A giant raft of rock may once have floated across Mars’ ancient ocean

By Jonathan O’Callaghan

NASA/JPL-Caltech/Univ. of Arizona

A giant floating raft of volcanic rock called pumice could have drifted across an ancient Martian ocean and created one of the most mysterious features we can see on the surface of Mars today.

The Medusae Fossae Formation (MFF), found near the Martian equator, spans about 5000 kilometres. Comprising rolling hills and mounds, scientists have previously suggested its origin was volcanic ash from the nearby Olympus Mons or Elysium Mons volcanoes.

However, the size of the MFF poses some problems for this theory. …