Martians can finally breathe easier. No, we haven’t terraformed the planet yet, but the chances of Comet C/2013 A1 (Siding Spring) hitting the Mars have just dropped from 1 in 8,000 to about 1 in 20,000 after new observations further refined the comet’s orbit. Interestingly, the closest approach has tightened a bit to 68,000 miles. No matter what the view from the planet’s surface should be spectacular.
If only you and I could be there. Closest approach happens at 1:51 p.m. Central Time October 19, 2014 on Mars’ sunward side. Since a comet’s coma (temporary atmosphere formed from ice and dust vaporized by the sun) can measure many thousands of miles across, there’s a slight possibility it could graze Mars’ atmosphere. Dust might then flare as meteors when heated by friction with the air.
One of the largest comas belonged to Comet Holmes. Astronomers don’t know for sure whether Holmes experienced an explosive event from within or was struck by a meteoroid, but it suddenly brightened by half a million times in October 2007. Within a week, the comet had released so much gas and dust, its coma ballooned to 869,900 miles or about 5,000 miles larger than the sun!
We’re not saying C/2013 A1 will even approach those dimensions, but it’s possible that dust from its coma might eventually drift toward Mars to create a meteor shower. My wish would be for NASA and the European Space Agency to point the rover and orbiting satellite cameras at the comet sometime during the flyby. Comet usually start to develop tails about the time they cross the orbit of Mars. The thought of seeing one arcing above a Mars landscape gives me the chills.