An international team of astronomers has used nearly three years of high precision data from NASA's Kepler spacecraft to make the first observations of a planet outside our solar system that's smaller than Mercury, the smallest planet orbiting our sun.
The planet is about the size of the Earth's moon. It is one of three planets orbiting a star designated Kepler-37 in the Cygnus-Lyra region of the Milky Way.
The findings are published were published online on Feb. 20 by the journal Nature. The lead authors are Thomas Barclay of the NASA Ames Research Center in California and the Bay Area Environmental Research Institute and Jason Rowe of NASA Ames and the SETI Institute in California.
Steve Kawaler, an Iowa State University professor of physics and astronomy, was part of a team of researchers who studied the oscillations of Kepler-37 to determine its size. "That's basically listening to the star by measuring sound waves," Kawaler said. "The bigger the star, the lower the frequency, or 'pitch' of its song."
The team determined Kepler-37's mass is about 80 percent the mass of our sun. That's the lowest mass star astronomers have been able to measure using oscillation data for an ordinary star.
Those measurements also allowed the main research team to more accurately measure the three planets orbiting Kepler-37, including the tiny Kepler-37b.
"Owing to its extremely small size, similar to that of the Earth's moon, and highly irradiated surface, Kepler-37b is very likely a rocky planet with no atmosphere or water, similar to Mercury," the astronomers wrote in a summary of their findings. "The detection of such a small planet shows for the first time that stellar systems host planets much smaller as well as much larger than anything we see in our own Solar System."
Kawaler said the discovery is exciting because of what it says about the Kepler Mission's capabilities to discover new planetary systems around other stars.