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J. E. Colwell, S. Sture (University of Colorado)
We describe the Physics of Regolith Impacts in Microgravity Experiment (PRIME) which performs impacts into granular materials at speeds of ~20 to 250 cm/s in microgravity on the NASA KC-135. The experiment is conceptually identical to the COLLisions Into Dust Experiment (COLLIDE) which has flown on the space shuttle (Colwell and Taylor, Icarus Vol. 138, 241-248, 1999; Colwell, Icarus in press, 2003). We have flown the experiment on five flight weeks (20 flights) between July 2002 and May 2003 with up to 8 impact experiments per flight. Typical accelerations during the experiment are less than 0.05 g. Impactors are spheres between 1 and 2 cm diameter of a variety of materials with different densities. Target materials are silica sand, JSC-1 lunar regolith simulant, and JSC-Mars-1 Martian regolith simulant. Impacts are at angles between 30 and 90 degrees to the surface.
A transition between the projectile embedding in the surface and rebounding from the surface occurs at impact speeds of about 50 cm/s. In the COLLIDE data the transition is at ~20 cm/s, probably due to the lower accelerations in the space shuttle. Ejecta are produced in all impacts at speeds greater than 40 cm/s at normal incidence, and more ejecta are produced in oblique impacts than normal impacts. Ejecta velocities are 10-20% of the impact velocity for most of the impacts. These results suggest that interparticle collisions in planetary rings are not a primary source of dust in the rings, but that micrometeoroid bombardment of ring particles and moons is releases most observed dust. We will also discuss the implications of our experiments for aggregation of small proto-planetesimals (1 cm to 10 m) in protoplanetary disks.
This research is supported by NASA’s Office of Biological and Physical Research.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.