A recently-discovered comet has a chance - albeit a small one - of hitting Mars in October next year.
Comet 2013 A1, or Siding Spring, will certainly get pretty close. The current best estimate from NASA's Near-Earth Object Program Office is that it'll miss Mars's surface by around 31,000 miles - that's about two-and-a-half times further away than Mars's outermost moon, Deimos.
The prediction's based on data gathered between October 2012 and March 1 this year - and will of course be refined as more data comes in.
"At present, Mars lies within the range of possible paths for the comet and the possibility of an impact cannot be excluded," says NASA - although it currently rates the chance at just one in 600.
If the comet doesn't hit, it won't be visible from Earth with the naked eye, although binoculars or small telescopes should do the trick. If it does, of course, it should be very visible indeed. Siding Spring's nucleus is estimated at anything from five to 30 miles across - and if it hits, the impact crater would be ten times wider.
"This kind of event can leave a crater 500km across and 2km deep," says Leonid Elenin, of Russia's Keldysh Institute of Applied Mathematics, who's been tracking the path of the comet.
"Such an event would overshadow even the famous bombardment of Jupiter by the disintegrated comet Shoemaker–Levy 9 in July 1994, which by some estimates was originally 15km in diameter."
Comet 2013 A1 was discovered by Rob McNaught on January 3 this year, at Siding Spring Observatory in Australia. Scientists at the Near-Earth Object Program Office believe it originated in our solar system's distant Oort cloud - the source of ISON, expected to be the brightest comet seen in 100 years when it approaches Earth later this year.
Earlier this week, another Oort cloud comet, called Pan-STARRS, passed within 100 million miles of Earth and is now heading towards the sun.