Sunao Hasegawa

The presence of water on the Moon and on asteroids that are thought to be poor in water, either because they formed inside the snow line or because they lost much of their water during differentiation, has been suggested by multiple studies; however, its form and origin remain unclear. In this study, we conducted hypervelocity impact experiments between serpentinite projectiles and steel targets. Serpentinite contains hydroxyl and simulates hydrated impactors such as primitive asteroids. The effects of impact velocity and angle on the survival and form of water delivered to the target surface were investigated using near-infrared reflectance spectroscopy and microscopic Raman spectroscopy. Reflectance spectra of projectile materials adhered to the crater surfaces suggested that, in all head-on impact experiments with velocities of 3─7 km s⁻¹, hydroxyl pre-existing in the projectile was almost completely lost. The spectra also showed olivine absorption features at shock pressures exceeding ∼80 GPa, and the olivine Raman peaks became narrower at higher impact velocities. Based on the comparisons with results from impact experiments with anhydrous projectiles, it is suggested that molecular water can be trapped in the melt at shock pressures below ∼100 GPa. In contrast, in the oblique impact experiments conducted in this study, decomposition of projectile material was suppressed, and hydroxyl was detected in crater samples. The current results, along with comparisons to impact velocities of asteroids in the main belt and on the Moon, suggest that molecular water derived from hydrated impactors can be detectable through spectroscopic observations....

Impact ejecta with velocities exceeding the escape velocity of planetary bodies become meteorites and dust particles in interplanetary space. We present a new method that allows simultaneous measurement of the size and velocity of the largest high-velocity ejecta. High-speed camera images revealed the time required for the ejecta to reach the secondary target, and ejecta size was determined after the experiment by analyzing the craters formed upon their impact on the secondary target. We defined the size─velocity relationships of submillimeter ejecta with velocities exceeding 1 km s⁻¹, focusing on the largest detectable ejecta in our experiments. The results show that millimeter-sized meteoroids impacting the rocky surfaces of planetary bodies at 7 km s⁻¹ eject particles up to a few tens of micrometers in size toward interplanetary space at velocities exceeding the escape velocity of the body, even when it is greater than 1 km s⁻¹....

In space, asteroids have collided with planets and satellites throughout their long history, and many types of organic molecules have been synthesized. In particular, on satellites with gas atmospheres such as titan, a satellite of saturn, asteroid impacts cause hot reactions in a hot gas plume. To investigate the effects of asteroid impacts, simulation experiment has been carried out using a two-stage light-gas gun in nitrogen gas. we used a small polycarbonate bullet to impact on an iron-based target in nitrogen gas at a pressure of 100 kpa and a speed of approximately 7 km/s. As a result, many carbonaceous nanoparticles were produced. By analyzing the produced soot, using a water extraction method, a dabsylation method and a liquid chromatography method, we detected markedly large amounts of amino acids (glycine and alanine). The reaction process in the hot gas plume was considered. Many types of radicals collide with each other in nitrogen gas and the impact provides a suitable environment for the synthesis of amino acids and precursors of amino acids....