A few BABloggees have emailed me about a possible -- stress the word "possible" -- asteroid impact on Mars in January.
The odds are low, about 1 in 75, but they're high enough to be interesting. The impactor is a small rock named 2007 WD5, and it's in the 100 meter diameter range, enough to make an explosion with a yield of several megatons. However, the orbit is not well-enough determined to know if it will hit. Follow-up observations will nail down the asteroid's path better. Most likely we'll find out it will miss, but it would be totally cool if it hits.
I don't have time right now to look into this much, but if I can tomorrow I'll try to make some phone calls and follow up. My gut feeling is that an explosion of that size wouldn't be visible from Earth even with big 'scopes, but I'll need to do some math to figure it out. Certainly any of the orbiters currently circling the planet would see something.
But again, that's only if it hits. Time will tell.