LASP Magnetosphere Seminars

Abstract

Induced magnetospheres of non-magnetized atmospheric planets, like Mars and Venus, are formed by the ionospheric currents induced by the solar wind interaction with the gravitationally bound electrically conducting ionospheres. When the interplanetary magnetic field (IMF) is predominantly aligned to the solar wind velocity, the convective electric field diminishes, leading to a degeneration of the induced magnetosphere. We use the term degenerate, induced magnetosphere to emphasize the fundamental difference in the structure and physics of such interaction. Based on a case study using both observations from Mars Atmosphere and Volatile Evolution (MAVEN) and Mars Express (MEX), and a hybrid model of the solar wind interaction with Mars, we find the distinctive features of this type of interaction: the absence of solar wind magnetic field piling up on the dayside, intense foreshock turbulence, disappearance of the subsolar bow shock, and the formation of a shock-like boundary at the flank though its true nature is not yet established. There are no signs of the nominal induced magnetosphere formation. The solar wind penetrates deep into the atmosphere and is absorbed through collisions, leading to a proton void behind Mars. The planetary ion escape rate increases by nearly an order of magnitude. The dayside ionospheric ions driven by the ambipolar field propagate along the magnetic field far upstream. A remarkable and truly unique feature of a degenerate induced magntosphere is a large-scale cross-flow plume, a population of ionospheric ions drifting along the E × B direction over distances of 10s Martian radii. The ambipolar field starts exceeding the convective electric field at cone angles of around 10°. This can be considered as the critical cone angle below which an induced magnetosphere degenerates. Degenerate induced magnetospheres are complex and not yet explored objects. While they are relatively rare for the solar system, it is the nominal case of the interaction for non-magnetized exoplanets located over distance 0.01 to 0.2 au from the sun-like stars.