Mars may appear dry and barren, but the Red Planet is hiding more water than it seems. Billions of years ago, Mars was covered in vast oceans and rivers, but today, the liquid water has vanished, leaving a dusty desert in its wake. However, as scientists continue to study the planet through orbiters, landers, rovers, and telescopic observations, they keep finding signs of water in various forms.
The discovery of water is exciting because it's essential for life and could be a vital resource for future explorers. Over the years, evidence of water has been found in several places on Mars. Here are five key locations where water has been detected.
Just beneath the surface of Mars lies a hidden treasure: water ice. These ice deposits are protected by a layer of dust, but erosion and meteor impacts occasionally expose them to our orbiters. One ice deposit recently detected by the Mars Express orbiter contains enough water to blanket the entire Martian surface with an ocean 1.5 to 2.7 meters deep.
But the ice beneath Mars’s surface isn’t the only source of water. There have been hints of a vast lake beneath the planet’s south pole, though this has been debated – it might just be wet silt or volcanic rock. A more recent study using data from the InSight lander uncovered another possible water reservoir near the Martian equator. InSight detected this water, buried 11.5 to 20 kilometers underground, by measuring how seismic waves from marsquakes moved through the rock. The findings suggest the rocks might be saturated with water.
While digging deep into Mars to access buried water would be a challenge, there is also ice right on the surface. Mars’s poles have ice caps similar to Earth’s, which have been known for decades. Many craters also contain smaller ice sheets. These are the only surface areas on Mars that remain cold enough for ice to persist.
Additionally, transient frost forms at high latitudes where the air is colder and more humid. On particularly cold Martian mornings, even volcanic peaks can frost over, likely due to water vapor freezing out of the atmosphere.
Due to Mars's extreme cold and thin atmosphere, any liquid water on the surface would quickly sublimate, turning into gas and dispersing into the air. Water vapor in the atmosphere hints at water and ice moving across the surface to form frost, but it’s present in only tiny amounts. Occasionally, there’s enough to form thin clouds, but these occurrences are rare.
One of the most debated signs of water on Mars are recurring slope lineae – dark streaks that appear on crater slopes. First observed in 2011, these streaks have sparked much discussion among scientists. They mainly occur during the warmest times of the year, which suggests they could be caused by ice melting and flowing down the slopes before evaporating. If true, this would be the only liquid water ever observed on Mars’s surface. However, many researchers now believe they are simply sand flows, though some still hope liquid water might be involved.
If Mars was once covered in water and now has only some ice and a lot of dust and rock, where did all the water go? One theory is that it was absorbed into the rocks. Mars rovers have found numerous minerals across the planet with water molecules incorporated into their structures.
This process is irreversible, so retrieving all that water isn’t possible. However, understanding where the water went is crucial for learning what Mars was like before it dried up. This knowledge might be our best chance to determine whether Mars was ever truly habitable.