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Artist's conception of the newly discovery planet orbiting two stars. (T. Pyle/NASA)
The European Southern Observatory dazzled the world on Monday with news it had discovered only the second, and smallest ever, planet orbiting within the habitable zone of a star other than our own.

Now it's NASA's turn to amaze us with a new exoplanet find.

The Kepler Mission, run out of the Ames Research Center, today announced the first discovery of a planet orbiting a binary star system. As many news outlets have noted, and as NASA itself promoted when announcing the discovery, the find is reminiscent of Luke Skywalker's home planet of Tatooine in Star Wars:

Like the imaginary Star Wars world Tatooine, a new planet found 200 light-years away has two suns, astronomers announced today.

NASA's Kepler spacecraft uncovered the new planet, dubbed Kepler 16b, as it transited—or crossed in front of—both its parent stars, causing the brightness of each star to dim periodically.

In addition to not being in a galaxy far, far away, there are some differences between Tatooine and Kepler 16b. In particular, Kepler 16b is cold and gaseous, rather than a habitable, rocky desert. Still, it is a remarkable find which greatly expands the potential number of habitable worlds:

"This discovery confirms a new class of planetary systems that could harbor life," Kepler principal investigator William Borucki said. "Given that most stars in our galaxy are part of a binary system, this means the opportunities for life are much broader than if planets form only around single stars. This milestone discovery confirms a theory that scientists have had for decades but could not prove until now."

Today's announcement is the latest in a growing string of amazing findings by the Kepler mission:

On 2 February 2011, the Kepler team announced the results from the data of May to September 2009. They found 1235 planetary candidates circling 997 host stars, more than twice the number of currently known exoplanets. The Kepler results included 68 planetary candidates of Earth-like size and 54 planetary candidates in the habitable zone of their star. The team estimated that 5.4% of stars host Earth-size planet candidates and 17% of all stars have multiple planets. As the mission continues, additional longer period candidates continue to be found - as of September 2011, there were 1781 candidates

Kepler is able to make so many exoplanet findings because it is a space-based observatory employing the transit method of exoplanet detection. By continually monitoring the brightness of 150,000 stars, Kepler finds exoplanets when they cross in front of their host star, thus reducing the brightness of those stars.

In contrast, the HARPS team at the European Southern Observatory uses the radial velocity method of exoplanet detection. By measuring how much a star moves, it is possible to determine if, and how much, gravity is being exerted on the star by orbiting planets.

The benefit of the transit system utilized by Kepler is that it can detect the presence of far more exoplanets, since it can monitor so many stars at once. The benefit of the radial velocity method is that it can detect exoplanets other than those which cross between their host star and an observer's line of sight (which are 99.8 percent of all exoplanets).

Both methods are indispensible, and are producing multiple breakthroughs every year. We should consider ourselves lucky if the two methods continue one upping each other, just as they have done this week.

Originally posted to Chris Bowers on Thu Sep 15, 2011 at 03:00 PM PDT.

Also republished by Astro Kos and Daily Kos.

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