How Planet Hunters are Going to Find the Next Earth With Space Telescopes
Finding Earth 2.0 won’t be easy. It’ll be an enormous effort, but the astronomers, planetary scientists, chemists and biologists leading the Carl Sagan Institute have a plan to get us there. Here’s how we’re trying to find the next pale blue dot and an end to our cosmic loneliness:
It’s a great time to be alive if you’re interested in worlds beyond our solar system. Over the past two decades, exoplanet science has undergone nothing short of a revolution, and even if you’re sceptical about the idea of alien life, the discoveries we’ve made are impressive.
Consider the numbers: twenty years ago, astronomers hadn’t confirmed a single planet outside our solar system. In the past six years, NASA’s Kepler mission, a space-based telescope that orbits our sun, looking at over 100 thousand stars simultaneously, has uncovered over 4,100 planetary candidates and 1,000 confirmed planets. Kepler is not scanning the whole sky. Rather, the scope monitors a tiny sliver of our galaxy, taking a cosmic census of sorts. With this census, astronomers have used statistics to extrapolate the distribution of planets throughout the Milky Way.
“We have learned most stars have planets, that Earth sized planets are common, and a good fraction are in the habitable zone of their star,” said Bill Borucki, the lead investigator for the Kepler mission. “And when you put the numbers together: 100 billion stars, 10 percent with Earth-sized planets, 10 percent stars like the sun, that’s a billion Earth-sized planets in the habitable zone of stars like the sun.”
Let me repeat that last bit. There may be a billion Earth-sized planets in the habitable zone of a sun-like star. Thirty years ago, astronomers weren’t sure of any. And that, of course, is just within our galaxy. “There are billions of stars in our galaxy alone, billions of galaxies out there,” Kaltenegger said. “The numbers are, fortunately, very much in our favour.”
So far, the galaxy has been full of surprises. Many stars harbor large worlds orbiting far closer than Mercury, a situation which was considered impossible thirty years ago. The two most common types of planets known to humanity right now, so called “super Earths” and “mini-Neptunes”, are not even represented in our solar system. We have hints of incredibly bizarre places out there, of gas giants as light as styrofoam, of ocean worlds and lava planets.
“There are planets orbiting binary stars, that have not one sun rising in the east and setting in the west but two,” said Batalha. “We find planets in star clusters, with 25 stars packed into a single cubic parsec of space. On these planets, you’d be look up and see a bejewelled sky. There’s an incredibly wondrous diversity of worlds out there, and we haven’t even started to scratch the surface”.
Through a pipeline of future space missions, beginning with the Transit Exoplanet Survey Satellite (TESS), which launches in 2017. While most of Kepler’s targets were 500-1,000 light years away, TESS is going to be our friendly neighbourhood planet hunter, it’ll scan the entire sky, monitoring more than half a million stars in our very close cosmic vicinity.
“TESS will be like Kepler, just doing transit, but instead of staring at one particular part of sky, it’ll scan the entire sky, focusing on our nearest neighbors. It’ll allow us to pick a lot of promising targets that are much closer than the Kepler planets.”
TESS may turn up many hopeful candidates, but it won’t be studying their atmospheres. That process starts gearing up with the James Webb Space Telescope, a 6.5 metre-long solar-powered observatory slated to launch in 2018. With unprecedented detection power, JWST will become the premier observatory of the next decade. Its sensitivity comes in part from a massive sunshield that chills the scope’s instruments to below -370 degrees Fahrenheit.
At such low temperatures, the JWST itself emits very little radiation, allowing for the detection of faint energy signatures from far away, including slight dips in the light emitted from a distant star as it filters through a planet’s atmosphere.