Asteroid 2007 WD5

That's the designation of the rock that may slam into Mars at 3,000 miles an hour this January 30. As of observations taken through January 2, astronomers have reduced the chance of an impact to 1-in-28 from 1-in-25, and further refinements could rule out a collision, at least for this time around.

Astronomers, however, are hoping those further refinements lead to an impact. As noted earlier in this blog, the flotilla of probes now studying Mars would allow extraordinary coverage of such an event. Asteroid 2007 WD5 is roughly the size of the body that produced Meteor Crater in Arizona. If it hits Mars, it could produce a crater a half-mile across and eject material high into Mars' atmosphere. By plowing well below the planet's surface, scientists also hope it would aid the search for life on Mars by revealing layers of Mars that we couldn't otherwise access for decades.