Mars Express observes aurora on the Red Planet / Scientific Frontline

Mars Express Mission News

Mars Express observes aurora on the Red Planet

Friday, November 21, 2008

An artist's impression of how the 'green' aurora may look to an observer orbiting on the night-side of Mars.

Credit: M. Holmström (IRF)

Scientists using ESA’s Mars Express have produced the first crude map of aurora on Mars. These displays of ultraviolet light appear to be located close to the residual magnetic fields generated by Mars' crustal rocks. They highlight a number of mysteries about the way Mars interacts with electrically charged particles originating from the Sun.

The aurora on Mars were discovered in 2004 using the SPICAM ultraviolet and infrared atmospheric spectrometer on board Mars Express. They are a powerful tool with which scientists can investigate the composition and structure of the Red Planet’s atmosphere.

Now Francois Leblanc, from the Service d’Aéronomie, IPSL/CNRS, France and colleagues have announced the results of coordinated observation campaigns using SPICAM, the MARSIS sub-surface sounding radar altimeter’s radar, and the energetic neutral atoms analyzer, ASPERA’s electron spectrometer on Mars Express.
They have observed nine new auroral emission events, which have allowed them to make the first crude map of auroral activity on Mars. They see that the aurora seem to be located near regions where the Martian magnetic field is the strongest. MARSIS had previously observed higher-than-expected electrons in similar regions. This suggests, although it does not prove, that the magnetic fields help to create the aurora

On Earth, aurora are more commonly known as the northern and southern lights. They are confined to the polar regions and shine brightly at visible as well as ultraviolet wavelengths. The existence of similar aurora is well known on the giant planets of the Solar System. They occur wherever a planet’s magnetic field channels electrically charged particles into the atmosphere.

In all of these planets, the magnetic fields are large-scale structures generated deep in the interior of the planet. Mars lacks such a large-scale internal mechanism. Instead, it just generates small pockets of magnetism where areas of rocks in the crust of Mars are themselves magnetic. This results in many magnetic pole-type regions all over Mars.

The aurora are caused by charged particles, in this case most probably electrons, colliding with molecules in the atmosphere. The electrons almost certainly come from the Sun, which constantly blows out electrically charged particles into space. Known as the solar wind, this constant stream of particles provides the source of electrons to generate the aurora, as suggested by MARSIS and ASPERA.

But how the electrons are accelerated to sufficiently high energies to spark aurora 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.

Any future astronauts expecting a spectacular light show, similar to aurora on Earth, may be in for a disappointment. “We’re not sure whether the aurora will be bright enough to be observed at visible wavelengths,” says Leblanc.

This is because the molecules responsible for the visible light show on Earth – molecular and atomic oxygen and molecular nitrogen – are not abundant enough in the Martian atmosphere. SPICAM is designed to work at ultraviolet wavelengths and cannot see whether visible light is being emitted as well.

Nevertheless, there is plenty of work for the scientists to do. “There's now a large domain of physics that we have to explore in order to understand the aurora on Mars. Thanks to Mars Express we have a lot of very good measurements to work with,” says Leblanc.

Source: ESA