Why Mars Once Had a Thick Atmosphere
Long ago, Mars had a warm climate and flowing water. It had a thick Martian atmosphere that trapped heat and helped water stay liquid on the Martian surface. Scientists found ancient riverbeds, lake beds, and signs of erosion, which means liquid water was present.
To keep water from turning into vapor, Mars’ atmospheric pressure must have been much higher in the past. This thicker atmosphere was likely made of carbon dioxide and other gases. But over time, this air thinned out. Understanding why this happened is key to learning more about Mars’ climate evolution.
Mars, the red planet, has no magnetic field to protect it from the solar wind, meaning it loses its atmosphere in a way that Earth doesn’t. Image credit: NASA/GSFC.
The Mystery Behind Mars’ Lost Water
Mars’ water history shows that it had enough water to cover its entire surface in an ocean up to 100 meters deep. Today, that water is either frozen underground or lost to space. Scientists think water escaped when the Martian atmosphere started. As the air thinned, the pressure dropped, and the water could no longer remain liquid.
Water molecules broke apart into hydrogen and oxygen. Hydrogen, being very light, escaped into space easily. Oxygen bonds with iron in the rocks, making Mars surface red. This is part of a bigger mystery called atmospheric escape from Mars, and researchers are still trying to find all the answers.
What Is Atmospheric Sputtering and How It Helped Mars Lose Its Atmosphere?
One reason Mars lost its air is a process called sputtering. Atmospheric sputtering happens when charged particles from the solar wind hit the upper air and knock gas particles into space. On Earth, our magnetic field protects us. But the Mars magnetosphere disappeared billions of years ago, leaving it exposed.
Space weathering Mars, caused by the solar wind, keeps stripping away the remaining gases. Over time, this atmospheric loss added up. Scientists think that most of the original air on Mars has already been lost through sputtering, photochemical escape, and thermal escape—all types of atmospheric escape on Mars.
Artist’s impression of Valles Marineris, as seen from orbit. Credit: NASA
MAVEN: NASA’s Atmosphere-Hunting Orbiter
To understand this loss, NASA launched the MAVEN mission in 2013. MAVEN stands for Mars Atmosphere and Volatile Evolution. The spacecraft orbits Mars and studies its upper atmosphere and how it reacts to the solar wind.
The MAVEN mission has helped scientists understand how gases escape and how space weathering affects Mars’ upper atmosphere. It looks at ionization, argon densities, and the impact of solar storms. One key goal of MAVEN is to measure how fast Mars is losing gas into space today.
First Direct Evidence of Atmospheric Loss
In 2024, a major discovery changed everything. Dr. Shannon M. Curry, a scientist at the University of Colorado Boulder and LASP, found clear proof of atmospheric loss. Her team used data from MAVEN to study argon isotopes, a type of gas that doesn’t react easily with other chemicals.
The study, published in Science Advances, showed that argon isotope data confirmed that Mars still loses its atmosphere every day. This was the first direct evidence of sputtering. It proved what scientists had long suspected—that the solar wind effects on Mars are still happening right now.
Why Mars Couldn’t Hold Onto Its Atmosphere and Water
Earth and Mars started in similar ways, but only Earth kept its air. The big reason is size. Mars is much smaller, with only about one-tenth the mass of Earth. Because of this, it has weaker gravity. Its escape velocity is lower, so light gases can fly off more easily.
Another reason is the loss of the Mars magnetosphere. Earth’s magnetic field protects our air from the solar wind, but Mars lost its magnetic field early in its history. Without protection, the solar wind stripped away its air, causing atmospheric loss over billions of years.
What We’ve Learned About Mars’ Habitability and Atmospheric Loss
The loss of atmosphere and water changed Mars’ habitability. A thick atmosphere is needed to keep the planet warm and protect against radiation. Without it, life would struggle to survive. But billions of years ago, Mars climate was different.
By studying signs of past water and comparing them with modern data, scientists believe early Solar System conditions allowed Mars to support life, at least for a short time. The challenge is finding any signs of ancient microbes that may still exist beneath the Martian surface.
How Scientists Reconstruct the Martian Past
Scientists use many tools to learn about Mars’ climate evolution. They study rock samples from rovers, measure gases in the air with orbiters like MAVEN, and build Mars climate models on computers. These models help simulate what the Mars atmosphere looked like billions of years ago.
A big part of this work includes looking at argon isotopes, chemical clues, and mineral deposits. Researchers also study volcanoes, ice layers, and craters. All of these help them understand how the Martian atmosphere loss happened and what it means for Mars’ habitability.
How You Can Help: Cloudspotting and Citizen Science
Even regular people can help explore Mars. NASA started a citizen science project called Cloudspotting on Mars. It asks volunteers to look at data and help find clouds in the Mars upper atmosphere. This helps researchers learn how air and water behave on the planet today.
By joining online, anyone can take part in real NASA research. This helps scientists find patterns in the data and build better Mars climate models. Public help is making a big difference in solving the mystery of how Mars lost its atmosphere and water.
The Future of Mars and Its Lost Atmosphere and Water
The story of Mars is not over. NASA and other space agencies plan to send new missions to collect rock samples and explore under the surface. These missions may answer questions about life, water, and atmospheric loss.
Some scientists even dream of terraforming Mars one day—bringing back the atmosphere and water. But that is far in the future. For now, learning about the MAVEN mission, sputtering, and solar wind gives us the best clues to understanding the Red Planet.
Atmospheric Escape Types on Mars
| Escape Process | Description |
|---|---|
| Sputtering | Solar wind particles knock gas atoms out of the upper air. |
| Photochemical escape | Sunlight breaks water molecules, letting hydrogen escape. |
| Thermal escape | Hot atoms move fast enough to escape Mars’ gravity. |
Conclusion
Mars is a frozen desert today, but it wasn’t always like this. It once had lakes, rivers, and a thick Martian atmosphere. The loss of its air and water changed everything. Thanks to the MAVEN mission, Science Advances studies, and researchers like Shannon M. Curry, we now know more about atmospheric sputtering, argon isotopes, and the power of the solar wind.
The mystery of how Mars lost its atmosphere and water is slowly being solved. You don’t need to be a scientist to join this journey—just a curious mind and maybe a few minutes to help spot clouds on another planet.
Want to help solve Mars’ greatest mystery? Join a citizen science project or share this article with someone who loves space exploration. The future of Mars starts with us.
Further Reading: Science Advances
FAQs
What is sputtering on Mars?
Sputtering on Mars is a process where high-energy particles from the solar wind hit the Martian atmosphere, knocking atmospheric particles into space.
Why is the Martian atmosphere so thin?
The Martian atmosphere is thin because Mars lacks a strong magnetic field, allowing solar wind to strip away gases over billions of years.
What happened to the Martian atmosphere?
Over time, space weathering and atmospheric sputtering caused most of the Martian atmosphere to escape into space, leaving it cold and dry.
What is sputtering in space?
Sputtering in space is when energetic particles, like those from the solar wind, hit a planet’s atmosphere or surface and eject material into space.
Is the air on Mars toxic?
Yes, the air on Mars is mostly carbon dioxide, with almost no oxygen, making it toxic and unbreathable for humans.
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