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US Astronomers discover ‘water planet’

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Photo courtesy: Harvard-Smithsonian Centre for Astrophysics

US astronomers have discovered a “water planet” bigger than the Earth. Zachory Berta and his colleagues at Harvard-Smithsonian Centre for Astrophysics have fund, a previously discovered world GJ1214b is a waterworld, enshrouded by a thick, steamy atmosphere.

The planet, about 2.7 times the Earth’s diameter and weighs almost 7 times as much, was first discovered in 2009 by ground-based telescopes. It orbits a red-dwarf star every 38 hours at a distance of 1.3 million miles, giving it an estimated temperature of 450 degree Fahrenheit, a release by the Centre said.

“GJ1214b is like no planet we know of,” said Berta. “A huge fraction of its mass is made up of water.”

Berta and his co-authors used Hubble Space Telescope to study the planet, 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. 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.

The astronomers found the spectrum of GJ1214b to be featureless over a wide range of wavelengths, or colours. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapour.

“The Hubble measurements really tip the balance in favour of a steamy atmosphere,” said Berta.

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 1g/cm3, while Earth’s average density is 5.5 g/cm3. This suggests GJ1214b has much more water than Earth, and much less 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,” said Berta.

Theorists expect 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. How long it lingered there is unknown.

GJ1214b is located in the direction of the constellation Ophiuchus, and just 40 light-years from Earth. Therefore, it’s a prime candidate for study by the next-generation James Webb Space Telescope.

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