Nick Hoffmann wrote: "Only a small turn of the dial in size, composition, and temperature leads to a very different outcome. Rare Earth has my vote.

(I'm sure there are lots of planets in the Universe that are waterworlds with biota ranging from green slime [through purple slime and orange slime] to fish, octopi, sponges, clams, and whatever you can imagine - but NOT space rockets, computers, and radio telescopes)"

Rare Earth has my vote, too. How lucky we are to even have a chance to exist. This just solidifies the notion that life is precious. However, Unique Earth does not have my vote. Given the estimated age of the universe, for us to assume that there are no other beings at least as evolved as Humans is insanely egotistical.

And what great news it is that there are vast stores of H2O on Mars that our future explorers can tap into, if we ever get our act together enough to establish a permanent presence there.