Tiny planet is a bit bigger than Earth’s moon

IOWA STATE (US) — A planet discovered outside our solar system is smaller than Mercury, the smallest planet orbiting our sun.

The planet, about the size of the Earth’s moon, is one of three orbiting a star designated Kepler-37 in the Cygnus-Lyra region of the Milky Way.

Using nearly three years of data from NASA’s Kepler spacecraft, astronomers 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.

The line up compares artist’s concepts of the planets in the Kepler-37 system to the moon and planets in the solar system. The smallest planet, Kepler-37b, measures about one-third the size of Earth. Kepler-37c, the second planet, is slightly smaller than Venus, measuring almost three-quarters the size of Earth. Kepler-37d, the third planet, is twice the size of Earth. (Credit: NASA/Ames/JPL-Caltech)


Those measurements allowed the main research team to more accurately measure the three planets orbiting Kepler-37, including the tiny Kepler-37b.

Steve Kawaler, professor of physics and astronomy at Iowa State University, 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 says. “The bigger the star, the lower the frequency, or ‘pitch’ of its song.

“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 write in a summary of their findings, published in the journal Nature.

“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.”

The discovery is exciting because of what it says about the Kepler Mission’s capabilities to discover new planetary systems around other stars, Kawaler says.

The Kepler spacecraft is orbiting the sun carrying a photometer, or light meter, to measure changes in the brightness of thousands of stars. Its primary job is to detect tiny variations in the brightness of the stars within its view to indicate planets passing in front of the star. Astronomers with the Kepler team are looking for Earth-like planets that might be able to support life.

Kepler is sending astronomers photometry data that’s “probably the best we’ll see in our lifetimes,” Kawaler says.  This latest discovery shows astronomers “we have a proven technology for finding small planets around other stars.”

That could have implications for some big-picture discoveries.

“While a sample of only one planet is too small to use for determination of occurrence rates,” the astronomers write, “it does lend weight to the belief that planet occurrence increases exponentially with decreasing planet size.”

Source: Iowa State University