Over the past year, NASA’s Kepler mission has found hundreds of possible planets outside of our solar system, and even a few candidates for Earth-like planets.

This week, astronomers revealed that a new system has been found that contains planets smaller than Earth. The new data has been presented in a paper published recently in the journal Nature.

The planets orbit around a star called Kepler-37, located around 210 light-years from our solar system. The smallest of the planest found, known as Kepler-37b, is only one-third the size of Earth – smaller than the planet Mercury and just slightly larger than Earth’s moon. The planet is not presumed to have an atmosphere, and scientists predict that life on the planet isn’t likely.

“Even Kepler can only detect such a tiny world around the brightest stars it observes,” said Jack Lissauer, planetary scientist at NASA‘s Ames Research Center. “The fact we’ve discovered tiny Kepler-37b suggests such little planets are common, and more planetary wonders await as we continue to gather and analyze additional data.”

Two other planets were found in the Kepler-37 system. Kepler-37c orbits further out and is slightly smaller than Venus, or around three-quarters the size of Earth. Kepler-37d is the furthest planet out, and is around twice the size of Earth. Kepler-37 itself is slightly smaller and cooler than the sun.

All three of the planets orbit Kepler-37 at less than than the distance between the sun and Mercury. They each also orbit their star in 40 days or less. The surface temperature of Kepler-37b is estimated to be higher than 800 degrees Fahrenheit.

“We uncovered a planet smaller than any in our solar system orbiting one of the few stars that is both bright and quiet, where signal detection was possible,” said Thomas Barclay, lead author of the paper and a Kepler scientist at the Bay Area Environmental Research Institute. “This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun.”

(Image courtesy NASA/Ames/JPL-Caltech