On Oct. 19, Comet C/2013 A1 Siding Spring will make an extremely close approach to the red planet; so close that astronomers at first had concerns (and some excitement) that it might actually hit Mars. Alas, mild disappointment to one side, Comet Siding Spring will narrowly miss the planet by a mere 82,000 miles (132,000 kilometers).
As solar system scales go, this is an interplanetary rimshot that will alter the comet’s orbit and provide incredible science opportunities for any assets orbiting Mars and roving its surface. But there are concerns: Could the high-speed cometary ejecta damage NASA’s Mars Reconnaissance Orbiter (MRO), Mars Odyssey, Mars Atmosphere and Volatile Evolution (MAVEN; which is due to arrive in Mars orbit on Sept. 21) and Europe’s Mars Express satellites?
Although the dust and icy debris will be small, any object traveling at 35 miles (56 kilometers) per second relative to the orbiters could cause significant damage and possible mission loss. So, in a news update issued by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif., today (July 25), mission managers have announced a strategy that will keep the satellites out of harms way — they’re going to use Mars as a shield.
“Three expert teams have modeled this comet for NASA and provided forecasts for its flyby of Mars,” said Rich Zurek, chief scientist for the Mars Exploration Program at JPL. “The hazard is not an impact of the comet nucleus, but the trail of debris coming from it. Using constraints provided by Earth-based observations, the modeling results indicate that the hazard is not as great as first anticipated. Mars will be right at the edge of the debris cloud, so it might encounter some of the particles — or it might not.”
So just to be safe, the MRO, Odyssey and MAVEN will be located on the far side of Mars relative to Siding Spring as it makes close approach.
The period of most risk to satellites will commence 90 minutes after closest approach and will last for approximately 20 minutes. All missions have planned orbital adjustments that will put them out of this “danger zone” while optimizing the historic opportunity to do science.
All three NASA satellites will use their individual talents to observe the various effects of the cometary flyby. MAVEN, for example, will measure the gases the comet is pumping out into space and measure the impact of cometary material on the Martian upper atmosphere; Odyssey will characterize the comet’s nucleus, studying its structure and thermal properties; and the MRO will image the nucleus in great detail. This campaign will provide scientists with a very privileged and detailed view of the comet, giving us an intimate look at material that has been, literally, frozen in time since the early formation of our solar system.
Though NASA’s orbiters will likely do most of the heavy lifting insofar as observations are concerned, NASA’s Curiosity and Opportunity rovers will be able to participate, making observations of the comet as it approaches Mars and spot possible meteors as comet material slams into the atmosphere.
This promises to be a very exciting time for Mars and the robotic armada we have in orbit, though I still would have been thrilled to see Mars take a direct hit (sorry rovers).