Over a decade ago, initial studies by Mars Express pointed to the existence of massive deposits in the MFF, as deep as 2.5 kilometers. However, the composition of these deposits remained a mystery until now. "We've explored the MFF again using newer data from Mars Express's MARSIS radar, and found the deposits to be even thicker than we thought: up to 3.7 km thick," revealed Thomas Watters of the Smithsonian Institution, USA, who led both the current and initial 2007 studies. He further noted that the radar signals were consistent with what would be expected from layered ice, drawing parallels to the signals from Mars's ice-rich polar caps.

The implications of this discovery are far-reaching. If melted, the ice within the MFF could cover Mars in a water layer approximately 1.5 to 2.7 meters deep. To put this in perspective, this quantity of water is sufficient to fill Earth's Red Sea, marking it as the most significant water reservoir ever found in this region of Mars.

The composition of the MFF, which spans hundreds of kilometers and rises several kilometers high, was previously thought to be either windblown dust, volcanic ash, or sediment. But new insights from the Mars Express's MARSIS radar paint a different picture. "This would create something far denser than what we actually see with MARSIS. And when we modelled how different ice-free materials would behave, nothing reproduced the properties of the MFF - we need ice," explained co-author Andrea Cicchetti of the National Institute for Astrophysics, Italy.

The new findings suggest a combination of dust and ice layers, topped by a dry dust or ash layer several hundred meters thick. This structure challenges previous understandings and hints at a complex climatic history for Mars. Colin Wilson, ESA project scientist for Mars Express and the ESA ExoMars Trace Gas Orbiter (TGO), emphasized the importance of these findings: "If confirmed to be water ice, these massive deposits would change our understanding of Mars climate history."

The presence of such vast ice deposits near Mars's equator is particularly intriguing because they could not have formed under the planet's current climate conditions, suggesting a significant shift in the Martian climate over time. These discoveries also have practical implications for future Mars exploration. As missions typically aim to land near the equator, far from the ice-rich polar regions, the presence of accessible water ice would be invaluable for human exploration.

However, accessing these MFF deposits poses a challenge, as they are buried under hundreds of meters of dust. Despite this, the continued mapping of Mars's water resources, including the recent discovery by TGO's FREND instrument of a hydrogen-rich area the size of the Netherlands in the Valles Marineris, is crucial for building a comprehensive understanding of the planet's water history.

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