Where Did Water on Mars Go? Maybe, Nowhere.

James Maynard
Mar 17 · 5 min read

Water on Mars disappeared long ago — or did it? Could Mars still hold onto to vast oceans worth of water?

Roughly four billion years ago, Mars was a water world. Is it possible that most of that water is still there? Image credit: ESO/M. Kornmesser/N. Risinger/skysurvey org

Mars was once a water world, filled with massive oceans, rivers and lakes. At one time, the Red Planet could have held onto enough water to cover that world with a global ocean between 100 to 1,500 meters (330 to 4,900 feet) deep — about half the volume of the Atlantic Ocean.

Then, nearly four billion years ago, most of that water was lost, leaving behind the arid desert world we know today. But where did all this water go?

Caltech researchers think they have a surprising answer — most of it may still be there.

Typically, it is believed that most of this Martian water was lost to space, desiccating the Red Planet four billion years ago. Astronomical observations with computer modeling, however, suggests that much of this water — perhaps 30 to 99 percent — may still be trapped in the Martian crust.

This new study examined the total mass of water on Mars in all forms — ice, water, and water vapor. Researchers examined this data alongside studies revealing the chemical composition of the Martian atmosphere and crust.

The landscape of Mars was far different when it was a water world than the desolate desert planet we see today. Image credit: NASA/GSFC

One of the markers researchers look for in these studies is the ratio of two forms of hydrogen — common hydrogen (known as protium) and deuterium. The lightest state of hydrogen — the simplest atom — consists of a single proton orbited by one electron. Within deuterium, also known as heavy hydrogen, a neutron joins the proton in the nucleus of the atom. Typically in nature, about one hydrogen atom out of every 5,000 are deuterium.

During the Noachian period on Mars between 4.1 and 3.7 billion years ago, the surface of the Red Planet likely lost between 40 and 95 percent of its liquid water. As water was lost from Mars, the planet would have lost protium at a greater rate than the more-massive deuterium.

Therefore, if a significant amount of Martian water was lost from the upper atmosphere, it would leave behind a greater amount of deuterium in the Martian atmosphere than would be found if the water had been trapped underground.

Observations reveal the ratio of the two stable isotopes of hydrogen seen in the atmosphere of Mars do not seem to account for the vast quantities of water thought to once be present on the surface of the Red Planet.

“There is abundant geomorphological evidence for large volumes of surface liquid water early in Martian history… Liquid water on Mars decreased over geological time; presently most water is stored in the polar ice caps or as subsurface ice,” researchers describe in the journal Science.

“The thing that makes me happy is that I know that on Mars, two hundred years from now, my books are going to be read. They’ll be up on dead Mars with no atmosphere. And late at night, with a flashlight, some little boy is going to peek under the covers and read The Martian Chronicles on Mars.”
Ray Bradbury

On Earth, chemical weathering forms clays, locking water up in hydrous minerals, holding onto water within their molecular structure. Tectonic processes drive this material into the mantle, forming new crust at plate boundaries, recycling water and gases to the atmosphere.

Just as on Earth, water on Mars was likely driven and locked into hydrous minerals. However, without active tectonic processes on the Red Planet, the water remained forever trapped in the Martian crust, this new study suggests.

A look at how a lack of tectonic activity on Mars could have locked water up in the Martian crust. Image credit: Eva Scheller/Caltech

“Atmospheric escape clearly had a role in water loss, but findings from the last decade of Mars missions have pointed to the fact that there was this huge reservoir of ancient hydrated minerals whose formation certainly decreased water availability over time,” explains Bethany Ehlmann, professor of planetary science at Caltech.

This new finding was made possible though the study from a wide range of sources, including meteorites, telescopes, and spacecraft above the Earth and at Mars.

A look at the Perseverance rover with Dr. Kirsten Siebach, participating scientist on the Perseverance mission. Video credit: The Cosmic Companion

The Perseverance rover, which touched down on Mars on February 18, will examine the Martian crust for signs of water. The main target for the rover is an ancient river delta, created billions of years ago, as a massive river poured into a lake which filled the Jezero Crater.

“The rover landed near outcrops of rock layers that may have originally been laid down before and after the lake and the delta. The NASA team will probe these rocks for their origin; if volcanic, the radiometric dates derived from them could provide clues to the nature and timing of the brief period when water flowed — and life might have flourished,” Paul Voosen writes for Science.

Three spacecraft have recently arrived at Mars — Perseverance, China’s Tianwen-1 mission, and the Hope orbiter from the UAE. Together with the robotic explorers already there, these missions are nearly certain to expand our knowledge of the Red Planet, revealing new wonders about this world which has always called to the human psyche.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

James Maynard

Written by

Writing about space since I was 10, still not Carl Sagan. Weekly video show, podcast, comics, more: www.thecosmiccompanion.net

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

James Maynard

Written by

Writing about space since I was 10, still not Carl Sagan. Weekly video show, podcast, comics, more: www.thecosmiccompanion.net

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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