While other Earth-like planets have been found, they've either been too hot or significantly larger than our planet — but Kepler 186f is only 10 percent bigger than Earth. And its 130-day orbit around its M dwarf sun (a star significantly smaller than our G Dwarf sun) suggests that it'll be in the right range to potentially support liquid water. However, it's worth noting that Kepler 186f is on the edge of that habitable zone. NASA says that the planet only receives one-third the energy from its star that the Earth gets from the sun; the brightness of the planet's star at high noon is about equal to the brightness we see on Earth about an hour before sunset.
Other knocks against Kepler 186f include the fact that its mass and composition aren't yet known, though NASA suspects it is a rocky planet much like Earth. However, there's also no evidence to suggest yet that the planet has an atmosphere that would be suitable to sustaining life, says professor Victoria Meadows, principal investigator for the Virtual Planetary Laboratory.
Still, Kepler 186f is the first planet discovered that is both a close size to Earth and also in the habitable zone of its sun — co-author of the study called the planet an "Earth-cousin, rather than an Earth-twin." Still, it's a lot closer to Earth than four other planets discovered in the system, all of which orbit their sun in about three weeks or less, making them far too hot to support life. Sadly, Kepler 186f is about 500 light-years away, so don't expect any expeditions in search of life any time soon.