Mars’ Missing Water Might Be Hiding in Its Minerals

New research estimates how much water was absorbed into the mineral makeup of Mars’ crust

An image of Mars, shadowed on the right side
Life on Earth began to appear at least 3.5 billion years ago; by then, Mars had already lost much of its water into the crust or outer space. Kevin M. Gill via Flickr under CC BY 2.0

The Martian landscape is an arid expanse of craters and sandstorms, but scientists have spotted several signs that at one point in its life, the Red Planet was awash with blue waters. Scientists have theorized that much of the planet’s water was lost to outer space as the atmosphere dissipated.

But the planet’s vast oceans couldn’t have been lost to space fast enough to account for other milestones in Mars’ existence. The water must have gone somewhere else. A new study presents a solution: the water became incorporated into the chemical makeup of the ground itself. The research uses new computer models and found that if Mars once had a global ocean between 328 and 4,900 feet deep, then a significant amount of that water might now be stored in the planet’s crust.

The study, published on March 16 in the journal Science and presented at the Lunar and Planetary Science Conference, incorporated data collected from Martian meteorites and by NASA’s Curiosity rover.

“The fact that we can tell that there used to be a lot of water on Mars has really big implications for the potential for Mars to have had life in the past,” says planetary scientist Tanya Harrison, director of science strategy of Planet Labs, to Inverse’s Passant Rabie.

Previous attempts to solve the puzzle did not take into account the fact that the crust can suck up water and lock it into hydrated minerals like clay and mudstone, Robin George Andrews reports for National Geographic. So the study’s lead author Eva Scheller, a planetary scientist at the California Institute of Technology, and the research team set out to design a more complete computer model of Mars’ 4.5-billion-year lifetime.

The new model uses constraints based on previous research about Mars’ water. For instance, the hydrated minerals found on Mars so far are all 3 billion years old or older. In the computer model, the process of incorporating water into the crust has to be done by that time. Scientists also know how quickly standard hydrogen is escaping Mars’ atmosphere today, while a heavier form of it called deuterium stays behind. So the model can use that information to estimate how much of Mars’ water escaped into space.

According to the study, up to 99 percent of a shallow Martian ocean would have been absorbed into the planet’s crust. If the oceans were on the deeper end of what’s considered possible—up to 4,900 feet deep—then about 30 percent of the water would have been absorbed into the crust.

The conclusion “helps bring focus to a really important mechanism for water loss on Mars,” says Rice University planetary geologist Kirsten Siebach, who wasn’t involved in the work, to Maria Temming at Science News. “Water getting locked up in crustal minerals may be equally important as water loss to space and could potentially be more important.”

A key finding of the paper is that much of the planet’s water was lost between 3.7 and 4.1 billion years ago, when Mars’ crust formed.

“That's really important because that means Mars already becomes pretty arid 3 billion years ago,” says Scheller to Inverse. “That kind of constraints when we think that Mars would have had this water, which ultimately has implications for habitability.”

Life on Earth began to appear at least 3.5 billion years ago; by then, Mars had already lost much of its water into the crust or outer space. The study also offers some explanation of why Mars transitioned from an ocean planet to a complete desert. Water on Earth also gets incorporated into minerals, too, but then geological activity releases that water back into the environment. Mars doesn’t have the same activity as Earth, so the water got trapped.

If future astronauts wanted to extract water from the minerals, they would have to bake it out, which isn’t energy efficient, says Purdue University planetary scientist Briony Horgan to National Geographic.

So while the study may not impact the future of Mars exploration, it offers a step forward in solving a mystery in the planet’s past.

“What this study does is that it says you have more water to play with early in Mars’s history,” says Siebach to National Geographic. “And that’s when Mars was most habitable.”

Get the latest stories in your inbox every weekday.