Earthsky.org - 10/1/13, Bruce McClure
On Tuesday (October 1, 2013), this year’s most anticipated comet – Comet ISON – will sweep closely past the Red Planet Mars. It’ll be on its way to a Thanksgiving Day (November 28) encounter with the sun, and hopefully to a good showing in Earth’s night sky. Right now, amateur astronomers with telescopes and photographic equipment are the main ones capturing images of Comet ISON. And they are sure to be trying already to captured Mars and the comet in the same photo in the predawn sky. But NASA and ESA are also readying a flotilla of spacecraft in Mars orbit or on Mars’ surface, which will attempt to record the comet’s passage near Earth’s neighboring planet.
And we do mean near. On October 1, Comet ISON will pass within 0.07 AU from Mars. That’s about six times closer than the comet will ever come to Earth.