Mars was once red with rivers. The telltale traces of rivers, streams and lakes of the past are visible today all over the planet. But about three billion years ago they all dried up – and no one knows why.
“People have come up with different ideas, but we don’t know what caused such dramatic climate change,” said Edwin Kite, a geophysicist at the University of Chicago. “We would really like to understand, especially because it’s the only planet that we know for sure went from habitable to uninhabitable.”
Kite is the first author of a new study that examines the traces of Martian rivers to see what they can reveal about the history of the planet’s water and atmosphere.
Previously, many scientists had assumed that the loss of carbon dioxide from the atmosphere, which helps keep Mars warm, was causing problems. But the new findings, published May 25 in Scientists progresssuggest the change was caused by the loss of another important ingredient that kept 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 amazed to see images of NASA’s Mariner 9 mission as it circled Mars from orbit. The photos revealed a landscape filled with riverbeds, proof that the planet once had plenty of liquid water, though it’s bone dry today.
Since Mars has no tectonic plates to move and bury rock over time, ancient river tracks still lie on the surface as hastily discarded evidence.
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 , analyze maps based on thousands of photos taken from orbiting satellites. Based on the overlapping tracks and how they are weathered, the team pieced together a timeline of how river activity changed elevation and latitude over billions of years.
Then they could combine that with simulations of different weather conditions and see which matched best.
Planetary climates are extremely complex, with very many variables to consider, especially if you want to keep your planet in the “Goldilocks” zone where it is exactly warm enough for water to be liquid but not so hot that it is. end. The heat can come from a planet’s sun, but it must be close enough to receive the radiation, but not so close that the radiation strips the atmosphere. Greenhouse gases, such as carbon dioxide and methane, can trap heat near a planet’s surface. The water itself also plays a role; it can exist as clouds in the atmosphere or as snow and ice on the surface. Snow caps tend to act like a mirror to reflect sunlight back into space, but clouds can either trap or reflect 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 make the planet warm enough for at least some liquid water to exist in rivers for more than billions of years. years, but then suddenly loses her.
But when comparing different simulations, they saw something surprising. Changing the amount of carbon dioxide in the atmosphere did not change the result. In other words, the driving force for change does not appear to be carbon dioxide.
“Carbon dioxide is a potent greenhouse gas, so it was really the leading candidate to explain the drying up of Mars,” said Kite, an otherworldly climate expert. “But these results suggest it’s not that simple.”
There are several alternative options. The new evidence fits well with a scenario, suggested in a 2021 study by 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 the hydrogen had been released from inside the planet, 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 explain the results,” Kite said.
There are several ways to try to reduce the possible factors; the team suggests several possible tests for NASA’s Perseverance rover to perform that could reveal clues.
Kite and his colleague Sasha Warren are also part of the science team that will lead NASA’s Curiosity rover to search for clues as to why Mars is drying up. They hope that these efforts, along with Perseverance’s measurements, can provide additional clues to the puzzle.
On Earth, many forces have combined to keep conditions remarkably stable for millions of years. But other planets may not be so lucky. One of the many questions scientists ask about other planets is how lucky we are, that is, how often this confluence exists in the universe. They hope that studying what happened to other planets, like Mars, can provide clues about planetary climates and how many other planets might be habitable.
“It’s really striking that we have this puzzle right next to it, and yet we still don’t know how to explain it,” Kite said.
Icy clouds could have kept Mars warm enough for rivers and lakes, study finds
Edwin S. Kite et al, Changing spatial distribution of water flow maps, major change in Mars greenhouse effect, Scientists progress (2022). DOI: 10.1126/sciadv.abo5894
Provided by the University of Chicago
Quote: Why did Mars dry up? New study indicates unusual responses (2022, May 26) Retrieved May 26, 2022 from https://phys.org/news/2022-05-mars-unusual.html
This document is subject to copyright. Except for fair use for purposes of private study or research, no part may be reproduced without written permission. The content is provided for information only.