Since 2009, the Kepler spacecraft has searched a patch of the sky for exoplanets orbiting other stars in our galaxy. The mission has been hugely successful and has identified thousands of exoplanet candidates, of which around 1000 had been verified as the real thing. Last night, NASA held a teleconference to announce the latest discoveries made by the Kepler spacecraft and the number of verified exoplanets has doubled. Of the approximately 5000 candidates there are now 3,200 verified exoplanets, 2,325 discovered by Kepler.
The boost comes from advances in analytical methods that use Kepler’s 2015 candidate of candidates. Usually the candidates are verified with imaging or radial velocity to rule out the possibility that their actually small stars like brown dwarfs. The new analytical technique speeds up the confirmations and looks to be highly accurate.
The technique assigns each candidate a likelihood of being a genuine exoplanet by taking all available information into account and correcting for the number of known false positives. It means NASA researchers can sift through the candidates faster than ever but it has to be accurate. They compared the results form the new technique with ground-based confirmation and found they overlap nicely. The new method confirms the same planets that reliable ground-based confirmations do, which is a great sign.
The initial candidates themselves are made by observing light from stars dipping as planets move in front of them:
The new technique presumes that candidates with a 99% or higher likelihood are the real deal. Planets just under that likelihood are possible but unconfirmed and lower percentages suggest the candidates are false positives. The new analysis moves 1,284 candidates from candidate to confirmed status, bring Kepler’s total to 2,325. It also correctly verified 984 of the previously confirmed exoplanets and identified 707 as likely imposters. Interestingly there were 1,327 planets that the technique identifies as likely exoplanets but fall under the 99% rule.
Not only does this announcement double the number of confirmed planets smaller than Neptune, it doubles the number of roughly Earth-sized planets. Chief scientist Ellen Stofan was excited by results. “This gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth.” Kepler’s entire mission is a statistical one as it’s job is to sample the galaxy and get an idea of the bigger picture so we can answer an important question: how many Earth-like planets are there in the galaxy?
From these new results, we now know of 9 more Earth-sized planets that sit in the so-called “habitable zone” of their stars, where temperatures allow liquid water to exist on their surfaces. It’s starting to look like planets are extremely common in the galaxy and that Earth-sized planets in habitable zones really aren’t all that rare. Most importantly, Kepler’s findings are going to be extremely useful to future missions that will teach us even more.
What comes next?
The Kepler spacecraft was the first to detect small, rocky exoplanets in habitable zones of nearby stars. It uses the transit method (starlight dipping) and only looked at a small portion of space over the years. From this we think most stars in our galaxy probably have at least one planet and that there are a number of potentially Earth-like worlds out there. Kepler’s exoplanet-hunting mission wraps up soon and the final summary of results will be made in October next year. Future missions will use Kepler’s data to take the next steps.
The next two years are very exciting in the hunt for Earth-like worlds. First there’s the Transiting Exoplanet Survey Satellite (TESS), that will also measure starlight dipping much like Kepler did but for the entire sky rather than a specific patch. We’ll get a better picture of how common planets are in our entire galaxy by observing new stars. It launches next year with the help of SpaceX.
In 2018, the James Webb Space Telescope (JWST) will replace the Hubble space telescope as the most powerful visible light telescope in orbit. Rather than using the transit method, the JWST can directly image distant objects in space and will be able to see billions of years back in time. It will work together with the TESS to look directly at verified exoplanets. By observing starlight that’s filtered through the exoplanet’s atmosphere, the JWST will be able to identify oxygen, methane, and other gases that could be evidence of life on these distant worlds.
The most exciting satellite mission will be the Wide-Field Infrared Survey Telescope (WFIRST), which will launch sometime in the mid 2020s. As well as studying infrared physics and dark energy, WFIRST will revolutionise the search for habitable worlds. It uses a coronograph to directly image exoplanets. When observing an exoplanet, the satellite’s design blocks out the light from the star so it can only see the planet itself. It should be able to directly image planets as small as Neptune and as far from their stars as Jupiter is from ours.
All of these missions will rely on findings already made by Kepler and will lead to future telescopes for directly imaging the tiny, rocky planets that might hold water and possibly life. The next decade will be an exciting time for planet hunters.
Main image: NASA/W. Stenzel