A large hidden ocean that could support life has been discovered beneath the surface of Mars. Scientists used seismic data collected by NASA’s InSight lander to locate the underground reservoir, which contains enough fluid to cover the entire planet’s surface to a depth of about a mile.

On Mars, the oceans disappeared over three billion years ago, so the new discovery is exciting. Unfortunately, the reservoir is far too deep to reach for research, lying 11 to 21 kilometers beneath the outer crust. Even on Earth, drilling a hole a mile deep is a challenge.

If humans one day reach the underground reservoir, they may find life there. The ability to study the reservoir could help scientists learn more about the Red Planet’s geological history.

“Water is necessary for life as we know it,” said Michael Manga, co-author of the study and professor of earth and planetary sciences at UC Berkeley.

“I see no reason why (the underground reservoir) shouldn’t be a habitable environment. That’s certainly the case on Earth – deep, deep mines host life, the sea floor hosts life.”

No evidence of life has been discovered on Mars so far, but the vast hidden ocean holds great potential.

Long ago, there were other bodies of water on the planet. Traces of dried-up riverbeds, lakebeds and deltas can be found all over the surface of Mars.

But about 3.5 million years ago, something happened that caused all the water on the planet’s surface to suddenly disappear.

It is unclear what caused the abrupt change, but scientists have suggested that an asteroid impact, the loss of the planet’s magnetic field, or ancient microbial life causing climate change could be the cause.

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