Once in a million years: Super-sized comet to buzz past Mars this weekend

The heavens are hosting an event this weekend that occurs once in a million years or so. A comet as hefty as a small mountain will pass mind-bogglingly close to Mars on Sunday, approaching within 147,000 km at a speed of 202,000 km/h. NASA’s five robotic explorers at Mars - three orbiters and two rovers - are being repurposed to witness a comet named Siding Spring make its first known visit to the inner solar system. So are a European and an Indian spacecraft circling the red planet. The orbiting craft will attempt to observe the incoming iceball, then hide behind Mars for protection from potentially dangerous dusty debris in the comet tail. Shielded by the Martian atmosphere, the Opportunity and Curiosity rovers may well have the best seats in the house, although a dust storm on Mars could obscure the view.

We certainly have fingers crossed for the first images of a comet from the surface of another world.

Jim Green, head of NASA’s planetary science division

Spacecraft farther afield, including the Hubble Space Telescope, already are keeping a sharp lookout, as are ground observatories and research balloons. “We’re getting ready for a spectacular set of observations,” said Jim Green, head of NASA’s planetary science division. Named for the Australian observatory used to detect it in January 2013, Siding Spring will approach Mars from beneath and zoom right in front Sunday afternoon, Eastern Time. On Earth, the best viewing, via binoculars or telescope, will be from the Southern Hemisphere - South Africa and Australia will be in prime position. In the Northern Hemisphere, it will be difficult to see Siding Spring slide by Mars.

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