In 2020, scientists discussed how they may have found one of the culprits in the ultimate martian cold case: how the once-wet planet lost its water. ScienceMagArchives
Fedorova and colleagues believe dust drives a positive feedback that pumps water into the upper atmosphere. Sun-warmed dust particles radiate heat into the lower atmosphere, driving winds that kick up more dust, which in turn leads to more heat and more dust. A warmer atmosphere can hold more water vapor, and the dust itself likely drags water along with it as it swirls into the upper atmosphere.
The TGO observations showed water levels gradually increase through the southern summer, but the MAVEN data suggest regional and global dust storms drive the largest spikes. Over the course of 2 days near the start of the 2018 storm, water abundance in the upper atmosphere, normally about 3 parts per million, more than doubled; by summer's peak, the storm and the overall warming ultimately combined to push those levels to 60 parts per million.
High in the atmosphere, UV light readily splits the water, allowing the hydrogen and oxygen to be lost to space. But Stone and his colleagues believe another destructive mechanism dominates. Their models suggest carbon dioxide, ionized by particles in the solar wind that bombards the atmosphere, vigorously splits the water molecules apart.
The MAVEN team has calculated that if the observed loss rates persisted throughout martian history, they believe Mars lost enough water that, if laid evenly atop the planet's surface, it wouldmore than 25 meters deep. But how long this dust-driven destruction has operated on Mars is anyone's guess, Stone adds. It could be recent, or it may have been key to drying out the planet billions of years ago.
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