Now they know why.
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Solar wind stripped Mars of most of its atmosphere billions of years ago, a NASA mission determined.
Solar wind is stripping gas away from the planet at a rate of about 100 grams, roughly a quarter of a pound, every second, Maven found.
The recent study published in journal Science and Geophysical Research Letters sheds light on the mystery of what happened to the once hospital Martian environment.
Since Mars does not possess a global magnetic field unlike Earth, the planet has no protection for its atmosphere from space radiation.
At that time Mars would have lost about the same amount of atmosphere that Earth has today, with its surface pressure of about 1,000 millibars. The consequences for any life that might have existed nearly certainly would have been disastrous.
NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) helped uncover Mars’s transition from a warm, wet environment to a barren dessert. The solar wind was a leading candidate. This interplanetary coronal mass ejection also generated massive, dramatic spikes in oxygen and carbon dioxide ion levels that are streaming into space.
“Solar-wind erosion is an important mechanism for atmospheric loss, and was important enough to account for significant change in the Martian climate”, says Joe Grebowsky, Maven project scientist from NASA’s Goddard Space Flight Center in Greenbelt, Md. Combined with previous evidence, this suggests that the erosion increases significantly during solar storms and that the loss of atmosphere to space was probably the key reason for the major change in the Martian climate. “This is exciting, because solar storms were more common and intense in solar system history”, said Dave Brain, a MAVEN scientist at the University of Colorado, during a news conference Thursday.
Big solar storms, like those that hit the planet last March, can accelerate the loss even further.
MAVEN will complete its primary mission on November 16 and then continue into extended duty. The mission, which NASA boasts is on time and under budget, sought to answer one question: What happened to the water on Mars?
NASA’s planning to launch humans to Mars from Florida in the 2030’s.
“People talk about terraforming Mars, taking the (carbon dioxide) that might be locked up in the crust and putting it back in the atmosphere”, Jakosky said. But there’s no rush. Thin as the Martian atmosphere may be, at its current rate of loss scientists estimate the red planet will not lose its entire atmosphere for about 2 billion more years.
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“This implies that not only is Mars’ atmosphere escaping today and has been escaping over time, but much of that atmosphere may have been lost early on”. Electrons can either collide with atoms in the upper atmosphere where the charged atom is later swept away by the strong electromagnetic fields emitted by the solar wind.
