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11.07.2014

Mars Spacecraft Reveal Comet Flyby Effects on Martian Atmosphere



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Mars Orbiter Observes Comet Siding Spring

This movie begins with an animation (artist's rendering) of NASA's Mars Reconnaissance Orbiter spacecraft above Mars. The scene zooms into an "X-ray" view of the spacecraft, revealing the High Resolution Imaging Science Experiment (HiRISE) camera. The movie then transitions to a sequence of HiRISE images of the comet taken as it flew past Mars. Credit: NASA/JPL-Caltech/University of Arizona
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Also watch Mars-Flyby Comet in False Color >>


Artist's concept of Comet Siding Spring approaching Mars, shown with NASA's orbiters preparing to make science observations of this unique encounter. Credit: NASA/JPL-Caltech
Emission from Ionized Magnesium in Mars' Atmosphere After Comet Flyby
Credit: NASA/JPL-Caltech/University of Arizona
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.

Artist's Concept of MAVEN's Imaging Ultraviolet Spectrograph at Work
Credit: NASA/Univ. of Colorado
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.

Radar-Detected Change in Mars' Near-Polar Ionosphere
Credit: ASI/NASA/ESA/JPL/Univ. of Rome/Univ. of Iowa
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.

Radar Indication of Effect of Comet Flyby on Martian Ionosphere
Credit: JPL/NASA/Univ. of Rome/ASI
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.
Mars Orbiter Sizes Up Passing Comet
Credit: NASA/JPL-Caltech/University of Arizona
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 and http://mars.nasa.gov/

Mars-Orbiting Spectrometer Shows Dusty Comet's Spectrum
Credit: NASA/JPL-Caltech/JHUAPL

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

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

Nancy Neal Jones/Elizabeth Zubritsky
Goddard Space Flight Center, Greenbelt, Md.
301-286-0039 / 301-614-5438
nancy.n.jones@nasa.gov / elizabeth.a.zubritsky@nasa.gov


All Related Images
  • Artist's concept of Comet Siding Spring approaching Mars, shown with NASA's orbiters preparing to make science observations of this unique encounter.
    NASA's Mars Orbiters Maneuvers as Comet Siding Spring Approaching Mars
  • This illustration depicts the Imaging Ultraviolet Spectrograph (IUVS) on NASA's MAVEN spacecraft scanning the upper atmosphere of Mars.
    Artist's Concept of MAVEN's Imaging Ultraviolet Spectrograph at Work
  • The places where the red line on this graph extends higher than the blue line show detection of metals added to the Martian atmosphere from dust particles released by a passing comet on Oct. 19, 2014. The graphed data are from the Imaging Ultraviolet Spectrograph (IUVS) on NASA's MAVEN spacecraft.
    Comet Meteor Shower Put Magnesium and Iron into Martian Atmosphere
  • These eight graphs present data from the Neutral Gas and Ion Mass Spectrometer on NASA's MAVEN orbiter identifying ions of different metals added to the Martian atmosphere shortly after comet C/2013 A1 Siding Spring sped close to Mars. Dust particles from the comet delivered the metals to Mars.
    Ions of Eight Metals from Comet Dust Detected in Mars Atmosphere
  • These spectrograms from the MARSIS instrument on the European Space Agency's Mars Express orbiter show the intensity of radar echo in Mars' far-northern ionosphere at three times on Oct. 19 and 20, 2014. The middle plot reveals effects attributed to dust from a comet that passed near Mars that day.
    Radar-Detected Change in Martian Near-Polar Ionosphere After Comet's Flyby
  • These plots portray data from radar sounding of Mars' mid-latitude ionosphere at three times on Oct. 19 and 20, 2014. The middle one shows effects of dust from a comet that passed near Mars that day. The data are from the MARSIS instrument on the European Space Agency's Mars Express orbiter.
    Change in Mars' Mid-Latitude Ionosphere After Comet Flyby
  • A comparison of two radargrams from the SHARAD instrument on NASA's Mars Reconnaissance Orbiter shows effects on the Martian ionosphere from the close passage of a comet.
    Radar Indication of Effect of Comet Flyby on Martian Ionosphere
  • This graph shows changes in apparent brightness of comet C/2013 A1 Siding Spring as it approached and receded from Mars, as seen by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. The pattern suggests the comet rotates once every eight hours.
    Brightness Rhythm of Mars Flyby Comet Is Clue to Rotation Rate
  • Five images of comet Siding Spring taken within a 35-minute period as it passed near Mars on Oct. 19, 2014, provide information about the size of the comet's nucleus. The images were acquired by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.
    Mars Orbiter Sizes Up Passing Comet
  • This graphic depicts what Mars' atmosphere would have looked like to a viewer with ultraviolet-seeing eyes after a meteor shower on Oct. 19, 2014. It combines an image from the Imaging Ultraviolet Spectrograph on NASA's MAVEN spacecraft with an illustration of how the atmosphere lies over Mars.
    Emission from Ionized Magnesium in Mars' Atmosphere After Comet Flyby
  • The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard NASA's Mars Reconnaissance Orbiter obtained this spectrum for comet C/2013 A1 Siding Spring during the comet's close approach to Mars.
    Mars-Orbiting Spectrometer Shows Dusty Comet's Spectrum

Credit: NASA/JPL-Caltech


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