Chinese probe to make daring flyby of asteroid Toutatis

Illustration of the Chang’e 2 probe flyby of Toutatis next week. Chang’e 2 originally was used to map the moon and then repurposed for the asteroid flyby. Chang’e is named after an ancient Chinese moon goddess. Credit: Andrzej Mirecki

If all goes according to plan, one week from today on Dec. 13, the Chinese Chang’e 2 probe will snap closeup photos of near-Earth asteroid 4179 Toutatis (too-TAT-us) from only 200 miles away. Toutatis will be making its own close approach the day before, zooming by Earth at a distance of 4.3 million miles.

Traveling at about 7 miles a second, the ship will have only the briefest of opportunities to shoot photos as it rapidly approaches and then departs the asteroid. High-resolution cameras should resolve features tens of meters (~65 to 150 feet) across, giving us our most detailed optical views ever of this 3-mile-long space rock shaped like a bowling pin.


Click to watch Toutatis’ topsy-turvy rotation. Images from NASA radar

Our best “photos” to date are a series of remarkable images made by beaming radio waves at the asteroid during previous close approaches and analyzing the reflected echoes. Those images reveal an irregular body with two pronounced lobes that may once have been two separate asteroids. Possibly an older asteroid was broken apart during an earlier collision, pieces later reassembling to form present-day Toutatis.

Unlike the planets, which spin on one axis in one direction, Toutatis spins about two axes, wobbling about like a poorly-thrown football pass. If you stood on the asteroid’s surface, the sun would rise at random times along random points on the horizon. Makes me dizzy just thinking about it.

Toutatis is a rocky asteroid about 3 miles long. These 1992 radar images from NASA’s Goldstone radar dish reveal an undulating surface, craters and two large lobes that may have once been separate asteroids. Courtesy Steve Ostro, JPL

Toutatis orbits the sun every 4 years in nearly the same plane as Earth’s orbit and is a frequent visitor to the inner planets. When closest to the sun, it’s located just inside Earth’s orbit; when farthest it travels among its fellow asteroids in the outer fringes of main asteroid belt between Mars and Jupiter.

Every four years Toutatis passes through our neighborhood, which is why it’s designated as a PHA or potentially hazardous asteroid. PHAs are asteroids that come within 5 million miles of Earth and are large enough to survive atmospheric entry and cause major destruction.

Radar picture of Toutatis taken by the Goldstone antenna on Dec. 3, 2012 as part of the 2012 campaign (see below). Credit: NASA/JPL

Toutatis is the largest asteroid we know of that approaches Earth most closely. That doesn’t mean it’s going to hit us, only that a collision is remotely possible. Calculations based on many observations since its discovery in 1989 have ruled out any chance of a hit for at least the next six centuries. Rest easy.

Toutatis came as close as 967,000 miles or just shy of 4 lunar distances on September 29, 2004. This time around, it will draw to within 4.3 million miles, more than four times farther away but still be bright enough at 10.5 magnitude to be seen in a small telescope. I’ll provide directions on how to find it early next week.The next time the asteroid makes a close close approach to Earth will be in November 2069 (7.7 lunar distances).

Toutatis is shown on Dec. 12 when nearest Earth. Its orbit (in blue) takes the asteroid to just within Earth’s orbit to well beyond Mars. Credit: JPL

The 230-foot radar dish at Goldstone has already swung in Toutatis’ direction and made early images of the flyby in a special 2012 campaign to better model its rotation, shape and surface features. Combined with the pictures from Chang’e 2, we’ll soon have a clearer portrait of this unique object.

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