Matrian water flowed beneath the surface of the red planet billions of years ago, scientists announced Wednesday, giving clues where all the water went on the formerly wet planet.

Scientists reviewed data from one of NASA's Mars rovers that combed the planet and found clay, which only appears in places where water has been. Yves Langevin, a planetary geologist from France, led the study that the journal Nature published on Wednesday.

The team of researchers observed minerals called phyllosilicates, which develop only in the presence of water and ice over the course of geologic time - billions of years.

This is potentially exciting news, Victor Baker, a planetary geologist at Arizona State University, said. Baker was not involved in the Nature review.

Everything we've been finding out is that it's a much more complicated and interesting place than we thought, Baker said. You don't get clay minerals without lots of water related activity.

Water beneath the Mars surface in the past means the planet is geologically complex. The rover currently on Mars is the first exploration equipment advanced enough to indentify clay.

Scientists still don't know whether or not water on Mars was above or below the surface, or both, because of a lack of data, Baker said.

Mars

Mars becomes more geologically interesting as scientists find more evidence of water.

Imagine sending a probe to one spot on Earth and trying to derive the Earth's makeup from that spot, Baker said. We could send a rover to the Grand Canyon, and it'd look a lot different than other places.

Water on Mars increases the possibilities that life existed on the red planet, a sought after hypothesis. Humans are social beings who have always sought out new life through exploration - whether it is in a neighboring, on an island, or across the solar system, Baker said. It's human nature. 

Baker believes the evidence of subsurface water on Mars is credible, but he is also almost certain that new missions to Mars with more modern equipment will reveal new results and new secrets about the planet's past. 

I have a suspicion that it's not the last word, he said.