The Interaction of the Solar Wind With Mars

The interaction of the solar wind with Mars is unique in the solar system because it combines many aspects of the solar wind interaction with other unmagnetized bodies. Like Venus, the Martian atmosphere is primarily responsible for diverting the solar wind around the planet since it lacks a significant global dipole field. Like comets, the neutral atmosphere extends into the interaction region and the ion gyroradius is comparable to the size of the obstacle, making the individual motions of particles an important component of the physical description of the interaction. And like the Moon, crustal magnetic fields (which are much stronger at Mars) locally perturb the solar wind plasma flowing past the obstacle. Aspects of all three interactions are observed at Mars, which over the past few decades has been visited by a number of instruments dedicated to observing how the solar wind influences the Martian upper atmosphere and plasma environment. A complete understanding of the solar wind interaction at Mars is relevant to a variety of other scientific areas. The near-Mars plasma environment provides the upper boundary condition for the atmosphere, and several lines of evidence suggest that the solar wind has played a significant role in long-term climate evolution. Similarly, recent work suggests that plasma in the solar wind can deposit significant energy into the upper atmosphere over short timescales, driving chemistry and dynamics. And the Martian environment is a natural plasma laboratory for the study of fundamental physical processes (such as particle acceleration, magnetic reconnection, and waves) that occur in different regimes at Earth and other planets. This presentation will provide an overview of the current state of understanding of this complex interaction, which extends from upstream of the bow shock to the thermosphere. Emphasis will be placed on recent advances in our understanding made through new observations by Mars Express, global modeling, and continued analysis of Mars Global Surveyor data. Lastly, outstanding questions and current frontiers in this research area will be identified.