Just when exoplanets became too numerous to bother counting, astrophysicists have discovered a new type of extrasolar planet — a steamy waterworld shrouded in a thick atmosphere. The planet, known as GJ1214b, has a diameter roughly 2.7 times that of Earth and a surface temperature of about 450 degrees Fahrenheit.
Originally discovered in 2009, subsequent studies the following year suggested GJ1214b was largely composed of water. At the time, however, scientists were not certain whether the atmosphere they were observing was haze or water vapor. More recently, the Hubble Space Telescope’s Wide Field Camera 3 (WFC3) was used to catch GJ1214b as it crossed in front of its host star.
Artist's conception of GJ1214b passing in front of its red dwarf sun, 40 light-years from Earth. Source: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)
During transit, the star’s light was filtered through the planet’s atmosphere — and since hazes are more transparent to infrared light than to visible light, Hubble was able to tell the difference between a steamy and a hazy atmosphere.
The result? The spectrum of GJ1214b’s atmosphere was featureless over a wide range of wavelengths — consistent with a dense atmosphere of water vapor.
Calculations of GJ1214b’s density indicate that it contains a much higher proportion of water — and less rock — than Earth, but its size and proximity to its red-dwarf sun make it much different than the watery world we might first imagine.
“The high temperatures and high pressures would form exotic materials like ‘hot ice’ or ‘superfluid water,’ substances that are completely alien to our everyday experience,” says Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) who, along with colleagues, conducted the Hubble observations.
Scientists theorize that GJ1214b formed farther out from its star, where water ice was plentiful, and migrated inward early in the system’s history. In the process, it would have passed through the star’s habitable zone, where surface temperatures would be similar to Earth’s. How long it lingered there is unknown.
GJ1214b is located about 40 light-years from Earth in the direction of the constellation Ophiuchus, and a prime candidate for further study by the planned James Webb Space Telescope. A paper reporting the recent results has been accepted for publication in The Astrophysical Journal.
