University of Hawaii System newsletter

Examining Asteroid Color

Posted on | January 29, 2010 | Comments Off on Examining Asteroid Color

Image of the Asteroid Itokawa taken by the Japanese spacecraft Hayabusa.

Mānoa Associate Astronomer Schelte Bus and Astronomer Alan Tokunaga are members of an international team who set out to understand why some asteroids have colors different from those of others. In particular, the team wanted to know why most asteroids have a comparatively dark surface—the result of slow weathering by interplanetary sunlight—but others have a paler color characteristic of fresh, unweathered rocks.

By looking very carefully at the various asteroids’ orbits around the sun, the team noticed that all those with pale colors had passed very close to Earth, while those with dark colors had not.

“We now suspect that most asteroids are loose conglomerations of rocks and boulders, rather than strong, monolithic objects,” says Bus. “When one of these rock piles passes close to Earth, it is shaken by the rapidly changing pull of Earth’s gravity. Landslides on the asteroid cause the dark weathered areas to be covered by fresh, lighter colored rocks. Hence the asteroid’s color, after the encounter, will appear paler than before.”

“The more we can learn about what holds an asteroid together, the better chance we have to reduce or eliminate damage to Earth,” says Tokunaga.

Read the news release.