A European Space Agency (ESA) spacecraft has uncovered compelling evidence of a vast deposit of water ice buried beneath the surface of Mars’ equator—enough to blanket the entire planet in a shallow ocean if it were to melt.

In a groundbreaking discovery, ESA’s long-serving Mars Express orbiter has detected these massive ice-rich deposits beneath the Medusae Fossae Formation (MFF), a sprawling and enigmatic geological region near the boundary between Mars’ southern highlands and northern lowlands. The MFF spans over 5,000 kilometers and is believed to be the largest single source of dust on the planet.

The radar data reveals that the ice-laden deposits are up to 3,000 meters (nearly 10,000 feet) thick, and if spread evenly across the Martian surface, the water volume would be enough to cover the planet in an ocean between 1.5 and 2.7 meters (4.9 to 8.9 feet) deep.

Not Just Dust: Evidence Points to Layered Water Ice

Previously, the MFF was thought to contain nothing more than deep valleys filled with dust or ash. But new radar observations from MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding), a subsurface radar onboard Mars Express, have transformed our understanding of this region.

“If the MFF were just a massive pile of dust, gravity would compact it over time into a denser formation,” explained Andrea Cicchetti from Italy’s National Institute for Astrophysics. “But the radar signals show low density and strong reflectivity—exactly what we expect from buried water ice.”

This water ice is not in the form of clean, crystal-clear blocks; rather, it is heavily mixed with dust and volcanic ash, making it more difficult to extract. It lies beneath a hardened layer of sediment hundreds of meters thick, effectively sealing it off from the Martian surface and atmosphere.

A Climate Time Capsule Beneath the Martian Surface

The presence of this equatorial ice challenges previous assumptions about where water can be stable on Mars today. Until now, the largest and most accessible ice reserves were thought to exist only near the poles or in the mid-latitudes. Discovering such a significant volume of ice near the equator is both scientifically and practically important.

“This is the largest known deposit of equatorial water ice on Mars,” said Thomas Watters, lead researcher from the Smithsonian Institution. “And its radar profile is strikingly similar to those of the ice-rich polar caps.”

Importantly, the MFF is not just a geological curiosity—it’s a climatic archive. These thick layers may preserve a frozen history of Mars’ past climate, including times when conditions were more favorable for the presence of liquid water and, potentially, microbial life.

How Did the Ice Get There? A Tilted History of Mars

The formation of this deposit is likely linked to Mars’ chaotic axial tilt, which has varied wildly over millions of years—from as little as 10° to as much as 60°, compared to Earth's relatively stable 23.5° tilt. During periods of high obliquity, when the poles tilt more directly toward the Sun, water from the poles could migrate to the equator, freezing out as ice and later becoming buried by layers of ash and dust from volcanic eruptions.

This theory is supported by other discoveries as well:

• In 2008, NASA’s Phoenix Lander directly dug up ice near Mars’ north pole.

• NASA’s Mars Odyssey and Mars Express have both hinted at water-related signatures in the MFF region before.

• The Trace Gas Orbiter found hydrogen deposits—a proxy for water—beneath the surface of Candor Chaos, part of the Valles Marineris canyon system.

• Recently, relict glaciers were discovered in Eastern Noctis Labyrinthus, just 7.3° south of the equator, further indicating that ice near the equator is not anomalous.

Even China’s Zhurong rover found 400,000-year-old features that suggest recent liquid water activity, possibly linked to changes in Mars’ axial tilt.

Implications for Future Mars Missions

While this buried equatorial ice is difficult to access, its strategic location is crucial. Equatorial regions are more temperate and solar-energy rich, making them the prime candidates for future crewed missions. If we could develop the technology to drill through the overlying dust and ash, this ice could one day become a critical resource for human explorers, providing water for drinking, agriculture, and even fuel production.

However, the difficulty lies in the depth. Accessing ice buried several kilometers beneath the surface is not feasible with current robotic technology, and would require massive infrastructure and energy resources—something that may only be achievable with long-term human presence.

An Evolving Understanding of Mars

“This latest analysis challenges our understanding of the MFF and raises as many questions as it answers,” said Colin Wilson, ESA Project Scientist for Mars Express and the Trace Gas Orbiter. “How long did these deposits take to form? What were the atmospheric and geological conditions like during that time?”

The discovery opens up new frontiers in the search for past habitability and future exploration. If confirmed, these ice-rich formations may reshape our plans for colonizing Mars and studying its climate evolution.

The full study is published in Geophysical Research Letters, offering a new lens through which to examine the Red Planet’s dynamic and still mysterious history.