Mars, a "One-Plate Planet," Was Once Soaked Through by Global Groundwater

Dried out river valley network on Mars

To the modern observer, Mars is a dry, red wasteland that choked our beloved Opportunity rover to death with a swirl of acrid dust. But Mars hasn’t been dry for the entirety of its 4.6-billion-year existence. Polar ice caps, smooth canyons, and atmospheric vapors have all whispered of its watery past. New research in the Journal of Geophysical Research: Planets now lays out evidence of a massive groundwater network that once soaked the entire planet.

Groundwater is moisture, held in the soil and the rocks beneath a planet’s surface, that wells upward as its volume increases. On Earth, groundwater makes up the largest reservoir of liquid fresh water and is found in aquifers, explains the paper’s lead author, Francesco Salese, Ph.D., to Inverse. His new research suggests Mars may have once had a similarly large reservoir of groundwater.

“On Mars we found geological evidence of water related environments that led us to infer the presence of a planetwide groundwater system, possibly interconnected,” says Salese, a planetary geologist at the Faculty of Geosciences at Utrecht University in the Netherlands.

That sort of interconnectivity couldn’t exist on Earth because our planet is made of multiple tectonic plates. Mars, on the other hand, is thought to be a “one-plate planet,” says Salese, “and this could facilitate the basins’ connection.”

martian basin
Features etched into the floors of Martian basins suggest that groundwater once rose through them.

Evidence Etched in Stone

Previous models of Mars had already predicted groundwater at the global scale and had been studied at the local or regional scale, says Salese. But this study represents the first geological evidence supporting these predictions.

He and his colleagues found this evidence by looking closely at photos of 24 craters in the northern hemisphere of Mars snapped by NASA’s Mars Reconnaissance Orbiter and the European Space Agency’s Mars Express orbiter. Near the floor of those craters, they found characteristics that could only have been left behind by rising and falling groundwater levels eroding the soil — valleys, channels, terraces, and deposits of sediment.

In many of the craters, the features appeared at roughly the same level — all at a depth between 4,000 and 4,500 meters below Martian “sea level” (an arbitrary designation, since there’s no more “sea”). This suggested that the craters were interconnected vessels, their water levels fluctuating in tandem with one another as liquid rose out of the ground. They may also have been connected to the putative Martian ocean that existed 3 to 4 billion years ago.

“[When] I saw that there were deposits that demonstrate a possible stationing of the water surface at a certain topographical level in all the basins I got excited!” Salese said. “In the following weeks I have deepened the analysis of these Martian lakes and I saw that it was more than just a coincidence!”

Signs of Life

Water on Mars is a very good hint that there might be life on Mars as well. Salese says his findings overlapped with mineral data from previous studies, showing that the basins are home to some water-related minerals, like iron-rich, magnesium-bearing smectite, deposits rich in serpentines, and ferrihydrite. These minerals, he says, make the basins “high-priority targets” in the search for life because they are linked to the preservation of organic material.

But like any good scientist, he cautiously notes that “scientists until today have never found life,” and they are not sure if it will ever happen.

Whether or not they ever point to signs of life, the data reveal a Mars very different to the one we know now. Where now we only see dust storms and icy poles, water used to gush out of the ground — just as it continues to do on Earth. Perhaps life on Mars once did the same.