July 26, 2014
NASA Mars Spacecraft Prepare For Close Comet Flyby
Dwayne Brown, NASA Jet Propulsion Laboratory
The comet's nucleus will miss Mars by about 82,000 miles (132,000 kilometers), shedding material hurtling at about 35 miles (56 kilometers) per second, relative to Mars and Mars-orbiting spacecraft. At that velocity, even the smallest particle -- estimated to be about one-fiftieth of an inch (half a millimeter) across -- could cause significant damage to a spacecraft.
NASA currently operates two Mars orbiters, with a third on its way and expected to arrive in Martian orbit just a month before the comet flyby. Teams operating the orbiters plan to have all spacecraft positioned on the opposite side of the Red Planet when the comet is most likely to pass by.
"Three expert teams have modeled this comet for NASA and provided forecasts for its flyby of Mars," explained Rich Zurek, chief scientist for the Mars Exploration Program at NASA's Jet Propulsion Laboratory in Pasadena, California. "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."
During the day's events, the smallest distance between Siding Spring's nucleus and Mars will be less than one-tenth the distance of any known previous Earthly comet flyby. The period of greatest risk to orbiting spacecraft will start about 90 minutes later and last about 20 minutes, when Mars will come closest to the center of the widening dust trail from the nucleus.
NASA's Mars Reconnaissance Orbiter (MRO) made one orbit-adjustment maneuver on July 2 as part of the process of repositioning the spacecraft for the Oct. 19 event. An additional maneuver is planned for Aug. 27. The team operating NASA's Mars Odyssey orbiter is planning a similar maneuver on Aug. 5 to put that spacecraft on track to be in the right place at the right time, as well.
For more information about the Mars flyby of comet Siding Spring, visit: http://mars.nasa.gov/comets/sidingspring
For more information about NASA's Mars Exploration Program, visit: http://www.nasa.gov/mars
Image 2 (below): This graphic depicts the orbit of comet C/2013 A1 Siding Spring as it swings around the sun in 2014. On Oct. 19, the comet will have a very close pass at Mars. Its nucleus will miss Mars by about 82,000 miles (132,000 kilometers). The comet's trail of dust particles shed by the nucleus might be wide enough to reach Mars or might also miss it. [ More information about this comet ]