Ryodo Hemmi

<jats:title>Abstract</jats:title> <jats:p> High-quality digital terrain models (DTMs) are essential for lunar polar missions, aiding mission planning and surface operations. The horizontal resolution and vertical accuracy of DTMs are generally limited by factors such as source image resolution, image noise, the precision of ground control points (GCPs), and data processing techniques. In this study, we produced advanced DTMs for the lunar south pole region by integrating seamless mosaics generated from multiple Lunar Reconnaissance Orbiter Camera Narrow Angle Camera image pairs captured under various illumination azimuths. To enhance accuracy and reduce artifacts, we employed bundle adjustment with hundreds of meticulously selected image-to-image tie points and precise GCPs, combined with an advanced multiview shape-from-shading technique. This technique, which utilizes multiple viewpoints to resolve topographic details with higher precision, significantly improves vertical accuracy and resolution. Our methodology achieves a spatial resolution of 1 m pixel <jats:sup>−1</jats:sup> and vertical precision of ±1.0 m, enabling clearer delineation of meter-scale lunar topographic features compared to previous models. These DTMs are expected to significantly support the Lunar Polar Exploration project and other forthcoming lunar exploration missions. </jats:p>

<jats:p>We present an automated and fully reproducible pipeline for restoring motion-smeared Mars Express SRC images of Phobos. A one-dimensional motion point spread function (PSF) is derived directly from SPICE geometry and microsecond-precision exposure timing, and Wiener deconvolution (SNR = 16 dB) is applied to recover image sharpness. Tested on 14 images from 4 orbits spanning slant distances of 52–292 km, exposures of 14–20 milliseconds, sampling of 0.47–2.7 m/pixel, and PSF lengths of 11–119 pixels, the method achieves up to 31.7 dB PSNR, 0.78 SSIM, and positive sharpness gains across all cases. The restored images reveal sub-meter surface features previously obscured by motion blur, with residual energy reduced relative to the acquisition model. The workflow relies solely on open data and open-source tools (ISIS, ALE/SpiceyPy, OpenCV), requires no star-field calibration, and generalizes to other motion-degraded planetary datasets, providing a fully transparent and reproducible solution for high-resolution planetary imaging.</jats:p>

Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high-resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble-pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well-defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter &gt; 100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (&lt;20 m) are characterized by smooth circular floors distinguishable from the boulder-rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (&lt;30 m) subsurface. Furthermore, the crater size-frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1-km asteroid. Our crater-counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23-30 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5-12 Myr ago. Subsequently, a large-scale resurfacing event formed the western bulge and the fossae 2-9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near-Earth orbit 0.2-7 Myr ago....

Estimating the regolith properties of Phobos' surface is of critical importance for the landing and performance of the Martian Moons eXploration (MMX) sample return mission. Regolith physical properties such as strength, regolith thickness, and the presence of regolith layers are related to morphologies of superposing impact craters. However, the accurate depths of Phobos' sub-kilometer-diameter craters including irregularly shaped craters have not yet been fully characterized. Here, by using our high-resolution (20 m/pixel) digital elevation model of the nearside (or the sub-Mars side) of Phobos, we investigate the topographic profiles of the sub-kilometer craters. We confirm the presence of crater rims, and bowl-shaped, central-mound, and flat-floored crater geometries. The topography of one flat-floored crater is consistent with a boundary of regolith layers at a depth of ~160-180 meters. Morphometric measurements of 35 sub-kilometer craters show that their depth-to-diameter (d/D) ratios are in the range of 0.037 and 0.174 (mean value = 0.089, median value = 0.093). This suggests either a surface layer composed of rocky debris that effectively dissipates impact energy and causes a reduction in crater depth, or subsequent resurfacing events changed the original crater topography....

Estimating the regolith properties of Phobos' surface is of critical importance for the landing and performance of the Martian Moons eXploration (MMX) sample return mission. Regolith physical properties such as strength, regolith thickness, and the presence of regolith layers are related to morphologies of superposing impact craters. However, the accurate depths of Phobos' sub-kilometer-diameter craters including irregularly shaped craters have not yet been fully characterized. Here, by using our high-resolution (20 m/pixel) digital elevation model of the nearside (or the sub-Mars side) of Phobos, we investigate the topographic profiles of the sub-kilometer craters. We confirm the presence of crater rims, and bowl-shaped, central-mound, and flat-floored crater geometries. The topography of one flat-floored crater is consistent with a boundary of regolith layers at a depth of ~160-180 meters. Morphometric measurements of 35 sub-kilometer craters show that their depth-to-diameter (d/D) ratios are in the range of 0.037 and 0.174 (mean value = 0.089, median value = 0.093). This suggests either a surface layer composed of rocky debris that effectively dissipates impact energy and causes a reduction in crater depth, or subsequent resurfacing events changed the original crater topography....

Based on these proximity observations and global observations, we infer the nature of stratigraphy expressed in color and albedo of Ryugu....

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&emsp;Ancient Mars is now considered to have had an environment somewhat similar to that of Earth in terms of the existence of large bodies of water, a wide range of surface oxidation states, an active dynamo and associated magnetic field, magmatism and tectonism which includes mountain building and basin formation, and appearances of variety of chemical components potentially building blocks of life. Similar to habitable Earth, ancient Mars included hydrological cycling among the atmosphere, ocean, and landmass (southern cratered highlands), and plate tectonism cannot be ruled out. Endogenic activities have continued until even very recently, and recent water-related geological features indicate prolonged existence of aquifer systems, where habitable environments may exist for a significant period of time. Occasional releases of volatiles from such aquifer systems may ultimately account for the detection of methane by the Curiosity rover in the Gale crater and the inconclusive result (i.e., not unambiguous denial) of metabolism-detection instrument onboard Viking landers. Unequivocal evidence of the existence of subsurface aquifers or extant endogenic activity is, however, still lacking possibly due to the existence of homogeneous regolith materials covering the surface of Mars. Also, even if a habitable environment exists at depth, accessing the environment by a spacecraft (either a lander or a rover) has been considered to be challenging especially because such an environment has been generally thought to exist more than several kilometers below the Martian surface. Recent findings of a recurring slope lineae (RSL) point to traces of possible seasonal liquid water flows along slopes, findings of which will likely change the above prevailing view; some of these features might result from the partial discharges from an aquifer. In other words, RSLs might provide a natural bridge between a subsurface aquifer and the surface accessible by a rover. Thus, subsurface structures near such features become prime targets to be explored through future missions. Once the presence of ground water is confirmed, especially an aquifer, mapping and characterizing the distribution of subsurface water would significantly help address the ever-important question of whether life exists on Mars.<br>&emsp;Given this view, we have selected possible landing sites for a future landing mission to detect life on Mars. Our selection is based on the possibility of the existence of near-surface water and recent geological and hydrological activities; specifically areas with (1) a higher possibility of releases of volatiles, (2) a relatively high water activity (Aw>0.6), (3) a relatively higher maximum environmental temperature (T>250K), and (4) an existence of gradients of free energy. We propose Melas Chasma in Valles Marineris as a prime candidate because of its long-term water enrichment and energy conditions as evidenced through it: (1) comprising confirmed recurring slope lineae (RSL); (2) being the widest and deepest part of the Valles Marineris and thus a major catchment basin of Mars since its formation; (3) being connected to the outflow channels; (4) possible fog for at least part of a Martian day; (5) containing Interior Layered Deposits (ILDs) which comprise various sulfates deposits, as well as phyllosilicates among the canyon units, both of which are suggestive of abundant past water; (6) comprising a volcanic field in its southeast part; and (7) being cut by deep-seated basement structures that served as conduits for the migration of both groundwater and heat. We also propose Tharsis/Elysium Corridor region as among the best candidates, which shows evidence of long-lived water enrichment and recent geologic activity.