Alte Mond-Impaktoren (> 3.4 Milliarden Jahre) homogener als angenommen

[karmaka]

Alte Mond-Impaktoren (> 3.4 Milliarden Jahre) homogener als angenommen

http://phys.org/news/2012-05-moon-barrage-million-years-asteroids.html

In so doing they found that many of the fragments were of nearly the same type as carbonaceous chondrite meteorites, which come from certain types of asteroids.

They also found a certain uniformity in the samples that is not present in samples from meteorites that have impacted the moon in more recent times, which the researchers write, suggests that such rocks striking the moon during the barrage were somewhat different from those that strike today which are quite diverse. They also found that the fragments found in different regolith breccias were sufficiently different from each other to rule out the possibility of them coming from a protoplanet that broke apart.

http://www.sciencemag.org/content/early/2012/05/16/science.1219633

ABSTRACT
The lunar surface, a key proxy for the early Earth, contains relics of the asteroids and comets that have pummeled terrestrial planetary surfaces. Surviving fragments of projectiles in the lunar regolith provide a direct measure of the types and, thus, sources of exogenous material delivered to the Earth-Moon system. In ancient [>3.4 billion years ago (Ga)] regolith breccias from the Apollo 16 landing site we located mineral and lithologic relics of magnesian chondrules from chondritic impactors. These ancient impactor fragments are not nearly as diverse as those found in younger (3.4 Ga to today) regolith breccias and soils from the Moon, or that presently fall as meteorites to Earth. This suggests that primitive chondritic asteroids, originating from a similar source region, were common Earth-Moon-crossing impactors during the latter stages of the basin forming epoch.