A Hidden Ocean Beneath Mars? Scientists Investigate

Mars has been wearing a convincing disguise for decades. It appeared to be exactly what most scientists believed it to be: a dead, desiccated planet where any water had long since disappeared into thin air or frozen into the poles. The exterior was covered in rust and dust. Now that image is slowly disintegrating.

A number of revelations over the last year have begun to construct a case that is hard to reject. There might be enough liquid water somewhere between three and five miles below the Martian surface to fill the entire planet with an ocean that is almost half a mile deep. That sum is not insignificant. That is about the amount of water trapped in the ice sheet of Antarctica, suspended in the cracked rocks of a once-dry world.

Seismic data provided the most striking hints. NASA’s InSight lander spent years pressing its instruments against the Martian surface and listening before it went silent in late 2022. Echoes were eventually extracted from that data by researchers at the Chinese Academy of Sciences and published in the journal National Science Review in early 2025. The way that seismic waves from earthquakes behave suggests that beneath the planet’s upper crust, there is a saturated rock layer that is porous and wet. This type of signal would immediately indicate a deep aquifer on Earth. On Mars, it suggests something that scientists are obviously excited about but are still hesitant to label as settled science.

One of the study’s authors, Weijia Sun, put it simply: Mars has continuously been at the center of the hunt for extraterrestrial life within our solar system. Water has always been at the center of that search. It appears that water may still exist today, but it may be much deeper than anyone was anticipating.

The fact that several separate research threads are coming to the same conclusion is what distinguishes this from a single fortunate data reading. Geologists at New York University Abu Dhabi were working on a completely different project while seismologists were analyzing the echoes of earthquakes. They noticed that the ancient sand dunes in Gale Crater, which NASA’s Curiosity rover has been traversing for years, had solidified into rock in a manner that isn’t possible in dry conditions. Groundwater once seeped upward through cracks and fractures, leaving chemical fingerprints behind, as revealed by the minerals embedded in those formations, especially gypsum. Mars didn’t just go from wet to dry, as Dimitra Atri, who oversaw that study, put it when describing the discovery. Long after the rivers and lakes vanished, water continued to flow underground.

The image of a planet losing its surface, retaining its water underneath, and withdrawing inward like a person who stops expressing emotion but hasn’t stopped feeling it has an almost subdued devastating quality.

Next came the Caltech study, which was just released in the journal Nature. Michael Lamb and Abdallah Zaki, two researchers, adopted a completely different strategy. Similar to draining a bathtub, they dried up Earth’s oceans in computer models and examined what geological features remained. Because shorelines erode and change, the most noticeable remnant was not a shoreline. It was the continental shelf, that level stretch of land where the ocean floor meets the land, encircling a continent like a ring that remains after the water has subsided. They discovered precisely that type of structure in the northern hemisphere of Mars, which would have covered about one-third of the planet’s surface, when they examined topographic data from the planet. They pointed out that a feature like this doesn’t develop around a lake. It requires time and an ocean.

Whether any of this water is reachable, whether it’s warm enough to stay liquid, and whether it could sustain life as we know it today are still unknown. Serious scientists are careful to point out that those are huge unknowns. However, it’s possible that the dark, pressurized, radiation-insulated subsurface of Mars is precisely the kind of safe haven where microbial life could have endured long after the surface became uninhabitable. Stranger locations on Earth have been discovered to support life, including deep ocean vents, Antarctic ice, and solid rock kilometers below the surface.

The idea that Mars is just dead is becoming more and more difficult to dispute. From minerals in old dunes to the subtle trembling of a planet that still has something to say, the geological evidence keeps mounting. No rover or orbiter has yet to determine whether that something contains life. However, it says something that the question seems more serious now than it did five years ago. Seldom is science a single, spectacular discovery. Usually, something like a bathtub ring here, a seismic echo there, or an incorrectly hardened sand dune gradually comes together to alter your perception of everything.