The Story of Water on Mars: Evidence of an Ancient, Wet Planet

Mars shines with a distinct red color. We call it “the Red Planet,” and it is a world that appears cold, dry, and dusty. The idea of water, and especially liquid water, seems impossible there today. But what if I told you that Mars was once a very different world? What if Mars once had rivers, lakes, and even a vast ocean?

Thanks to decades of robotic exploration, we now have a lot of evidence that Mars was once a much warmer and wetter planet. The story of water on Mars is a central part of our search for ancient life and our understanding of how a planet can change over billions of years. In this article, we will take a deep dive into the evidence for past water on Mars, the missions that have found it, and the reasons why Mars is a dry planet today.

The Early Mars: A World of Rivers and Lakes

The most compelling evidence for a watery past on Mars comes from its surface. From orbit, we can see huge networks of riverbeds, deltas, and what look like ancient shorelines. These features are very similar to the ones we see on Earth that are created by flowing water.

• Riverbeds and Deltas: We have found huge canyons and valleys on Mars that look like they were carved by flowing water. We have also found what look like deltas, which are formations that are created when a river flows into a lake or an ocean.
• Ancient Oceans: Recent research, using data from rovers and orbiters, has suggested that Mars might have once had a vast ocean that covered almost half of its northern hemisphere. The discovery of what looked like ancient beaches and coastal deposits has bolstered this idea and has given us a new picture of a much wetter and more active Mars.

The evidence for these ancient rivers and oceans shows that Mars was not just a cold, dry planet. It had a long period in its history when it was a much warmer and wetter place, with a huge amount of liquid water on its surface.

Our Eyes on Mars: The Rovers and Orbiters

The story of water on Mars is a story of our robotic explorers. Since the first orbiters and landers of the Viking program, every mission to Mars has helped us to put together a more complete picture of the planet’s watery past.

• The Viking Program: The Viking orbiters of the 1970s took the first pictures of ancient riverbeds and canyons, which was the first hint that Mars had a watery past. The Viking landers also performed biology experiments on the surface, which showed some chemical reactions that could have been caused by life, but they also showed a soil that was very rich in chemicals that could have caused the same reactions.
• The Mars Exploration Rovers (Spirit and Opportunity): These twin rovers, which landed on Mars in 2004, were sent to find evidence of past water. They found a lot of mineral evidence, including small, round mineral concretions that are known as “blueberries,” which are formed in water. They also found a patch of pure silica that is often formed in hot springs or hot steam vents on Earth, suggesting a warmer and wetter past.
• The Curiosity and Perseverance Rovers: The Curiosity rover, which landed on Mars in 2012, was sent to explore the Gale Crater, a place that was once a lake. It has found a lot of evidence of ancient riverbeds and a lake that could have existed for millions of years. The Perseverance rover, which landed in 2021, is exploring a different ancient lakebed, the Jezero Crater, and is collecting samples that a future mission will bring back to Earth.

The discoveries from these missions have completely changed our understanding of Mars. They have shown us that Mars was once a much more dynamic and possibly habitable planet.

The Clues in the Rocks: Minerals and Mars’s Watery Past

The most compelling evidence for water on Mars is found in the rocks and minerals on its surface. When water flows over a rock, it leaves a kind of chemical “fingerprint” that tells us about its presence.

• Rounded Pebbles: The Curiosity rover has found smooth, rounded pebbles and rocks on Mars. These kinds of rocks are formed in rivers and streams as the water rolls them over and over again. The presence of these rocks is a very strong sign that there were once rivers and streams on Mars.
• Water-Formed Minerals: The rovers have also found a lot of minerals that are formed in the presence of water, such as clays, sulfates, and hematite. These minerals are like a chemical signature of water’s presence.
• Ancient Ripples: In 2022, the Curiosity rover found ancient wave ripples in a rock formation in the Gale Crater. These ripples are the same as the ripples that are found in the sandy shores of lakes and beaches on Earth. The discovery of these ripples is a very strong sign that Mars once had open bodies of water with waves and wind.

These discoveries have shown us that Mars had a long and complex watery past, with periods of warmth and wetness that were much longer than we once thought.

The Story of the Atmosphere: How Mars Lost Its Water

So, if Mars once had a lot of liquid water, where did it all go? Scientists believe that the story of Mars’s water is linked to the story of its atmosphere.

• Loss of the Magnetic Field: In its early history, Mars had a magnetic field that protected its atmosphere from the Sun’s solar wind. But its core cooled down, and the magnetic field died. Without this protective shield, the solar wind from the Sun began to slowly strip away its atmosphere.
• The Escape of Water: As the atmosphere became thinner, the planet got colder. The water on the surface either evaporated or froze. The Sun’s radiation also broke apart the water vapor in the atmosphere, and the individual hydrogen atoms, which are very light, escaped into space. Over billions of years, Mars lost most of its water and became the cold, dry desert that we see today.

The story of Mars’s water is a great reminder of how important Earth’s magnetic field is for life. It is a story of how a planet can lose its life-giving blanket and become a barren world.

The Search for Water Today: Is There Still Water on Mars?

While Mars is a dry planet, there is still a lot of water there today, but it is not in a liquid form. It is mostly frozen.

• Polar Ice Caps: Mars has two polar ice caps, one at the north pole and one at the south pole. These ice caps are made of a mix of water ice and frozen carbon dioxide. They are a huge reserve of water on the planet.
• Water Ice Under the Surface: We have found a lot of evidence of water ice just under the surface of the planet, especially in the polar and mid-latitude regions. This ice is protected from the Sun’s heat by a layer of dust and soil.
• Liquid Water Flows: While the surface of Mars is too cold and the atmosphere is too thin for liquid water to exist for a long time, we have found some evidence of liquid water flows on the surface. These are small, dark lines that flow down crater walls and hillsides during the summer. Scientists believe that these are flows of very salty water, or brines, which have a lower freezing point than pure water.

The search for water on Mars is still a top priority for scientists. The search for ancient water is a key part of our search for ancient life, and the search for water today is a key part of our plan to send humans to Mars.

Conclusion

The story of water on Mars is a story of a planet that was once warm and wet but is now a cold and dry desert. The evidence of ancient riverbeds, deltas, and mineral deposits has completely changed our view of the Red Planet. The missions that have been sent to Mars have shown us that the planet had a long and complex watery past. The story of Mars’s water is a reminder that planets can change dramatically over billions of years.

The search for water today, in the form of polar ice caps and water ice under the surface, is a crucial part of our plan to send humans to Mars. The mission to bring back Martian rock samples to Earth will give us an even more detailed look at the story of water on Mars. The story of water on Mars is a key part of our search for life, and it is a story that we are still trying to read.