Inner Workings: How diamonds embedded in meteorites could offer a glimpse into the mantle of Mars

Abstract

On October 7, 2008, a 13-foot-long asteroid burst through Earth’s atmosphere and exploded above Sudan’s Nubian Desert. Its arrival created a stir because it was the first time that an asteroid that had been tracked and studied in space had collided with our planet. Even more intriguing, the bulk of the fragments that landed on Earth, collectively referred to as Almahata Sitta—the Arabic name of the train station near their landing site—turned out to be carbon-rich meteorites containing graphite and diamonds.\n\n\n\nAs it descended to Earth, the asteroid known as 2008 TC3 left this contrail, captured by a cellphone camera. The asteroid’s scattered fragments and their composition have been the subject of intense study. Image credit: Mohamed Elhassan Abdelatif Mahir (Noub NGO), Dr. Muawia H. Shaddad (Univ. Khartoum), and Dr. Peter Jenniskens (SETI Institute/NASA Ames).\n\n\n\nSuch meteorites are called ureilites, and they usually contain tiny diamonds about 100 to 1,000 nanometers long. But a few of the Almahata Sitta meteorites had diamonds up to 100 times larger (1). “It was kind of an unusual sample,” says Meenakshi Wadhwa, director of the Center for Meteorite Studies at Arizona State University (ASU) in Tempe.\n\nIt was thought that diamonds in ureilites formed when a massive asteroid collided with a planet, with the planet destroyed in the collision. The ensuing high temperatures and pressures would have turned the asteroid’s graphite into diamond. But a new theory suggests that the Almahata Sitta ureilites may have come from material ejected from Mars when it was barely a few million years old. If so, the meteorites and the diamonds in them could be giving us our first glimpse of the interior of another planet besides Earth.\n\nThe Almahata Sitta diamonds pose many puzzles. First, they are so large that scientists have recently begun to question …