[meteorite-list] Mars Spacecraft Reveal Comet Flyby Effects on Martian Atmosphere

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 7 Nov 2014 22:31:58 -0800 (PST)
Message-ID: <201411080631.sA86VwUq029303_at_zagami.jpl.nasa.gov>

November 7, 2014
     
Mars Spacecraft Reveal Comet Flyby Effects on Martian Atmosphere

Two NASA and one European spacecraft that obtained the first up-close
observations of a comet flyby of Mars on Oct. 19, have gathered new
information about the basic properties of the comet's nucleus and directly
detected the effects on the Martian atmosphere.

Data from observations carried out by NASA's Mars Atmosphere and Volatile
Evolution (MAVEN) mission, NASA's Mars Reconnaissance Orbiter (MRO), and a
radar instrument on the European Space Agency's (ESA's) Mars Express
spacecraft have revealed that debris from the comet added a temporary and
very strong layer of ions to the ionosphere, the electrically charged layer
high above Mars. In these observations, scientists were able to make a direct
connection from the input of debris from a specific meteor shower to the
formation of this kind of transient layer in response; that is a first on any
planet, including Earth.

Comet C/2013 A1 Siding Spring traveled from the most distant region of our
solar system, called the Oort Cloud, and made a close approach around 2:27
p.m. EDT within about 87,000 miles (139,500 kilometers) of the Red Planet.
This is less than half the distance between Earth and our moon and less than
one-tenth the distance of any known comet flyby of Earth.

Dust from the comet impacted Mars and was vaporized high in the atmosphere,
producing what was likely an impressive meteor shower. This debris resulted
in significant temporary changes to the planet's upper atmosphere and
possible longer-term perturbations. Earth-based and a host of space
telescopes also observed the unique celestial object.

"This historic event allowed us to observe the details of this fast-moving
Oort Cloud comet in a way never before possible using our existing Mars
missions," said Jim Green, director of NASA's Planetary Science Division
at the agency's Headquarters in Washington. "Observing the effects on
Mars of the comet's dust slamming into the upper atmosphere makes me very
happy that we decided to put our spacecraft on the other side of Mars at the
peak of the dust tail passage and out of harm's way."

The MAVEN spacecraft, recently arrived at Mars, detected the comet encounter
in two ways. The remote-sensing Imaging-Ultraviolet Spectrograph observed
intense ultraviolet emission from magnesium and iron ions high in the
atmosphere in the aftermath of the meteor shower. Not even the most intense
meteor storms on Earth have produced as strong a response as this one. The
emission dominated Mars' ultraviolet spectrum for several hours after the
encounter and then "dissipated" over the next two days.

MAVEN also was able to directly sample and determine the composition of some
of the comet dust in Mars' atmosphere. Analysis of these samples by the
spacecraft's Neutral Gas and Ion Mass Spectrometer detected eight different
types of metal ions, including sodium, magnesium and iron. These are the
first direct measurements of the composition of dust from an Oort Cloud
comet. The Oort Cloud, well beyond the outer-most planets that surround our
sun, is a spherical region of icy objects believed to be material left over
from the formation of the solar system.

Elsewhere above Mars, a joint U.S. and Italian instrument on Mars Express
observed a huge increase in the density of electrons following the comet's
close approach. This instrument, the Mars Advanced Radar for Subsurface and
Ionospheric Sounding (MARSIS), saw a huge jump in the electron density in the
ionosphere a few hours after the comet rendezvous. This spike occurred at a
substantially lower altitude than the normal density peak in the Martian
ionosphere. The increased ionization, like the effects observed by MAVEN,
appears to be the result of fine particles from the comet burning up in the
atmosphere.

MRO's Shallow Subsurface Radar (SHARAD) also detected the enhanced
ionosphere. Images from the instrument were smeared by the passage of the
radar signals through the temporary ion layer created by the comet's dust.
SHARAD scientists used this smearing to determine that the electron density
of the ionosphere on the planet's night side, where the observations were
made, was five to 10 times higher than usual.

Studies of the comet itself, made with MRO's High Resolution Imaging Science
Experiment (HiRISE) camera, revealed the nucleus is smaller than the expected
1.2 miles (2 kilometers). The HiRISE images also indicate a rotation period
for the nucleus of eight hours, which is consistent with recent preliminary
observations by NASA's Hubble Space Telescope.

MRO's Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) also
observed the comet to see whether signs of any particular chemical
constituents stood out in its spectrum. Team members said the spectrum
appears to show a dusty comet with no strong emission lines at their
instrument's sensitivity.

In addition to these immediate effects, MAVEN and the other missions will
continue to look for long-term perturbations to Mars' atmosphere.

MAVEN's principal investigator is based at the University of Colorado's
Laboratory for Atmospheric and Space Physics in Boulder, and NASA's Goddard
Space Flight Center in Greenbelt, Maryland, manages the mission. NASA's Jet
Propulsion Laboratory, a division of Caltech in Pasadena, manages the Mars
Reconnaissance Orbiter. Mars Express is a project of the European Space
Agency; NASA and the Italian Space Agency jointly funded the MARSIS
instrument.

For more information about NASA's Mars missions, visit:

http://www.nasa.gov/mars

-end-

Dwayne Brown
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

Nancy Neal Jones/Elizabeth Zubritsky
Goddard Space Flight Center, Greenbelt, Md.
301-286-0039 / 301-614-5438
nancy.n.jones at nasa.gov / elizabeth.a.zubritsky at nasa.gov
Received on Sat 08 Nov 2014 01:31:58 AM PST