Low Frequency Plasma Oscillations Observed at Mars During 2003 Solar Storms

J. R. Espley¹, P. A. Cloutier1, D. A. Brain², D. H. Crider³, and M. A. Acu??a⁴

¹Department of Physics and Astronomy, Rice University (espley@rice.edu); ²Laboratory for Atmospheric and Space Physics, University of Colorado; ³Catholic University of America, Department of Physics; ⁴ NASA Goddard Space Flight Center

Because of Mars's lack of an intrinsic global magnetic field, the solar wind interacts directly with the Martian ionosphere.

The scientists used observations from Mars Global Surveyor's magnetometer instrument. The observations are from an altitude of approximately 400 km covering solar zenith angles from approximately 30 degrees (2 pm) to 150 degrees (2 am). They were then able to calculate the amplitudes, likely directions of propagation (using minimum variance analysis) and senses of polarization for the oscillations. Several intervals chosen from the data illustrate these calculations.

Spectral-power diagrams from the Martian magnetotail during the solar storm.They show powerful oscillations at the proton gyrofrequency (the dashed line) and thus indicate atmospheric loss.

Findings showed that oscillations in the dayside MPB at 400 km are significantly enhanced in amplitude and regularity during the passage of the solar storm, though their general characteristics remain similar. This speculation raises the interesting question of the relative magnitudes of total atmospheric loss due to steady state processes versus that from episodic events such as large solar storms.

Significance to Solar System Exploration

Because of Mars's lack of an intrinsic global magnetic field, the solar wind interacts directly with the Martian ionosphere. This interaction produces plasma and magnetic turbulence. This turbulence is interesting because it is relevant to studies of:

• Atmospheric loss to space -- both contemporary and historical.
• Comparative space physics (both Venus and comets have similar interactions, and these interactions can be contrasted with magnetospheres such as the Earth's).
• Comparison with other possible sources of low frequency oscillations (such as dust devils) detectable at the surface.

Implications

Besides the intrinsic scientific interest in understanding what sorts of plasma waves occur under solar storm conditions at Mars, these observations have important implications for atmospheric loss (and therefore climate change) at Mars. Because during the solar storm plasma waves associated with planetary ions in the normally quiet magnetotail were observed, it appears atmospheric loss may be significantly enhanced during large solar storms.

For further information about science highlights and having your research highlighted, please contact Samantha Harvey at NASA's Jet Propulsion Laboratory, Samantha.K.Harvey@jpl.nasa.gov.

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