Express observes aurora on the Red Planet
Friday, November 21, 2008
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
artist's impression of how the 'green' aurora may look to an
observer orbiting on the night-side of Mars.
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
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.
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
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.
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