Much of the water that once flowed across Mars is now locked up in minerals in the planet’s rocks.
Geological features, such as channels and shorelines, on Mars show that rivers and oceans covered much of the planet eons ago. Over time, that water vanished, leaving the planet mostly arid, except for ice at its poles and beneath its surface. One leading theory is that the water escaped to space.
Eva Scheller at the California Institute of Technology in Pasadena and her colleagues used observations from spacecraft and data from Martian meteorites to develop a detailed picture of where those ancient oceans might have gone.
The team’s models show that during the first one billion to 2 billion years of Martian history, roughly a third to nearly all of the water on the planet’s surface became incorporated into minerals in its crust. As rocks on the surface weathered, they sequestered water from the atmosphere.
This process is at least as important as atmospheric escape in explaining the drying of Mars.