New analysis of Mars reveals that the planet has undergone a "series of global volcanic upheavals". These violent episodes spewed lava and water onto the surface, according to the images sent back to earth today by the European Space Agency's (ESA's) Mars Express.

Using images from the High Resolution Stereo Camera (HRSC) on Mars Express, Gerhard Neukum, Freie University, Berlin, Germany, and colleagues can now determine the ages of large regions and resurfacing events on the planet.

He explained that he newly received data suggests that the sculpting of the Martian surface has not proceeded in a steady fashion, as it does on Earth. Rather, the team have discovered that Mars has been wracked by violent volcanic activity five times in the past, after the early supposedly warmer and wetter phase, more than 3.8 thousand million years ago. In between these episodes, the planet has been relatively calm.

The five volcanic episodes stretch throughout Martian history, occurring around 3.5 thousand million years ago, 1.5 thousand million years ago, 400-800 million years ago, 200 million years ago and 100 million years ago.

Neukum estimates that the dates of the earlier episodes are correct to within 100-200 million years and that the later dates are correct to within 20-30 million years.

The ages have been estimated by counting the number of small craters that appear on the landscape. The idea is simple: the older the surface, the more craters it will have accumulated as meteorites of all sizes have struck over the ages.