Monday marks the day when astronomers made a startling announcement: after years of searching, they’ve discovered an Earth-like planet outside the solar system that may very well be habitable.

The new planet Kepler 22b circles a star about 600 light years away — close by astronomical standards — and has a size and distance from its own star that could make for an average surface temperature of just 72 degrees.

Scientist Natalie Batalha of the Kepler space telescope discovery team said the planet is “right smack in the middle of the habitable zone” since it isn’t too hot or too cold to harbor oceans as Earth does. Liquid water has long been considered key for development of life on a planet’s surface.

“This is a phenomenal discovery in the course of human history,” says planet hunting pioneer Geoff Marcy of the University of California-Berkeley, a Kepler investigator, adding Kepler 22b “is the smallest, most nearly Earth-size, planet ever found in the lukewarm zone around another sun where life could thrive.”

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