Late last month, NASA announced the discovery of 715 more exoplanets, nearly doubling the number of planets beyond our Solar System. These newly-verified worlds orbit 305 stars, revealing multiple-planet systems outside of our own, with four of them within their stars habitable zones. It’s the single largest windfall of new confirmations at any one time, and its all thanks to a new verification technique employed by the Kepler space probe’s scientists.

Nearly 95 percent of these planets are smaller than Neptune, which is almost four times the size of Earth. What’s more, this latest batch of exoplanets puts the total number of those confirmed from about 1000 to just over 1700 – and increase of 70% that occurred overnight! This discovery marks a significant increase in the number of known small-sized planets more akin to Earth than previously identified exoplanets.

John Grunsfeld, associate administrator for NASA’s Science Mission Directorate in Washington, had this to say in a press release:

The Kepler team continues to amaze and excite us with their planet hunting results. That these new planets and solar systems look somewhat like our own, portends a great future when we have the James Webb Space Telescope in space to characterize the new worlds.

Since the discovery of the first planets outside our solar system roughly two decades ago, verification has been a laborious planet-by-planet process. Now, scientists have a statistical technique that can be applied to many planets at once when they are found in the same planetary systems. From NASA’s Ames Research Center in Moffett Field, Calif, the Kepler research team used a technique called verification by multiplicity, which relies in part on the logic of probability.

The Kepler space probe observes some 150,000 stars and has found a few thousand of those to have planet candidates. If the candidates were randomly distributed among Kepler’s stars, only a handful would have more than one planet candidate. However, Kepler observed hundreds of stars that have multiple planet candidates. Through a careful study of this sample, these 715 new planets were verified.

This method can be likened to the behavior we know of lions and lionesses – where the lions are the Kepler stars and the lionesses are the planet candidates. The lionesses would sometimes be observed grouped together whereas lions tend to roam on their own. If more than two large felines are gathered, then it is very likely to be a lion and his pride. Thus, through multiplicity the lioness can be reliably identified in much the same way multiple planet candidates can be found around the same star.

Jack Lissauer, c0-leader of the Kepler science team at NASA’s Ames Research Center, explains the difference this process ushers in:

Four years ago, Kepler began a string of announcements of first hundreds, then thousands, of planet candidates –but they were only candidate worlds. We’ve now developed a process to verify multiple planet candidates in bulk to deliver planets wholesale, and have used it to unveil a veritable bonanza of new worlds.

Of these planets, the vast majority are small, boosting 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), a 200% boost for Neptune-sized planets, and just 2% for Jupiter-sized planets. The 305 solar systems are also quite similar to our own, with the planets orbiting along a flat plane in tightly-packed, nearly circular orbits.

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, are less than 2.5 times the size of Earth, and all orbit around M and K stars. Kepler-296f is especially interesting, in that it orbits a star half the size and 5 percent as bright as our sun, and is either a gaseous planet composed of hydrogen-helium, or a water world surrounded by a deep ocean.

In the meantime, NASA has released this animated graph (shown above) to put all the discoveries into context. And while the discovery of only four potentially habitable planets amongst 715 (a mere 0.0056% of the total) may seem discouraging, each discovery brings us one step closer to a more accurate understanding of our place in the galaxy. The findings papers will be published March 10 in The Astrophysical Journal.

Sources: IO9, (2), nasa.gov