New view of giant Martian volcano

Olympus Mons, the largest volcano in the Solar System

By BBC News Online science editor Dr David Whitehouse

Laser beams bounced off the surface of Mars have produced a unique view of the largest volcano in the Solar System.

Olympus Mons is 27 km (17 miles) tall, three times the height of Mount Everest, and twenty times wider than it is high.

Looking down from Viking

Images mapped by the Mars Global Surveyor spacecraft have enabled a profile of the Martian volcano to be produced with unprecedented accuracy.

Astronomers say it is raising many questions about the still poorly understood, extinct volcano.

Mars mission

Since it started its mapping mission around Mars in 1998, the Mars Global Surveyor has sent back thousands of high quality images.

It has also scanned the surface of the planet using Mola (Mars Orbiter Laser Altimeter), which beams an infrared laser pulse towards the surface of the Red Planet 10 times a second. Mola then measures how long it takes for a reflection to return to the spacecraft.

A profile of the surface can be obtained to an accuracy of 37 cm (15 inches) with this data. The measurements have been used to construct a precise topographical map of Mars with many applications in geophysics, geology and atmospheric circulation.

The volcano data have been merged with an image of Olympus Mons taken by the Viking Orbiter spacecraft of the 1970s and vertically exaggerated by a factor of 10.

Astronomers say that Mola's data are giving them a new view of the volcano. It shows that Olympus Mons sits off to the west of the main Tharsis rise rather than on its western flank as was thought.

The topography also clearly shows the relationship between the scarp of the Olympus Mons, unique on Mars, and structures produced by the collapse of the flanks of the volcano.