This mission is AWESOME. Have you heard of this? Probably not because news like this is doomed to be buried on the science page (NASA could really use some better promotion). But here's what's happening: A few years ago NASA launched a new space telescope called Kepler in honor of this guy.

Future missions will be named in honor of Kepler's mustache, beard, and neck ruffle.

You're probably familiar with the Hubble Space Telescope, which has shown us the glories of the universe in ways never before imagined (although it will soon be eclipsed by the totally awesome new James Webb Space Telescope). But Kepler is not like the Hubble. It will never take amazing pictures of distant galaxies or star-forming nebulae. No - Kepler is a telescope with but one simple, profound purpose: find other earths. Along the way it will find gas giants, super-earths, and earth-sized planets that orbit too close or too far from their star to support life as we know it, but its main goal is to find rocky planets of roughly earth size that orbit within their star's habitable zone - the region where liquid water could persist on a planet's surface. This is no small goal. Whether it finds that earth-like planets are common or rare, that knowledge will help us place our earth in the context of our galaxy and will give us a better idea of how abundant life in the galaxy might be.

This is also no small technical challenge. Planets are so small and dim compared to the stars they orbit that detecting exoplanets from earth has been impossible until the last two decades, and until now the nascent technology and techniques for planet finding have mainly limited astronomers to finding huge, Jupiter-like worlds that orbit very close to their star. Even so, 529 exoplanets are already known. To find more - lots more - including earth-like planets, Kepler's eye is designed to stare unblinking at a specific patch of sky in the area of the constellations Lyra and Cygnus. Its mirror reflects onto Kepler's solitary scientific instrument, an array of 42 charge-coupled devices (there's a CCD in your digital camera, too) that form a 95 megapixel photometer, or light meter. This device allows Kepler to simultaneously monitor all of the stars in its field of view... over 156,000 of them.

It does not see planets directly - again, Kepler isn't in the picture-taking business - rather, it measures the brightness of each star, looking for the tell-tale dip in brightness that occurs when a planet crosses between its star and Kepler, blocking out some of the star's light. This is called a transit, and that dip in brightness is very small, 1-2% for a Jupiter-sized planet and 84 parts per million (that's less than 0.01%) for an Earth-sized planet. It's been compared to the change in brightness caused by a flea crawling across a car's headlight, viewed from several miles away. But with that big, fat photometer and an orbit trailing the earth where it's free from the atmospheric distortions that plague ground-based telescopes, Kepler can measure it.

We ain't one-at-a-timin' it here. We's MASS planet-findin'! (image via NASA)

Kepler's confirmed discoveries to date include a rocky planet that's 20 times closer to its star than Mercury is to the sun and a tightly packed, six planet system where the nearest five planets would all fit within the orbit of Mercury, with the sixth only slightly beyond (Mercury is apparently the Rhode Island of astronomical comparisons.) But the big news released is that during its first four month observation period from May to September 2009, Kepler discovered over 1,100 planet candidates, of which 54 orbit in their star's habitable zone, and of those, 5 are Earth-size planets (NASA). If confirmed by repeated observations, this would triple the number of known exoplanets and raise from 0 to 5 the number of known exoplanets that might be something like the Earth: planets that might harbor life.

And here's the punch line: the transiting method of planet detection that Kepler's using? It can only detect planets that happen to orbit in a plane that allows them to pass between Kepler and their star. If Kepler is looking "up" or "down" at a planetary system, rather than viewing it edge on, the planets will never transit between their star and Kepler, rendering them effectively invisible. So what are the chances of a planet being properly aligned for Kepler to view its transit? That turns out to be equal to the diameter of the star divided by the diameter of the planet's orbit. The smaller the star or the larger the orbit, the less likely the planet is to be aligned for Kepler to view a transit.

When smart people crunch the numbers, they find that for giant planets in tight orbits the probability is as high as 10%, but for a planet orbiting a sun-sized star in an Earth-like orbit, the probability drops to 0.5%. If I'm doing the math right, that means that for every one Earth-like planet that Kepler sees, there are about 200 it can't. If the five Earth-like planet candidates are confirmed, it will mean, statistically, that they are just five of 1000 habitable, Earth-like planets in Kepler's field of view (seriously, am I doing the math right?) Oh, and that patch of sky Kepler is studying? It covers only 1/400th of the sky. For Kepler to find so many planets so quickly in a relatively small patch of sky, the true number of worlds in the galaxy surrounding us must be, well, astronomical.

And we could have started looking sooner if this ninja hadn't stolen the photometer on five separate occasions
(photo via NASA/Ball Aerospace)

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