Bit too hot for Kevin Costner, though
Posted in Space, 17th December 2009 10:35 GMTspotted a super-Earth waterworld orbiting a red type M star some 40 lightyears from Earth.
The body - dubbed GJ1214b - is circling dim host star GJ1214 every 38 hours at a distance of just 1.3 million miles. The star's modest surface temperature of 2,700°C, though, means that GJ1214b itself is a balmy 200°C.
The planet has a mass and radius of 6.5 and 2.7 times that of Earth, respectively. The density obtained from these figures "suggests that GJ1214b is composed of about three-fourths water and other ices, and one-fourth rock".
CfA graduate student Zachory Berta, who first identified the planet, said: "Despite its hot temperature, this appears to be a waterworld. It is much smaller, cooler, and more Earthlike than any other known exoplanet."
The discovery was made as part of the ground-based MEarth Project, which uses "an array of eight identical 16-inch-diameter RC Optical Systems telescopes that monitor a pre-selected list of 2,000 red dwarf stars".
CfA elaborates: "Each telescope perches on a highly accurate Software Bisque Paramount and funnels light to an Apogee Alta U42 camera containing a charge-coupled device (CCD) chip, which many amateurs also use."
The 'scopes keep an eye out for dips in brightness where an exoplanet transits its host star. Whereas super-Earths (between five 5 and 10 Earth masses) transiting bright stars such as our Sun are impossible to spot from Earth, those like GJ1214b which transit a dim host are within the capability of ground-based technology.
In this case, GJ1214 is around one-fifth the size of the Sun with a luminosity "only three-thousandths as bright".
Having made their discovery, the CfA team then used the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at the European Southern Observatory "to measure the companion's mass and confirm it is a planet".