Astronomers Discover 'Waterworld' Planet
February 21, 2012

Astronomers Discover ‘Waterworld’ Planet

Astronomers using NASA's Hubble Space Telescope have discovered a new class of planet, completely enveloped by water.

The "waterworld" planet has a thick, steamy atmosphere and is smaller than Uranus but larger than Earth.

"GJ1214b is like no planet we know of," Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) said in a press release. "A huge fraction of its mass is made up of water."

The planet 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.

The astronomers said that GJ1214b has an estimated surface temperature of 450 degrees Fahrenheit.

CfA scientist Jacob Bean and colleagues said they measured the atmosphere of the planet in 2010 and found that it likely composed mainly of water.  However, their observations could also be explained by the presence of a haze in its atmosphere.

The team used Hubble's Wide Field Camera 3 (WFC3) to study the planet when it crossed in front of its host star.  During the planet's transit, the star's light is filtered through the planet's atmosphere, giving researchers clues to the mix of gases.

Hazes are more transparent to infrared light than to visible light, so the Hubble observations help tell the difference between a steamy and a hazy atmosphere.

They found that the atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.

"The Hubble measurements really tip the balance in favor of a steamy atmosphere," Berta said.

The astronomers said the density of the planet is about 2 grams per cubic centimeter.  In comparison, water has a density of 1 gram per cubic centimeter, while Earth's average density is 5.5 grams per cubic centimeter.

The team said that because of its density, GJ1214b would contain much more water than Earth does, and much less rock.

They said that the internal structure of GJ1214b would be extraordinarily different than the Earth.

"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," Berta said.

Theorists say the planet originally formed out from its star, where water ice was plentiful, but slowly migrated closer towards its star.  During this process, GJ1214b would have passed through the star's habitable zone, where surface temperatures would be similar to Earth's.

The planet is located in the direction of the constellation Ophiuchus and sits 40 light-years away from Earth.


Image Caption: GJ1214b, shown in this artist's conception, is a super-Earth orbiting a red dwarf star 40 light-years from Earth. New observations from NASA's Hubble Space Telescope show that it is a waterworld enshrouded by a thick, steamy atmosphere. GJ1214b therefore represents a new type of world, like nothing seen in our solar system or any other planetary system currently known. Credit: NASA, ESA, and D. Aguilar (Harvard-Smithsonian Center for Astrophysics)


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