A Close Encounter of the Martian Kind

A comet on express delivery from the Oort cloud of rock and ice that surrounds our Solar System makes a close approach of Mars this weekend. Martian satellites are already hunkering down against the potential onslaught of debris. Comet C/2013 A1, aka Siding Spring, shown as the reddish central object in four snapshots by NASA's NEOWISE mission in July 2014. Credit: NASA/JPL On Sunday October 19th, comet C/2013 A1, familiarly known as comet Siding Spring, will fly within 87,000 miles of the M...