NASA’s MAVEN spacecraft tracks massive water loss from ancient Mars
Dust storms have triggered the loss of massive amounts of water from Mars’ atmosphere, according to a new analysis of data collected by NASA’s MAVEN spacecraft. For the first time, water has been tracked to the upper atmosphere of Mars, say the authors of a new article in the journal Science.
Data from the Mars Atmosphere and Volatile Evolution (MAVEN) mission shows that the abundance of water at these altitudes increases dramatically when there is a dust storm – dust allows water to be transported to higher altitudes, Bruce Jakosky, principal investigator at MAVEN and a planetary scientist from the University of Colorado at Boulder, told me.
The greater abundance of water at these altitudes leads directly to a greater rate of hydrogen escape, Jakosky explains. It is possible that much of the hydrogen escape into space occurs during dust storms that occur every few years, rather than spreading throughout the year, he says. .
“Understanding the loss of hydrogen is key to sorting out the history of water on Mars, so this is an important new finding,” Jakosky said.
Water only has a lifespan of about four hours in the upper atmosphere of Mars, which means that it is destroyed about 10 times faster in the upper atmosphere than if it stopped in the average. atmosphere, Shane Stone, a planetologist at the University of Arizona’s Lunar and Planetary Laboratory and the lead author of the article told me.
Stone and his team linked this new mechanism for water release to the seasonal variations in Mars’ atmosphere. Mars is at its hottest when it is closest to the Sun during the summer in its southern hemisphere, he says. This is when these regional and global dust storms occur. During such periods, hygropause (a cold layer in the atmosphere to which water condenses from a vapor to a liquid, producing clouds) is warmed and weakened. This, in turn, allows water to enter the upper atmosphere.
During these hot periods, water ice in the polar caps of Mars is converted from ice to vapor, Stone explains. The water is then transported upward after low hygropause and into the upper atmosphere, he says. Once there, it is dissociated into its constituent hydrogen and oxygen atoms.
These measurements show that the H2O vapor is transported at higher altitudes than previously thought – to the MAVEN space probe, at about 150 km above sea level, Jakosky explains. From there, it’s much easier to separate the H2O and then the hydrogen to escape into space, he says.
The team estimates that this high-speed water loss to the upper atmosphere has likely been a continuous process for at least a billion years. And just over the past billion years, Mars may have lost as much as a global body of water approximately 17 inches deep due to this process.
During its 4.5 billion-year history, however, the authors estimate that Mars likely lost enough water to cover the planet’s surface from an ocean tens to hundreds of meters deep, and that H2O loss rates must have been even higher in the past.
We still don’t know exactly when this mechanism started to work, Stone explains. Extrapolating atmospheric exhaust rates over time to over 4.5 billion years was already an incredibly difficult thing to do, he says. “This new mechanism only makes that calculation more difficult,” Stone said.