This NASA handout shows an image by the Perseverance rover using its onboard Right Navigation Camera (Navcam) on Mars.
Billions of years ago, Mars was home to lakes and oceans — but where all the water went to transform the planet into the desolate rock we know today has been something of a mystery.
Most of it was thought to have been lost to space, but a new study funded by NASA proposes that it didn’t go anywhere but is trapped within minerals in the crust.
“We’re saying that the crust forms what we call hydrated minerals, so minerals that actually have water in their crystal structure,” said Eva Scheller, lead author of the new paper in Science.
Scheller’s model suggests anywhere between 30 to 99 percent of the initial water remains trapped inside these minerals.
Early Mars was thought to have enough water to cover the whole planet in roughly 100 to 1,500 meters of ocean.
Because the planet lost its magnetic field early in its history, its atmosphere was progressively stripped away, and it was assumed this was how it lost its water.
But the study says while some of the water disappeared, most remained.
It’s still there
Using observations made by Mars rovers as well as of meteorites from the planet, the team focused on hydrogen, a key component of water.
There are different kinds of hydrogen atoms. Most have just one proton in their nucleus, but about 0.02 percent, have both a proton and a neutron, making them heavier. These are known as deuterium, or “heavy” hydrogen.
Because the lighter kind escapes the planet’s atmosphere at a faster rate, the loss of most of the water to space would leave relatively more deuterium behind.
But given how much water the planet is believed to have started with, and the current rate of hydrogen escape observed by spacecraft, the current deuterium-to-hydrogen ratio cannot be explained by atmospheric loss alone.
The study instead says there was a combination of the trapping of water in minerals in the planet’s crust as well as loss to the atmosphere.
“Anytime that you have a rock and it’s interacting with water, there’s a series of very complex reactions that form a hydrated mineral,” said Scheller.