Transporting water into Mars’ upper atmosphere dominates the planet’s water loss into space

Transporting water into Mars’ upper atmosphere dominates the planet’s water loss into space

Press release from: American Association for the Advancement of Science
Published: Thursday 12 November 2020

Instead of its sparse atmospheric water confined to Mars’ lower atmosphere, a new study finds evidence that water on Mars is transported directly to the upper atmosphere, where it is converted into atomic hydrogen that escapes into space. This is a more evident pattern during sandstorms, including the 2018 global sandstorm, the authors say. “The supply of water in the upper atmosphere mediated by sandstorms and seasonality may have played a substantial role in the evolution of the Martian climate from its hot and humid state billions of years ago to the cold and dry planet we observe today,” Shane Stone and colleagues write. This process dominates the current loss of water from Mars.

Mars was once a wet planet: ancient river beds and relic coasts record a period when abundant liquid water flowed freely across the surface. While water still exists on Mars, there is far less than it once flowed across the surface and most of it is locked away in the planet’s polar ice caps, with only traces of water vapor in its atmosphere. Most of Mars’ water was slowly converted to hydrogen in the atmosphere, which is lost in space. This has gradually removed the planet’s water over several billion years, in a process that continues today.

Models of the process suggest that water is converted to molecular hydrogen at lower altitudes, before being transported to the upper atmosphere. Using in situ measurements made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft as it flew through the red planet’s upper atmosphere, Shane Stone and colleagues found the water at higher altitudes than expected. The results show that water is transported directly into the upper atmosphere and converted into atomic hydrogen there by reactions with atmospheric ions. The authors also found that the abundance of water in Mars’ upper atmosphere varies seasonally, peaking in the southern summer and increasing during regional and global dust storms.

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