Scientists find the first large body of liquid water on Mars. It’s about 30 kilometers wide and it lies under a layer of Martian ice.

Scientists have long suspected that Mars isn’t as dry as it looks. Over the years, spacecraft and rovers have uncovered evidence of its watery past. Thanks to these machines, we’ve seen images of streaks on its surface carved from hydrated minerals, chemical fingerprints of clay minerals inside its rocks, and signs of water-ice at its poles.

This is the largest body of liquid water we’ve ever found on the Red Planet.

The announcement came at a press briefing held by the Italian Space Agency in Rome, concerning a paper published today in Science.

“This is a stunning result that suggests water on Mars is not a temporary trickle like previous discoveries but a persistent body of water that provides the conditions for life for extended periods of time,” said Alan Duffy, an associate professor at Swinburne University in Australia, who was not involved in the study.

The European Space Agency’s Mars Express provided the report. The second-oldest spacecraft still operating at Mars its known for the beautiful color stereo images from its High-Resolution Stereo Camera. However, media is currently talking about a different instrument, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS).

“MARSIS was born to make this kind of discovery, and now it has,” says Roberto Orosei, a radio astronomer at the National Institute for Astrophysics, who led the investigation.

MARSIS Instrument

So, the instrument works by transmitting pulses of low-frequency electromagnetic waves toward the red planet. The radio waves interact with features at and below the Martian surface and they reflect back toward the spacecraft. So, MARSIS measures the time it takes for the waves to travel there and back. The radio waves carry clues about the planet’s geological composition.

The long radio waves from the 40-meter antenna can actually penetrate as many as 5 kilometers into the Martian surface.

However, in may of 2012, experts did some software upgrade that enabled Marsis to acquire more detailed data. Therefore the researchers began their survey.

Three and a half years and 29 observations later, they had a radiogrammatic map of Mars’ southern polar plane. When they did all their measurements a layer that had a particularly bright reflection seized their attention. The area is some 12 miles across and several feet deep, roughly one mile beneath the surface of the polar ice cap.

At upper right is the planet’s southern ice cap. The inset image (lower right) shows the area where radar readings were made. AP

“This subsurface anomaly on Mars has radar properties matching water or water-rich sediments,” said Roberto Orosei, lead author of the paper and principal investigator of the MARSIS experiment.

Such discoveries are key to unlocking the mystery of whether life ever formed on Mars in its ancient past, or if it might persist today. But being able to access water sources could also help humans survive on a future crewed mission to the red planet.

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Thumbnail image: Mars’ south pole, as seen from Mars Express. Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO