Mars hides perhaps most of its old water underground, scientists say

Scientists report in the journal that large amounts of ancient Martian water were buried beneath the surface instead of escaping into space. Science. The findings, published Tuesday, could help disrupt a clash between theories trying to explain the disappearance of Mars’ water, a source that was abundant on the planet’s surface billions of years ago.

Through modeling and data from Mars probes, robbers and meteorites, researchers from the California Institute of Technology found that a wide range – between 30 and 99 percent – of the earliest amounts of water from the Red Planet through a geological process of the surface could disappear. called cross-hydration, where water is trapped in the rocks of Mars.

Evidence of previous water on Mars is written on its rocky surface, where dried-out lake beds and rock formations illustrate a world formed by fluids more than 3 billion years ago. For years, scientists thought that this water mostly escaped into space, leaving the planet in its current – very dry – state.

But it takes time. And the rate at which water could escape the atmosphere, combined with the predicted amount of water that once existed on the Martian surface, is not in line with modern observations of the planet. “If it continues for the past 4 billion years, it could only account for a small fraction of water loss,” says Renyu Hu, one of the study’s co-authors. This left researchers with an important question: where exactly did the rest of the water on Mars go?

The study, led by Eva Scheller, a graduate student in geology at Caltech who studies planetary surface processes, may provide an answer. The study found that most of the water loss occurred between 3.7 billion and 4.1 billion years ago during Mars’ Noah period. During that time, the water on Mars could have interacted and merged with minerals in the earth’s crust – in addition to escaping the planet’s atmosphere – as much water as about half of the Atlantic Ocean.

Image: NASA / JPL

‘One of the things our team realized early in the study is that we need to pay attention to the evidence from the last 10 to 15 years of Mars exploration in terms of what’s going on with our discoveries about the Mars crust, and in particular the nature of water in the Mars crust, ”says Bethany Ehlmann, co-author of the study and professor of geological and planetary sciences at Caltech.

Water can break down rocks through chemical weathering, which sometimes results in minerals being hydrated. Hydrated minerals absorb water and store it. For example, gypsum, a water-soluble mineral found naturally on Mars, can keep its water trapped unless heated at temperatures above 212 degrees Fahrenheit.

For years, scientists have observed the distribution of aquifers across the Martian surface thanks to spacecraft such as NASA’s Mars Reconnaissance Orbiter, which has been mapping the planet’s geology and climate since 2006. But these views alone are sometimes limited. “You have to wave your hands and extrapolate over the thickness of the layer you see on the surface,” said Michael Meyer, chief scientist at NASA’s Mars Exploration Program.

Only by taking measurements at certain places on the surface with your rovers or landers, such as Phoenix, or by occasionally seeing a fresh crater, do you get an idea of ​​how thick the specific place on the planet is for the hydrated minerals you look at, ”he says. “So the answers are there, but they build slowly over time as you get more data.”

This is what led to the findings of the study that the ancient water in the ocean could possibly have escaped inward, not outward. “We wanted to understand it on different scales,” Scheller says.

Cross-hydration occurs on Earth, but our active plate-tectonic system recovers rocks deep in our planet, heats rocks and releases water in the process. The water is sent back to the surface by volcanic activity, says Christopher Adcock, a planetary geochemist at the University of Nevada at Las Vegas.

Mars, on the other hand, is not as geologically active as Earth, which may explain why it has only limited water on its surface. The clearest evidence of water on Mars comes in the form of ice at the poles of the planet and in small amounts in the atmosphere. Scientists have studied hydrated rocks on the Moon, Mars and other planetary bodies as a possible source of potable water for future space missions or fuel that could propel habitats and rockets.

Adcock, whose studies include how people can synthesize and use minerals on Mars for drinking water and rocket fuel, says the findings of Scheller’s team do not change the game for resource utilization, but it is certainly an encouraging reminder that the water we need long-term mission to Mars can be at our feet when we get there. ”

Last month, NASA landed its Perseverance Rover on the Jezero crater of Mars, the site of a dried-up multi-bed whose ground may contain the most pristine evidence of hydrated minerals and petrified microbial life. Perseverance will scoop up small soil samples and spread across the crater’s surface for a future ‘fetch’ rover to fetch it. This provides a tantalizing opportunity for the researchers behind Science study.

“Samples from Jezero will help us test this model,” says Ehlmann. “It increases the importance of bringing the samples back.”