By Dr David Whitehouse BBC News Online science editor

Scientists have produced their most detailed atlas yet of Mars, and have made it freely available on the internet.

It will provide a background for further detailed studies of the geology and geological history of Mars

Mike Malin

The atlas is based on the accurate images sent back from the Mars Global Surveyor (MGS), which has been in orbit around the Red Planet since 1997.

Even though other spacecraft are mapping Mars, the atlas is unlikely to be bettered for many years and researchers say it will play a crucial role in planning future landings.

It will also assist those who hope to prove that Mars is still an active world. Many suspect that changes still occur occasionally, but so far little has been seen.

Global data

The atlas has been produced by Malin Space Science Systems, which processes the data obtained by the camera on board the MGS.

According to Dr Mike Malin, it took about a month to acquire the data for the atlas in May and December 1999, with some additional data from the polar regions in 2001. It then took a further two months to develop the software needed to stitch the data together.

Mars Global Surveyor has been in orbit since 1997

Finally, it took about two days of continuous computer processing, using a Sun SunBlade 1000 system with dual 750-Mhz UltraSPARC III processors and four gigabytes of Ram to assemble the final map.

Dr Malin told BBC News Online: "It is one of several new maps we are creating that will show at 250-metre scale how Mars has changed since the Mariner 9/Viking era in the mid-1970s.

"It will provide a background for further detailed studies of the geology and geological history of Mars. It will be the best global data set for some time to come, so future exploration missions will base their location knowledge on comparisons with these maps."

Rare events

While scientists have been able to study individual MGS images to scrutinise detailed areas of the planet, the atlas provides a unique global view of Mars.

"I like the overall map because, for the first time, you can see both the morphology and the brightness variations... this is something new for digital maps of Mars," said Dr Malin.

But even with the aid of such a detailed map of Mars, scientists have not seen much change on the surface of the Red Planet.

"There are a number of ephemeral and small changes that have occurred," Dr Malin said, "such as occasional small dust avalanches, dust-devil streaks, the waxing and waning polar caps, and the enlargement of the pits in the south polar cap.

"But we have not yet seen any movement of sand dunes or formation of new gullies - but we have come not to expect these latter things to occur. We think they are still rare on a 1-2 year timescale."