SPICAM and the Aurora at Terra Cimmeria

Credit (Map): NASA/MGS
Credit (Photo): NASA/ESA

Another instrument aboard Mars Express is SPICAM (Spectroscopy for the Investigations and the Characteristics of the Atmosphere on Mars), developed by the Service d'Aéronomie du CNRS/IPSL (Verrières-le-Buisson, France) ,the Belgian Institute for Space Aeronomy (BIRA-IASB; Brussels, Belgium), and the Space Research Institute of the Russian Academy of Sciences (IKI; Moscow, Russia). SPICAM was originally on board the ill-fated Mars 96. However, a new instrument was placed aboard Mars Express, and a similar instrument (SPICAV) is on the European Space Agency's (ESA) Venus Express.

SPICAM is a lightweight (4.7 kg) ultraviolet-infrared dual spectrometer dedicated primarily to the study of the atmosphere of Mars. SPICAM makes measurements of the Martian atmosphere mainly through stellar and solar occultations. Through this method, SPICAM can make measurements of the Martian atmosphere's chemistry, the atmosphere's structure and dynamics (including its density and temperature) through vertical profiles, measurements of aerosols and dust particles and their vertical distribution, and measurements of the ionosphere and the rate of escape of atmospheric molecules. The ultraviolet sensor also measures the level of ozone in the Martian atmosphere, and the infrared sensor measures water vapor.

On August 14, 2004, SPICAM detected a new type of aurora on Mars. On Earth and among the gas giants (Jupiter, Saturn, Uranus, and Neptune), aurorae occur along the planetary magnetic field lines near the poles, and are produced by charged particles (electrons, protons and ions) precipitating along those lines. Venus also produces aurorae, although of a different type. Because Venus has no "intrinsic" (planetary) magnetic field, Venusian aurorae appear as bright and diffuse patches of varying shape and intensity, sometimes distributed across the full planetary disc. Venusian aurorae are produced by the impact of electrons originating from the solar wind and precipitating in the night-side atmosphere.

Like Venus, Mars is a planet with no intrinsic magnetic field. However, it was suggested that Mars could have aurorae as well, and this hypothesis was reinforced by Mars Global Surveyor's discovery of crustal magnetic anomalies, most likely the remnants of an old planetary magnetic field.

SPICAM detected light emissions in the southern hemisphere on Mars, in Terra Cimmeria, during night-time observations in the region of 177º East, 52º South. The total size of the emission region was about 30 km across, and possibly about 8 km high. By analyzing the map of crustal magnetic anomalies compiled with Mars Global Surveyor’s data, scientists observed that the region of the emissions corresponds to the area where the strongest magnetic field is localized. This correlation indicates that the origin of the light emission actually was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.

The above map shows the crustal magnetic field intensity in the Terra Cimmeria region. The aurora was located in an area where the crustal magnetic field is very strong (dark red in the image). The photo underneath is of the same region as the map.