Using a new verification technique, Kepler scientists have confirmed the existence of 715 new exoplanets — four of which are located within their star's habitable zone. It's the single largest windfall of new confirmations at any one time.
NASA made the stunning announcement earlier today at a news teleconference. Presenters included NASA scientists Douglas Hudgins and Jack Lissauer, who were joined by SETI's Jason Rowe and MIT's Sara Seager.
Validation by Multiplicity
Prior to today's announcement, planetary scientists had confirmed the existence of about 1,000 exoplanets. So, overnight, that figure jumps by a factor of 70% to 1,715.
It's important to note that confirmed planets are not the same thing as planetary candidates. It takes considerable time and effort to verify that candidates — the vast majority of which are detected using the transmit method (the tell-tale signature of a far-away planet as it briefly dims the light of its parent star as it passes in front of it) — are in fact actual planets and not some kind of celestial anomaly or data glitch.
But these 715 planets are no longer mere candidates, they're all totally legit — the result of a new technique called "validation by multiplicity." The method only works for solar systems in which multiple planets orbit around a single star, and in which the transit method yields consistent results. Multiple star systems are far too chaotic and unpredictable to produce such data — they don't look anything like standard solar systems. It's this fundamental assumption that forms the basis of the new validation technique. As Lissauer noted during the teleconference, it "provided the additional crucial evidence."
By applying the new method, the validation bottleneck was significantly reduced, allowing the Kepler scientists to make this sweeping one-time confirmation. And amazingly, these results are based on the first two years of Kepler data. There's another two years to analyze, which means there's a lot more to come. As Seager noted, "Kepler is the gift that keeps on giving." And the space telescope certainly appears ready to keep on giving.
"Small Planets Are Extremely Common"
The 715 confirmed exoplanets orbit a total of 305 stars. Of these planets, the vast majority are small. The new figure boosts the number of known small Earth-sized planets by a factor of 400%. Other jumps include a 600% increase is known Super-Earths (or Mini-Neptunes), 200% for Neptune-sized planets, and just 2% for Jupiter-sized planets.
The 305 solar systems are quite similar to our own, just scaled down a bit. These planets tend to orbit along a flat plane in nearly circular orbits. They're packed tightly around their host stars, many as tight as Venus and Mercury.
As noted, the Kepler scientists confirmed the existence of four planets situated within their solar system's habitable zone. They are Kepler-174d, Kepler-296f, Kepler-298d and Kepler-309c, and they all orbit around M and K stars.
Now, 4 out of 715 might seem discouraging (that's 0.0056%), but it's the result of a selectional effect produced by the transit technique. Planets with short periods are detected more often. As a planet moves further away from its star (and into the habitable zone), the probability of detecting its transit drops, so scientists are not going to see as many though many are likely there. But as Seager pointed out, "There's plenty of room for solar systems like ours to exist."
Interestingly, Seager also pointed out that, because so many solar systems feature multiple planets in tight orbits, planetary migration is likely an indelible aspect of solar system configurations and development. Also, many of these systems have mini-Neptunes — planets that are two to three times the size of Earth and for which we have no counterpart in our own solar system. They're actually quite strange. Scientists don't know their composition or how they came to exist.