Mars had lakes and oceans billions of years ago, but where all the water went to turn the earth into the desert rock we know today has remained a mystery.
The majority of it was believed to have been lost to space, but a recent NASA-funded analysis suggests that it didn’t go anywhere and is now embedded inside minerals in the crust.
“We’re suggesting that the crust forms what we call hydrated minerals, which are minerals that have water in their crystal structure,” Eva Scheller, lead author of the latest Science article, told AFP.
According to Scheller’s model, anywhere from 30 to 99 percent of the original water is locked within these rocks.
Originally, it was believed that Mars had enough water to flood the whole earth in an ocean ranging from 100 to 1,500 meters (330 to 4,4920 feet).
Since the earth’s gravitational field was lost early in its history, its atmosphere was gradually taken away, and it was thought that this was how the earth lost its water.
However, the new study’s authors conclude that although some of the water did evaporate, the vast majority persisted.
The team focused on hydrogen, a main component of water, using measurements from Mars rovers as well as meteorites from the earth.
There are different kinds of hydrogen atoms. Most have just one proton in their nucleus, but a tiny fraction, 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’s authors instead say there was a combination of two mechanisms: the trapping of water in minerals in the planet’s crust as well as the loss of water 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.
This process, called “chemical weathering,” also takes place on Earth — for example, in clay, also found on Mars.
But on our planet volcanoes recycle the water back into the atmosphere. Mars, however, doesn’t have tectonic plates, making the changes permanent.
According to the teams’ simulations, the planet lost between most of its water between four to 3.7 billion years ago, which means “Mars was pretty much like we see how it is today for the past three billion years,” said Scheller.
She added she was excited about what the Perseverance rover, which landed last month for a multiyear science mission on the planet, might be able to contribute to the area of research.
“The Perseverance rover is actually going to investigate exactly these processes and reactions that cause the sequestration of water in the crust,” she said.
The team’s model contains multiple scenarios, which they to compare to new data acquired by the rover.
“We can start to say, ‘These parts of the model aren’t working right and these parts are’ and that’s going to help us get closer and closer and closer to the answer,” said Scheller.