Feb 28, 2012; 4:20 PM ET
Our solar system contains three types of planets: rocky, terrestrial worlds, such as Mercury, Venus, Earth and Mars; gas giants like Jupiter and Saturn; and ice giants, like Uranus and Neptune. Planets orbiting distant stars come in an even wider variety, including lava worlds and “hot Jupiters.”
Observations by NASA’s Hubble Space Telescope have added a new type of planet to the mix. By analyzing the previously discovered world GJ 1214b, astronomer Zachory Berta at the Harvard-Smithsonian Center for Astrophysics and his colleagues proved that it is a “water world” enshrouded by a thick, steamy atmosphere.
GB 1214b is about 2.7 times Earth’s diameter and weighs almost seven times as much. It 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.
Since the planet’s mass and size are known, astronomers can calculate the density, which works out to about 2 grams per cubic centimeter. Water has a density of 1 g/cm3, while Earth’s average density is 5.5 g/cm3. This suggests that GJ 1214b has much more water than Earth and also much less rock.
GJ 1214b is located in the direction of the constellation Ophiuchus, just 40 light-years from Earth. It is a prime candidate for study by the next-generation James Webb Space Telescope.