Mars mystery revealed as massive volcanic deposit

A mysterious Martian rock formation one-fifth the size of the continental United States is likely the largest explosive volcanic deposit so far discovered in the solar system, research reveals.

The rock deposit, known as the Medusae Fossae Formation, sits near the planet’s equator, and was first observed by NASA’s Mariner spacecraft in the 1960s. Until now, however, its origin has remained unexplained.

In a paper published in the Journal of Geophysical Research: Planets, Lujendra Ojha and Kevin Lewis from Johns Hopkins University in the US report that measurements of the formation’s gravity and topography signatures, together with previous radar readings, show that it comprises dry and porous rock – very likely the result of volcanic explosions.

The scientists estimate that a series of eruptions took place around three billion years ago. The events were so huge and so violent that they would have changed the face of the planet.

As well as ejecting enormous amounts of lava, the eruptions would have spewed out enough water to cover the whole of Mars to a depth of about nine centimetres. And the newly-made ocean would have remained liquid, because greenhouse gases also ejected would have warmed the atmosphere – in the process infusing it with large quantities of hydrogen sulfide and sulfur dioxide.

The end result, say the researchers, was a rock deposit 100 times more massive than any volcanic formation found on Earth.

“This is a massive deposit, not only on a Martian scale, but also in terms of the solar system, because we do not know of any other deposit that is like this,” says Ojha.