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Science 17 February 2006:
Vol. 311. no. 5763, pp. 980 - 983
DOI: 10.1126/science.1122071
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Reports
Plasma Acceleration Above Martian Magnetic Anomalies
R. Lundin,1
D. Winningham,2
S. Barabash,1
R. Frahm,2
M. Holmström,1
J.-A. Sauvaud,3
A. Fedorov,3
K. Asamura,4
A. J. Coates,5
Y. Soobiah,5
K. C. Hsieh,6
M. Grande,7
H. Koskinen,8,9
E. Kallio,8
J. Kozyra,10
J. Woch,11
M. Fraenz,12
D. Brain,12
J. Luhmann,12
S. McKenna-Lawler,13
R. S. Orsini,14
P. Brandt,15
P. Wurz16
Auroras are caused by accelerated charged particles precipitating along magnetic field lines into a planetary atmosphere, the auroral brightness being roughly proportional to the precipitating particle energy flux. The Analyzer of Space Plasma and Energetic Atoms experiment on the Mars Express spacecraft has made a detailed study of acceleration processes on the nightside of Mars. We observed accelerated electrons and ions in the deep nightside high-altitude region of Mars that map geographically to interface/cleft regions associated with martian crustal magnetization regions. By integrating electron and ion acceleration energy down to the upper atmosphere, we saw energy fluxes in the range of 1 to 50 milliwatts per square meter per second. These conditions are similar to those producing bright discrete auroras above Earth. Discrete auroras at Mars are therefore expected to be associated with plasma acceleration in diverging magnetic flux tubes above crustal magnetization regions, the auroras being distributed geographically in a complex pattern by the many multipole magnetic field lines extending into space.
2 Southwest Research Institute, San Antonio, TX 7228–0510, USA.
3 Centre d'Etude Spatiale des Rayonnements, BP-4346, F-31028 Toulouse, France.
4 Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamichara, Japan.
5 Mullard Space Science Laboratories, University College London, Surrey RH5 6NT, UK.
6 Department of Space Physics, University of Arizona, Tucson, AZ 85721, USA.
7 Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK.
8 Finnish Meteorological Institute, Box 503 FIN-00101 Helsinki, Finland.
9 Department of Physical Sciences, University of Helsinki, Helsinki, Finland.
10 Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI 48109–2143, USA.
11 Max-Planck-Institut für Sonnensystemforschung, D-37191 Katlenburg-Lindau, Germany.
12 Space Science Laboratory, University of California, Berkeley, CA 94720–7450, USA.
13 Space Technology Ltd., National University of Ireland, Maynooth, County Kildare, Ireland.
14 Instituto di Fisica dello Spazio Interplanetari, I-00133 Rome, Italy.
15 Applied Physics Laboratory, Johns Hopkins University, Laurel, MD 20723–6099, USA.
16 Physikalisches Institut, University of Bern, CH-3012 Bern, Switzerland.
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