Mars could be hit by a comet with the power of a billion megatons in 2014, astronomers have said.
The comet C/2013 A1 was discovered earlier this year by Robert McNaught at Siding Spring Observatory in Australia.
While discovered between Jupiter and Saturn, it was projected that it would make a close pass by the planet next year.
But according to a new recalculation, the comet may hit our nearest planetary neighbour after all.
Researcher Leonid Elenin said there is now a slightly higher chance of the impact occurring - even if the actual odds are still quite low.
In fact the path of the comet is so uncertain it may still end up more than a million kilometres from its surface.
The movements of comets are difficult to predict, because as they approach the sun their structure is affected by increases in temperature which can throw it off course.
But if it were to hit the planet, the result could be major disruption. It has a speed relative to mars of about 56 kilometres/second, and could leave a crater about 500km across and 2km deep.
Either way, it appears that the rovers currently on Mars - including Curiosity - as well as the Mars Reconnaissance Orbiter could capture a view of the ball of ice and dust as it passes by - or into - the planet.