An international team of space physicists reports that Mars is constantly losing part of its atmosphere to space as a result of pressure from solar wind pulses. Their new study in Geophysical Research Letters should help scientists better understand the evolution of Mars's atmosphere.

The researchers analyzed solar wind data and satellite observations that track the flux of heavy ions leaving Mars's atmosphere. Results of the analysis showed that Mars's atmosphere does not drift away at a steady pace; instead, atmospheric escape occurs in bursts.

Those bursts of atmospheric loss are likely related to solar events known as corotating interaction regions (CIRs). CIRs form when regions of fast solar wind encounter slower solar wind, creating a high-pressure pulse. When these CIR pulses pass by Mars, they can drive away particles from Mars's atmosphere.

During times when these CIRs occurred, the outflow of atmospheric particles from Mars was about 2.5 times the outflow when these events were not occurring. Furthermore, about one third of the material lost from Mars into space is lost during the impact and passing of CIRs.

Professor Mark Lester, Head of the Department of Physics and Astronomy at the University of Leicester said: "The main reason it happens at Mars and not at Earth is the lack of a magnetic field produced by the planet, which protects the atmosphere at Earth.

"One other aspect of this work is that the observations were made during a very quiet period in the eleven year solar cycle and so we would expect the effect of these and other large scale disturbances to be higher at other times in the solar cycle."

Citation: Edberg et al., 'Pumping out the atmosphere of Mars through solar wind pressure pulses', Geophys. Res. Lett., March 2010, 37, L03107; doi:10.1029/2009GL041814