A possible collision - Comet C/2013 A1 (Siding Spring) heads for Mars

Comet 2013 A1 (Siding Spring) was discovered on Jan. 3, 2013 by Rob McNaught, at Siding Spring Observatory in Australia.

"There is a small but non-negligible chance that Comet 2013 A1 will strike Mars next year in October of 2014," says Don Yeomans of NASA's Near-Earth Object Program at JPL. "Current solutions put the odds of impact at 1 in 2000."
The comet's nucleus is about 1 to 3 km in diameter, and it will pass Mars at a relative velocity of approximately 56 km/s (125,000 mph). "It if does hit Mars, it would deliver as much energy as 35 million megatons of TNT," estimates Yeomans.
"For comparison, the asteroid strike that ended the dinosaurs on Earth 65 million years ago was about three times as powerful, 100 million megatons. Another point of comparison is the meteor that exploded over Chelyabinsk, Russia, in February of 2013, damaging buildings and knocking people down. The Mars comet is packing 80 million times more energy than that relatively puny asteroid."
http://science.nasa.gov/science-news/science-at-nasa/2013/26mar_marscomet

Orbit diagram:
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013%20A1;orb=1

More information at:
http://en.wikipedia.org/wiki/C/2013_A1
http://www.minorplanetcenter.net/mpec/K13/K13A14.html

Asteroid image
http://photojournal.jpl.nasa.gov/jpeg/PIA15679.jpg
Mars image
http://photojournal.jpl.nasa.gov/jpeg/PIA02004.jpg

Credit: NASA/JPL-Caltech