Could Martians be hiding underneath Mars' surface? A new study from NASA released on Wednesday brought up the possibility that life on the planet Mars would have occurred not on the surface of the Red Planet but below in subsurface rocks.

For years scientists had believed that Mars had liquid water in some point in its history. What wasn't clear was how long this liquid water existed in the surface or if it was long enough to foster life. Now after analyzing the mineral-mapping data obtained by NASA's Mars Reconnaissance Orbiter and the European Space Agency's Mars Express, scientists believe that water only existed for short periods of time in the surface.

The team led by Bethany Ehlmann of the California Institute of Technology in Pasadena concluded that Mars' ancient clay minerals formed within the planet's crust when warm water interacted with the rock. Minerals like iron-magnesium clay need water and heat to form.

"These minerals cannot have been formed on the surface, because water would have boiled," says planetary geologist and study author Scott Murchie of Johns Hopkins University's Applied Physics Laboratory in Laurel, Md. "We are seeing a record of warm, circulating, subsurface water."

The discovery could lead to a drastic re-imagining of where life would have existed on Mars. While the surface of the planet was slowly stripped of liquid water, a more stable environment where water interacted happened in the subsurface.

This means that instead of little green men on the surface of Mars or bacteria as the case maybe, life could have flourished in substrate clay. The new evidence also points to a Martian landscape that was mostly cold and dry.

If Martian life had ever existed it would probably be more like bacteria and it wouldn't have evolved beyond a single-celled bacteria. Bacteria can exist in the most hostile environments such as sub-freezing or above-boiling. Bacteria like these would have existed in the subsurface of Mars.

In fact evidence of Martian bacteria was discovered in August 1996 by a group of scientists in the Martian meteorite ALH 84001. The meteorite which crashed in Antarctica had traces of tiny "ovoids" which may actually be fossil remains of bacteria.