Planet Hunters has grown to around 300,000 users. Debra Fischer said they've put in more than 100 years of cumulative work.
If you're looking for life elsewhere in the universe, there's a lot to look at, and computers are pretty good at it. At least, they're good at analyzing the stuff you tell them -- for example, the brightness of stars in our sky.
"The brightness of stars, you might, at first, think should be constant. Stars are emitting the same amount of energy constantly," said Debra Fischer, professor of astronomy at Yale University. "However, if a planet in its orbit crosses the face of the star, the planet will cut out some of the light of the star. And we’ll see the star dim temporarily."
This way of searching for planets is called the "transit method." When NASA launched the Kepler Mission back in 2009, this is the method its orbiting telescope used to hunt for planets. Scientists pointed Kepler to a chunk of sky containing about three million stars, captured their light, and sent that data to computers to figure out which stars may have orbiting planets.
"What we learned was what we should have known from the beginning," Fischer said. "The computer algorithms are fantastic at finding the things that we tell them to find. If there is a system that is really unusual for some reason, the computer algorithm will entirely miss it."
This is why Fischer said a website run in collaboration with Yale called Planet Hunters is so important. She thinks -- maybe -- humans can beat computers at this analysis game.
Planet Hunters recruits the crowd to look at Kepler data and analyze light curves that are too tricky for machines. So far, they've identified more than 60 new candidates, including their most recent discovery: a new planet called PH3c, which is about four times as big as Earth.
Fischer discovered the first known multiple planet system outside our solar system in 1999. She said we're entering a golden age in exploration.
Fischer said PH3c is a classic example of an outlier Kepler computers would miss. "The algorithms missed it because you’re expecting planets to go around the star, and just like clockwork, they come back and cross the face of the star," she said. "It just, you know, goes one, two, three, just keeping rhythm perfectly."
But scientists found that other massive planets in the same system as PH3c exerted their own gravitational tug, which changed the planet's orbital clock. "The computer algorithms are looking for something that is perfectly or nearly perfectly periodic. In the case of PH3c, the orbit was off by as much as a day," Fischer said. "So it slipped through the net, but humans beings looked and said, look, there’s a transit here; the starlight is dimming in a very predictable way."
Volunteers sent that flagged data to Fischer's team, which reviewed the information and published their findings in The Astrophysical Journal. In the graph below, green represents the number of planets (like PH3c) that have been found via the transit method.
Today, Planet Hunters has grown to around 300,000 users. Fischer said they’ve put in more than 100 years of cumulative work. "No eating; no sleeping; no blinking; you just sit there, and you classify light curves for 100 years," she said. "Obviously, that’s beyond the ability of any single human being. That’s what makes this project so powerful."
Fischer, who discovered the first known multiple planet system outside our solar system in 1999, said we’re entering a golden age in exploration. In recent years, Kepler has identified nearly 1,000 so-called exoplanets, including one Earth-sized body orbiting in the “habitable zone” of another star.
"The one thing we know now from the Kepler Mission is that in fact almost every star forms with planets, and forms with many planets. Multiple planet systems are the norm," Fischer said. "I think we could be in a point where a decade from now, two decades from now, we have one example of life elsewhere. Two examples. Three. And then maybe imagine hundreds of examples of life elsewhere and how that will impact our perspective."
In other words, the hunt for alien life is just beginning.
