In the past, those planets haven't fit all the criteria that would make them right for life of any kind, from microbes to humans.
Many planets aren't in the habitable zone - where it's not too hot nor too cold for liquid water. Until now, the few found in that ideal zone were just too big. Those are likely to be gas balls like Neptune, unsuitable for life.
In the Goldilocks game of looking for other planets like ours, the new discoveries, called Kepler-62-e and Kepler-62-f are just right. And they are fraternal twins. They circle the same star, an orange dwarf, and are next to each other - closer together than Earth and its neighbor Mars.
The planets are slightly wider than Earth, but not too big. Kepler-62-e is a bit balmy, like a Hawaiian world and Kepler-62-f is a bit frosty, more Alaskan, Borucki said.
The pair are 1,200 light-years away; a light-year is almost six trillion miles.
"This is the first one where I'm thinking 'Huh, Kepler-62-f really might have life on it,' " said study coauthor David Charbonneau of Harvard. "This is a very important barrier that's been crossed. Why wouldn't it have life?"
The planets circle a star that is seven billion years old - about 2.5 billion years older than our sun.
"If there's life at all on those planets, it must be very advanced" evolutionarily because the planets are so old, Borucki said.
All told, researchers announced seven new exoplanets Thursday, upping the total found so far by Kepler and Earth-bound telescopes to about 850.
Pennsylvania State's James Kasting called the findings "a big discovery." He and Sara Seager of MIT, who were not part of the research, noted Kepler's job is to look at one distant corner of the sky and to find what fraction of stars seemed to have the right-sized planets in the habitable zone.
"This is HUGE," Seager wrote in an e-mail. "Do you realize that as soon as Kepler could find close-to-Earth-size planets in the habitable zone of sun-like stars, Kepler found it. Goldilocks planets must be everywhere."