On December 13, 2012, a Chinese Moon Probe on an Unplanned Second Career Flew Past the Asteroid Toutatis
On Dec. 13, 2012, a spacecraft built to orbit the Moon passed within a few kilometers of an asteroid. Chang'e 2 was a Chinese lunar probe that had launched in 2010. By the time it reached Toutatis, it was more than seven million kilometers from home and well past the end of its original assignment. The flyby made China the fourth space program, after the United States, Europe and Japan, to photograph an asteroid up close.
The Bonus Mission
Chang'e 2 launched in October 2010 as a scouting vehicle for China's lunar program, and it mapped the Moon's surface in fine detail from a low orbit. Once that work was done in 2011, its engineers could have let it idle. Instead they sent it toward Lagrange point L2, a gravitationally balanced spot far beyond the Moon on the side of Earth facing away from the Sun. From there the craft was steered toward Toutatis, an asteroid that swings through the inner solar system on a roughly four-year orbit and passes close to Earth's own path. Toutatis is a known tumbler, spinning around more than one axis at once, which makes it hard to study from a distance. A probe designed for lunar mapping had ended up being China's first deep-space asteroid scout, and nobody had put that on the original mission plan.
Chinese space officials announced that the encounter took place on Dec. 13, 2012, and the probe's camera returned a series of images as it passed. They showed Toutatis as an elongated, lumpy body more than four kilometers long, with a pronounced neck-like narrowing and a surface strewn with boulders and craters. The pictures let scientists compare long-held radar-based models of the asteroid with direct views, and they offered clues that it may be made of two joined pieces. Chang'e 2 then flew on, becoming a spacecraft with no destination left on its itinerary, still sending signals from deeper and deeper in space. The probe built to study the neighbor next door ended up with a snapshot of a stranger passing through.
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