"Scientists undertake sophisticated calculations to verify that such signals are planets and not astrophysical phenomena mimicking the signature of a planet," Anglada-Escude said.
By contrast, scientists who worked on the Gliese 667C system used the radial velocity method. With this, scientists look for wobbles in the motion of a star, which happens in response to the gravity of nearby planets.
How about all of those other planets that have been found previously to be in the habitable zone?
You may recall planet Kepler-22b, which was announced in December 2011 and also was hailed as a potential candidate for hosting life. That planet had a radius 2.4 times that of Earth and is 600 light-years away.
There is also a planet called Gliese-581g, discovered in September 2010, which is thought to be even more like Earth than Kepler-22b in terms of its suitability for plants and animals. It's only 20 light years from Earth, though there has been some controversy about its existence. In its solar system there is another planet, Gliese-581d, that is also of interest in the search for life, according to the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo. The group's catalog lists a few other candidates.
But do they really have life?
Because they are so far away, the composition of the atmospheres of all of these planets outside our solar system remains unknown. Whether life truly roams or swims out there is still to be seen.
"Whether the planets are actually habitable would be pure speculation," Seager said. "There's currently no way to observe surface liquid water (our habitability requirement) or even infer the presence of surface liquid water."
Still, Anglada-Escude says the existence of star systems packed with potentially habitable planets, and the diversity of planets that Kepler has found, suggest there are more exciting discoveries yet to come.