We all know that Earth is not the only planet at risk of collisions with asteroids and comets. However, for the first time NASA is taking measures to protect its Mars Reconnaissance Orbiter (MRO) and Mars Odyssey orbiter, currently circulating above the planet, as well as the recently launched Mars Atmosphere and Volatile Evolution (MAVEN), due to arrive there in September, by positioning them on the opposite side of the planet as Comet C/2013 A1 Siding Spring heads toward a close flyby on Oct. 19. At the same time they will use the spacecraft to gather valuable data about the comet itself, noting that this is the first time C/2013A Sliding Spring has ever entered the inner solar system, thus offering scientists a brand insight into our solar system's earliest days.
The MRO will be used to study gases in the comet’s coma, as well as garner detailed views of the comet’s nucleus and potentially reveal its rotation rate and surface features, while Odyssey will examine thermal and spectral properties of the comet's coma and tail. It will also monitor Mars’ atmosphere for possible temperature increases and cloud formation, as well as changes in electron density at high altitudes. In the meantime MAVEN will study gases coming off the comet's nucleus into its coma as it is warmed by the sun, as well as seek out any effects the comet flyby may have on the planet’s upper atmosphere and observe the comet as it travels through the solar wind.
Although the nucleus of the comet is expected to miss Mars by approximately 82,000 miles, there is extreme danger that material shed by its tail at about 35 miles per second could do great damage to the orbiting spacecraft.
“At that velocity, even the smallest particle (estimated to be about 1/50th of an inch across) could cause significant damage to an orbiter, " commented Rich Zurek, chief scientist for the Mars Exploration Program at NASA's Jet Propulsion Laboratory (JPL) 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,” he continued."
The smallest distance between Siding Spring's nucleus and Mars on October 19th is expected to be less than 1/10th the distance of any previously known comet flyby past Earth, with the greatest risk to the NASA orbiters suspected of lasting around 20 minutes beginning around 90 minutes after Mars will come closest to the center of the widening dust trail from the nucleus.
For more information about the Mars flyby of comet Siding Spring, visit http://mars.nasa.gov/comets/sidingspring/