Mysterious patch on Mars appears to be enormous lump of ice

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…