There is a notion -- strangely, embraced by both ultra-liberal tree huggers and rabid reactionary exploiters -- that the Earth is somehow a self-regulating über-organism. This idea implies that Terra's vast mass and complex biosphere will adapt to human-induced alteration in a manner that is ultimately favorable to that biosphere as a whole system (though not necessarily good for humans). But why would it be that Earth can do that, while Mars seems to have "areo-formed" itself from a warm wet world to a cold, dry barren wasteland? As Jim Bell puts it: "How do you go from an Earth-like place, to a Mars-like place?"

That is a central question behind the current Spirit/Opportunity missions. And their Principal Investigator, Steve Sqyures, has this to say about terraforming: "We are very far from being able to control -- or even fully understand -- the climate of our own planet. And I think that changing the climate of an entire planet in an intended direction, getting an intended outcome and betting people's lives on that outcome strikes me as a chancy proposition for the foreseeable future. It sounds like a tough thing to do."

Perhaps this whole business may turn out to be about simply taking control of the pace of biological change rather than about redirecting towards or away from Earth's biology.

Astrogeophysicist Chris McKay, one of the first scientists to look seriously into the notion of purposefully guiding the biological evolution of Mars -- and one of the founders of the so-called Mars Underground -- thinks of a Red Planet re-engineered, but for the original residents. "If there is life on Mars, it's not doing very well. We know that from just looking at the planet. And it could use some help," McKay believes. "I think we would be ethically on good grounds to support it, to encourage it to flourish into a global scale biota like we have on Earth, especially if it was on the verge of extinction which it could well be."

McKay would champion a technological effort to nurture these, presumably microbial, or at least miniature, Martians: "They would have the right to evolve on their own biological trajectory. Although Mars is a very interesting world without life, my own personal judgment is that life is a more intrinsically valuable, beautiful phenomena." Chris McKay perceives a marked difference between warming the planet up to support simple, stupid life and fully engineering a human-shirtsleeve balanced Nitrogen/Oxygen atmosphere at water cycling temperatures. On McKay's Mars, the first is possible and desirable; the second is not.

To do either requires giving the rusty red world a much thicker atmosphere. Mars atmospheric scientist Scot Rafkin isn't sanguine about that possibility: "I think it would be tough. And more than the technical aspect, you have to wonder how expensive it would be versus, say, enclosing huge regions of Mars and modifying the environment for human habitation. It might make more sense to do that than to try and add significantly more mass to the entire atmosphere."

"Life on Mars probably died out young when the planet went through this transformation to a thin, cold atmosphere," says planetary scientist David Grinspoon. "There's nothing about the ancient past of Mars that was so different from Earth that the origin of life should not have happened. I think it's quite reasonable to look for fossils on Mars (but) in my opinion Mars at present is dead, dead, dead."

Lacking any other examples of life in the Universe, there's no denying that Earth life's propensity to begat more life is spectacular. "The fundamental policy of life is one of talking barren environments and transforming them into those that are friendly to the propagation of life," opines Mars Society founder Robert Zubrin. "That is why we have oxygen in Earth's atmosphere and why there is soil on Earth's continents. It's an artifact of life. Symbiotic communities of plants and animals have transformed the Earth."

Earth life and Mars life could be rooted in the same DNA. Or they could have had independent origins. "The question of going to Mars if there are, in fact, Martians - even microbes - is a question that tends to be glossed over by people that are really excited about the idea of going to Mars," David Grinspoon adds. "The good news is that there aren't Martians, I'm pretty sure. But we have to be a lot more sure before we go starting to set up our strip malls and sports stadiums."

Given our track record of modifying Earthly environments, can we safely conclude that Nature has pre-destined -- or at least deputized -- Homo sapiens to be the agent of its spread to the stars?

Again, Bob Zubrin: "Human beings in bringing life to Mars will be, in a very real sense, continuing the work of Creation. We will not be playing God but engaging in that activity that God gets the most credit for doing. By so doing, we will show the divine nature of the human species and, therefore, the precious nature of every member of it. No one will be able to look at a terraformed Mars and not be prouder to be human."

Designer Humans