Observations by NASA’s Hubble Space Telescope (HST), a sophisticated observatory exploring the universe from Earth orbit, have yielded a new class of planet, a watery world blanketed by a thick steamy atmosphere. It is smaller in size than Uranus, the third largest planet, but larger than Earth.
An international team of astronomers, led by Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA), made the observations of the planet, technically known as GJ 1214b.
“GJ 1214b is like no planet we know of,” said Berta. “A huge fraction of its mass is made up of water.”
GJ 1214b was discovered in 2009, at the Whipple Observatory, Arizona, USA, by a research team, led by CfA’s David Charbonneau. It is 2.7 times larger than Earth in size, and its mass is almost seven times that of Earth. It orbits a red-dwarf star, every 38 hours, at a distance of only 2 million km, giving it an estimated temperature of 230 degrees Celsius. For comparison, Earth orbits the Sun every 365.25 days, at an average distance of approximately 150 million km.
In 2010, a team led by CfA researcher Jacob Bean announced they had measured the atmosphere of GJ 1214b, finding it likely that it consists mainly of water. However, their observations could also be explained by the presence of haze in GJ 1214b’s atmosphere.
Berta and his colleagues used HST to study GJ 1214b, when it passed in front of its parent star. This transit allowed examining the star’s light as it filtered through the planet’s atmosphere. By observing the spectrum of the star, during the transit, astronomers were able to determine the constituent gases of GJ 1214b’s atmosphere. The team’s observations revealed that GJ 1214b has a dense atmosphere of water vapor.
“The Hubble measurements really tip the balance in favor of a steamy atmosphere,” Berta said.
Since GJ 1214b’s mass and size are known, astronomers have calculated its density of only 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 hints at GJ 1214b has much more water than Earth does, and much less rock. As a result, the internal structure of GJ 1214b would be extraordinarily different from that of our world.
“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 believe that GJ 1214b formed further out from its star, where water ice was plentiful, then its orbit shrank to its present size. In the process, it would have passed through the star’s habitable zone, where surface temperatures would be similar to Earth’s, and liquid water would exist on an Earth-like planet. How long it dwelled in the habitable zone is unknown.
References
NASA
www.nasa.gov/
The Hubble Space Telescope
www.spacetelescope.org/
http://hubblesite.org/
Wikipedia