The planet Mars does have an atmosphere, but it is exceedingly thin, and planetologists from NASA now have direct evidence of how and why.

NASA's Maven Shows How Solar Winds Strip Martian Atmosphere

New data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission shows that incoming solar winds literally strip the atmosphere off the Red Planet.

More on NASA’s MAVEN mission to Mars

MAVEN has been a smashing success, and the new data from the Mars probe have enabled calculation of the rate at which the Martian atmosphere is losing gas to space by stripping of the solar wind. The researchers conclude that the “stealing” of Mars’ atmosphere increases notably during solar storms. A paper on the results from the MAVEN mission appear in the November 5 issues of the academic journals Science and Geophysical Research Letters.

Several powerful solar storms hammered Mars in March of this year, and MAVEN found that the Red Planet’s atmosphere was being stolen even more rapidly. This together with data showing strong solar storms in the past suggests that loss of atmosphere to space has played a major role in the evolution of the Martian climate from warm and wet to cold and dry.

The solar wind is particles (largely protons and electrons) that is ejected from the atmosphere of the sun at a speed of close to one million mph. The magnetic field of the solar wind produces an electric field that interacts with the atmosphere of Mars as it passes by. This electric field of the solar wind accelerates ions in Mars’ upper atmosphere and they fly off into space.

One of the research projects undertaken by MAVEN is to determine how and where solar wind and ultraviolet light strip gas from the atmosphere of Mars. The new data suggest the loss is found in three different regions of the atmosphere: down the “tail,” where the solar wind moves behind the planet, above the poles of Mars in a “polar plume,” and from the cloud of gas that extends out around the Red Planet.

It turns out that nearly 75% of the escaping ions are energized from the tail region, and close to 25% are from the plume region, meaning just a percent or so of the stolen gas ions are from the (thinning) gas cloud around Mars.

Statement from NASA administrators

“Mars appears to have had a thick atmosphere warm enough to support liquid water which is a key ingredient and medium for life as we currently know it,” noted John Grunsfeld, astronaut and associate administrator for the NASA Science Mission Directorate in Washington. “Understanding what happened to the Mars atmosphere will inform our knowledge of the dynamics and evolution of any planetary atmosphere. Learning what can cause changes to a planet’s environment from one that could host microbes at the surface to one that doesn’t is important to know, and is a key question that is being addressed in NASA’s journey to Mars.”

Data from MAVEN show that the solar wind removes gas at a rate of about 100 grams every second. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” explains Bruce Jakosky, MAVEN principal investigator from the University of Colorado, Boulder. “We’ve seen that the atmospheric erosion increases significantly during solar storms, so we think the loss rate was much higher billions of years ago when the sun was young and more active.”