Mars Express finds evidence of huge underground network of water in Mars' wet past

Craters that were once lakes may have had the same water levels as oceans on Mars, findings indicate.

In 2018, the European Space Agency's Mars Express with the help of ISRO's Chandrayaan-2 spacecraft detected a frozen pool of water under Mars' south pole.

Now, new data from Mars Express has brought to light just how much water might have been part of Mars' geological past. Mars had lots and lots of water — on its surface and in liquid form.

Researchers found evidence of large amounts of water by studying 24 deep, enclosed craters in the northern hemisphere of the planet. Some of the features they noticed in and around these craters couldn't have been made any other way, they said in a statement.

Mars Express finds evidence of huge underground network of water in Mars wet past

Example of a crater on Mars with features that are visibly similar to basins. Image: ESA/Mars Express

The above image, titled "ancient northern ocean on Mars", features in the first study published on Mars’ ocean using Mars Express' data, seven long years ago.

A radar instrument called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) on Mars Express was used to search Mars for water below the surface. It found sediments that were "reminiscent of an ocean floor" on the surface. These findings almost mirror what the new study has found independently, and many years later.

A map of Mars showing how once-watery basins on the planet could have distributed. image courtesy: ESA

A map of Mars showing how once-watery basins on the planet could have distributed. image courtesy: ESA

Sea levels on Mars?

The water levels mapped seven years ago match those found in the 2019 study. The more recent findings point to Mars potentially having a 'sea level', as Earth does.

While on Earth, these levels describe actual depths of actual bodies of water on the planet, 'sea levels' on Mars won't take on the same meaning. It's a broader term used to compare the elevation of objects with respect to the planet.

The new evidence that could be an actual 'water level' seems to confirm (or get closer to the truth, at least, about) a real, historical ocean on Mars. The crater-lakes were also probably full at the time they co-existed with the Martian ocean, the study suggests.

How the water-filled basins evolved over time. image courtesy: ESA/NASA

How the water-filled basins evolved over time. image courtesy: ESA/NASA

The new study points to the first evidence of the two water levels not just co-existing, but aligning with one another. The crater-lakes indicate that Mars once had an interconnected system of underground lakes spreading planet-wide, the researchers said.

"We think that this ocean may have connected to a system of underground lakes that spread across the entire planet," Gian Gabriele Ori, the study’s co-author, said in a statement.

They estimate that these basins of water existed on Mars roughly 3.5 billion years ago.

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