Mars' night-time aurora
Using 10 years of data from Mars Express, scientists have for the first time combined remote sensing observations of localised ultraviolet aurora with in situ measurements of electrons hitting the atmosphere, finding these rare light emissions only occur under special magnetic field conditions.
Centre: Locations of the 19 auroral detections (white circles) by SPICAM on the Mars nightside in the southern hemisphere, over locations already known to be associated with residual crustal magnetism. The data is superimposed on the magnetic field line structure (from NASA's Mars Global Surveyor) where red indicates closed magnetic field lines, grading through yellow, green and blue to open field lines in purple. The auroral emissions are very short-lived, they are not seen to repeat in the same locations, and only occur near the boundary between open and closed magnetic field lines (also visualised top right).
Bottom right: SPICAM limb observations enabled the altitude of some of the auroral events to be determined as 137±27 km.