Exoplanet is more diminutive than Mercury

By Andrew Grant

Web edition: February 20, 2013

Mercury may be the runt of the solar system, but it still can beat up on the newly discovered Kepler-37b, the smallest planet known.

Scientists used NASA’s Kepler space telescope to detect the shadow the planet casts when it crosses in front of its star, 215 light-years from Earth in the constellation Lyra. Most planets are large enough to block several hundred parts per million of their stars’ light, but astronomer Thomas Barclay from NASA’s Ames Research Center in Mountain View, Calif., and his team managed to home in on a dimming of 22 parts per million — Kepler’s most sensitive detection to date. The planet has just 80 percent of Mercury’s diameter, the team reports online February 20 in Nature.

Kepler-37b orbits its sun-sized star closely, so it is likely a scorched world unsuitable for life, Barclay says. Two other planets around that star, including one three-quarters the size of Earth, are also too hot. Nonetheless, Barclay says that detecting these small planets gives astronomers confidence that they can spot the worlds they’re really after: small, rocky planets temperate enough to support life.