By Darren Orf
Comet Siding Spring sounds like such a tranquil name for a planet killer. Afters traveling millions of years at the leisurely pace of about 33 miles per second, the comet will fly by Mars at around 2:25pm EDT or so, passing only 138,000 kilometers from the red planet. This is a little bit more than one-third the distance of the Earth from the Moon.
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