Astro Blog

Source:   By Kenneth Chang, The New York Times Excerpt: ...one might think that meteorites that fall on Earth ought to be just like the asteroids that pass through Earth’s neighborhood. “That’s what everybody would have expected,” said Philipp R. Heck, the curator in charge for the meteorite and physical geology collections at the Field Museum of Natural History in Chicago. Planetary scientists were surprised almost a decade ago when they discovered that the most plentiful types of meteorites they had collected and studied on Earth were actually not common in space. In a paper published Monday by the journal Nature Astronomy, an international team of researchers led by Dr. Heck says it has uncovered part of the explanation. Mineralogical evidence in some meteorites had already pointed to a cataclysmic collision in the asteroid belt about 466 million years ago — long before dinosaurs, when multicellular animals were still fairly new. (Dr. Heck estimated that any skywatchers back the

Source:   By Raluca Rufu, Oded Aharonson, & Hagai B. Perets, published in Nature Abstract: The hypothesis of lunar origin by a single giant impact can explain some aspects of the Earth–Moon system. However, it is difficult to reconcile giant-impact models with the compositional similarity of the Earth and Moon without violating angular momentum constraints. Furthermore, successful giant-impact scenarios require very specific conditions such that they have a low probability of occurring. Here we present numerical simulations suggesting that the Moon could instead be the product of a succession of a variety of smaller collisions. In this scenario, each collision forms a debris disk around the proto-Earth that then accretes to form a moonlet. The moonlets tidally advance outward, and may coalesce to form the Moon. We find that sub-lunar moonlets are a common result of impacts expected onto the proto-Earth in the early Solar System and find that the planetary rotation i