By Helen Briggs BBC News Online science reporter

People will one day step on Mars but perhaps not for hundreds of years, says an Apollo astronaut.

David Scott, the seventh man to walk on the Moon, was mission commander of Apollo 15 in 1971.

But he says going to Mars will be 10 times more difficult and costly, and there is currently little incentive to commit the resources.

He says, however, that he has no doubt that people will eventually land on the Red Planet.

"Is the technology available to go to Mars? The answer is yes," he told an audience at the Royal Society in London, UK.

"The adventure is what will drive us in the long term," he added. "The long term will be hundreds of years."

'Beauty of space'

Dr Scott was speaking at a debate on the future of space exploration to mark World Space Week.

He was joined by Colin Pillinger, lead scientist of the Beagle 2 Mars lander project, and David Southwood, director of science at the European Space Agency (Esa).

Europe's first mission to the Red Planet departs next summer

Dr Scott said intelligent microbots and probes could now do almost everything the Apollo astronauts did on the Moon but they could not experience the spirit that takes humans into space.

When astronauts do go to Mars, the crew should include an artist, poet or writer to communicate the "beauty of space" to everyone, he said.

People spending money on going into space for their own purposes should support artists who would bring something back for the rest of humanity, he added.

But Professor Pillinger said space tourism was "no bad thing".

"It's going to make space exploration go much faster," he said.

Nuclear rockets

Professor Southwood said that if people really wanted to travel long distances in space, chemically propelled rockets would probably not be good enough.

Other alternatives, such as nuclear power, might have to be addressed, he said.

Esa missions to the Moon, Mars and a distant comet are due for launch next year.