriate for geophysical interpretation. We present a geophysical application that invokes possibility of impact-induced formation of the Ryugu's western bulge. • Hayabusa2 LIDAR data contribute to quick improvement of the spacecraft trajectory • With this trajectory, topography of Ryugu is delineated by scan observations. • Formation of Ryugu's western bulge may have been triggered by an oblique impact. [ABSTRACT FROM AUTHOR]

Asteroid 162173 Ryugu has numerous craters. The initial measurement of impact craters on Ryugu, by Sugita et al. (2019), is based on Hayabusa2 ONC images obtained during the first month after the arrival of Hayabusa2 in June 2018. Utilizing new images taken until February 2019, we constructed a global impact crater catalogue of Ryugu, which includes all craters larger than 20 m in diameter on the surface of Ryugu. As a result, we identified 77 craters on the surface of Ryugu. Ryugu shows variation in crater density which cannot be explained by the randomness of cratering; there are more craters at lower latitudes and fewer at higher latitudes, and fewer craters in the western bulge (160°E – 290°E) than in the region around the meridian (300°E – 30°E). This variation implies a complicated geologic history for Ryugu. It seems that the variation in crater density indicates that the equatorial ridge located in the western hemisphere is relatively young, while that located in the eastern hemisphere is a fossil structure formed during the short rotational period in the distant past. • We examined the spatial distribution of impact craters on Ryugu. • We completed a global impact crater catalogue of Ryugu (D > 20 m). • Crater density variations cannot be explained by the randomness of cratering. • More craters are seen at lower latitudes and less at higher latitudes. • There are fewer craters in the western bulge and more around the meridian. [ABSTRACT FROM AUTHOR]

This paper provides a unique data set representing the taxonomic type of near-Earth asteroids (NEAs) accessible by available spacecraft. The research on NEAs has entered upon a new phase, thanks to sample-return space explorations together with state-of-the-art large ground-based telescopes. We made observations of 13 asteroids with the Subaru, GEMINI-North, GEMINI-South, and Okayama 188 cm telescopes. Twelve of them have low delta-v orbits with the potential to be investigated by manned/unmanned spacecraft. Also, ten subkilometer-sized bodies are included among them, and are one of remarkable characteristics in terms of their evolutionary scenario. We have found that eleven asteroids are classified as S-complex, and one asteroid as the V-type. Most S-complex asteroids (eight out of eleven, ∼ 70%) have spectra similar to subgroups of Q- or Sq-type, suggesting that these objects are less matured by space weathering. We discuss the dominance of S-complex asteroids based on previous research. [ABSTRACT FROM AUTHOR]