The water of Mars is siphoned off from above. NASA’s MAVEN spacecraft found water in the upper Martian atmosphere, where its hydrogen and oxygen atoms are being torn apart, scientists report on November 13th science.
“This completely changes the way we thought hydrogen in particular was being lost into space,” says Shane Stone, a planetary chemist at the University of Arizona in Tucson.
The surface of Mars was shaped by flowing water, but today the planet is an arid desert (SN: December 8th, 2014). Previously, scientists thought the water of Mars was being lost in a “slow and steady trickle” as sunlight split the water in the lower atmosphere and hydrogen gradually diffused upward, Stone says.
But MAVEN, orbiting Mars since 2014, collected water molecules in Mars’ ionosphere at an altitude of about 150 kilometers. That was surprising – previously the highest water seen was about 80 kilometers long (SN: 01/22/18).
The concentration of this flood varied as the seasons changed on Mars, culminating in the southern summer when seasonal dust storms are most common (SN: 07/14/20). During a global dust storm in 2018, the water level rose even further, suggesting dust storms raised the water in a “sudden splash,” says Stone.
The top of the Martian atmosphere is full of charged molecules prepared for rapid chemical reactions, especially with water. So the water up there splits quickly, for an average of only four hours, and hydrogen atoms swim away (SN: 11/27/15). This process is ten times faster than previously known ways for Mars to lose water, calculated Stone and his colleagues.
This process could cause Mars to lose the equivalent of a 44 centimeter deep global ocean plus another 17 centimeters deep ocean during every global dust storm over the past billion years, the team found. That may not explain all of Mars’ water loss, but it is a start.