Planet hunters sift through data


An artist’s interpretation shows NASA’s Kepler space telescope observing a distant planetary system (alien star and planet not to scale).



By Alan Boyle

Months of data from more than 150,000 stars are due to be dumped upon the scientific community today, and planet hunters are ready to sift through those readings in search of the signatures of alien worlds.

NASA’s Kepler spacecraft has been monitoring all those stars for the telltale dips of light that occur when a planet passes over the disk of a faraway star. The $600 million mission has already identified nine confirmed planets, based on earlier releases of data. Still more findings are due to be announced at a news conference to be televised by NASA TV at 1 p.m. ET on Wednesday.

The Kepler mission is all about being able to find Earth-size planets in Earth-type orbits around sunlike stars. But it will take a few years to make confirmed detections of such planets: Kepler’s scientists want to see three instances of planetary transits before they add a particular prospect to their list of planetary candidates — which means it would take up to three years to detect a planet exactly like Earth.

And that’s not the end of the process: Kepler can tell scientists how wide a planet (or something else, such as an eclipsing binary star) appears to be. But in order to confirm an object’s planetary status, the scientists would like to know how massive that object is — either by analyzing the gravitational wobbles it creates in its parent star, or by even more subtle methods. Such methods are how the scientists make sure that the candidates are really planets rather than variable stars or data glitches.

This is why the Kepler team has confirmed only nine planets so far, even though the probe was launched almost two years ago. When the mission’s first set of readings was released, last June, the Kepler scientists said they had found 706 potential planets. The scientists held back the detailed data about the 400 most promising candidates, however, to give themselves the first chance to confirm their planetary status. (That created a stir among astronomers who weren’t part of the Kepler team.)

The “Kepler 400” are to be made public as part of this week’s data release, along with the mission’s raw data from June to September 2009. Once again, some of the most promising candidates from the new data dump will be held back for further scrutiny by the Kepler team.

Other planet-hunters are on the trail as well, and you can join them in the search.

Planet Hunters on the case is a citizen-science project backed by Zooniverse (the creators of the galaxy-sifting effort known as Galaxy Zoo) as well as Yale University’s exoplanet program. The Planet Hunters team already has enlisted thousands of Internet users to look for the signals of planetary transits in Kepler’s light curves.

Over the past month or so, users have made 1.2 million light-curve classifications, and the team leaders used those assessments to winnow the database of 150,000 stars down to 90 possible planets and 42 possible eclipsing binaries. John M. Brewer, a graduate student in Yale’s astronomy program and one of the project leaders, explains the process today in a blog post.

Those candidates will be subjected to further data analysis, and eventually the confirmed planets (or eclipsing binary stars) will become the subject of scientific papers. Brewer told me that the first papers to be published would likely look at “statistics on how people are doing on finding these.”

Brewer said the Planet Hunters team is also ready to add this week’s fresh Kepler readings to its database, at the rate of roughly 5,000 stars a day. Last year’s data release took in only about a month’s worth of readings. This new release will add three more months of observations — which means you and other planet hunters are in for not just double the fun, but four times the fun. Check out the Zooniverse and take your pick from the Planet Hunters, Galaxy Zoo, Moon Zoo and all the other offerings for citizen scientists. Then, on Wednesday, check back with us to learn all about Kepler’s latest and greatest.

More on the planet quest:

* Join a worldwide planet search * Probe finds planetary ‘missing link’ * Planets spotted in changing orbits * Kepler finds five lightweight worlds * Millions of Earths? Talk causes a stir * Doubt cast on existence of super-Earth * More about planets from Cosmic Log

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Join the Cosmic Log community by hitting the “like” button on the blog’s Facebook page or following b0yle on Twitter. For more about the planet search, click into the website for my book, “The Case for Pluto.”


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