At present its surface temperature can plunge to minus 60?C and below.
However, both goals -- heating and thickening -- could be achieved together, say researchers. One idea is to build a large mirror, many miles in diameter, and place it orbit above Mars. This would then be used to focus the Sun's rays onto a polar icecap, melting it and releasing its frozen carbon dioxide contents. The carbon dioxide would then trigger greenhouse heating.
The alternative would be to construct plants for generating super-greenhouse gases -- made of complex combinations of carbon, chlorine and fluorine, and which are thousands of times more effective than carbon dioxide at trapping heat.
These would be built at strategic sites across the planet and should also trigger global temperature rises.
Thickening the Martian atmosphere would also protect its surface from the ultra-violet radiation that bombards its surface and which would otherwise kill off most Earth-like lifeforms on the planet.
According to Chris McKay -- based at NASA's Ames Research Centre in California and a participant in this week's terraforming debate -- either method could provide the terraforming project with a crucial kick-start. With a thicker, warmer atmosphere, ice trapped in the Martian soil would melt and could be used to sustain agriculture.
With plants and trees imported from Earth growing and producing oxygen, the atmosphere would become slowly more Earth-like.
"We should get serious about sending life to Mars," McKay said.
Other scientists remain cautious.
"We now know Mars used to have an atmosphere, but it disappeared for reasons that are still unclear," said Monica Grady, a planetary scientist at the Natural History Museum, London. "If we restore Mars's atmosphere, we could easily find it disappeared again. We would have done some devastating things to the planet for a temporary effect. That is certainly not ethical."
The point is backed by Pratt.
"If we find life on Mars, the philosophical implications will be profound," she said. "If it is unlike earthly life and has a different genetic code, this will show that living beings evolved separately on two neighboring worlds.
"Life is therefore likely to be ubiquitous throughout the galaxy.
"If it has the same genetic code, however, it will indicate that one planet must have contaminated the other -- probably by rocks being blasted across the solar system following meteorite impacts. We may really be Martian in origin.
"Given the importance of these issues, we simply cannot risk starting a global experiment that would wipe out the precious sensitive evidence we are seeking," she added. "This is just not on."
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