Now, two scientists have made the fairly bold prediction that we're going to find a watery, warm planet such as our own in the first half of next year!
"In the past decades, the number of known extrasolar planets has ballooned into the hundreds, and with it the expectation that the discovery of the first Earth-like extrasolar planet is not far off," writes Greg Loughlin of the University of California, Santa Cruz and Sam Arbesman of Harvard. "Here we develop a novel metric of habitability for discovered planets, and use this to arrive at a prediction for when the first habitable planet will be discovered. Using a bootstrap analysis of currently discovered exoplanets, we predict the discovery of the first Earth-like planet to be announced in the first half of 2011, with the likeliest date being early May 2011."
Of course, we want to find another Earth because we want to find ourselves, intelligent life -- or failing that, just life. Judging by the organisms we have here on Earth, that knocks out nearly every spot in universe, except for the trillions of planets orbiting stars at just the right distance and with the right elemental composition. The easiest planets to discover turn out to be the worst for hosting life because they are big and very close to their home stars.
It's exceptionally difficult to find the habitable ones that we want to. We generally find planets by detecting the way they distort their star's orbit (the wobble method) or by measuring the very slight dimming that occurs when a planet passes in front of its star (the transiting method).
Neither of these is an easy task under any circumstances, but if you're looking for something like Earth in a solar system with a star like ours, you're trying to detect a planet that is 300,000 times less massive than its star.
Astronomers developed special techniques and telescopes to aid the quest. As the years have gone by, we've gotten better and better at spotting smaller and smaller planets hanging out in orbits more conducive to liquid water's presence. We even launched a space telescope called Kepler with the express mission of finding earth-like planets. The Kepler group will release the data on their 400 best planetary candidates next February, which is awfully close to the May 2011 date the Loughlin and Arbesman came up with, a fact that did not escape them.
"It does seem to accord well with outside considerations," Arbesman told me.
The paper was posted to arXiv, a repository for papers in math and physics, and will be published early next month in the open-access journal PLoS One.
Beyond the stunning topline of the paper, it's fascinating to see the field of scientometrics, which tries to measure science quantitatively, in action. It got me wondering: could we use a similar methodology to predict other scientific discoveries or breakthroughs? A better way of asking the question is really: in what circumstances could we imagine trying to extrapolate from current data to some future date?
"It makes the most sense in pretty carefully delimited and defined areas, where we have a very good sense of the properties of that discovery. We know the contours and shape of that discovery," said paper co-author Arbesman.
For other areas, like "finding a cure for cancer," it's not so easy to know what you'd need to discover or create to have a solution. "When will a cure for cancer occur? It will be a lot of successive small things. It's hard to know how to quantify it," Arbesman said.
Image: NASA rendering, i.e. not a real photo.