The Mars Plasma Environment

Mars sits very exposed to the solar wind and, because it is a small planet, has but a weak hold on its atmosphere. The solar wind therefore plays an important role in the evolution of the martian atmosphere. Over the last four decades a series of European missions, first from the Soviet Union and more recently from the European Space Agency, together with a single investigation from the U.S., the Mars Global Surveyor spacecraft, have added immeasurably to our understanding of the interplay between the solar wind and Mars atmosphere. Most recently the measurements of the plasma and fast neutral populations, conducted on the Mars Express spacecraft by the ASPERA-3 instrument have been acquired and analyzed. Their presentation to the public, most notably at the workshop "The Solar Wind Interaction and Atmosphere Evolution of Mars" held in Kiruna in early 2006, was the inspiration for this series of articles. However participation in the Kiruna conference was not a selection criterion for this volume. The papers cover the ancient sun and evolution of the solar wind, the physics of the solar wind interaction, the measurements of the hot plasma and fast neutrals by ASPERA-3, the ionosphere by MARSIS, and the x-rays emitted by the atmosphere. The authors of this volume include many international scientists at the cutting edge of research into the Mars plasma environment. The volume documents the impressive leap forward in our comprehension of this complex environment in the years since the orbit insertion of Mars Express.