Water Ice Buried at Mars’ Equator Is Over 2 Miles Thick
A massive deposit of water ice lies buried beneath the equator of Mars. The ice is stacked in layers up to 2.3 miles thick. If melted, it would cover the entire planet in an ocean between 5 and 9 feet deep.
The find came from radar data collected by the European Space Agency’s Mars Express spacecraft. A team led by Thomas Watters at the Smithsonian Institution analyzed signals from the MARSIS radar instrument. They pointed it at the Medusae Fossae Formation, a vast windswept region along Mars’ equator.
The radar bounced back with a clear signature. It matched what scientists expect from layered ice (ESA, 2024). The signal looked similar to what Mars Express detects at the planet’s polar ice caps, which are known to be packed with water ice.
A mystery from 2007
This was not the first time the Medusae Fossae Formation caught scientists’ attention. Watters and his team reported deposits in the region in 2007. At that time, the radar showed material buried up to 1.6 miles deep. The team could not determine what the material was. It could have been dust. It could have been volcanic ash. It could have been ancient sediment. Or it could have been ice.
New radar data changed that. The team re-examined the formation with updated observations and better analysis tools. The deposits turned out to be even thicker than the 2007 data suggested. They reach 2.3 miles deep. More important, the models revealed that only ice could explain the radar signals.
“If the MFF was simply a giant pile of dust, we’d expect it to become compacted under its own weight,” said Andrea Cicchetti, a physicist at Italy’s National Institute for Astrophysics and co-author on the study. “This would create something far denser than what we actually see with MARSIS. When we modeled how different ice-free materials would behave, nothing reproduced the properties of the MFF. We need ice.”
What the deposit looks like
The Medusae Fossae Formation consists of wind-sculpted mounds each hundreds of miles across and several miles high. The new analysis suggests these mounds contain alternating layers of ice and dust. On top sits a protective cap of dry dust or volcanic ash several hundred meters thick.
The total amount of water locked in these layers is staggering. It equals the volume of Earth’s Red Sea. Spread across Mars, that water would form a global layer 1.5 to 2.7 meters deep.
Why this matters for future missions
Mars appears bone dry on the surface today. But evidence of ancient water is everywhere. Dried river channels cut across the terrain. Old lake beds and ocean shorelines mark places where water once pooled. Scientists have also found water ice at the polar caps and in glaciers closer to the equator. Some ice is mixed into the soil near the surface.
But large equatorial deposits like the Medusae Fossae Formation are a different story. Ice buried that deep could not have formed in Mars’ current climate. It must have accumulated during a much earlier, wetter epoch.
This discovery matters for a practical reason. Future human missions to Mars will likely land near the equator. The polar regions are far too remote and harsh. Crews will need water to survive. They will need it to drink. They will need it to grow food. They will need it to make rocket fuel. Carrying all that water from Earth is prohibitively expensive. Finding it on Mars is the only realistic option.
The Medusae Fossae ice, however, is buried under hundreds of meters of Martian dust. Current technology cannot reach it. That makes it useless for near-term missions.
But the find raises an important question. If massive ice deposits exist at the equator in one location, do they exist in others? Are there shallower, more accessible deposits nearby? Every new pocket of ice scientists locate helps build a clearer map of where future crews might find water.
“What Mars looks like today is just one chapter in its history,” Watters said. “These deposits are a window into what the planet was like billions of years ago. They tell us that Mars had a very different climate, one that allowed water ice to accumulate in places we never expected.”
What comes next
ESA’s Mars Express has been orbiting Mars since 2003. Its MARSIS radar continues to probe the subsurface. Another orbiter, the Trace Gas Orbiter, carries an instrument called FREND that maps hydrogen in the top meter of Martian soil. Hydrogen is a proxy for water ice. Together, these spacecraft are building a three-dimensional picture of where water hides on Mars.
The Medusae Fossae Formation remains out of reach for now. But every ice deposit scientists confirm brings humanity one step closer to answering the biggest question about Mars. Where did all its water go? And can we use what’s left to stay there?
The study appears in Geophysical Research Letters.
References
Watters, T. R., Campbell, B. A., Leuschen, C. J., Morgan, G. A., Cicchetti, A., & Holt, J. W. (2024). Evidence of ice-rich layered deposits in the Medusae Fossae Formation of Mars. Geophysical Research Letters, 51(2), e2023GL105490. https://doi.org/10.1029/2023GL105490
European Space Agency. (2024, January 18). Mars Express finds evidence of large water deposit at the Medusae Fossae Formation. https://www.esa.int/Science_Exploration/Space_Science/Mars_Express/Buried_water_ice_at_Mars_s_equator
