Gliese 581 g
I suppose most, if not all, of you have read in the news recently about an "Earth-like" planet orbiting a red-dwarf star some twenty million light years away. The name Gliese comes from Wilhelm Gliese, a German astronomer responsible for cataloging a number of nearby stars. The planet, which I doubt will long keep the name "Gliese 581 g" is rocky and inhabits an orbit which would permit the pooling of liquid water on its surface. These would indeed be conditions permissible for life, but I bristle a bit at the insinuation that life and water are in some way inextricably linked on all worlds. DNA, protein based life here on earth is indeed dependent on water as both a solvent for its biochemistry and as an environment. Still, this does not mean that organic or non-organic (here organic is used to denote carbon-based), self-replicated macromolecules necessitate water. So perhaps it is not the idea that life could exist here on Gliese 581 g, but that Earth-like life might have evolved or, at least, be supported. Remember, our own solar system contains planets and satellites that have liquid water as well as other liquid solvents pooling, running and dripping over their surfaces.
The twilight zone.
Gliese 581 g is approximately eight times closer to its star than we are to ours. Gliese 581 is a red dwarf and is nearly one fourth as large as the sun, meaning that the sky of this rocky planet must contain a magnificent view of its star, large and ruddy and terrible to behold should you be on the wrong side of the planet. Whereas our Earth rotates about its axis, tidal forces have ground the rotation of Gliese 581 g to a halt, just as the Earth's gravitation has stopped the rotation of our moon. So then, if you are on the sunny side of Gliese 581 g, you would not only be straining under gravitation that is estimated to be as much as twice that of Earth's, but you would also be baking inside a deep atmosphere that is continually heated by its nearby star. On the other side of the planet, although you would undoubtedly have breathtaking views of the universe (views not unlike our own given its distance of less than a parsec), you would likely freeze in the deep cold of eternal night. In the middle, however, is the twilight zone and a photographer's (at least this photographer's) dream. The position of the alien sun is determined only by one's longitude and latitude on Gliese 158 g, and one could position the star in the sky simply by choosing his favorite geographical location. From death and sun to death and ice, a narrow zone encircles the planet that has perpetual, crimson sunset in the sky followed in turn by a continuum of rings possessing every character of light from this sunset to the darkest and most saturated shades of purple hour, where the alien sun is several days hike over the horizon. I imagine a future society of humans, having made the twenty-plus year journey to live on the planet's surface, occupying this strange and beautiful ring of perfect weather around the planet and eventually establishing cities in a belt circumscribing the alien globe.
Thoughts like this make our own world all the more beautiful and strange to me. I wonder, how many planets within the nearest 10,000 suns have a moon nearly one quarter their own size? How many have such a rotation so as to produce such a mild, temperate climate and shed every hue of color and stroke of luminosity on all landscapes in turn? We take seasons and sunsets and twilights as a matter of course, but there are, and will be here on Earth in the fullness of time, eternal seasons and constancy of light where the rush of a summer twilight on the shores of the Pacific may no longer exist - or, perhaps, become the only condition.