It's the tiniest yet, CBC news reports, and it's roughly the size of the moon.
Kepler-37b, a newly-discovered planet outside our solar system, is "significantly smaller" than Mercury, the smallest planet orbiting our sun since Pluto was demoted to a dwarf planet. This info comes from a paper published online in the journal Nature.
The planet, described as hot and rocky, was discovered using the Kepler space telescope. As of Wednesday, the Kepler mission had confirmed the detection of 105 planets, the CBC News report says.