The collisional evolution of chondritic parent bodies

J. BLUM(*); E. BEITZ(*); M. G. PARISI; (*) TECHNISCHE UNIVERSITAT BRAUNSCHWEIG, INSTITUT FUR GEOPHYSIK UND ETECHNISCHE UNIVERSITAT

Washington,

Workshop; American Astronomical Society, DPS meety ing #47, id.302.01; 2015

Divison For Planetary Sciences

Most meteorites are fragments form recent collisions in the asteroidbelt. The collision speed between two objects of the asteroid belt isgiven by the eccentricity and inclination of their respective Keplerianorbits. Typical values are on the order of a few km s-1. Insuch a hyper-velocity collision, the smaller collision partner(projectile) is destroyed, whereas, depending on the mass ratio of thecolliding objects, a crater on the larger body (target) is formed or thetarget is entirely destroyed, too. The present size distribution of theasteroid belt suggests that an asteroid with 100 km radius isencountered ~1014 times during the lifetime of the SolarSystem by objects larger than 10 cm in radius, the formed craters coverthe surface of the asteroid about 100 times.We will present a numericalstudy that simulates the statistical bombardment on an asteroidalsurface and tracks the resulting morphological changes of the parentbody due to the formation of craters, the compaction of the materialbeneath the craters as well as the formation of a regolith layer. Thecrater ejecta from recent impacts on a consolidated asteroid are thencompared to the known meteorites, particularly concerning thedistribution of shock stages.Comparing the compaction of ejectedmaterial from the simulated collisions that occurred during the last 20Myrs, which is the mean cosmic ray exposure age of meteorites, withshock stages of meteorites, we find that meteorites most likely stemfrom smaller parent bodies that do not have a significant regolithlayer. For larger objects that inevitably accrete regolith layers, aprediction of the thickness depending on the largest visible crater canbe made. Additionally, we compare the crater distribution of aninitially 100 km (radius) large object with a shape model of asteroid(21) Lutetia, assuming it to be initially formed spherical with a radiusthat is equal to its longest present ellipsoid length, and find areasonable agreement. Following our study, predictions of the porosityof the surface and the interior of the asteroid as well as the shockstages of ejected material can be made.