Diamond Asteroids: How Bennu and Ryugu Got Their Fancy Shapes

The asteroid Ryugu, as seen by Japan’s Hayabusa2 spacecraft on June 26, 2018. Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST
The striking diamond shapes of the space rocks Ryugu and Bennu — the targets of the sample-return missions Hayabusa2 and OSIRIS-REx, respectively — apparently result from the near-Earth asteroids‘ rubble-pile composition, scientists said.

By Mike Wall | SPACE.com

„We think they’re very loose aggregates. They’re not solid through and through,“ Melissa Morris, OSIRIS-REx deputy program scientist at NASA Headquarters in Washington, D.C., said during a webcast „Science Chat“ on Wednesday (Nov. 7). „And so, as they rotate, you can actually basically spin things out and create almost that top shape.“ [OSIRIS-REx: NASA’s Asteroid Sample-Return Mission in Pictures]

Both Ryugu and Bennu are also likely rich in organic molecules, the carbon-containing building blocks of life as we know it. Despite such similarities, however, the two rocks are far from clones. For example, Ryugu, at about 3,000 feet wide (900 meters), is much bigger than the 1,650-foot-wide (500 m) Bennu. And the former asteroid’s surface is of fairly uniform brightness, whereas Bennu sports a diversity of light and dark patches, Morris added.

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