Map of suspected ice at Mars’s equator

Mars’s Medusae Fossae Formation (MFF) consists of a series of wind-sculpted deposits measuring hundreds of kilometres across and several kilometres high. Found at the boundary between Mars’s highlands and lowlands, the features are possibly the biggest single source of dust on Mars, and one of the most extensive deposits on the planet.

But this dry layer seems to hide a secret. A team of researchers used Mars Express radar data to peer below the surface. What they found was a top layer of dust that covers what seems to be a thick layer of deposits rich in water ice. This map shows the estimated amount of ice within the mounds that form the MFF, indicating that the ice-rich deposits are up to 3000 m thick.

The researchers estimate that the layer of dry material (likely dust or volcanic ash) covering the ice is 300–600 m thick. This map shows the ice thickness if we assume that the dust is 300 m thick. In this case, the total volume of water ice contained within the MFF deposits would be 400 000 km3, or if it melted, enough to cover Mars in an ocean of water 2.7 m deep.

If the dust layer is instead 600 m thick, the water ice layer would be thinner, and the total volume of water ice contained within the MFF deposits would be 220 000 km3, or if it melted, enough to cover Mars in an ocean of water 1.5 m deep.

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[Image description: Grey planetary surface with coloured blobs. The blobs are blue around the outside, then go to green, yellow, orange, red then white towards the centre. A scale at the bottom reads 'Potential Ice Thickness' and runs from 0 m (dark blue) to 3000 m (red-white)]