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).
Image Credit:
NASA/JPL-Caltech
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 (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."
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:
For more information about NASA's Mars Exploration Program, visit:
NASA
Guillermo Gonzalo Sánchez Achutegui
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