We keep finding water on Mars – here are all the places it might be

Mars isn’t as dry as it seems. Billions of years ago, oceans and rivers of liquid water rippled across its surface, but now it appears that all of that liquid has disappeared, leaving behind a dusty barren landscape. But as we explore Mars with probes, landers, rovers, and even distant telescopic images, more and more traces of water are popping up.

Each hint fascinates researchers about how important water is to life and how it could aid future exploration. Water has now been found in various forms all over Mars. Here are five places where water has been found.

1. Buried underground

Just beneath Mars’ dry surface lies an icy wonderland. These deposits are insulated by an overlying layer of dust, but erosion or meteorite impacts could expose them to the watchful eye of Mars orbiters. A single icy deposit recently identified using data from the Mars Express spacecraft appears to contain enough water to cover the entire Martian surface with an ocean 1.5 to 2.7 meters deep.

It’s not just ice buried under the orange sand. There’s a controversial theory that there’s a huge lake beneath Earth’s Antarctic pole. It could just be wet silt or volcanic rock. But… New Research Using data from the InSight lander, researchers have uncovered the possibility of another reservoir of water near the Martian equator. InSight found this water, buried 11.5 to 20 kilometers underground, by sensing Martian earthquakes and measuring the speed at which seismic waves travel. The results revealed that the rocks through which the earthquakes travel appear to be saturated with water.

2. Frost the pole

Reaching buried water on Mars will be difficult. For future explorers, the more promising reservoirs are probably exposed on the surface. Mars has ice caps at both poles, just like Earth’s, and we’ve known about them for decades. Many of Mars’ craters also contain small ice sheets inside them, the only places on the Martian surface cold enough to hold ice.

However, at higher latitudes on Mars, the air is cooler and more moist, and temporary frosts can occur. On frigid Martian mornings, volcano peaks are also covered in frost, likely caused by water vapor in the atmosphere freezing.

3. Floating in the atmosphere

Due to Mars’ extreme cold and thin atmosphere, liquid water on the surface sublimates directly into gas and floats in the air. Water vapor in the atmosphere is evidence of water and ice moving across the Martian surface to form frost, but the amount is very small. Occasionally there may be enough water vapor to form a few thin clouds in some places, but most of the time it is negligible.

4. Running downhill

Perhaps the most controversial sign of the possible presence of water on Mars are the recurring slope lines, which are sporadically appearing black streaks running down the sloping rims of craters. They were first discovered in 2011, and since then, researchers have been actively debating their cause. As they occur mainly during the warmest periods of the year, they could be caused by ice melting, running down the slopes and evaporating, which would make them the only liquid water confirmed so far on the Martian surface. Alternatively, they could simply be sand flows. Over time, the latter hypothesis has gained support, but some researchers are hopeful that liquid water could exist in trickles on the Red Planet.

5. Trapped in a rock

If Mars was once covered in water, and all that’s left now is a small amount of ice and lots of dust and rock, where did that water go? One possible answer is that the water was absorbed into the rocks themselves. Mars rovers have found that throughout Mars, there is no shortage of minerals that have water molecules built into their chemical structure.

This process is irreversible, so there’s no way to bring all the water back. But explaining where all the water went is key to understanding what Mars was like before it dried out. This may be our best chance to understand whether Mars was ever truly habitable for life.