NASA’s Kepler mission has detected two extrasolar Earth-sized planets, reported in a press release from the Harvard-Smithsonian Center for Astrophysics.
The two planets, named Kepler-20e and 20f, are the smallest worlds found to date.
Both planets orbits Kepler-20, a G-type star slightly cooler than the Sun and located 950 light-years from Earth.
Kepler-20e is the smallest planet found orbiting a Sun-like star. It circles its star every 6.1 days at a distance of 4.7 million miles. At that distance, its temperature could be as high as 1,400 degrees F.
An artist's impression of Kepler-20e (NASA/JPL-Caltech/T. Pyle)
Kepler-20f orbits its star every 19.6 days at a distance of 10.3 million miles. Its temperature is expected to be about 800 degrees F.
An artist's impression of Kepler-20f (NASA/JPL-Caltech/T. Pyle)
Planets have diameters of 6,900 miles and 8,200 miles and are expected to have rocky compositions.
In addition to these worlds, the Kepler-20 system contains three larger planets.
All five planets have orbits closer than Mercury in our Solar system. They also show an unexpected arrangement. In our Solar system small, rocky worlds orbit close to the Sun and large worlds orbit farther out. In contrast, the planets of Kepler-20 are organized in alternating size: big, little, big, little, big.
“We were surprised to find this system of flip-flopping planets. It’s very different than our solar system,” said David Charbonneau from the Harvard-Smithsonian Center for Astrophysics, co-author on the paper, to be published in the journal Nature.
“The planets of Kepler-20 could not have formed in their current locations. Instead, they must have formed farther from their star and then migrated inward, probably through interactions with the disk of material from which they all formed. This allowed the worlds to maintain their regular spacing despite alternating sizes.”
