Astronomers have discovered the first Earth-sized planet in the "habitable zone," or the distance from a star that a water can pool on the planet's surface.

While other Earth-like planets have been found, they've all been bigger than Earth, making understanding what they're made of a bit more challenging to understand.

Nasa Nasa / Reuters / Reuters

The new planet, Kepler-186f, resides about 500 light-years away from us in the constellation Cygnus (pictured below).

What scientists know: Its year is 130 days and that it gets one-third the heat energy that we do from our sun.

What scientists don't know (yet): Kepler-186f is likely to be very rocky, but researchers can't confirm its mass, density, or composition.

Astrobobo/Astrobobo

Wait, rewind. What is Kepler?

Kepler-186 is another system found using NASA's Kepler space telescope. The telescope, launched in March 2009, has discovered thousands of possible exoplanet candidates, with hundreds confirmed.

NASA / Via youtube.com