October Rendezvous of Comet with Mars Has NASA Assets on Alert

August 5, 2014 – October 19th is the date when Comet Siding Spring makes its Mars flyby. The distance will be 132,000 kilometers (82,000 miles) from the planet’s surface. The tail of the comet will potentially threaten the NASA’s two orbiters as well as one operated by the European Space Agency. And NASA has a third orbiter, MAVEN, expected to arrive at Mars in September, just a month before Siding Spring passes.

What could a comet passing so far from the planet possibly do to Martian orbiters? Certainly the main body of the comet won’t come near them. But the debris sloughing off the comet surface which creates its tail can endanger the Martian spacecraft. The shed materials will be traveling at speeds of 56 kilometers (35 miles) per second. So even fine particles at that speed would pack considerable force.

Remember the scene in Gravity? That was a mixture of big and small debris traveling at 8 kilometers (5 miles) per second striking the shuttle and International Space Station which itself was traveling at a similar speed but in an opposite direction. Those impacts and the damage done were very much reality say the scientists and engineers. NASA computes the time of greatest danger will occur about 90 minutes after the comet’s closest approach and will last for a period of 20 minutes.

So what to do? Well NASA is already adjusting the orbits of its spacecraft to position them on the opposite side of Mars during the flyby. MAVEN, the latest to arrive, will perform a safety maneuver ten days before the close encounter. All the orbiters will focus on the comet’s passing, studying it and its tail. While on the ground, the rovers Opportunity and Curiosity will try and capture images of the flyby and monitor any effects to the atmosphere from the passing of the tail.

Siding Spring, seen in a recent image taken by the Hubble Space Telescope, was discovered in January 2013. Its orbit around the Sun takes one million years. And its orbital plane is almost 90 degrees from those of the planets within the Solar System. That makes the rendezvous with Mars an unusual event and one unlikely to happen again for many millions of years. At its closest, six days after rendezvous with Mars, Siding Spring will be 209 million kilometers (130 million miles) from the Sun. At no point will we be able to see it from here on Earth without a telescope. But because of our eyes on and around Mars we will study it in great detail.