As a consequence, both worlds are extremely hot as they are much closer to their star than the innermost limit of their habitable zone - the zone at which water can exist in a liquid state on the planet's surface.
In the quest for Earth 2.0, the potential to support liquid water on a planetary surface is of paramount importance. Liquid water, after all, is crucial for terrestrial biology.* Kepler-20e and Kepler-20f may be the right size, but both are in the wrong place to be called "Earth analogs."
Now, turn the clock back to Dec. 5, when another Kepler announcement confirmed the discovery of a world orbiting its star within the habitable zone.
Naturally, the mere fact that Kepler-22b orbits smack bang in the middle of the habitable zone surrounding a sun-like star was enough to get the world excited about the potential for life. Kepler-22b also has an orbital period approaching the length of one Earth year - 290 days.
It's sounding pretty Earth-like, right? Sadly, there's a catch.
Wrong Size, Right Place
Astronomers consider Kepler-22b to be a "super-Earth," as it's 2.4 times wider than our planet, but they're not sure whether it's a small gas giant (like a dinky Neptune) or a large rocky world ... or something in between. It may be the smallest world discovered orbiting within a star's habitable zone, but physically it's not very Earth-like.