In case you just can't get enough impact news, it looks like Mars may actually get hit by a comet in 2014! As it stands right now, the chance of a
direct impact are small, but it's likely Mars will get pelted by the debris associated with the comet.
I
know. This is pretty amazing. Still, let me preface this with a caveat: Trying to get precise predictions of comet orbits can be difficult, and for this one we?re talking about a prediction for 20 months from now! Things may very well change, but here's what we know so far.
Comet What May
The comet is called
C/2013 A1 (Siding Spring), discovered on Jan. 3, 2013 by the Australian veteran comet hunter Robert McNaught.
As soon as it was announced, astronomers at the Catalina Sky Survey looked at their own data and found it in observations from Dec. 8, 2012, which helped nail down the orbit (I explain how that works
in a previous article about asteroid near-misses). Extrapolating its orbit, they found it will make a very near pass of Mars around Oct. 19, 2014,
missing the planet by the nominal distance of about 100,000 kilometers (60,000 miles).
Observations taken at the ISON-NM observatory in New Mexico just this week have tightened up the orbit a bit more, allowing for better predictions. Given this new data, the comet may actually pass closer to Mars; another veteran comet hunter, Leonid Elenin, predicts it may get as close as 37,000 km (23,000 miles) of the surface of Mars!
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If the nucleus does hit the planet, well.
That will be amazing, and by 'amazing' I mean 'apocalyptic'. The nucleus size is not well known, but may be as small as 15 kilometers (9 miles) or as big as 50 km (30 miles). Even using the small number means Mars would be slammed by an unimaginable impact. The comet is orbiting the Sun backward (more on that in a second), so it will be moving at a speed of about 55 kilometers per second (120,000 miles per hour!) upon impact. That means the comet has a huge amount of kinetic energy, the energy of motion. That energy will be released at impact as an explosion. A big one.
A
really big one.
Doing a rough calculation, I get an explosive yield of roughly one billion megatons: That?s a million
billion tons of TNT exploding. Or, if you prefer,
an explosion about 25 million times larger than the largest nuclear weapon ever tested on Earth.
So, yeah.
The crater left behind would be
hundreds of kilometers across, and be the largest impact Mars has seen in a long, long time. Mind you, once again, there is no guarantee this comet will hit Mars. The most likely scenario is a close pass, which is still incredible.
In one sense, an impact would be pretty bad for us on Earth: we'd almost certainly lose all our robotic probes in orbit and on the surface. An impact that size would blast debris all over the planet, and the rovers could be damaged or destroyed. Even something in orbit wouldn't be safe; the ejecta would come screaming off the planet and sent every which way in orbit around Mars. It would be like orbiting into a shotgun blast.
Even a near miss may prove dangerous for the probes, since as I pointed out there will be debris anyway. If we're lucky, they'll make it through this just fine, and we may very well get some spectacular images from them (as usual,
Emily Lakdawalla at The Planetary Society Blog has that story). We'll just have to wait and see what happens over the next few months.
.../cont/...
