Mars loses magnetic shield under certain solar wind conditions
Mars's protective magnetosphere can collapse when solar winds hit at shallow angles, leaving the planet vulnerable to atmospheric erosion. The finding reshapes models of planetary habitability and informs strategies for long-term human missions, where understanding atmospheric loss becomes critical for life support planning.
Originaltitel: Mars’s induced magnetosphere can degenerate
<p>The interaction between planets and stellar winds can lead to atmospheric loss and is, thus, important for the evolution of planetary atmospheres<sup>1</sup>. The planets in our Solar System typically interact with the solar wind, whose velocity is at a large angle to the embedded stellar magnetic field. For planets without an intrinsic magnetic field, this interaction creates an induced magnetosphere and a bow shock in front of the planet<sup>2</sup>. However, when the angle between the solar wind velocity and the solar wind magnetic field (cone angle) is small, the interaction is very different<sup>3</sup>. Here we show that when the cone angle is small at Mars, the induced magnetosphere degenerates. There is no shock on the dayside, only weak flank shocks. A cross-flow plume appears and the ambipolar field drives planetary ions upstream. Hybrid simulations with a 4° cone angle show agreement with observations by the Mars Atmosphere and Volatile Evolution mission<sup>4</sup> and Mars Express<sup>5</sup>. Degenerate, induced magnetospheres are complex and not yet explored objects. It remains to be studied what the secondary effects are on processes like atmospheric loss through ion escape.</p>