Astronomers found the new planet using the MEarth (pronounced “mirth”) Project - an array of eight identical 16-inch-diameter RC Optical Systems telescopes that monitor a pre-selected list of 2,000 red dwarf stars. Although the super-Earth is too hot to sustain life, the discovery shows that ground-based technologies are capable of finding almost-Earth-sized planets in warm, life-friendly orbits.
A super-Earth is defined as a planet between one and ten times the mass of the Earth. The newfound world, GJ1214b, is about 6.5 times as massive as the Earth. Its host star, GJ1214, is a small, red type M star about one-fifth the size of the Sun. It has a surface temperature of only about 4,900 degrees F and a luminosity only three-thousandths as bright as the Sun.
GJ1214b orbits its star once every 38 hours at a distance of only 1.3 million miles. Astronomers estimate the planet’s temperature to be about 400 degrees Fahrenheit. Although warm as an oven, it is still cooler than any other known transiting planet because it orbits a very dim star.
Since GJ1214b crosses in front of its star, astronomers were able to measure its radius, which is about 2.7 times that of Earth. This makes GJ1214b one of the two smallest transiting worlds astronomers have discovered (the other being CoRoT-7-b). The resulting density suggests that GJ1214b is composed of
about three-fourths water and other ices, and one-fourth rock.
There are also tantalizing hints that the planet has a gaseous Earthlike atmosphere. The team also notes that, if it has an atmosphere, those gases are almost certainly not primordial. The star’s heat is gradually boiling off the atmosphere. Over the planet’s multiple-billion-year lifetime, much of the original atmosphere may have been lost.
“Despite its hot temperature, this appears to be a waterworld,” said Zachory Berta, a graduate student at the Harvard-Smithsonian Center for Astrophysics (CfA) who first spotted the hint of the planet among the data. “It is much smaller, cooler, and more Earthlike than any other known exoplanet.”
Berta added that some of the planet’s water should be in the form of exotic materials like Ice VII - a crystalline form of water that exists at pressures greater than 20,000 times Earth’s sea-level atmosphere.
In contrast, a super-Earth transiting a small, red dwarf star yields a greater proportional decrease in brightness and a stronger signal detectable from the ground. Astronomers then use instruments like the HARPS (High Accuracy Radial Velocity Planet Searcher) spectrograph at the European Southern Observatory to measure the companion’s mass and confirm it is a
planet, as they did with this discovery.
When astronomers compared the measured radius of GJ1214b to theoretical models, they found that the observed radius exceeds the model’s prediction, even assuming a pure water planet. Something more than the planet’s solid surface may be blocking the star’s light - specifically, a surrounding
atmosphere.
The next step for astronomers is to try to directly detect and characterize the atmosphere, which will require a space-based instrument like NASA’s Hubble Space Telescope. GJ1214b is only 40 light-years from Earth, within the reach of current observatories.
Since this planet is so close to Earth, said David Charbonneau of CfA, Hubble should be able to detect the atmosphere, which would 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.
Casey Kazan
Image: Planet GJ 1214b orbiting its red dwarf star. The Hubble telescope will reveal whether it is suitable for life. Artist’s impression: David A. Aguilar/CfA
Source: the Harvard-Smithsonian Center for
Astrophysics (CfA) -a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory
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