Impact experiments with a new technique for acceleration of projectiles to velocities higher than Earth's escape velocityof 11.2 km/s

摘要

The impact velocities of asteroids on Earth and other terrestrial planets can be greaterthan 10 km/s, and impacts at these high velocities can produce significant effects on theplanetary surfaces. However, since macroscopic (>~0.1 mm) projectiles with an aspectratio of –1 are not easily accelerated to more than 10 km/s in laboratories, there are fewdetailed experimental studies. In this paper, we demonstrate that impact velocities greaterthan 10 km/s can be achieved with glass and aluminum projectiles of 0.1-0.3 mm indiameter using a high-power laser, GEKKO XII-HIPER at Institute of Laser Engineering,Osaka University. The velocity of the projectiles is estimated based on the images taken byhigh-speed X-ray streak and framing cameras. Projectiles collide into copper or LiFplate targets. The copper plates are recovered for analysis. The sizes of craters on thecopper plates are not far from the extrapolations from previous work with lower velocities.A tantalum witness plate placed near the copper plates records a large number ofsecondary craters from each impact. In the case of the impacts of the LiF plates, weobserve two emission lines of Li gas using a spectrometer with a streak camera. Thus, wecan simulate the hypervelocity impacts with velocities higher than 10 km/s in laboratories.