February 3rd, 2011
We’ve just had a major announcement concerning first results from NASA’s Kepler Mission.
Before providing links to the details and reactions to the details, let me describe what the mission does and what it will continue to do. Kepler is basically just a big digital camera in space that takes pictures of a field of stars over and over again, every half an hour. Computer software analyzes the images looking to see if any of those stars dim periodically from an orbiting planet passing in front. How much dimmer, how long the dimming lasts, and the period of the dimming, together with information about the star itself tells us the size of the planet and how far it is from its central star. Thus we can figure out, roughly speaking, the temperature of the planet and if liquid water can exist on its surface.
This is an effective approach and has previously been used to discover planets, but the stars need to align for success. Or the planets and stars, that is. The plane of the planet’s orbit must cross in front of its star from Kepler’s perspective. Furthermore, orbital periods can be centuries long in principle, and the software is only flagging planets when multiple episodes of dimming are observed consistent with a single period. Less than a year of Kepler data is so far being analyzed (out of a total expected mission duration of three years), so in this initial announcement only a small fraction of what Kepler will find could have been found so far, and that’s a tiny fraction of the total planets out there.
The New York Times has a story, and Phil Plait at Bad Astronomy has his usual great and enthusiastic write up. Space.com has an interview with a planet-hunting astronomer that’s really interesting, too. From the NYT:
In a long-awaited announcement, scientists operating NASA’s Kepler planet-hunting satellite reported Wednesday that they had identified 1,235 possible planets orbiting other stars, potentially tripling the number of known planets in the universe.
Of the new candidates, 68 are one-and-a-quarter times the size of the Earth or smaller — smaller, that is, than any previously discovered planets outside the solar system. Fifty-four of the possible exoplanets are in the so-called habitable zones, where temperatures should be moderate enough for liquid water, of stars dimmer and cooler than the Sun; four of these are less than twice the size of Earth, and one is even smaller.
Since Kepler is only looking at about 150,000 stars, and the Milky way has a million times more than that, Phil Plait estimates (too low as he acknowledges) that there are potientially a million Earth-like planets out there. And let me emphasize that he’s WAY TOO LOW with his estimate, as Kepler will find more longer period planets still, and is only finding planets with their orbits lined up just right to cross in front of their star. The first factor will drive up the number by factors of several, but the second is a larger factor, something like a couple of orders of magnitude (depending on the details of the size of the star, the size of the planet, and the orbital radius of the planet). So to be conservative, let’s call it over 100 million Earth-like planets likely in the Milky Way. This is likely still be an order of magnitude low.
It would imply that the chances of any given star system having an Earth-like planet is probably better than 1/100, and that there are on order of a billion of them in the Mily Way.
That’s a lot of planets.
Science fiction positing that inhabitable planets are few and far between (e.g. Battlestar Galactica) seems to be unlikely.
Now, life could still be rare, but there are probably a lot of planets out there with warm oceans. I think that makes life probable given how quickly it popped up on the early Earth. It took a lot longer for there to be multi-cellular life.
So, maybe most systems don’t have Earth like planets, but every few dozen radomly sampled will. Most of those will probably only have bacterial-type life, depending on the age of the system.
Still, I’m seeing a galaxy filled with life and the chances of other intelligent species out there to communicating with skyrocketing.
Solar systems like ours seem, based on Kepler, more common than some of the weird things we’ve found with the Doppler method.
This is exciting. Ensuring years will give us many thousands of planets, hundreds of Earth-like planets, and within my lifetime I expect astronomical detection of evidence of life on an alien world (through atmospheric analysis).
We are living science fiction here, folks, and it’s cool!