Comet Siding Spring will sweep past Mars in October, then follow other recent comets around the sun and back into deep space.
On Oct. 19, the comet is expected to pass within 82,000 miles of Mars, a stone’s throw in astronomical terms — one-third the distance between Earth and the moon, and closer to Mars than any comet has come to Earth in recorded history.
The dust, water vapor and other gases spewed by a comet can spread for tens of thousands of miles, so the upper reaches of the Martian atmosphere are expected to be showered by Siding Spring (pictured below). Shock waves may rock the atmosphere.
The dust particles may be tiny, but at 125,000 mph (35 miles per second) they would pierce the skin of any satellite orbiting the planet. “Essentially, they would be like bullets out there,” said Richard Zurek, chief scientist of the Mars program at NASA’s Jet Propulsion Laboratory.
He added that although the danger to satellites and rovers appears to be limited, there’s a small possibility the comet could break up near Mars — as Comet ISON did near the sun last year. As a precaution, five satellites’ orbits have been tweaked so they will be on the far side of the planet when the greatest threat from dust arrives.