[meteorite-list] NASA Mars Spacecraft Prepare for Close Comet Flyby (C/2013 A1 Siding Spring)

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2014-244

NASA Mars Spacecraft Prepare for Close Comet Flyby
Jet Propulsion Laboratory
July 25, 2014

NASA is taking steps to protect its Mars orbiters, while preserving opportunities 
to gather valuable scientific data, as Comet C/2013 A1 Siding Spring heads 
toward a close flyby of Mars on Oct. 19.

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.

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft is on 
its way to the Red Planet and will enter orbit on Sept. 21. The MAVEN 
team is planning to conduct a precautionary maneuver on Oct. 9, prior 
to the start of the mission's main science phase in early November.

In the days before and after the comet's flyby, NASA will study the comet 
by taking advantage of how close it comes to Mars. 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.

MAVEN will study gases coming off the comet's nucleus into its coma as 
it is warmed by the sun. MAVEN also 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.

Mars' atmosphere, though much thinner than Earth's, is thick enough that 
NASA does not anticipate any hazard to the Opportunity and Curiosity rovers 
on the planet's surface, even if dust particles from the comet hit the 
atmosphere and form into meteors. Rover cameras may be used to observe 
the comet before the flyby, and to monitor the atmosphere for meteors 
while the comet's dust trail is closest to the planet.

Observations from Earth-based and space telescopes provided data used 
for modeling to make predictions about Siding Spring's Mars flyby, which 
were in turn used for planning protective maneuvers. The three modeling 
teams were headed by researchers at the University of Maryland in College 
Park, the Planetary Science Institute in Tucson, Arizona, and JPL.

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

Dwayne Brown
NASA Headquarters, Washington
202-358-1726
dwayne.c.brown at nasa.gov

Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.webster at jpl.nasa.gov

244-2014