It is a bit bigger and somewhat colder, but a planet circling a star 500 light-years away is otherwise the closest match of our home world discovered so far, astronomers announced on Thursday.

The planet, known as Kepler 186f, named after NASA’s Kepler planet-finding mission, which detected it, has a diameter of 8,700 miles, 10 percent wider than Earth, and its orbit lies within the “Goldilocks zone” of its star, Kepler 186 — not too hot, not too cold, where temperatures could allow for liquid water to flow at the surface, making it potentially hospitable for life.

“Kepler 186f is the first validated, Earth-size planet in the habitable zone of another star,” Elisa V. Quintana of the SETI Institute and NASA’s Ames Research Center in Mountain View, Calif., said at a news conference on Thursday. “It has the right size and is at the right distance to have properties similar to our home planet.”

Dr. Quintana is the lead author of a scientific paper describing the findings in this week’s issue of the journal Science. Kepler 186f is the latest planet to be sifted out of the voluminous data collected by Kepler, which kept watch over 150,000 stars, looking for slight drops in brightness when a planet passed in front.