With NASA’s Curiosity rover hogging the limelight, snapping selfies and beautiful panoramic images of the Red Planet, it’s easy to forget the six active satellites orbiting Mars, quietly getting on with their job.

But one of these—the European Space Agency (ESA)’s Mars Express—hit the headlines recently when researchers discovered the most compelling evidence yet of liquid water on Mars.

This water wasn’t in a pond on the surface that researchers just happened to miss. It was lurking 1.5km under Mars’ south pole, forming a 20km long shallow lake.

Led by Adjunct Professor Roberto Orosei of the National Institute of Astrophysics in Bologna, Italy, the ESA team found the lake by painstakingly analysing measurements from a radar instrument called MARSIS on board the satellite.

MARSIS fires radio waves at the planet that penetrate the ground. These waves reflect back in different ways depending on whether they hit rock, ice or water.

“Echoes are much stronger—sometimes stronger than echoes from the top of the ice—when liquid water lies beneath the ice sheet,” Roberto reveals.



The lake is deep underground and must be very salty to stop it from freezing, given it has frozen carbon dioxide above it, which freezes at -125°C. Nevertheless, some experts believe the discovery raises hope that life could persist there.

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