Astronomy: Close encounters of a near-Earth-asteroid kind

A close flyby by the Chinese lunar probe Chang’e-2 of the near-Earth asteroid 4179 Toutatis reveals new insights into the geological features and formation of the ginger-root-shaped asteroid. The findings are published in the journal Scientific Reports this week.

In December 2012, Chang’e-2 completed a flyby of 4179 Toutatis at distances as close as 770 metres. The high-resolution images provide a number of new discoveries about the asteroid, the reports the Chang’e-2 mission team of China's Lunar Exploration Program. Toutatis has an irregular, faceted surface and its shape resembles a ginger root with a smaller ‘head’ lobe and a larger ‘body’ lobe connected at a perpendicular angle by a neck region. The authors identify an 800-metre basin at the end of the large lobe, which could be the result of a large impact, as well as more than 50 craters on the asteroid’s surface.

The observations indicate that Toutatis is probably a rubble-pile asteroid, which could reassemble itself into a weak aggregate of large fragments through a heavy impact or many smaller impacts. The two-lobed configuration and the different orientations of the asteroid’s head and body hint that Toutatis could have formed from two separate objects that merged as a contact binary, although the exact events in the formation of the asteroid remain uncertain.