Dusty, airless Mars could be a perfect place to live

It may sound like science fiction but Nasa astrophysicists are taking seriously the idea of transforming Mars into an Earth-like planet fit for life.

It may sound like science fiction but Nasa astrophysicists are taking seriously the idea of transforming Mars into an Earth-like planet fit for life.

The Martian environment is at present cold, dry and almost airless but some senior scientists within the American space agency believe it may be possible to "terraform" the red planet into another warm, blue oasis with a rich atmosphere where life can thrive.

Nasa's Ames Research Center in California will host a two-day summit next week of some of the world's most radical thinkers in the field of planetary exploration who believe they can make Mars habitable by drastically altering its climate for the first time in 4 billion years, the last time that Mars was a warm, wet planet.

Christopher McKay - one of the Nasa scientists who claimed in 1996 to have discovered evidence of life on a Martian meteorite and who has long believed that the red planet is ripe for terraforming - is organising the conference.

"With today's technology, we could transform the climate of Mars, making it suitable once more for life. Such an experiment would allow us to examine, on a grand scale, how biospheres grow and evolve and it would give us the opportunity to spread and study life beyond Earth," Dr McKay said.

But he and his colleagues accept that, even if there was the technical ability and political will to transform Mars, there would have to be a global debate about the ethics of such a severe interference in another planet's environment.

Calculations at the Ames Research Center suggest that it is theoretically possible to start the process of transforming the thin atmosphere of Mars into a thick, gaseous mixture that can trap sufficient heat in the Martian equivalent of the greenhouse effect.

Margarita Marinova, a Nasa researcher, has shown that it would be possible to trigger a runaway greenhouse effect on Mars by introducing some man-made gases into the planet's atmosphere. "The current Martian atmosphere is very thin and does not provide good insulation to the planet - very little solar energy is retained in the atmosphere. A demonstrated method of warming up a planet is by using super-greenhouse gases," Dr Marinova said.

"Super greenhouse gases are very efficient and even at a concentration of only a few parts per million will warm up the planet significantly," she said. "They are non-toxic, have long lifetimes, can be easily made on the Martian surface, and can keep Mars warm."

Dr McKay has calculated that adding super-greenhouse gases would increase the temperature of Mars from the present minus 60C to minus 40C, enough to trigger the release of the frozen carbon dioxide locked in the Martian polar caps. "Carbon dioxide would then augment the greenhouse effect even further, driving the release of more carbon dioxide and water vapour into the atmosphere. Such positive feedback would be sufficient to create a thick, warm atmosphere," Dr McKay said.

Nasa engineers have calculated that it is possible to scatter "Volkswagen-sized machines" around Mars for producing perfluorocarbons (PFCs), gases that are thousands of times more effective than carbon dioxide at trapping heat yet would not destroy any ozone layer that might form around Mars later. The machines would use solar energy to convert minerals in the Martian soil to release PFCs into the atmosphere.

Heating the deep-frozen polar regions of Mars, rich in carbon dioxide and possibly water, could be speeded up by focusing sunlight from a large space mirror or by scattering black powder over the reflective ice fields to encourage the absorption of solar heat.

Such actions would give Mars a carbon-dioxide-rich atmosphere, which would be warm enough for liquid water and for plants to grow, Dr McKay said. "This carbon-dioxide atmosphere would support plant and microbial life but would not contain enough oxygen for animals," he said. But, "the higher temperatures and atmospheric pressures would make bulky space suits and pressure domes unnecessary. And the natural growth of plants would allow the cultivation of farms and forests on Mars's surface, thus providing food for human colonists and visitors."

The change would not be quick, however. Nasa's most optimistic estimate suggests it would take 60 years to bring the average temperature up to a balmy 15C. More realistically, it could take 600 years to turn Mars into a water-rich world.

Colin Pillinger, a professor of planetary science at the Open University, said that terraforming Mars could not occur until the red planet is first thoroughly explored, which itself is unlikely to begin until at least 2020. "One day, who knows? I cannot believe we won't go to Mars and make small pockets of it habitable. Whether we'd want to transform the whole planet is another thing, however."