When I was a physics student, I had to do a personal project for presentation (with slides). On the basis of a Scientific American that I’d just read, I chose the subject to be the search for planets round other stars. At the time, none had been detected, but I was able to discuss the upcoming technologies that would crack the problem. And in fact, something like 500 planets have been found in the last ten years. The cutting edge is probably represented by the Kepler spacecraft, which watches stars for the tiny flicker caused by one of its planets passing in front. (Stars, obviously, are hugely bigger than planets.)
It’s in the news today that astronomers have confirmed the existence of a “Goldilocks planet”, not too hot, not too cold, around the star Gliese 581, about 20 light years from Earth. Gliese 581 is a small, dull, red star, but it has a complete family of planets, at least six, the largest a gas giant the size of Neptune. Planet ‘g’, the one in the news, is about three times the mass of Earth, and therefore is almost certainly a rocky world, but the excitement is that it is likely to have conditions suitable for water to exist as a liquid.
Because the star, the planet’s sun, is so small and dim, the “Goldilocks zone” is close in, meaning that there’s an additional complication: the planet does not spin independently, like Earth, instead it is locked with one side permanently facing the star. That means that it has a hot side, probably approaching 100°C and a cold side at a chilly -30°C, but somewhere in between, in the permanent twilight zone, it might be quite comfortable. (I expect it’s very windy though.)
I read a lot of science fiction in my youth, and although I can’t now remember a story based on a twilight planet like this, I’m sure there must have been one. Red dwarf stars are by far the most common in the universe, so putting life on a tidally-locked, rocky world around one is an obvious plot idea.
The obviousness, actually, is why scientists are looking for Goldilocks planets, and while it is exciting to think that earthlike planets might really be as common as they are in Star Trek, I still have a large niggle. We have one, exactly one, example of life. It’s formed out of carbon molecules, and it always needs water. And it works stupendously well, having been honed by evolutionary processes for about four billion years. The perfection of living systems on Earth has led some scientists (perhaps the majority) to assume that carbon and water life is the only type possible.
Well, maybe it is; maybe it isn’t. We simply don’t know, but it seems to me to be a very limited point of view to start out by assuming that our type of life is the only one that can exist. It looks like a complete negation of what life is, and what it’s all about. On Earth, it’s everywhere, from black smokers deep in the oceans to the ice of Antarctica, squirming and excreting and breeding. I know that all life on Earth is related, but that unbridled fecundity could be a universal property.
Every time I read a justification for what more imaginative scientists derisively call “carbon chauvainism”, whether it’s arguments based on earthlike temperatures being optimum for biological information processing, or assertions based on the chemistry of carbon or water, I’m reminded of the Victorians who calculated why heavier-than-air flight was impossible, or those who insisted that when a train exceed the heady speed of 21 miles per hour, all of the air would be sucked out of the passengers lungs, and they would die.
One day, life not related to us will be discovered. I’m certain of it. But I’m also certain that it will not be what anyone expected. And quite likely not in a place where people have been looking for life, so I think that specifically searching for goldilocks worlds is the wrong focus. Just look, and learn, and keep an open mind.