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Mars spacecraft prepare for comet encounter

Jenny Winder, News Writer
Jul 26, 2014, 16:20 UTC

Sen—As Comet C/2013 A1 Siding Spring heads toward a close flyby of Mars on 19 October, NASA and ESA are preparing to protect their space probes in orbit about the Red Planet.

NASA currently operates two Mars orbiters, with a third expected to arrive in Martian orbit just a month before the comet flyby. ESA operates one, Mars Express.

The comet's nucleus will miss Mars by about 82,000 miles (132,000 kilometres), shedding dust at about 35 miles (56 kilometres) per second, relative to Mars and Mars-orbiting spacecraft. At that velocity, even the smallest particle could cause significant damage to a spacecraft.

Teams operating the orbiters plan to have all spacecraft positioned on the far side of Mars when the comet is most likely to pass by, in order to shield them, while allowing them to continue their work.

"The hazard is not an impact of the comet nucleus, but the trail of debris coming from it,” Rich Zurek, chief scientist for the Mars Exploration Program at NASA's Jet Propulsion Laboratory said. “Mars will be right at the edge of the debris cloud, so it might encounter some of the particles, or it might not."

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This graphic depicts the orbit of comet Siding Spring as it swings around the sun in 2014. Image credit: NASA/JPL-Caltech

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 centre of the widening dust trail from the nucleus.

NASA's Mars Reconnaissance Orbiter (MRO) made one orbit-adjustment manoeuvre on July 2. An additional correction is planned for August 27.  NASA's Mars Odyssey orbiter is planning a similar manoeuvre on August 5.

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NASA's Mars Odyssey spacecraft passes above a portion of the planet that is rotating into the sunlight in this artist's concept illustration. Image credit: NASA/JPL

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft will enter orbit on September 21. The MAVEN team is planning to conduct a precautionary manoeuvre on October 9.

Researchers plan to use several instruments on the Mars orbiters to study the nucleus, the coma surrounding the nucleus, and the tail of Siding Spring, as well as the possible effects on the Martian atmosphere. This particular comet has never before entered the inner solar system, so it will provide a fresh source of clues to our Solar System's earliest days.

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This artist's concept shows the MAVEN spacecraft orbiting Mars. Image credit: NASA/Goddard Space Flight 

MAVEN will study gases coming off the comet's nucleus into its coma as it is warmed by the Sun, and will look for effects the comet flyby may have on the planet's upper atmosphere and observe the comet as it travels through the solar wind.

Odyssey will study thermal and spectral properties of the comet's coma and tail. MRO will monitor Mars' atmosphere for possible temperature increases and cloud formation, as well as changes in electron density at high altitudes. The MRO team also plans to study gases in the comet's coma. Along with other MRO observations, the team anticipates this event will yield detailed views of the comet's nucleus and potentially reveal its rotation rate and surface features.

NASA does not anticipate any hazard to the Opportunity and Curiosity rovers on the planet's surface. Rover cameras may be used to observe the comet before the flyby, and to monitor the atmosphere for meteors.

ESA's Mars Express team have earlier written in their blog of their plans to reorient the spacecraft to shield it from comet dust.