According to earlier theories, radiation from the early Sun blew out of the Red Planet’s atmosphere but new research has revealed that Mars’ atmosphere could not have been lost to solar wind.
A recent study showed that despite the absence of a global Earth-like magnetic dipole, Mars’ atmosphere is well protected from the effects of the solar wind on ion escape from the planet. With less than one per cent of Earth’s atmospheric pressure at the surface. Today’s Mars is a dry and cold planet.
Scientists from Swedish Institute of Space Physics said that many geological features indicate that about three to four billion years ago, the planet had an active hydrological cycle.
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.
Causing the greenhouse effect, and thus the hydrological cycle, to collapse, the solar wind over time has eroded the early martian atmosphere, a common hypothesis claims.
Creating an induced magnetosphere unlike Earth, the solar wind induces currents in the ionised upper atmosphere (the ionosphere), But Mars has no global magnetic dipole.
From Swedish Institute of Space Physics and Umee University, Ramstad said: “It has long been thought that this induced magnetosphere is insufficient to protect the Martian atmosphere – However, our measurements show something different,” Since 2004, the Swedish-led ion mass analyser on Mars Express spacecraft has been measuring the ion escape from Mars.
In his research, Ramstad combined and compared measurements of the ion escape under varying solar wind conditions and levels of ionising 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,” said 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,” he said.