The finding suggests that ancient volcanic eruptions may have been major sources of water on early Mars—and could have created habitable environments.

According to a new study, Martian meteorites contain a surprising amount of hydrated minerals, which have water incorporated in their crystalline structures.

In fact, the study authors estimate that the Martian mantle currently contains between 70 and 300 parts per million of water—enough to cover the planet in liquid 660 to 3,300 feet (200 to 1,000 meters) deep.

"Basically the amount of water we're talking about is equal to or more than the amount in the upper mantle of the Earth," which contains 50 to 300 parts per million of water, said study leader Francis McCubbin, a planetary scientist at the University of New Mexico in Albuquerque.

And if water exists today in the Martian mantle, that means the red planet likely had a lot of water in its interior all the way back to the moment the planet formed.

"We don't have to rely on sources like comets and asteroids to bring in water afterward," McCubbin said.