Astronomers have found a mini planet beyond our solar system that is the smallest of more than 800 extra-solar planets discovered, scientists said on Wednesday.

The planet, known as Kepler-37b, is one of three circling a yellow star similar to the sun that is located in the constellation Lyra, about 210 light years away. One light year is about 6 trillion miles (10 trillion km).

“We see very large planets and they’re uncommon. Earth-sized planets seen to be pretty common, so our guess is that small planets must be even more common,” said Thomas Barclay, with NASA’s Ames Research Center in Mountain View, California.

The smaller the planet, the more difficult it is to find.

Kepler-37b, as well as two sibling planets, were discovered with a NASA space telescope of the same name, which studies light from about 150,000 sun-like stars.

The Kepler telescope works by detecting slight dips in the amount of light coming from target stars caused by orbiting planets passing by, or transiting, relative to the observatory’s line of sight. The smaller the planet, the less pronounced the dip.

Of the 833 confirmed planets found beyond the solar system, 114 were discovered by the Kepler science team, according to the project’s website. Nearly 3,000 more Kepler candidate planets are being analyzed.