Space Physics encompass the physics of the (Earth-near) open space, mainly the magnetosphere and solar wind. In a wider sense they include the application of knowledge obtained on the system Earth to other planets and moons, for example the investigation of the interactions between the magnetosphere of Saturn and the moon Titan. Main topics of the research group of Prof. Joachim Saur are magnetic fields and plasma, which is why the following paragraph is devoted to (extraterrestrial) plasma physics alone.

What are Extraterrestrial Plasma Physics about?

In everyday life we normally only encounter three states of matter: solid, liquid, and gaseous. The plasmatic state is seldomly observed, for example in technical constructions such as light bulbs, fluorescent lamps, or phenomenons such as lightning. A plasma consists of matter which is partly or completely atomised into charged particles, like negative electrons and mainly positive ions. Such a plasma shows strong interaction with electrical and magnetic fields and exhibits a large variety of phenomena which are for most parts unbeknown for the other three states of matter.

Even though the plasmatic state of matter may appear exotic in everyday life, it is the normal state for the largest part of matter in the universe, as well as for the largest part of matter in our solar system if we include the sun itself. But even the closer surrounding of planets and their satellites - asteroids and comets - as well as the interplanetary space between planets, is filled by plasma with multiple properties. These plasma which are situated above the Earth also also terminated as extraterrestrial plasma. The physics of these plasma is called extraterrestrial plasma physics - in contrast to laboratory plasma physics (e. g., fusion experiments). Extraterrestrial plasma physics are a comparably young field of research, beginning round about 70-80 years ago. Only with the beginning of the exploration of space by means of rockets and since 1957 with satellites and spacecrafts did this branch of physics boom. Plasma in our solar system is often not visible. Exceptions are northern lights (see figure above) and comet tails. Instruments for experimental survey of plasma are matter detectors and magnetic and electrical field detection instruments.

The focus of research of the group is the plasma of the interplanetary space; from the corona of the sun to the interstellar medium. For this, data of magnetic fields, plasma, and radio soundings from missions such as Ulysses, Helios, Wind, and in future Phoenix, Cassini, Rosetta, etc. are analysed. The data analysis is supported by theoretical-numerical model simulations, with the goal to physically understand the investigated phenomena. 

A second focus is the investigation of the plasma surrounding of comets, for example with data from the spacecrafts such as Giotto and in future Rosetta.

Finally, the research group also investigates the magnetised plasma surrounding - the magnetospheres - of the larger planets in our solar system, of Jupiter, Saturn, Uranus, and Neptun. The focus is on the plasma flow around the satellites of the large planets. Up to now, the galileic satellites of Jupiter, Io and Europa, were investigated, as well as the largest satellite of Saturn, Titan, and a satellite of Neptun, Triton. The work commenced with the Voyager and Cassini missions, where the research group is involved in the magnetic field experiments, amongst others. 

Extraterrestrial plasma physics investigate non-everyday states of matter, which exhibit a complex but interesting behaviour. Plasma in our solar system offers us the unique possibility to investigate processes with all diagnostic subtleties we have at hand. In the rest of our cosmos, this can only be assessed roughly with remote sensing methods. In the laboratory again, these processes can only be investigated with large errors from wall effects. This is why extraterrestrial plasma of our solar system is a unique laboratory which nature has provided us with.