Mars may still rumble

The lava flows are a mere 20 million years old

By BBC News Online science editor Dr David Whitehouse

Mars may not be volcanically dead. Lava may have flowed over its surface just a few tens of millions of years ago.

The planet apparently continues to have at least some localised, sporadic activity

Dr William Hartmann

Geologists say this is so recent that they cannot rule out the possibility that the Red Planet may burst into life again.

A team of US scientists have identified young lava flows on the flanks of two of Mars' largest, thought to be extinct, volcanoes.

They say that to settle the issue a lander will be required to visit the sites and analyse the surface rocks.

So young

The evidence that Mars could still be active comes from the Mars Global Surveyor (MGS) spacecraft in orbit around the planet.

Elysium Mons rises 13 km (8 miles) above the surrounding plains

Dr William Hartmann, from the Planetary Science Institute in Tucson, Arizona, US, together with Dr Alfred McEwen, from the University of Arizona, and colleagues, have used images from the MGS camera to estimate the age of lava flows on the slopes of an extinct volcano called Elysium Mons.

These flows are a mere 20 million years old. Elysium Mons is one of three large volcanoes on Elysium Planitia, the second largest volcanic region on Mars. It is 1,700 by 2,400 km (1060 by 1490 miles) in size.

Elysium Mons is the largest volcano in this region, measuring 700 km (435 miles) across and rising 13 km (8 miles) above the surrounding plains.

Counting craters

"Some individual flow units could be as young as 10 million years or less," says Dr Hartmann. "In geological terms, that's so recent that volcanic activity might start up again at any time somewhere on the Red Planet."

The suggestion comes just a few months after scientists found convincing evidence that water may have flowed on the surface of Mars in the past few million years.

The scientists say that the clue lies with the numbers of craters.

They counted the number of impact craters of various sizes on lava flows on the planet. The reasoning is that the older a surface, the more impact craters it will have because it has been exposed for longer.

Olympus Mons volcano: The Solar System's biggest

But the method of estimating the age of a lava flow is uncertain by a factor of up to four and the team's conclusions have yet to be universally accepted.

"If I tell you I have an area with an age of 20 million years and I'm out by a factor of four, then the true age could be as much as 80 million years. But that's still within the last few per cent of Martian history," said Dr Hartmann.

"This means volcanism did not shut off in the first 2.5 billion years, as some early scientific papers proposed. Rather, the planet apparently continues to have at least some localised, sporadic activity."

The researchers have also found evidence for flows less than 100 million years old on the slopes of Olympus Mons, the Solar System's largest volcano, thought to be long extinct.

Definitive answers could only come from a robotic mission to sample surface conditions.