Planet Hunters, the crowdsourced search for exoplanets


Planet Hunters lets over 280,000 people around the world search for exoplanets - planets orbiting othe stars - in data from Nasa’s Kepler space telescope. These amateur exoplanet-hunters found four exoplanets and several more candidates that Kepler’s sophisticated software missed.

Over the past five years the Kepler science team confirmed 961 exoplanets* and identified more than 3,800 candidates* for follow-up observations. They don’t slog through the data themselves. They let an automatic algorithm do the work. It applies rules for what an exoplanet signal looks like and flags potential candidates. That’s when the scientists look at the data. Their analysis and follow-up observations on other telescopes confirm that the candidates really are exoplanets. The automatic algorithm does a lot of the low-level grunt-work that lets the science team produce so many discoveries. But an algorithm is only as good as the assumptions programmed into its code. It inevitably misses exoplanets when the data doesn’t fit within the algorithm’s rules.

Yale University’s Exoplanet Group didn’t want those exoplanets to fall through the cracks so they turned to the amateur space explorers at Zooniverse for help. Planet Hunters presents you with a light curve - Kepler’s measurements of a star’s brightness over time. You check the light curve for signs that a planet passed between the star and Kepler, briefly dimming the star’s light. When dozens of people spot the same dip in brightness, it becomes a Planet Hunter candidate. The project’s scientists then conduct follow-up observations using different telescopes and techniques to confirm that the dip in brightness actually came from a planet.

The amateur Planet Hunters analyzed over twenty-one million observations and identified thirty-four exoplanet candidates that Kepler’s algorithm either missed or ignored. The first confirmed Planet Hunter discovery, announced in 2012, is a Neptune-sized planet in a four-star system. The team published this and other exoplanet discoveries in peer-reviewed journals. In every case the list of co-authors includes the amateur space explorers who spotted the exoplanet. Their work hasn’t gone unnoticed by the professional community. When the Kepler team reviewed the mission’s first sixteen months in Astrophysical Journal, they recognized the contribution of Planet Hunters in identifying planet candidates that their automated software missed: 

“With its power in numbers, the citizen science project is a welcome complement to the automated detection algorithms in Kepler’s software pipeline”


*As of March 17, 2014. The numbers climb fast.