Mars may look like a dry, dusty planet today. But scientific models indicate that it was likely once home to massive amounts of water, both above and below its surface - and now, researchers have evidence to back those models up.
"Early Mars was a watery world, but as the planet's climate changed this water retreated below the surface to form pools and 'groundwater'," European Space Agency (ESA) researcher Francesco Salese said in a press release.
"We traced this water in our study, as its scale and role is a matter of debate," he continued, "and we found the first geological evidence of a planet-wide groundwater system on Mars."
Using data from a trio of instruments - the High Resolution Stereo Camera (HRSC) aboard the ESA's Mars Express spacecraft, NASA's High Resolution Imaging Science Experiment (HiRISE), and the Context Camera aboard NASA's Mars Reconnaissance Orbiter - the ESA researchers explored two dozen enclosed craters in Mars' northern hemisphere.
On the floors of these craters, the team found features that suggest the craters once contained "pools and flows of water that changed and receded over time".
They were even able to estimate past water levels and found they matched up with the expected shorelines of an ocean that many believe existed on Mars between three and four billion years ago - and which may have been connected to a system of subterranean lakes.
Water is a key indicator of life, so any evidence of water on Mars lends credence to the idea that the planet might have once been home to living organisms.
But evidence of a groundwater system isn't the only ESA discovery with life-on-Mars implications - within five of the craters they examined, the team also found signs of minerals that past research has connected to the emergence of life on Earth.
As Mars Express project scientist Dmitri Titov noted, the discovery could help researchers pinpoint the spots on Mars most likely to contains evidence of past life on the Red Planet - potentially putting us one step closer to finding extraterrestrial life.