Posted: 24 November, 2008
Scientists using ESA's Mars Express have produced the first crude map of aurorae on Mars.
The aurorae on Mars were first discovered in 2004 using the SPICAM ultraviolet and infrared atmospheric spectrometer onboard Mars Express, which revealed displays of ultraviolet light associated with the residual magnetic fields generated by Mars' crustal rocks. Now, using coordinated observations from SPICAM, the MARSIS sub-surface sounding radar altimeter's radar, and the energetic neutral atoms analyser ASPERA, Francois Leblanc from the Service d'Aeronomie and colleagues have observed nine new auroral emission events, which have allowed them to make the first crude map of auroral activity on Mars.
Artist impression of how the 'green' aurorae may look to an observer orbiting on the night-side of Mars. Image: M. Holmström (IRF).
The observations show that the aurorae seem to be located near regions where the Martian magnetic field is the strongest, confirming earlier MARSIS detections of higher-than-expected electrons in similar regions. This tentatively suggests that the magnetic fields help to create the aurorae, but there is still a lot of work to do in determining how they arise, since Mars lacks the same large scale internal mechanism that drives the magnetic fields on other planets. Instead, it just generates small pockets of magnetism where areas of rocks in the crust of Mars are themselves already magnetic, resulting in many magnetic pole-type regions all over Mars.
On Earth, aurorae are usually confined to the polar regions and shine brightly in visible light as well as at ultraviolet wavelengths. The existence of similar aurorae is also well known on the giant planets of the Solar System and occur wherever a planet's magnetic field channels electrically charged particles blown out from the Sun in the solar wind into the planet’s atmosphere. But how the electrons are accelerated to sufficiently high energies to spark aurorae on Mars remains a mystery. "It may be that magnetic fields on Mars connect with the solar wind, providing a road for the electrons to travel along," says Leblanc.
Terrestrial aurorae are displayed typically in reds and greens, as a result of the interaction of molecular and atomic oxygen and molecular nitrogen in the atmosphere with the solar wind particles. These molecules are not abundant enough in the Martian atmosphere and so it is uncertain if similar light shows would be observed from the red planet’s surface. Furthermore, SPICAM is designed to work at ultraviolet wavelengths and cannot see whether visible light is being emitted as well. But the new results will provide plenty of work for the scientists in the months and years to come, and will offer new insight to the composition and structure of the Martian atmosphere and how the planet interacts with electrically charged particles originating from the Sun.
"There's now a large domain of physics that we have to explore in order to understand the aurorae on Mars,” says Leblanc. “Thanks to Mars Express we have a lot of very good measurements to work with."