Control/Tracking Number: 06-RC-322-AAS Activity: Research Contributed Current Date/Time: 7/25/2006 7:16:50 PM
Boulders Ejected From Small Impact Craters
Author Block: Gwendolyn D. Bart1, H. J. Melosh1 1Univ. of Arizona.
We investigate the distribution of boulders ejected from lunar craters
by analyzing high resolution Lunar Orbiter images. Our previous study
(DPS 2004) of four small craters indicated that larger boulders are
more frequently found close to the crater rim rather than far away, and
that the size of the ejecta drops off as a power law with distance from
the crater. Our current study adds more than ten new bouldery craters
that range in size from 200 m to several kilometers and are found on a
variety of terrain (mare, highlands, and the Copernicus ejecta
blanket.) For each crater we plot the boulder diameter as a function of
the ejection velocity of the boulder. We compare this size-velocity
distribution with the size-velocity distribution of ejecta from large
craters (Vickery 1986, 1987) to ascertain the mechanism of fracture of
the substrate in the impact. We also make cumulative plots of the
boulders, indicating the number of boulders of each size present around
the crater. The cumulative plots allow us to compare our boulder
distributions with the distributions of secondary craters from large
impacts. Material thrown from a several-hundred-meter diameter crater
may land intact as boulders, but material thrown from a
tens-of-kilometers diameter crater will travel at a significantly
higher velocity, and will form a secondary crater when it impacts the
surface. Our data helps elucidate whether the upturn, at small
diameters, of the cratering curve of the terrestrial planets is due to
secondary impacts or to the primary population. This work is funded by
NASA PGG grant NNG05GK40G.
Category (Complete): 15. Mercury and Moon Facility Keywords (Complete): None selected Presentation Preference (Complete):  Oral Preferred Additional Information (Complete): Student Status: : Graduate Student Is this your first presentation at a DPS Meeting? : No I am willing to serve as a Chair: : No Newsworthy? : No I have a video for Press Officer review, : No
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