Remember that scene in ‘Star Wars: A New Hope‘ when Luke and Obi Wan go into the Mos Eisley cantina? The place was full of aliens. Leaning on the bar, arguing, drinking various foaming substances and playing cool, swing music. If you’ve any sort of interest in science, you’d be like me and go directly into ‘go along for the ride’ mode. It just isn’t probable.
But wait a minute. Just the other day we were told that our very own Milky Way could contain up to 2 billion (yes, billion with a ‘b’) ‘earthlike planets’. Gosh. Two billion planets that could potentially support life like us. http://www.dailygalaxy.com/my_weblog/2011/12/the-milky-ways-two-billion-earthlike-planets-an-update.html
Wait a moment, though. What does ‘earthlike’ mean in this context? The report comes from Kepler’s search for planets orbiting planets like our sun and in the ‘Goldilocks’ zone. Which means the planet is ‘not too hot for liquid water and not too cold’. Kepler can’t actually see any of these planets, their presence is surmised from periodic dimming of the sun’s light as something passes in front of it and from slight perturbations in the sun’s orbit. But scientists can calculate the likely size of the body. For instance, Kepler 22-B is estimated at 2.4 times the size of Earth.
But there’s much more to life on Earth than liquid water and reasonable temperature. The article goes on to quote from “Rare Earth”, a book by Peter Ward and Donald Brownlee, which discusses in detail what would be needed to define a planet as an ‘earth analog’. Some of the things they list don’t readily spring to mind, such as a giant like Jupiter acting as a mine sweeper to reduce the amount of debris penetrating to habitable zones to pose a threat to life. We also need that molten metal core inside the Earth to generate a magnetic field which protects us from harmful cosmic rays. Then we need a breathable atmosphere, a year length not too much different from our own, and gravity at least 80% of our own. (Less than that and the planet wouldn’t hold atmosphere) I don’t think I’d like to live on a planet 2.4 times the size of Earth. It would be pretty hard to move around.
We just don’t know enough about any of these planets to know if they’re really ‘earthlike’. The point is made that both Venus and Earth are in the habitable zone around our sun and they are much the same size. But we won’t be setting up a colony on Venus any time soon.
Yes, but that’s humans. Getting back to the cantina scene, we are presented with a number of alien species, all presumably capable of space flight. So what about other life forms on these earthlike planets? Sure, that’s possible – but then we come up against the famous Drake equation (http://en.wikipedia.org/wiki/Drake_equation), which considers variables such as technology and the life of civilisations.
Mind you, Kepler’s discoveries are a breakthrough from the time not too many decades ago (maybe only two) when scientists could do no better than to say that our sun was nothing special so other stars would quite probably have planets. The Drake equation dates back to those times. This is such an exciting time to be interested in the universe. I keep getting this feeling that space travel as written in science fiction might not be all that far away. Soon, it seems, we’ll have places to visit, too.
I’m not too sure I’ll be running auditions for a new cantina scene, though.