Swedish instrument studies auroras on Mars
Scientists at the Swedish Institute of Space Physics (IRF) in Kiruna, Sweden, have found structures (inverted-V features) of accelerated electrons and ions above the night side of Mars that are almost identical to those that occur above auroras on Earth. They have also found that the structures are associated with the magnetic anomalies at Mars, but that strong acceleration mainly occurs in a region close to local midnight. Their results appear in today's issue of the journal Science (17 February).
"Auroras are created when energetic charged particles collide with the upper atmosphere,” says Rickard Lundin from the Swedish Institute of Space Physics. “When they are deaccelerated, energy is released that causes emissions of light--aurora. During strong auroras the precipitating particles are accelerated and gain energy, leading to more intense light." Auroras reflect the strong coupling between charged particles and magnetic fields. Auroras occur close to the magnetic poles and the particles that create them follow the direction of the magnetic field into the atmosphere.
These features are well-known on Earth, but auroras have also been observed on other planets with strong magnetic fields, such as Jupiter and Saturn. "Mars lacks a strong dipole field, and therefore we have not had reason to believe that auroras occur there," says Rickard Lundin. The discovery of strong remnant magnetic fields in the crust, magnetic anomalies, (Acuna et al., 1999) started speculation that auroras could also occur at Mars. Bertaux and associates (2005) observed emissions of light above magnetic anomalies with the SPICAM experiment on board Mars Express, emissions that could be due to precipitating energetic particles.
The results from the Swedish instrument ASPERA-3 on-board the European satellite Mars Express show that the energy flux of the precipitating particles is large enough that it would lead to auroras that would be of weak or medium intensity at Earth. 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 authors speculate that the classical “green” line of oxygen might be present. "As we see it Mars is always sunlit, so the auroras on the night-side of Mars cannot be observed from Earth," says Rickard Lundin.
Prof. Rickard Lundin, IRF, tel. +46-90-786 9205, +46-70-589 2119, rickard.lundin*irf.se
Ass. Prof. Mats Holmström, IRF, tel. +46-980-79186, mats.holmstrom*irf.se
Rick McGregor, Information Officer, IRF, tel. +46-980-79178, +46-70-276 6020, rick.mcgregor*irf.se
The Swedish Institute of Space Physics (IRF) is a governmental research institute which conducts research and postgraduate education in atmospheric physics, space physics and space technology. Measurements are made in the atmosphere, ionosphere, magnetosphere and around other planets with the help of ground-based equipment (including radar), stratospheric balloons and satellites. IRF was established (as Kiruna Geophysical Observatory) in 1957 and its first satellite instrument was launched in 1968. The head office is in Kiruna (geographic coordinates 67.84° N, 20.41° E) and IRF also has offices in Umeå, Uppsala and Lund.
Institutet för rymdfysik, IRF, är ett statligt forskningsinstitut under Utbildningsdepartementet. IRF bedriver grundforskning och forskarutbildning i rymdfysik, atmosfärsfysik och rymdteknik. Mätningar görs i atmosfären, jonosfären, magnetosfären och runt andra planeter med hjälp av ballonger, markbaserad utrustning (bl a radar) och satelliter. För närvarande har IRF instrument ombord på satelliter i bana runt tre planeter, jorden, Mars och Saturnus. IRF har ca 100 anställda och bedriver verksamhet i Kiruna (huvudkontoret), Umeå, Uppsala och Lund.