PASADENA, Calif., Nov. 2 (UPI) -- NASA says a study of Mars data gathered over years by orbiters suggests if life ever existed on the red planet it was mostly underground.
Mineral-mapping evidence from more than 350 sites on the planet shows episodes of abundant liquid water on the planet's surface were short-lived, while water could have been reacting with subsurface rock for much longer periods of time, a NASA release said Wednesday.
"The types of clay minerals that formed in the shallow subsurface are all over Mars," John Mustard, professor at Brown University, said in a study published in the journal Nature. "The types that formed on the surface are found at very limited locations and are quite rare."
The discovery of clay minerals on Mars in 2005 indicated the planet once hosted warm, wet conditions, but the new analysis of the data gives clues that warm water was confined to the subsurface with only brief periods when liquid water was stable at the surface.
"If surface habitats were short term, that doesn't mean we should be glum about prospects for life on Mars, but it says something about what type of environment we might want to look in," said the report's lead author, Bethany Ehlmann at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"The most stable Mars habitats over long durations appear to have been in the subsurface. On Earth, underground geothermal environments have active ecosystems."