Mars was once a wet world, with plenty of water on its surface. But this changed dramatically billions of years ago, leaving behind the desolate landscape we know today. So what happened to the water? Scientists have a new hypothesis.
Researchers said this week that somewhere between 30% and 99% of it could now be trapped in minerals in Martian bark, contradicting the long-held notion that it was lost into space by escaping through the high atmosphere.
“We find that most of Mars’ water has been lost to the crust. The water was lost 3 billion years ago, making Mars the dry planet that has been today for the past 3 billion years, ”said California Institute of Technology PhD candidate Eva Scheller , lead author of the NASA – funded study published Tuesday in the journal Science.
Early in history, Mars may have had melting water on its surface equal in size to half of the Atlantic Ocean, enough to have covered the entire planet with water probably up to nearly a mile (1.5 km) deep.
Water is made up of one oxygen and two hydrogen atoms. The amount of a hydrogen isotope, or variable, called deuterium present on Mars gives some ideas of water loss. Unlike most hydrogen atoms which have only one proton inside the atomic nucleus, deuterium contains a proton and a neutron – or “heavy” hydrogen.
Normal hydrogen can escape through the atmosphere into space more easily than deuterium. Loss of water through the atmosphere, according to scientists, would leave a very large ratio of deuterium compared to normal hydrogen. The researchers used a model that was similar to the composition of a hydrogen isotope and the size of Mars’ water.
“There are three main processes in this model: the introduction of water from volcanism, the loss of water into space and the loss of water into the crust. Through this model and matching it to our hydrogen isotope data set, we can work out how much water has been lost to the place and peeled off, ”said Scheller.
The researchers suggested that not much of the water left the planet, but instead was trapped in several minerals that contain water as part of their mineral structure – clay and sulfates in particular.
This trapped water, while likely to be abundant when taken in its entirety, may not provide a practical resource for future astronaut missions to Mars.
“The water level in a rock or mineral is very low. You had to heat a lot of rock to release water in large quantities, ”said Scheller.