Astronomers have realised that a comet discovered last month appears to be on course for a close flyby of Mars next year -- and uncertainty in its projected path means that it could hit the Red Planet.

C/2013 A1, discovered by Robert McNaught at Siding Spring Observatory in Australia, was spotted on 3 January out between the orbits of Jupiter and Saturn. After digging into data from other observatories, astronomers were able to reconstruct its orbit going back 74 days. Projecting that forward, it became clear that it would fly pretty close to Mars sometime on 19 October 2014 -- which means there is a slight chance of it impacting the planet, according to astronomer Ian Musgrave. Now, further observations have increased that chance (though it's still not very likely, before anyone starts panicking about the fate of the Curiosity rover).

The current estimate is that C/2013 A1 will come within 0.00073AU (109,000km) of Mars, but uncertainty in measurements of its path thus far mean that it could end up as far away as 0.008AU (1,197,000km) or plowing straight into the planet's surface. It has a retrograde orbit around the Sun, giving it a high velocity relative to Mars of 56km/s -- that, combined with its relatively large size (estimated as around 50km) could leave a crater on Mars of 500km across and 2km deep, according to astronomer Leonid Elenin.


Even if it misses Mars, its projected path will pass by further away than asteroid 2012 DA14 flew past the Earth on 15 February, at 27,700km.

0.00073AU is just under a third of the distance between the Earth and the Moon, though, and the comet will appear clearly in the sky somewhere between the brightness of Venus and Jupiter. From Earth, you'll need a telescope that can see something of the same order of brightness magnitude as Neptune. Rovers on Mars' surface may be able to capture images of it, as might the Mars Reconnaissance Orbiter if its cameras are able to be turned around.

Over the next few months further measurements should determine whether Mars is about to get hammered by the largest impact event in recorded history, or if it's just getting a close escape.

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