Looking into the future, Graham said he assumes an opening chapter of planetary engineering will be giving Mars a denser atmosphere. That condition is one in which liquid water is stable, and a higher average surface temperature is present on the planet.

Given those conditions, Graham said, there are Earth organisms that might one day be transplanted to Mars to effect the early stages of the biological terraforming of the Red Planet.

There are two start-up stages, Graham outlined, in giving Mars a makeover.

First, the microbial stage where a variety of photosynthetic microbes, including algae and cyanobacteria would establish a self-sustaining biosphere and begin the transformation of the Martian regolith and atmosphere.

Fast growing green algae, like that found in the Antarctic, Graham reported, are able to survive repeated freezing and thawing - of considerable value in an early terraformed Mars environment. Another class of algae, Micrasterias denticulata, which grows in ponds within the alpine moorlands, has been shown to have a high resistance to strong radiation, he said.

Following the transformations effected by the microbial stage, Graham said he terms the next step as the "bryophyte stage" of terraforming. Bryophytes are extremely important in terrestrial polar and alpine ecosystems where the severe climate prohibits flowering plants.

"More than 460 million years ago, bryophytes once had a significant part in terraforming Earth. Perhaps at some point in the future, they will repeat their role on Mars," Graham noted.

In a second stage, mosses and lichens would be introduced on Mars. They would fix atmospheric carbon dioxide into degradation-resistant organic compounds and transform the atmosphere into one with appreciable amounts of oxygen. This action, in turn, opens the way for flowering plants and eventually agriculture on the surface of Mars, Graham said.

"Lichens are important as Martian colonists. They are a pioneer species that can break down rocks, helping to form mineral soils and create conditions permitting other plants to be introduced to Mars," Graham emphasized. Mosses, too, will likely play an important role in terraforming by sequestering large amounts of carbon dioxide in the form of decay-resistant organic compounds in future Martian peatlands, he added.

Graham advised that further research is needed to improve our understanding of the physiological and ecological roles organisms might play in terraforming Mars.

At present, cyanobacteria, algae, lichens and mosses, he concluded, are top candidates in kick-starting the renovation of the Red Planet into an Earth II.

So, the Moon or Mars … which shall it be? As the AIAA program ended, while many were enlightened about the prospects for human explorers tromping across those worlds this century, the real debate here in America must play out in the halls of Congress and in the minds of the taxpaying public.