Astronomers using NASA’s Hubble Space Telescope have identified a new class of planet, a waterworld enshrouded by a thick, steamy atmosphere.
An artist's impression of exoplanet GJ1214b orbiting a red dwarf star (NASA / ESA / D. Aguilar / Harvard-Smithsonian Center for Astrophysics)
“GJ1214b is like no planet we know of,” said Dr. Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA), a co-author on a paper published in the Astrophysical Journal. “A huge fraction of its mass is made up of water.”
The planet GJ1214b was discovered in 2009 by CfA’s astronomers.
It is about 2.7 times Earth’s diameter and weighs almost seven times as much.
GJ1214b is located in the constellation Ophiuchus about 40 light-years away. This super-Earth orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degrees Fahrenheit.
Now, Dr. Berta and his co-authors have used Hubble’s Wide Field Camera 3 to study GJ1214b when it crossed in front of its host star. During such a transit, the star’s light is filtered through the planet’s atmosphere, giving clues to the mix of gases.
“We’re using Hubble to measure the infrared color of sunset on this world,” Dr. Berta said.
The astronomers found that the spectrum of GJ1214b is featureless over a wide range of wavelengths, or colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.
Astronomers also determined the density of the planet, which is about 2 grams per cubic centimeter. Water has a density of 1 gram per cubic centimeter, while Earth’s average density is 5.5 grams per cubic centimeter. This suggests that GJ1214b has much more water than Earth does, and much less rock.
“The Hubble measurements really tip the balance in favor of a steamy atmosphere,” Dr. Berta said.
“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.”
Researchers expect that GJ1214b formed farther out from its star, where water ice was plentiful, and migrated inward early in the system’s history.
Further monitoring of the system should help shed light on its hidden secrets.
