Scientists at NASA's Near Earth Object Program updated the odds of asteroid 2007 WD5 impacting on Mars from 1 in 350 to 1 in 75. If the asteroid hits, the impact will likely be in the area that Mars rover Opportunity is in. The robot is believed to be outside the immediate impact zone so it should be able to safely observe the explosion that would result from the asteroid hitting at 13.5 km/s, releasing the equivalent of 3 MT of TNT. The resulting crater could be a half a mile wide. Impacts of this size are estimated to occur only once every one thousand years. The impact would occur near the end of January 2008. Data from additional observatories is being gathered now and scientists hope to calculate an updated trajectory that will tell them whether or not the asteroid will hit Mars. For more details see the NEO report or the JPL orbital diagram for 2007 WD5 (requires Java).