Water world
A steamy ‘waterworld‘ six times bigger than Earth has been discovered orbiting a faint star 40 light years away.The planet is believed to be too hot to sustain Earth-type life, but could consist of 75 per cent water. Evidence suggests it has an atmosphere, and astronomers believe it to be more Earth-like than any ‘exoplanet’ previously found outside the Solar System.The planet is classified as a ‘super-Earth‘, half-way in size between small rocky planets such the Earth and ice giants similar to Uranus and Neptune. Although its parent star is a dim ‘red dwarf’ 3,000 times less bright than our sun, it hugs the star so closely that its surface temperature is 200C.At a distance of just 1.3million miles, the planet makes one year-long orbit of the star every 38 hours.The planet was discovered circling the star GJ1214 with an array of small ground-based telescopes no larger than those used by many amateurs.
The MEarth Project employs eight identical 16-inch diameter telescopes monitoring a 2,000 red dwarf stars. Red dwarfs are the most common type of star in the Milky Way galaxy.The telescopes are looking for changes in brightness that might betray the presence of a planet crossing in front of a star. Red dwarfs lend themselves to this approach to planet finding because they are so faint.
By measuring the dip in brightness caused by the crossing, scientists can calculate a planet’s density and make an educated guess about its composition.The new planet, GJ1214b, is thought to be three-quarters water and ice and about one-quarter rock.
‘Despite its hot temperature, this appears to be a water world,’ Harvard-Smithsonian Center graduate student astronomer Zachory Berta, who discovered the planet, said.’It is much smaller, cooler and more Earth-like than any other known exoplanet.’
Water world close up
The scientists believe something besides the planet’s surface must be blocking light from the parent star – probably a surrounding atmosphere that may contain hydrogen and helium.Turning the Hubble Space Telescope towards the planet may allow astronomers to discover its composition.MEarth Project head Dr David Charbonneau said: ‘Since this planet is so close to Earth, Hubble should be able to detect the atmosphere and determine what it’s made of.That will make it the first super-Earth with a confirmed atmosphere – even though that atmosphere probably won’t be hospitable to life as we know it.‘The discovery was reported today in the journal Nature. In an accompanying article, renowned planet-hunter Professor Geoffrey Marcy, from the University of California, speculated about what the waterworld might be like.
He wrote: ‘It probably has an extraordinarily deep ocean, which would be liquid given its equilibrium surface temperature of some 190C due to heating from the host star. A sauna-like steam atmosphere is possible.’
