Two magazines host a number of articles describing the results of a year of the mission of NASA’s MAVEN space probe, “Science” and “Geophysical Research Letters”. The conclusions about why Mars lost most of its atmosphere were also explained in a NASA press conference held yesterday. Simply put, it was solar wind, which could take away the atmosphere thanks to the absence of a protective magnetic field transforming a planet that was originally similar to Earth in the desolate red planet we know today.

The planet Mars has been studied in various ways by space probes, landers and rovers over the past decades helping to find various pieces of the puzzle of the planet’s history. The MAVEN (Mars Atmosphere and Volatile Evolution) space probe, which reached the red planet a little over a year ago, aims to complete this study by providing the data that were missing on the evolution of the Martian atmosphere.

The Earth is hit by the solar wind with an intensity greater than Mars because it’s closer to our star but has a magnetic field that protects its atmosphere. Originally, Mars also had a magnetic field but this planet is much smaller than the Earth therefore cooled down rapidly losing this shield, which depends on the liquid-iron core.

The result is that more than 4 billion years ago Mars atmosphere was left without protection and began to be scorged by the solar wind. Over time, the loss of atmosphere reduced the planet, on which there was water in the liquid state, to the current conditions. So far, this theory was supported by various data but direct measurements of the effects of the solar wind on Mars atmosphere were missing. In the last year, the MAVEN spacecraft filled this gap.

MAVEN’s measurements indicate that the solar wind is stripping away gas of Mars atmosphere at about 100 grams (a little less than 1/4 pound) every day. At first it seems a negligible amount but without the protection of a magnetic field this phenomenon has been going on for over 4 billion years. In essence, it took many millions of years just to collapse the Martians ecosystems until the presence of liquid water on the planet’s surface was almost completely eliminated.

Solar storms increase the power of the solar wind flows so sometimes a greater amount of gas is stropped from Mars atmosphere. Probably this kind of activity was more common when the Sun was young so it’s possible that initially the rate of atmospheric erosion was higher. The MAVEN spacecraft recorded an acceleration of this phenomenon in March 2015, during a series of solar storms.

MAVEN is ending its primary mission and these results show that it’s already been a success. The spacecraft will keep on studying Mars atmosphere in its extended mission to understand even better the mechanisms of the solar wind’s impact on it. If the gas leak will continue that way it’s estimated that within a couple of billion years Mars will have no atmosphere.

This type of study is reassuring because it shows that this phenomenon requires a very long time to devastate a planet’s atmosphere. That means that when on the Earth there will be a reversal of the magnetic poles with a temporary weakening of the magnetic field there will be no real danger to the Earth’s atmosphere.

This video contains an animation that shows the solar wind striping gas ions from the upper atmosphere of Mars taking them away in space.