Finding a planet-candidate smaller than Earth was one thing. Finding Kepler-37b was quite another.
Kepler-37b isn't just smaller than Earth. It's smaller than Mercury. That makes it slightly larger than the moon, which is 27 percent of Earth's size.
Kepler-37b orbits its star at 9.3 million miles, leading to a year of 13.4 Earth days.
The discovery, announced this February, was seen as an important step toward finding more Earth-like planets. The tug on a star of a distant Earth-size planet in an Earth-like orbit would seem very faint from here. In general, planets' influence on their stars increases with size and proximity – one reason large, close-in planets are easier to detect. But Kepler-37b is so small that its influence on its star is similar to that of an Earth-size planet at an Earth-like distance.
