ESA’s Mars Express Found Surprising New Water Ice Deposits at Martian Equator

ESA’s Mars Express Space Probe has explored one of the most fascinating features of Mars, highlighting new information about the significant presence of buried water ice at the Martian equator that could redefine our understanding of Martian climate history.

Exploration of the Medusae Fossae Formation

The large geological formation Medusae Fossae (MFF), is a region close to the equator composed of a series of massive wind-sculpted deposits, it is possibly the biggest single source of dust on Mars.

Previously studied more than 15 years ago, MFF was recently reanalyzed using new data acquired by the Mars Express radar MARSIS. The results indicate the presence of water ice layers extending several kilometers below the Martian surface, representing the highest concentration of water ever identified in this region.

*View of the MFF from Mars Express’s High-Resolution Stereo Camera. Credits: ESA/DLR/FU Berlin*

MFF’s early exploration revealed massive deposits up to 2.5 km deep, but the composition remained uncertain. This recent research, led by Thomas Watters of the Smithsonian Institution, USA, lead author of the 2007 study, suggests that the deposits are even more extensive than previously assumed, reaching a depth of up to 3.7 km.

“Excitingly, the radar signals match what we’d expect to see from layered ice, and are similar to the signals we see from Mars’s polar caps, which we know to be very ice-rich.”
— Thomas Watters, Smithsonian Institution, USA

New discoveries about MFF

The MFF, which is characterized by wind-sculpted structures hundreds of kilometers long and several kilometers high, is located on the border between the highlands and lowlands of Mars.

Location of Mars’s Medusae Fossae Formation. This image shows a height map of the martian surface, with lowest land in blue and highest in white. Standing at an impressive 22 km, Olympus Mons is the tallest volcano in the entire Solar System. Credits: ESA

With the initial information, scientists could not determine with certainty if the structures were composed of ice deposits or giant accumulations of windblown dust, volcanic ash, or sediment.

“Here’s where the new radar data comes in! Given how deep it is, if the MFF was simply a giant pile of dust, we’d expect it to become compacted under its own weight [..]This would create something far denser than what we actually see with MARSIS. And when we modeled how different ice-free materials would behave, nothing reproduced the properties of the MFF – we need ice.”
— Andrea Cicchetti, National Institute for Astrophysics, Italy

So the new results suggest the presence of layers of dust and ice, all topped by a protective layer of dry dust or ash several hundred meters thick.

A Planet rich in water

The amount of water ice inside the MFF is remarkable: if melted, it could cover the entire planet with a layer of water 1.5 to 2.7 meters high, surpassing any previously identified water reserve in this part of the planet.

Map of suspected ice at Mars’s equator. The researchers estimate that the layer of dry material (likely dust or volcanic ash) covering the ice is 300–600 m thick. The total volume of water ice contained within the MFF deposits would be 400 000 km3. Credits: Planetary Science Institute/Smithsonian Institution

Despite the current arid conditions on Mars, evidence suggests that in the past water was abundant on the planet’s surface. Ancient river canals, ocean and lake beds, and water-carved valleys suggest the water-rich past of Mars.

The discovery of large deposits of water ice near the equator challenges current understanding of climate, indicating that when these deposits formed the planet was in a different climate epoch.

Relevance and Prospects for Future Missions

“This latest analysis challenges our understanding of the Medusae Fossae Formation, and raises as many questions as answers,” says Colin Wilson, ESA project scientist for Mars Express and the ESA ExoMars Trace Gas Orbiter (TGO). “How long ago did these ice deposits form, and what was Mars like at that time? If confirmed to be water ice, these massive deposits would change our understanding of Mars climate history. Any reservoir of ancient water would be a fascinating target for human or robotic exploration.”

These ice accumulations at the equator also have potential value for future Martian exploration, serving as crucial resources for possible human or robotic missions. Missions to the Red Planet will need to land near the planet’s equator, away from the ice-rich polar ice caps or glaciers in the high latitudes. Access to water is necessary for these missions, making the discovery of ice in this equatorial region almost essential for human missions to the planet.

“Unfortunately, these MFF deposits are covered by hundreds of meters of dust, making them inaccessible for at least the next few decades. However, every bit of ice we find helps us build a better picture of where Mars’s water has flowed before, and where it can be found today” adds Colin.

*Eumenides Dorsum, suspected to contain the thickest MFF ice-rich deposit. Captured by Mars orbiter TGO. Credits: Caltech/JPL Global CTX Mosaic of Mars/Smithsonian Institution*

In addition, while Mars Express explores water ice kilometers deep, the TGO Orbiter, with the FREND instrument, is collaborating by mapping hydrogen near the Martian ground surface, revealing shallow water deposits. In 2021, FREND identified a hydrogen-rich area in Mars’ Valles Marineris the size of the Netherlands, contributing significantly to our understanding of the Red Planet.

Together, these missions are revealing important secrets of the Red Planet, improving our understanding of this Earth-like planet and bringing us one day closer to the day when our visit will be possible.