Plasma processes at comet 67P/Churyumov-Gerasimenko
Rosetta, the comet chaser, finally arrived at comet 67P/Churyumov–Gerasimenko in August 2014 after a ten year cruise through the solar system. In November 2014 it even put down a lander on the cold and dark surface of the comet, and is since then busy exploring the nucleus itself as well as the dusty coma around it (see figure below). Rosetta will carry on close exploration of the comet (sometimes just a few kilometres from the nucleus) at least through 2015, probably most of 2016 as well. By this time, the comet will have been at its closest to the Sun and is again receding into the cold regions well beyond Mars' orbit.
IRF Uppsala contributes one of the instruments on board the Rosetta orbiter, a kind of weather station known as a Langmuir probe (LAP). Together with the other instruments in the Rosetta Plasma Consortium, we investigate the ionized component of the gas oozing out of the icy nucleus and how it interacts with the dust from the comet and the ever changing solar wind. At other comets, the environment is known to structure itself into several regions with different properties. From Rosetta, we are already learning that this picture is very simplified, as we follow how the comet environment changes with distance to the Sun.
Rosetta is not like any other comet mission. Previous spacecraft have just flown by at high speed, at best catching a few shots, recording some waves and perhaps a few dust grains during a few minutes or (at best) hours. Rosetta will spend two years close to the nucleus, moving at relative speed to the nucleus of around a meter per second or even slower. This exploration at walking pace is something really unique not only for comets but for space science as a whole, allowing studies of complex plasma phenomena in a way that has never before been possible.