2017-01-23. Ancient Bits of Rock Help Solve an Asteroid Mystery.

posted Jan 26, 2017, 9:04 AM by Alan Gould

By Kenneth Chang, The New York Times. For GSS A Changing Cosmos chapter 7. 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 then would have seen about 100 times as many shooting stars as crisscross the night sky today.). ...The findings fits in with the new understanding that a mix of meteorites is determined more by the history of collisions in the asteroid belt rather than by the mix of asteroids whose orbits around the sun are close to Earth’s....  https://www.nytimes.com/2017/01/23/science/ancient-bits-of-rock-help-solve-an-asteroid-mystery.html