In the high-latitude regions of Earth, aurorae are the often-spectacular visual manifestation of the interaction between electrically charged particles (electrons, protons or ions) with the neutral upper atmosphere, as they precipitate along magnetic field lines. More generally, auroral emissions in planetary atmospheres “are those that result from the impact of particles other than photoelectrons” (ref. 1). Auroral activity has been found on all four giant planets possessing a magnetic field (Jupiter2, Saturn3, Uranus4 and Neptune5), as well as on Venus, which has no magnetic field6. On the nightside of Venus, atomic O emissions at 130.4 nm and 135.6 nm appear in bright patches of varying sizes and intensities6, which are believed to be produced by electrons with energy <300 eV (ref. 7). Here we report the discovery of an aurora in the martian atmosphere, using the ultraviolet spectrometer SPICAM on board Mars Express. It corresponds to a distinct type of aurora not seen before in the Solar System: it is unlike aurorae at Earth and the giant planets, which lie at the foot of the intrinsic magnetic field lines near the magnetic poles, and unlike venusian auroras, which are diffuse, sometimes spreading over the entire disk. Instead, the martian aurora is a highly concentrated and localized emission controlled by magnetic field anomalies in the martian crust.
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Mars Express is a space mission from ESA (European Space Agency). We thank all ESA members who participated in this mission, in particular M. Denis at ESOC for the controlling of the spacecraft, and R. Pischel and T. Zeghers at ESTEC for planning exercises; Astrium Corp. for the design and construction of the spacecraft; our collaborators at the three institutes for the design and fabrication of the instrument (Service d'Aéronomie/France, BIRA/Belgium and IKI/Moscow), and in particular E. Dimarellis as SPICAM Project Manager and E. Van Ransbeeck at BIRA for mechanical design and fabrication. We also thank CNRS and CNES for financing SPICAM in France, the Belgian government, the Russian Academy of Sciences and NASA for support of US co-investigators. B.R.S. was supported by the Jet Propulsion Laboratory.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Bertaux, JL., Leblanc, F., Witasse, O. et al. Discovery of an aurora on Mars. Nature 435, 790–794 (2005). https://doi.org/10.1038/nature03603
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