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Emily LakdawallaJanuary 8, 2008

Mars impact probability now 1 in 40

...or, there's a 39 in 40 chance that nothing too exciting will happen on January 30, 2008, when near-Earth asteroid 2007 WD5 will make its closest approach to Mars. According to the latest news from the Near Earth Object Program, a few more observations of the position of WD5 have been performed by the Calar Alto Observatory in Spain. These observations have not changed the best estimate of the closest approach distance of WD5 to Mars -- that remains constant at about 30,000 kilometers -- but the uncertainty in our prediction of WD5's position at close approach has decreased by a factor of three. Since it's now more certain that the asteroid will pass 30,000 kilometers from Mars (as opposed to any other distance), the impact probability has been reduced.

(Here are my past posts on WD5: December 21, with chances at 1 in 75; December 27, at 1 in 25; and January 2, at 1 in 28.)

A question I've received a few times is whether any of the Mars orbiters can take photos of the asteroid as it passes by. The uncertainty in its position would make this a little difficult, and since it's approaching from the direction of the Sun, it's not the best direction to point your camera. What would be great is if there were a nice wide-angle camera in space with enough sensitivity to cover a broad area of WD5's possible paths immediately after the flyby, when it will be well-lit by the Sun. The uncertainty in its present position "blows up" after the Mars flyby because how close it gets to Mars has a strong effect on how much its orbit will be bent by Mars' gravity; having a photo taken from Mars right after the flyby will be quite valuable in pinning down its future orbit (beside the fact that it would be a pretty cool feat for a Mars orbiter to pull off). I don't have any conclusive answers yet, whether any of the orbiters definitely will or definitely won't take any photos. I'll let you know if and when I get any information.

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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Emily Lakdwalla
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