When Comet Siding Spring came within 140,000 kilometers of Mars last month, it dumped several tons of magnesium and iron into the planet’s atmosphere, researchers reported at a November 7 press conference. “There was a spectacular meteor shower on Mars that night,” said University of Colorado, Boulder planetary scientist Nick Schneider. Martian stargazers would have witnessed several thousand meteors per hour at the height of the storm.
All the Mars orbiters used the planet as a shield during the comet’s closest approach — and it’s a good thing they did. While earlier observations suggested that the spacecraft would have been safe where they were during the comet flyby, subsequent measurements of the Martian atmosphere indicate that the probes could have been damaged in the surprising onslaught of dust and ice grains.