Mysterious patch on Mars appears to be enormous lump of ice

A large formation near the equator of Mars is now thought to be made of water ice, which could indicate that the Martian climate went through huge temperature swings in the past

Mysterious patch on Mars appears to be enormous lump of ice
A massive deposit near the equator of Mars may be made up of water ice
(Credit: Paopano / Alamy Stock Photos)

A colossal slab of ice may be hiding at Mars’s equator. The composition of this deposit, called the Medusae Fossae Formation, has long been debated, but new data indicates that it contains enough water to cover the entire surface of Mars in an ocean 1.5 to 2.7 metres deep.

When the Mars Express orbiter first took radar measurements of Medusae Fossae in 2007, it wasn’t clear what the formation was made of. But new, more detailed data from the same orbiter shows that it is a huge deposit of water ice, similar to the planet’s polar ice caps.

The data revealed layers within the deposits, with major contrasts between the density and electrical conductivity of each layer. While previous research had suggested that the deposit could be made up of dust or volcanic ash, those materials don’t quite fit the new data. Instead, the layering closely resembles what researchers have seen in radar studies of the Martian polar ice caps.

“Dry material, no matter what it is, just doesn’t fit,” says Tom Watters at the Smithsonian Institution in Washington DC. “We just can’t come up with another material other than water ice that fits the electrical properties, that also has this layering that we’re finding.” Watters led this new research as well as the observations in 2007.

Mysterious patch on Mars appears to be enormous lump of ice
A martian site called Eumenides Dorsu, which is suspected to contain water ice (Credit: ESA) 

This is the largest deposit of water ice found near Mars’s equator, which could potentially be useful for future Mars explorers. However, the ice appears to be buried under several hundred metres of dust and rocks, so it would be extremely difficult to access.

Nevertheless, its very existence is a significant clue to the climate history of Mars. For this huge chunk of ice to have formed, the area near the equator must have once been much colder than it is now, perhaps due to dramatic swings in the planet’s axis. “The Martian climate could have gone through some periods of pretty radical changes,” says Watters. “That would have set the stage for this deposit to have accumulated where it did.”

Journal reference

Geophysical Research Letters DOI: 10.1029/2023GL105490

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