For years, Earth has been known as the Blue Planet. It was the only home to liquid water in our solar system, with 71% of its surface covered in the stuff.
But a decade of new research has been challenging this idea.
Though liquid water on the surface is still something only found on Earth, there's plenty of ice, or frozen water. Distant moons like Europa, Ganymede, Callisto, Enceladus and Titan are all known as icy moons. And even more incredibly, some of these moons are showing signs that they have huge oceans underneath their frozen surfaces. There is even a probe—called JUICE—being sent to some of these moons to investigate this possibility!
And then there's Mars.
Yes, Mars! Back in 2018, satellite scans found underground water at the planet's frozen south pole. It was a groundbreaking discovery. And now, further scans have confirmed that this find wasn't just a one-off.
There is an entire network of underground lakes at the Martian south pole. There's a lot of water there!
Martian subglacial lakes
Astronomers are calling these 'subglacial lakes'. This is because they are found underneath—or 'sub-'—the planet's southern polar ice cap. The device making these discoveries is the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument.
In short, this radar is used to probe below the surface of the planet to give scientists guesses as to what is there. Here is a radar image of the south pole.
The areas that are coloured blue are the spots where scientists believe there is water. How do they know? Because different materials reflect radar signals better than others. Liquid water is highly reflective, and it reflects differently than both ice and solid rock. In the image above, the original lake that was discovered in 2018 is in the middle. But the image clearly shows that it is surrounded by other lakes, too.
How is there water underground?
This is a question that will take more research to answer fully. After all, Mars is a really, really cold planet. Even if it is water that is there, how is it not frozen solid?
There's likely two reasons. One, underground volcanic chambers could be warming the area. So while the surface is frozen solid, enough heat is radiating from magma in the Martian mantle to melt the underground water.
Two, it is probably very salty water. Even here on Earth, salt lowers the freezing point of water. That is why so much of the Arctic Ocean is still liquid instead of being a massive ice cube—the salt keeps it from freezing entirely, even though its average temperature is technically below freezing.
Deep sea alien life?
Which gets us to the big question: Can anything be living in these subglacial lakes?
It's possible! From caves to the ocean floor, we have plenty of examples here on Earth of marine life that lives trapped in cold, dark, aquatic habitats. Sadly, we're a long way from knowing the answer to this question for sure. But with more Mars missions on the horizon, we will know the answer eventually.
Who's up for some Martian ice fishing?
If this all has your brain buzzing, be sure to check out the upcoming November issue of OWL magazine. We speak with an expert from the Canadian Space Agency to look at how humans might one day live on the Moon and Mars—underground water is a big part of the plan!