Scientists have found what they believe are the two most Earth-like exoplanets yet, shedding new light on the possibility of life outside our solar system. In a press conference, NASA announced a series of discoveries from its Kepler probe program, revealing the existence of three planets that appear to be in the orbital "habitable zone" that could support liquid water. Since they also exist in systems anchored by sun-like stars, the planets are among the strongest candidates for supporting life, though researchers are just beginning to explore the implications of their discovery.

The three planets were discovered orbiting two different stars. Two of them, Kepler-62e and Kepler-62f, are anchored around a star somewhat smaller and cooler than our sun, while a third orbits Kepler-69, a star similar to Earth's. NASA isn't calling the planets "Earth-like" exactly; instead, they're described as "Super Earths" that are anywhere from 40 to 70 percent larger than our planet. However, that's still much smaller than the habitable zone planets that have been discovered so far, including predecessor Kepler-22b. The smallest, shown above, is Kepler-69f, believed to be a rocky planet based on its size; there's also the possibility of water. The larger Kepler-69e could be either rocky or a "water world," and the even bigger Kepler-69c is described as potentially a "Super Venus," situated on the hotter side of the habitable zone.

As of this January, the Kepler mission had uncovered 2,740 planet candidates, and scientists are increasingly finding that smaller planets in the habitable zone are more common than once believed. As a NASA panel conceded, it's not inconceivable that we could find life on a planet different to our own, or one orbiting a non-sun-like star. But looking for environments like our own is a way to narrow the search, and it can give us insights about Earth. Finding Earth-like planets, says Harvard astronomer Lisa Kaltenegger, is a way to see what our own planet might be going. It's also a way to visualize different types of solar systems: if Kepler-62e is indeed a water planet, it would be unlike anything in our own solar system. "What it shows you is the diversity we're discovering out there," says Kaltenegger.