“With your help, we are looking for planets around other stars.” So begins a first-time user’s introduction to Planet Hunters, an online citizen science project that delivers exactly what many of us have been hoping for since the first Kepler results came in — a chance to use our own computers to help analyze data taken by the mission. Kepler has been in operation for the better part of two years now, accumulating what Yale astronomer Kevin Schawinski calls ‘another mountain of data to sort through.’ What better way to sort than with distributed computing?

Schawinski is a co-founder of Planet Hunters, and was deeply involved in the creation of the successful Galaxy Zoo project several years back. In the latter, the involvement of average citizens in astronomy took off, to the tune of hundreds of thousands of Web users sorting through a million images of galaxies and classifying them. Kepler presents its own challenges, monitoring almost 150,000 stars in the constellations of Cygnus and Lyra. The trick with Kepler is to look for the characteristic dimming of a star that could signify a planetary transit.

From the Planet Hunters site:

NASA’s Kepler spacecraft is one of the most powerful tools in the hunt for extrasolar planets. The Kepler team’s computers are sifting through the data, but we at Planet Hunters are betting that there will be planets which can only be found via the remarkable human ability for pattern recognition.

This is a gamble, a bet if you will, on the ability of humans to beat machines just occasionally. It may be that no new planets are found or that computers have the job down to a fine art. And yet, it’s just possible that you might be the first to know that a star somewhere out there in the Milky Way has a companion, just as our Sun does. Fancy giving it a try?

Not every star that dims is experiencing a transit, but some are, and our profoundest hope for Kepler is that it will tease out the signature of a planet not so different from our Earth, a small world in an orbit that would keep water liquid at the surface. Planet Hunters draws on the fact that Kepler data are being released into the public domain. It’s not directly tied to the Kepler mission, but should serve as a useful adjunct to what the Kepler team is doing as it sorts through Schawinski’s ‘mountain.’ The more human intelligence on the job, the better.

Not that computers aren’t critical to the work at hand. But another co-founder of Planet Hunters, Yale’s Meg Schwamb, notes what a good set of eyes and human intelligence bring to the data our computers deliver to the desktop:

“…computers are only good at finding what they’ve been taught to look for, whereas the human brain has the uncanny ability to recognize patterns and immediately pick out what is strange or unique, far beyond what we can teach machines to do.”

That’s the great virtue, proven over time, of the Galaxy Zoo project. In the case of Planet Hunters, the method is to answer a series of questions about the light emitted by a particular star over time, its light curve. Such graphs help astronomers identify the dimming caused by a planetary transit. Planet hunter extraordinaire Debra Fischer notes that even with data from an instrument as precise as the Kepler telescope, picking out the transit signal is exceedingly hard. “Planet Hunters is an experiment,” adds Fischer. “We’re looking for the needle in the haystack.”

Here’s a Planet Hunters video that walks you through the basics of using the site:

Planet Hunters Tutorial from The Zooniverse on Vimeo.

Have a look at some of the Planet Hunters introductory material to see how absorbing this work can be. Light curves are stuffed with scatter and often reveal nothing but statistical noise. Some, however, show variability with time. Variability in a light curve is readily caused by starspots, but there are planets hiding within some of these curves, and human classification supplements computer analysis to flag patterns whose variability appears particularly promising. Obviously, large planets with short orbital periods are the easiest targets, while small planets with long periods — the ultimate quarry in the eyes of many planet hunters — require long observation.

It should be obvious by now that citizen science can make serious contributions. If Planet Hunters finds a possible transiting planet, the procedure is to match that potential world up against the Kepler team’s own list of transiting planets. It may be that the light curve is already under investigation, and users will be notified of that fact.

If not, and if several of the Planet Hunters team are flagging the same data, the science team investigates and, if a discovery appears in the offing, the team will obtain spectroscopic data using the Keck instrument in Hawaii. A transit candidate that gets through all these tests will be submitted for publication, with the Planet Hunters participants involved listed as co-authors. Interested? I hope the Planet Hunters site is ready to go, because I expect the initial response will be robust.