Why Did Mars Dry Out? Mystery Deepens As New Study Points to Unusual Answers

Billions of years ago, a river flowed across this scene in a Mars valley called Mawrth Vallis. A new study examines the tracks of Martian rivers to see what they can reveal about the history of the planet’s water and atmosphere. Credit: NASA/JPL Caltech/University of Arizona

Study led by University of Chicago scientist deepens the mystery about the climate of early Mars.

Mars once ran red with rivers. The telltale tracks of past rivers, streams, and lakes are still visible today all over the planet. But about three billion years ago, they all dried up—and no one knows why.

“People have put forward different ideas, but we’re not sure what caused the climate to change so dramatically,” said University of Chicago geophysical scientist Edwin Kite. “We’d really like to understand, especially because it’s the only planet we definitely know changed from habitable to uninhabitable.”

Kite is the first author of a new research study that examines the tracks of Martian rivers to see what they can reveal about the history of the planet’s water and atmosphere.

Many scientists had previously assumed that losing carbon dioxide from the atmosphere, which helped to keep Mars warm, caused the trouble. But the new research findings, published on May 25, 2022, in the journal Science Advances, suggest that the change was caused by the loss of some other important ingredient that maintained the planet warm enough for running water.

But we still don’t know what it is.

Water, water everywhere—and not a drop to drink

In 1972, scientists were astonished to see pictures from NASA’s Mariner 9 mission as it circled Mars from orbit. The photos revealed a landscape full of riverbeds—evidence that the planet once had plenty of liquid water, even though it’s dry as a bone today.

Since Mars doesn’t have tectonic plates to shift and bury the rock over time, ancient river tracks still lie on the surface like evidence abandoned in a hurry.

This allowed Kite and his collaborators, including University of Chicago graduate student Bowen Fan as well as scientists from the Smithsonian Institution, Planetary Science Institute, California Institute of Technology Jet Propulsion Laboratory, and Aeolis Research, to analyze maps based on thousands of pictures taken from orbit by satellites. Based on which tracks overlap which, and how weathered they are, the team pieced together a timeline of how river activity changed in elevation and latitude over billions of years.

Then they could combine that with simulations of different climate conditions, and see which matched best.

For years, researchers have debated whether Mars once even had enough water to form an ocean, as depicted in this concept illustration. Credit: NASA/GSFC

Planetary climates are enormously complex, with many, many variables to account for—especially if you want to keep your planet in the “Goldilocks” zone where it’s exactly warm enough for water to be liquid but not so hot that it boils. Heat can come from a planet’s sun, but it has to be near enough to receive radiation but not so near that the radiation strips away the atmosphere. Greenhouse gases, such as carbon dioxide and methane, can trap heat near a planet’s surface. Water itself plays a role, too; it can exist as clouds in the atmosphere or as snow and ice on the surface. Snowcaps tend to act as a mirror to reflect away sunlight back into space, but clouds can either trap or reflect away light, depending on their height and composition.

Kite and his collaborators ran many different combinations of these factors in their simulations, looking for conditions that could cause the planet to be warm enough for at least some liquid water to exist in rivers for more than billion years—but then abruptly lose it.

But as they compared different simulations, they saw something surprising. Changing the amount of carbon dioxide in the atmosphere didn’t change the outcome. That is, the driving force of the change didn’t seem to be carbon dioxide.

“Carbon dioxide is a strong greenhouse gas, so it really was the leading candidate to explain the drying out of Mars,” said Kite, an expert on the climates of other worlds. “But these results suggest it’s not so simple.”

There are several alternative options. The new evidence fits nicely with a scenario, suggested in a 2021 study from Kite, where a layer of thin, icy clouds high in Mars’ atmosphere acts like translucent greenhouse glass, trapping heat. Other scientists have suggested that if hydrogen was released from the planet’s interior, it could have interacted with carbon dioxide in the atmosphere to absorb infrared light and warm the planet.

“We don’t know what this factor is, but we need a lot of it to have existed to explain the results,” Kite said.

There are a number of ways to try to narrow down the possible factors; the team suggests several possible tests for NASA’s Perseverance rover to perform that could reveal clues.

Kite and colleague Sasha Warren are also part of the science team that will be directing NASA’s Curiosity Mars rover to search for clues about why Mars dried out. They hope that these efforts, as well as measurements from Perseverance, can provide additional clues to the puzzle

On Earth, many forces have combined to keep the conditions remarkably stable for millions of years. But other planets may not be so lucky. One of the many questions scientists have about other planets is exactly how lucky we are—that is, how often this confluence exists occurs in the universe. They hope that studying what happened to other planets, such as Mars, can yield clues about planetary climates and how many other planets out there might be habitable.

“It’s really striking that we have this puzzle right next door, and yet we’re still not sure how to explain it,” said Kite.

Reference: “Changing spatial distribution of water flow charts major change in Mars’s greenhouse effect” by Edwin S. Kite, Michael A. Mischna, Bowen Fan, Alexander M. Morgan, Sharon A. Wilson and Mark I. Richardson, 25 May 2022, Science Advances.
DOI: 10.1126/sciadv.abo5894

Funding: NASA

GeophysicsMarsPlanetsPopularUniversity of Chicago
Comments ( 14 )
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  • Richie

    “On Earth, many forces have combined to keep the conditions remarkably stable for millions of years.”

    Stability is relative, I guess. On Earth, mile-thick ice has advanced and retreated, and sea level has risen and fallen hundreds of feet, numerous times since the beginning of the Pleistocene.

    Eden-esque stability, Paradise Lost, climate equilibrium — this is a fairy tale as climate scientists well know.

  • Don

    Perhaps the ancient rivers beds formed under ice. Snowball Mars covered completely in ice. The rivers? were warmed by the early planets warm interior core. As the planets core cooled the water went underground.

  • Lello Rispoli

    I found the book by John Brandenburg ” Death on Mars” quite compelling. Eventually some answers can be found there.

  • The Captain

    I don’t get how in every field, people seem to forget what was already known.
    I was taught that a planetoid collision a billion years ago shifted the core and caused it to cool rapidly and stop rotating. The subsequent loss of the radiation belts generated the oobleck like iron core allowed solar radiation to simply strip the atmosphere right off the planet.
    The lower the pressure dropped, the lower water’s boiling point became; just like here on Earth. This process continues today, and Mars’s atmosphere is virtually non-existent.

  • Scott

    We have too many models for Earth’s climate that are wildly inaccurate. The addition of the moons mass to our orbit would have pushed and fluctuated Mars’ Orbit. The trick is pinpointing the arrival of the moon every explanation I’ve heard of its inception has been lazy, but then again our physics models are incomplete so what can you expect we are stabbing in the dark. Those dating techniques based on decay rates of atoms are going to change, eventually. QM and relativity require dark variables that represent the difference between prediction and observation proof the theories are wrong sorry “incomplete”

    • Awake

      Are you high?

  • Eric

    Probably global warming

  • DtMille

    Losing it’s magnetic field explains it fairly well, no?

  • shaunob

    Interesting how a person who came up with a new theory on how mars lost water is now disproving (or attempting to) the competing theory. I worry about their objectiveness

  • Mike Smith

    Ah of course, it had to be global warming! But did the gas stations go out of business, before or after they were no longer able to fill the radiatirs of cars with water?

  • Ewen G Bogle

    The saying is “water water everywhere NOR any drop to drink” not as you have quoted “and NOT a drop to drink”. Regards

  • Prince Maxsamillion Prince

    My philosophy is that it doesn’t have no moisture over time these things will come crumbled so with no moist it will lose its momentum of its speed so yeah it will dry faster almost like quantum mechanics maybe Mars need a little spin

  • Ashok Nighoskar

    The Jurisdiction of the universe was tired of one house and wanted to shift to another place. That is why he changed the whole environment process and made earth suitable for life. Billions of years ago Mars had a habitable climate, now earth and which planet is next.?.one will never be able to find the answers for all these questions. Even if they find it, it is a natural cycle which billions of years after will again occur. It is a game which the jurisdiction wants to play with the human race. Every thing was very similar to earth, but how dinosaurs vanished in a fraction of a second. Similarly the existing life of Mars vanished billions of years before the new dawn ie. EAAAARTH

  • Brett

    Mars is only a little over half the size of Earth and therefore it’s Core cooled faster and early on led to the loss of the Red Planets Magnetic Field which protects a planet from the effects of our suns Solar Wind which…over time ( with no Magnetic Field to deflect the high speed photons in the solar wind )stripped Mars of most of its atmosphere, along with any protection from the deadly solar radiation which over the billions of years has also irradiated much of the Martian ” soil/ground” the very low atmospheric pressure caused water to boil away at a much lower temperature than found here on Earth …although substantial amounts are known to remain frozen underground ( especially at the poles). Not helping matters, Mars has always been at the furthest edge of the so called “Goldilocks Zone” which is the distance from the Sun where water can exist in its liquid form…and thus ideal for the possibility of life arising…(life as we know it)

    So …I think we already know the reasons for and behind Mars losing it’s water …the writers of their paper on the subject should mingle more with other scientists and researchers also in this field of study