Volcanic activity could occur on Mars today, scientists have concluded, from the most recent analysis of images sent back by the Mars Global Surveyor (MGS).

The images cast new light on Mars's most recent and most distant past.

The study in Nature magazine suggests that volcanic activity has occurred on Mars in the past 50 million years. This is relatively recently in geological terms - Mars is 4.5 billion years old - and so volcanic activity may not have died out completely.

An ancient extinct volcano

The scientists analysed the number and size of craters on the Martian surface. This gives a measure of how old the surface is, as the longer ago the surface was formed, the more pitted it will be.

Previous surveys could only see craters hundreds of meters across but the new work spotted those as small as 16m (50 feet) across. Their work suggests that new lava flows have spilled out over Mars in very recent geological time.

One region, the great shield caldera of Arsia Mons, is no older than 40-100 million years.

Turbulent youth

Other new results show that Mars' youth may have been more turbulent than was thought.

Martian history is recorded in the rocks laid down on its surface. Scientists have got a good view of these layers by looking at the sides of the 4,000km (2,500 mile) long Valles Marineris canyon system.

American scientists say this layering suggests intense volcanic activity for up to the first billion years of Mars' history.

Previous studies suggested that the main forces at work in shaping the young Mars were meteorite impacts fracturing the surface.

The early volcanism would have released torrential floods of water from sub-surface ice deposits.

The new interpretations of Mars' history are based on analysis of MGS images but these cover only a tiny fraction of the surface.

Scientists say that there are images already taken but not yet studied that promise many future revelations.