An international team of astronomers using NASA’s Kepler Space Telescope has made the first observations of a planet outside our Solar System that’s smaller than Mercury.
Artist’s concept of the newly discovered planet Kepler-37b (NASA / Ames / JPL-Caltech)
The planet, dubbed Kepler-37b, is the innermost of three planets that orbit the sun-like host star Kepler-37 located about 210 light-years away in the constellation Lyra.
Kepler-37b is estimated to be a similar size to the Moon, which is only 3,475 km in diameter. Owing to this extremely small size and its highly irradiated surface, the planet is believed to be a rocky planet with no atmosphere or water, similar to Mercury.
“That we have found one of these small and hard-to-detect planets suggests that they are abundant around other stars and lends weight to the belief that as planet size decreases their occurrence increases exponentially,” said Dr Dennis Stello of the University of Sydney’s School of Physics, co-author of a paper reporting the discovery in the journal Nature.
“While theoretically such small planets are expected, detection of tiny planet Kepler-37b is remarkable given its transit signal is detectable on less than 0.5 percent of stars observed by Kepler,” said co-author Prof Tim Bedding, also from the University of Sydney’s School of Physics.
This image shows artist’s concepts of the planets in the Kepler-37 system, the Moon and planets in the Solar System (NASA / Ames / JPL-Caltech)
“Since the discovery of the first exoplanet we have known that other planetary systems can look quite unlike our own, but it is only now, thanks to the precision of the Kepler Space Telescope that we have been able to find planets smaller than the ones we see in our own Solar System.”
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 team to more accurately measure the three planets orbiting Kepler-37, including the tiny Kepler-37b.
“Knowing this stellar radius is very important because the accuracy with which we can measure the radius of the planet Kepler-37b is limited by how accurately we can calculate the radius of Kepler-37,” Dr Stello said.
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Bibliographic information: Thomas Barclay et al. A sub-Mercury-sized exoplanet. Nature, published online February 20, 2013; doi: 10.1038/nature11914
