Hip-hip hooray for citizen scientists! The first two exoplanet candidates have been identified by members of the public through the citizen science project Planet Hunters. The project, which began in December 2010, uses public archive data from the planet-hunting Kepler mission, and excitingly, the planets were found within the first month after the project began. One planet is potentially a rocky Earth-like planet, while the other is likely a gas-giant like Jupiter.
“I think it’s truly amazing that someone sitting at home at their computer was the first to know that a star somewhere out there in our Milky Way likely has a companion,” said Meg Schwamb, a Yale University researcher and Planet Hunters co-founder.
By all accounts, the Kepler mission has been a spectacular success – with over 1,200 planet candidates detected so far– and the data obtained by the spacecraft has been a treasure trove for scientists. But over 40,000 web users from around the world have been helping professional astronomers analyze the light from 150,000 stars in the hopes of discovering planets – and especially Earth-like planets — orbiting around them.
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“These planet candidates just show what wealth of interesting gems still remaining to be found in the Kepler data,” Schwamb told Universe Today. She added that for the science team, the Planet Hunters project was somewhat of a gamble, as no one was sure human eyes would be able to spot things possibly missed by automated routines.
“The gamble paid off, and we’re all very excited about the discovery of these planet candidates,” she said. “These candidates have demonstrated the truly amazing power of human pattern recognition. Planet Hunters doesn’t replace the great work and the analysis being done by the Kepler team. But it has proven itself to be a valuable and complementary tool in the search for extrasolar planets.”
The Planet Hunters team sent the top 10 candidates found by the citizen scientists to the Kepler team, and two of the planets have survived the initial checks for false-positives, whether they are masquerading as eclipsing binaries, for example. Scientists used the Keck Observatory in Hawaii and the Two Micron All Sky Survey (2MASS) at Caltech to analyze the host stars and determined that two of the 10 met their criteria for being classified as planet candidates.
The two candidates were flagged as potential planets by several dozen different Planet Hunters users, as the same data are analyzed by more than one user.
The two candidate planets orbit their host stars with periods ranging from 10 to 50 days — much shorter than the 365 days it takes the Earth to orbit the Sun — and have radii that range in size from two-and-a-half to eight times Earth’s radius. Despite one planet having the potential to be a rocky world, it does not lie in the so-called “habitable zone” where liquid water, and therefore life as we know it, could exist.
Schwamb said to confirm a transiting planet, the team scientists will look at the radial velocities to measure the wobble of the star back and forth caused by the orbiting body.
“This allows you to get the mass of the orbiting companion,” she said. “Kepler was always intended to be a statistical mission. The majority of the over 1,200 Kepler planet candidates and the planet candidates found by Planet Hunters will not be confirmed with radial velocity measurements either because the star is too faint or the radial velocity signal caused by the orbiting planet would be smaller than the current sensitivity limits of the world’s best spectrographs. If it’s possible that we can confirm the presence of these planets with radial velocities measured on the Keck telescopes, we will definitely try.”
As of now, the Planet Hunter scientists, which also includes Yale astronomer Debra Fisher, say there is at least a 95% chance that these two candidates are bona fide planets.
Spurred by success, the Planet Hunters citizen scientist are now sifting through a new round of publicly available data from the Kepler mission in hopes of finding even more planets. “This is what we found after just a preliminary glance through the first round of Kepler data,” Fischer said. “There’s no doubt that, with each new round of data, there will be more discoveries to come.”
Read the team’s paper here. It has been submitted to the journal Monthly Notices of the Royal Astronomical Society.