Sen—NASA's Kepler space telescope, which is searching the Galaxy for planets, has found a planetary system with the smallest planet so far discovered around a Sun-like star.
The star system, designated Kepler-37, is located 210 light years away. Three planets have been detected orbiting the star.
Kepler-37b is about one-third the size of Earth, slightly larger than the Moon but smaller than Mercury. It is the tiniest planet so far discovered by Kepler.
The tiny planet is believed to be rocky, like the inner planets of our Solar System. Kepler-37b orbits its parent star every 13 days at less than one-third of the distance at which Mercury orbits the Sun. Scientists believe the surface temperature would be more than 800 degrees Fahrenheit. The scorched rock has no atmosphere and is not capable of supporting life as we know it.
Jack Lissauer, a planetary scientist at NASA's Ames Research Center, said: "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."
The two other planets discovered are designated Kepler-37c and Kepler-37d. Kepler-37c is slightly smaller than Venus, whilst the largest of the three planets, Kepler-37d, is twice the size of Earth.
All three planets orbit their parent star at a distance closer than the orbit of Mercury around the Sun. Although the star is slightly smaller and cooler than the Sun, all three worlds are considered to be extremely hot due to the close proximity of their orbit.
The line up shows the relative sizes of our Moon, Mercury, Mars and Earth with Kepler-37b, Kepler-37c and Kepler-37d. Image credit: NASA/Ames/JPL-Caltech
Kepler-37c orbits the star every 21 days, whilst Kepler-37d completes an orbit every 40 days.
"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, Kepler scientist and lead author of the new study which is being published in the journal Nature. "This discovery shows close-in planets can be smaller, as well as much larger, than planets orbiting our sun."
NASA's Kepler telescope was launched on March 6, 2009 and last year NASA made the decision to extend the Kepler mission until 2016.
As a space telescope Kepler sits above the atmosphere and has a uninhibited view of the light from distant stars. The telescope constantly monitors more than 150,000 stars for dips in their light which might be caused by a planet transiting in front of them. Just as the transit of Venus was observed from Earth last year, other planets can also be seen crossing the face of their parent star.
Finding the dip in a light curve which indicates that a planet might be orbiting a star is only the first step in the process. These dips could also be caused by binary stars, and so follow up Doppler spectroscopy must be performed to confirm the mass of the transiting object, and thus if it is actually a planet. So far Kepler has confirmed 114 planets and is carrying out further research on over 2,700 planet candidates.
Kepler's objective is to find Earth-like planets orbiting in the habitable zone of stars where the temperature of the planet is just right for liquid water and potentially life to exist. The planet most similar to Earth discovered so far is Kepler-22b, which is 2.4 times the radius of the Earth and orbits a Sun-like star in the habitable zone.