NASA's Kepler mission, which has been searching the skies for Earth-like planets since 2009, has confirmed the discovery of a whopping 715 new planets orbiting around 305 stars. That bring the count of exoplanets, which exist outside of our solar system, up to nearly 1,700. This galaxy's getting crowded. 

Most of the planets are smaller than Neptune (which is four times the size of the Earth), but four of them are less than 2.5 times the size of our planet and the right distance from the Sun to possibly support liquid water. The research team behind the findings has not yet determined whether the planets are gaseous or water worlds. 

NASA Ames/W Stenzel

NASA's Science Mission Directorate associate administrator John Grunsfeld lauded the discovery, saying "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." 

Golden years for exoplanet discovery. ASA Ames/SETI/J Rowe

The James Webb Space Telescope is slated to take the Hubble telescope's place in 2018, and will be used to help scientists search for the universe's first galaxies, as well as check out nascent planetary systems. 

According to NASA, it wasn't easy to confirm the existence of these 715 planets, and some guesswork was involved. The researchers employed a logic-based technique called verification by multiplicity. Basically, they singled out stars with the potential for multiple nearby planets, and analyzed those, rather than attempt to sweep through 150,000 stars. NASA offers this analogy

This method can be likened to the behavior we know of lions and lionesses. In our imaginary savannah, 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 you see two lions it could be a lion and a lioness or it could be two lions. But 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.

According to Jason Rowe, one of the scientists who discovered the planets, science has already gained from the discovery: "From this study we learn planets in these multi-systems are small and their orbits are flat and circular — resembling pancakes — not your classical view of an atom." 

A paper detailing the findings will be published in the Astrophysical Journal in March.