Scientists announced Monday that for the first time, they've found evidence of liquid water on Mars – which they say is buried in cracks several miles under the Red Planet's surface.

This is the "best evidence yet" that Mars still has liquid water in addition to frozen water at its poles, according to the University of California, San Diego's Scripps Institution of Oceanography, which led the research.

Before this discovery, "we did not know there was liquid water there," study lead author Vashan Wright told USA TODAY. Finding water on Mars isn't itself a new discovery; the planet's polar regions are full of ice.

But the new research paves the way for future study into Mars' habitability and the search for life somewhere besides Earth. The findings were published in the journal Proceedings of the National Academy of Sciences.

Where is the water on Mars?

Study results suggest that the Martian "midcrust" – 6 to 12 miles below the surface – is composed of igneous rock with thin fractures filled with liquid water.

This is important because "understanding the Martian water cycle is critical for understanding the evolution of the climate, surface and interior,” Wright, an assistant professor at Scripps, said in a statement. “A useful starting point is to identify where water is and how much is there.”

How much water is on Mars?

Scientists say there's enough water on Mars to fill "oceans" on the planet's surface. If the area studied is a representative location, the Martian midcrust could contain a volume of liquid water "exceeding that of hypothesized ancient oceans," the study said. (Scientists believe that about 3 billion years ago, oceans, lakes and rivers were common on Mars.)

In fact, they estimate that the amount of groundwater now locked up under the Martian surface could cover the entire planet to a depth of about a mile.

How did scientists make the discovery?

Researchers used seismic data from NASA's InSight lander to probe the interior of Mars.

They used a mathematical model of rock physics and concluded that InSight's seismic data are best explained by a deep layer of fractured igneous rock saturated with liquid water.

Could the water be used or harvested?

Unfortunately, the water wouldn't be of much use to anyone trying to tap into it to supply a future Mars colony, according to a statement from the University of California, Berkeley, which added that even on Earth, drilling a hole a half-mile deep is difficult.

"Accessing the water could be challenging," Wright acknowledged. Study co-author Michael Manga, a UC Berkeley professor of Earth and planetary science, said jokingly that it could be a challenge for Elon Musk to solve.

What does this mean for life on Mars?

"Establishing that there is a big reservoir of liquid water provides some window into what the climate was like or could be like," Manga, a UC Berkeley professor of Earth and planetary science, said in a statement. "And water is necessary for life as we know it."

He said he believes Mars' underground reservoirs could be harboring some form of life.

"It's certainly true on Earth − deep, deep mines host life, the bottom of the ocean hosts life," he said. "We haven't found any evidence for life on Mars, but at least we have identified a place that should, in principle, be able to sustain life."