"It has long been thought that this induced magnetosphere is insufficient to protect the Martian atmosphere," says Robin Ramstad. "However our measurements show something different." The Swedish-led ion mass analyser on Mars Express has been measuring the ion escape from Mars since 2004. In his research, Robin Ramstad has combined and compared measurements of the ion escape under varying solar wind conditions and levels of ionizing solar radiation, so-called extreme ultraviolet (EUV) radiation. The results show that the solar wind has a comparatively small effect on the ion escape rate, which instead mainly depends on the EUV radiation. This has a large effect on estimations of the total amount of atmosphere that has escaped to space. "Despite stronger solar wind and EUV-radiation levels under the early Sun, ion escape can not explain more than 0.006 bar of atmospheric pressure lost over the course of 3.9 billion years," says Robin Ramstad. "Even our upper estimate, 0.01 bar, is an insignificant amount in comparison to the atmosphere required to maintain a sufficiently strong greenhouse effect, about 1 bar or more according to climate models."

The results presented in the thesis show that a stronger solar wind mainly accelerates particles already escaping the planet’s gravity, but does not increase the ion escape rate. Contrary to previous assumptions, the induced magnetosphere is also shown to protect the bulk of the Martian ionosphere from solar wind energy transfer. Robin Ramstad is from from Västerås in Sweden and has a Master of Science degree in Engineering Physics from Luleå University of Technology.

Thesis defence

On Friday 8 December 2017 Robin Ramstad of the Swedish Institute of Space Physics in Kiruna and Umeå University will defend his PhD thesis entitled Ion escape from Mars: measurements in the present to understand the past. The thesis defence will take place at 9 am in the Aula at the Swedish Institute of Space Physics in Kiruna. The faculty opponent is Assoc. Prof. David Brain, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, USA. The candidate's supervisors are Prof. Stas Barabash and Assoc. Prof. Yoshifumi Futaana at the Swedish Institute of Space Physics, Kiruna.