Solar wind and radiation are responsible for stripping away the ancient Martian atmosphere, transforming Mars from a planet that could have supported life billions of years ago into the frigid Red Planet we see today, according to new results from NASA’s MAVEN spacecraft.

“We’ve determined that most of the gas ever present in the Mars atmosphere has been lost to space,” said Bruce Jakosky, principal investigator for the Mars Atmosphere and Volatile Evolution Mission (MAVEN), University of Colorado in Boulder. “The team made this determination from the latest result, which reveals that about 65 percent of the argon that was ever in the atmosphere has been lost to space.”

In 2015, MAVEN team members had previously announced results showing that atmospheric gas was being lost to space and that described the processes by which atmosphere was being stripped away. The present analysis uses measurements of today’s atmosphere to give the first estimate of how much gas has been removed through time.

Liquid water, essential for life, is not stable on the Red Planet’s surface today because the atmosphere is too cold and thin to support it. However, evidence such as features resembling dry riverbeds and minerals that only form in the presence of liquid water indicates the ancient Martian climate was much different – warm enough for water to flow on the surface for extended periods.

There are many ways a planet can lose some of its atmosphere. For example, chemical reactions can lock gas away in surface rocks, or an atmosphere can be eroded by radiation and a stellar wind from a planet’s parent star. The new result reveals that solar wind and radiation were responsible for most of the atmospheric loss on Mars, and the depletion was enough to transform the Martian climate. The solar wind is a thin stream of electrically conducting gas constantly blowing out from the surface of the sun.

Our early Sun had far more intense ultraviolet radiation and solar wind than today, so atmospheric loss by these processes was likely much greater in Mars’ history. According to the team, these processes may have been the dominant ones controlling the planet’s climate and habitability. It’s possible microbial life could have existed at the surface early in Mars’ history. As the planet cooled off and dried up, any life could have been driven underground or forced into rare surface oases.

Video credit and article source: NASA