Maytrayee Bose and Ziliang Jin, two astrophysicists at the University of Arizona, analyzing the very small amount of material returned to Earth by the Japanese Hayabusa probe and measuring the abundance of isotopes in the water, advance the theory that at least half of Earth’s oceans are of asteroidal origin, not cometary, as previously believed. Uranium was also detected in Itokawa, allowing them to determine the age of the layers. The asteroid is dated to 4.64 billion years ago, when the Solar System was still forming. It was part of a body at least 19 kilometers in size, which broke apart 8 million years ago.
