Where is most of the water on Mars?

The Martian Water Hunt: Where’s the H2O Hiding?

Okay, Mars. We see it up there, that rusty-red dot in the night sky, and we can’t help but wonder: is there water? Was there ever? And if so, where the heck did it all go? For years, scientists (and let’s be honest, the rest of us space geeks) have been obsessed with this question. The Mars we see today is bone-dry, but the evidence is mounting: this wasn’t always the case. So, the big question remains: where’s the water hiding on the Red Planet? Turns out, it’s mostly locked up as ice, playing a cosmic game of hide-and-seek in the polar regions and buried beneath the surface.

Polar Ice Caps: Mars’s Frozen Reservoirs

Like Earth, Mars has ice caps at both poles. Think of them as giant, frozen reservoirs. But there’s a Martian twist: these caps aren’t just water ice.

• A Seasonal Cocktail: The composition of these ice caps is constantly changing with the seasons. During the Martian winter, it gets so cold that carbon dioxide in the atmosphere freezes solid, forming a layer of dry ice on top of the water ice. Then, as summer rolls around, the dry ice turns back into a gas, leaving the water ice exposed. It’s like a cosmic popsicle melting and refreezing! Interestingly, the north and south caps are different. The northern cap is the big kahuna, mostly water ice with just a bit of carbon dioxide. The southern cap, on the other hand, is colder and keeps a thicker layer of dry ice year-round.
• Seriously Big Ice: Just how much ice are we talking about? Well, the northern polar cap can stretch out to about 1,000 kilometers across during the Martian summer. That’s like covering the entire state of Texas in ice! If you melted it all and spread it out evenly, it would create a global ice sheet about 2 kilometers thick. The southern cap is smaller, but still impressive, reaching about 350 kilometers in diameter and 3 kilometers thick. Radar measurements tell us that the northern cap alone holds about 821,000 cubic kilometers of water ice. To put that in perspective, that’s about 30% of the ice currently sitting on Greenland!
• Layer Upon Layer: Underneath the seasonal ice, there are these things called polar layered deposits. Imagine thousands of thin layers of water ice mixed with dust, like a giant ice cream cake made of cosmic history. These layers tell the story of Mars’s climate changes over hundreds of thousands of years. It’s like reading the rings of a tree, but on a planetary scale.

Subsurface Ice: The Hidden Water

But wait, there’s more! The polar ice caps aren’t the only place to find water on Mars. A huge amount of it is also buried underground as subsurface ice.

• Ice, Ice Everywhere: Orbiting spacecraft with ground-penetrating radar have shown us that water ice is hiding just beneath the surface across large swathes of Mars. In the mid-latitudes, you can find it in craters, along steep cliffs, and in gullies. In some places, you can even see exposed sheets of water ice, sometimes 100 meters thick, covered by just a thin layer of soil. These icy patches are found under about a third of the Martian surface.
• Equatorial Surprise: Here’s a real head-scratcher: scientists have found evidence of massive water ice deposits near the Martian equator! I know, right? Who would expect ice at the equator? This ice is buried within the Medusae Fossae Formation (MFF), under a layer of hardened ash and dry dust. It’s estimated that there’s enough ice there to cover the entire planet in a layer of water 1.5 to 2.7 meters deep! The catch? It’s buried under a crust of hardened ash and dry dust, making it tough to get to.
• Deep, Dark Water: And the plot thickens! Recent studies using seismic data from NASA’s InSight lander suggest there might even be a huge reservoir of liquid water deep down in the Martian crust. We’re talking kilometers below the surface! This underground lake (or more likely, water trapped in cracks and pores in the rock) could be big enough to cover the whole planet in a layer of water 1 to 2 kilometers deep. Now, we can’t get to it with current technology, but it’s a game-changer for understanding Mars’s past and future.

Mars: An Icy Tale

So, where’s most of the water on Mars? The answer is a mix of polar ice caps and subsurface ice deposits. While you won’t find any flowing rivers or lakes on the surface today (at least, not that we know of!), there’s still plenty of water locked up as ice. And who knows, maybe someday we’ll figure out how to tap into those resources and turn Mars into a slightly less dry place. The hunt for Martian water continues, and the discoveries are just getting started!