How do the ions in the solar wind react with Martian atmosphere? This question has been studied in a doctoral thesis by Catherine Diéval, a PhD student at the Swedish Institute of Space Physics (IRF) and the Luleå University of Technology.
A stream of electrically charged particles is emitted from the Sun. This flow is called the solar wind, and consists of electrons and ions (atoms that have lost one or more of their electrons).
Mars, unlike Earth, does not possess a magnetic field, and therefore one could be led to believe that the planet’s atmosphere is totally unprotected against the solar wind, but the interaction of the solar wind and the ionized part of Mars atmosphere form a so-called induced magnetosphere around the planet.
Previous satellite measurements have shown that solar wind ions can penetrate through the induced magnetosphere and down into the upper atmosphere of Mars. Earlier models suggested that such an intrusion would be ongoing and that the penetrating particles could transfer significant amounts of energy, momentum and material from the solar wind to the planet's atmosphere.
The thesis presents measurements of the plasma environment around Mars. It turns out that the number of solar wind ions reaching the upper atmosphere is much smaller than previously predicted by the computer models. Nor do the ions appear to penetrate the atmosphere continuously:
"It is just under 3 percent of the available observing time that we see really penetrating solar wind particles in our data", says Catherine Diéval.
It is suggested that a large proportion of solar wind ions are stopped by the magnetic barrier (part of the induced magnetosphere). The effectiveness of the barrier is dependent on the energy of the incoming particles and on the strength of the magnetic field.
"The stronger the magnetic field, the fewer particles can penetrate the magnetic barrier", explains Catherine Diéval.
Catherine Diéval has also used computer models to investigate what happens to the solar wind particles that manage to cross the magnetic barrier. They show, among other things, how important the magnetic field in the magnetic barrier is. A key finding of the thesis is that Mars's atmosphere is well protected against the intrusive solar wind ion particles.
"My thesis will help us to understand how the solar wind interacts with the atmosphere around a planet. It is important not only to understand our own solar system, but to eventually determine how atmospheres are formed and evolve on planets around other stars."
Catherine Diéval was born in Amiens, 150 km north of Paris, France. She grew up in Rivery, a small community near Amiens. She has a master's degree in astrophysics, planetary- and space research from the University Paul Sabatier Toulouse and is a part of the research programme "Solar System Physics and Space Technology” at the Swedish Institute of Space Physcis. She is also enrolled at Luleå University of Technology, in the Department of Computer Science, Electrical and Space Engineering as well as belonging to the Graduate School in Space Technology.
On 14 December 2012 Catherine Dieval will defend her PhD thesis titled “Solar wind ions inside the induced magnetosphere of Mars” in the Aula of the Swedish Institute of Space Physics in Kiruna. Faculty opponent is Dr. Christian Mazelle, Institut de Recherche en Astrophysique et Planetologie, Toulouse (France).
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.