17 February 2006
Mars Express studies possible aurorae above Mars
ESA’s Mars Express spacecraft has seen more evidence that aurorae occur
over the night side of Mars, especially over areas of the surface where
variations in the magnetic properties of the crust have been detected.
Observations from the ASPERA instrument on board ESA’s Mars Express
spacecraft show structures (inverted-V features) of accelerated electrons
and ions above the night side of Mars that are almost identical to those
that occur above aurorae on Earth.
Aurorae are spectacular displays often seen at the highest latitudes on
Earth. On our planet, as well as on the giant planets Jupiter, Saturn,
Uranus and Neptune, they occur at the foot of the planetary magnetic field
lines near the poles, and are produced by charged particles – electrons,
protons or ions – precipitating along these lines.
“Aurorae are created when energetic charged particles collide with the
upper atmosphere,” says Rickard Lundin, Principal Investigator for ASPERA,
from the Swedish Institute of Space Physics Physics (IRF), Kiruna, Sweden.
“When they are decelerated, energy is released that causes emissions of
light – aurorae. During strong aurorae the precipitating particles are
accelerated and gain energy, leading to more intense light,” said Lundin.
The scientists have found that the energy flux of the precipitating
particles is large enough that it would lead to aurorae comparable to
those of weak or medium intensity at Earth.
“Mars lacks a strong intrinsic magnetic or dipole field, and therefore we
have not had reason to believe that aurorae occur there,” said Lundin.
A few years ago it was suggested that auroral phenomena could exist on
Mars too. This hypothesis was reinforced by the Mars Global Surveyor
discovery of ‘crustal magnetic anomalies’, most likely the remnants of an
old planetary magnetic field.
This discovery started speculation that auroras could also occur at Mars.
In 2004, the SPICAM instrument on board Mars Express observed emissions of
light during a magnetic anomalies investigation – emissions that could be
due to precipitating energetic particles.
The ASPERA scientists have now found that the structures of accelerated
particles are indeed associated with the ‘crustal magnetic anomalies’ at
Mars, but that strong acceleration mainly occurs in a region close to
The precise emissions of light that occur remain to be studied since the
composition of the upper atmosphere on the night side is not well known.
On the basis of atmospheric models, the scientists speculate that the
classical ‘green’ emission line of oxygen might be present.
“But, as we see Mars as always sunlit, the aurorae on the night side of
Mars cannot be observed from Earth,” added Lundin.
Notes to editors:
This result appears in the 17 February issue of the journal Science.
For more information:
Rickard Lundin, IRF
Tel: +46 90 786 9205
E-mail: rickard.lundin @ irf.se
Mats Holmström, IRF
Tel: +46 980 79186
E-mail: mats.holmstrom @ irf.se
Rick McGregor, Information Officer, IRF
Tel: +46 980 79178, E-mail: rick @ irf.se
Agustin Chicarro, ESA Mars Express Project Scientist
E-mail: agustin.chicarro @ esa.int
Fred Jansen, ESA Mars Express Mission Manager
E-mail: fjansen @ rssd.esa.int
- Buried craters and underground ice – Mars Express uncovers depths of
- Mars Express evidence for large aquifers on early Mars
- Mars Express radar reveals complex structure in ionosphere of Mars
- Mars Express discovers new layer in Martian ionosphere
- At Saturn and Titan
- Looking at Mars
- Mars Express instruments
- Huygens instruments
- Cassini instruments
An artist’s impression of how the ‘green’ aurorae may look to an observer
orbiting on the night-side of Mars.
Credits: M. Holmström (IRF)
On our planet, as well as on the giant planets Jupiter, Saturn, Uranus and
Neptune, aurorae occur at the foot of the planetary magnetic field lines
near the poles, and are produced by charged particles electrons, protons
or ions precipitating along these lines.
This aurora was seen from Fairbanks, Alaska. The dark band in the green
aurora pictured here is an example of a black aurora. A black aurora isn’t
an aurora at all; rather it is a lack of auroral activity. The black
aurora is only visible to the naked eye if it is embedded in a region of
diffuse (faint) aurora.
Credits: Jan Curtis, Fairbanks, Alaska