Sunao Hasegawa

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....