Mars was once a humid world, with abundant bodies of water on its surface. But this changed dramatically billions of years ago, leaving behind the desolate landscape that is known today. So what happened to the water? Scientists have a new hypothesis.
The researchers said this week that somewhere between about 30% and 99% of it may now be trapped within minerals in the Martian crust, contradicting the long-held notion that it was simply lost in space when escape through the upper atmosphere.
“We found that most of the water on Mars was lost in the crust. The water was lost 3 billion years ago, which means that Mars has been the dry planet it is today for the last 3 billion years, ”said California Institute of Technology doctoral candidate Eva Scheller, lead author of the study funded by NASA and published Tuesday in the journal Science.
At the beginning of its history, Mars may have possessed liquid water on its surface roughly equivalent in volume to half the Atlantic Ocean, enough to have covered the entire planet with water perhaps up to almost a mile (1.5 km) deep.
Water is made up of one atom of oxygen and two of hydrogen. The amount of a hydrogen isotope, or variant, called deuterium present on Mars, provided some clues about the loss of water. Unlike most hydrogen atoms that have a single proton within the atomic nucleus, deuterium, or “heavy” hydrogen, has one proton and one neutron.
Ordinary hydrogen can escape through the atmosphere into space more easily than deuterium. The loss of water through the atmosphere, according to the scientists, would leave a very large proportion of deuterium compared to ordinary hydrogen. The researchers used a model that simulated the composition of the hydrogen isotope and the volume of water on Mars.
“There are three key processes within this model: entry of water from volcanism, loss of water to space, and loss of water to the crust. Through this model and comparing it with our hydrogen isotope data set, we can calculate how much water was lost in space and in the crust, ”said Scheller.
The researchers suggested that much of the water did not actually leave the planet, but instead ended up trapped in various minerals that contain water as part of their mineral structure, particularly clays and sulfates.
This trapped water, although apparently abundant as a whole, may not provide a practical resource for future astronaut missions to Mars.
“The amount of water inside a rock or mineral is very small. You would have to heat a lot of rock to release water in an appreciable amount, “said Scheller.