Mars could hide most of its ancient water underground, scientists say

Large amounts of ancient Martian water may have been buried beneath the surface rather than escaping into space, scientists report in the journal. ScienceThe findings, released Tuesday, could help disentangle a clash of theories seeking to explain the disappearance of Mars’ water, a resource that was abundant on the planet’s surface billions of years ago.

Using models and data from Mars probes, rovers and meteorites, researchers at the California Institute of Technology found that a wide range – between 30 and 99 percent – of the Red Planet’s earliest amounts of water was removed from the surface by a geological process. could have disappeared called crustal hydration, where water was trapped in the rocks from Mars.

Evidence of past water on Mars has been written all over the rocky surface, where parched lake beds and rock formations illustrate a world formed by liquids over 3 billion years ago. For years, scientists believed that most of this water had escaped out of space, leaving the planet in its current – very dry – state.

But that takes time. And the rate at which the water could have escaped from the atmosphere, combined with the predicted amount of water that once existed on the surface of Mars, didn’t quite match modern observations of the planet. “If that continues for the past 4 billion years, it could only explain a small fraction of the water loss,” said Renyu Hu, one of the study’s co-authors. That gave researchers an important question: Where exactly did the rest of the water on Mars go?

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

Image: NASA / JPL

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

Water can break down stones through a process called chemical weathering, which sometimes leads to minerals becoming hydrated. Hydrated minerals absorb, store and trap water. For example, gypsum, a water-soluble mineral found naturally on Mars, can hold its water unless heated at temperatures above 212 degrees Fahrenheit.

For years, scientists have observed the spread of aquiferous minerals across the surface of Mars, thanks to spacecraft such as NASA’s Mars Reconnaissance Orbiter, which has been mapping the planet’s geology and climate since 2006. But those views alone are sometimes limited. “You have to wave your hands and extrapolate about how thick that layer is that you see on the surface,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program.

“Only by having measurements at certain places on the surface with your rovers or landers, like Phoenix, or seeing a fresh crater every now and then, can you get an idea of ​​how thick the specific spot on the planet is for the hydrated minerals. the ones you’re looking at, “he says.” So the answers are there, but they slowly build up as you collect more data. “

That’s what led to the study’s findings that the value of ancient water has escaped ancient water inward, not outward. “We wanted to understand this at different scales,” says Scheller.

Hydration of the Earth’s crust takes place on Earth, but our active plate tectonic system recycles rock deep within our planet, heating rocks and releasing water. That water is sent back to the surface by volcanic activity, says Christopher Adcock, a planetary geochemist at the University of Nevada in Las Vegas.

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

Adcock, whose studies include how humans can synthesize and use minerals on Mars for drinking water and rocket fuel, says Scheller’s team findings don’t completely change the game for resource use, “but it’s certainly an encouraging reminder that the water The need for long-term human missions to Mars may be at our feet when we get there. ”

Last month, NASA landed its Perseverance rover on Mars’ Jezero crater, the site of a parched lake whose bottom contains perhaps the most pristine evidence of hydrated minerals – and fossilized microbial life. Persistence will scoop up tiny soil samples and spread them across the surface of the crater for a future “fetch” rover to retrieve. That presents a tempting opportunity for the researchers behind the Science study.

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