Red planet is safe from solar winds
The atmosphere of Mars is well protected from the effects of the solar wind on ion escape from the planet, despite the absence of a global Earthlike magnetic dipole, a study has found. Present-day Mars is a cold and dry planet with less than one per cent of Earth’s atmospheric pressure at the surface.
However, many geological features indicate the planet had an active hydrological cycle about three to four billion years ago, said researchers from Swedish Institute of Space Physics. An active hydrological cycle would have required a warmer climate in the planet's early history and therefore a thicker atmosphere, one capable of creating a strong greenhouse effect.
A common hypothesis maintains that the solar wind over time has eroded the early martian atmosphere, causing the greenhouse effect, and thus the hydrological cycle, to collapse. Unlike Earth, Mars has no global magnetic dipole, but the solar wind instead induces currents in the ionised upper atmosphere (the ionosphere), creating an induced magnetosphere.
“It has long been thought that this induced magnetosphere is insufficient to protect the martian atmosphere”, said Robin Ramstad, from Swedish Institute of Space Physics and Umee University, Sweden.
“However, our measurements show something different,” said Ramstad. The Swedish-led ion mass analyser on Mars Express spacecraft has been measuring the ion escape from Mars since 2004.
In his research, Ramstad combined and compared measurements of the ion escape under varying solar wind conditions and levels of ionising solar radiation, socalled 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.