Earlier this week, NASA announced the discovery of seven Earth-size planets around a single star.
The star itself is an ultra-cool dwarf, burning at much lower temperatures then our own sun. All seven of the TRAPPIST-1 planets are closer to their star than Mercury is to the sun, but the cooler temperature of the sun keeps them from being broiled like Mercury is.
All of these seven planets could have liquid water on their surfaces, but three of them are in the habitable zone of the star, meaning they are the right distance from the star to have Earth-like temperatures.
At about 40 light-years — 235 trillion miles — from Earth, we don’t have the kind of technology to visit this system, but future study can unlock more details about the planets.