Here’s something to think about whilst waiting to see if Comet ISON will fizzle, or sizzle. The latest Science at Nasa video looks at the trajectory, and consequences for Mars missions, of Comet 2013 A1 (Siding Spring).
Discovered as recently as 3 January this year, this Oort cloud object will pass “extraordinarily close” to the planet Mars on 19 October 2014 – an actual collision, although unlikely, has not been ruled out yet [1:2000]. It’s estimated that an impact of the ~1-3 km-wide Comet 2013 A1, travelling at around 56 km/s (125,000 mph), would unleash 80 million times more energy than the meteorite which exploded above the Chelyabinsk region of Russia in February. [Image credit: NASA/JPL-Caltech]
Even so, a near miss would be spectacular, and somewhat unsettling, for any inhabitants of the Red Planet. Earth is a similar sized target in our solar system. So, let’s be careful out there…
Here’s the ScienceAtNasa video – “Collision Course? A Comet Heads for Mars”
And from the video transcript
A direct impact remains unlikely. Paul Chodas of NASA’s Near-Earth Object Program stresses that a 1 in 2000 chance of impact means there’s a 1999 in 2000 chance of no impact. “A near-miss is far more likely,” he points out.
Even a near miss is a potentially big event. The latest orbit solutions put the comet somewhere within 300,000 km of the red planet at closest approach. That means Mars could find itself inside the comet’s gassy, dusty atmosphere or “coma.” Visually, the comet would reach 0th magnitude, that is, a few times brighter than a 1st magnitude star, as seen from the Red Planet.
Astronomers around the world are monitoring 2013 A1. Every day, new data arrive to refine the comet’s orbit. As the error bars shrink, Yeomans expects a direct hit to be ruled out. “The odds favor a flyby, not a collision,” he says.
Either way, this is going to be good. Stay tuned for updates as the comet approaches.