矢野 創

In response to the growing importance of space exploration, the objectives of the COSPAR Panel on Exploration (PEX) are to provide high quality, independent science input to support the development of a global space exploration program, to promote space sciences as a key element of this program, to contribute to maximize its scientific return via enhanced international cooperation, and to take action to safeguard the scientific assets of solar system bodies. This paper summarizes the presentations of the two panel sessions at the COSPAR assembly 2024 and identifies the most intensely discussed recent topics of interest or concern for space exploration. These topics include environment stewardship of celestial bodies, space debris, resource utilization, the Moon, Mars, and other celestial bodies that we want to explore with planetary protection measures, preservation of dark and quiet skies, potential atmospheric pollution, space as an independent goal of sustainable development, human spaceflight, agile and affordable space programs, and the early preparation of a new edition of the COSPAR exploration roadmap.

Chondrules are a characteristic feature of primitive Solar System materials and are common in all primitive meteorites except the CI-chondrites. They are thought to form owing to melting of solid dust aggregates by energetic processing within the solar nebula and thus record fundamental processes within protoplanetary disks. We report the discovery of abundant altered microchondrules (>350 ppm) with modal sizes of 6–8 µm within sample A0180 from C-type asteroid Ryugu. These microchondrules have similar log-normal size and shape distributions to normal-sized chondrules, implying evolution by similar size-sorting. We suggest here formation of microchondrules in an outer Solar System chondrule factory, located in the Jovian pressure-bump, followed by turbulent diffusion and concentration relative to chondrules by intense turbulence. Meridional flows could have also separated microchondrules from chondrules and deliver them sunwards of the pressure bump via Lindblad torque flows. Contrary to conventional wisdom, we thus propose that the concentration of fine-grained, unprocessed grains could mean the most primitive asteroids did not have to form at the largest heliocentric distances.

The Tanpopo experiment is Japan's first astrobiology mission aboard the Japanese Experiment Module Exposed Facility on the International Space Station. The Tanpopo-1 mission exposed silica aerogel panels to low Earth orbit from 2015 to 2016 to capture micrometeoroids. We identified an impact track measuring approximately 8 mm long, which contained terminal grains in the silica aerogel panel oriented toward space. The impact track exhibited a bulbous cavity with two thin, straight tracks branching from it, each preserving a terminal grain at their ends. The terminal grains were extracted from the silica aerogel and analyzed using scanning transmission electron microscopy and scanning transmission X-ray microscopy to investigate their X-ray absorption near-edge structure (STXM-XANES). Both grains are Fe-bearing and relatively homogeneous orthopyroxene crystals (En88.4±0.4 and En88.2±1.8). The recovery of Fe-bearing low-Ca pyroxene aligns with previous studies of micrometeoroids captured in LEO. Micrometeoroids containing Fe-bearing olivine and low-Ca pyroxene are likely abundant in LEO.