Water world is new type of planet

The Hubble space telescope has found one of the steamier spots in the Universe – a planet that is a big ball of vapour.

An artist's conception of the new water world orbiting its red dwarf star
An artist's conception of the new water world orbiting its red dwarf star. Credit: David A. Aguilar (CfA)

Scientists say this new water world, dubbed GJ 1214b, is an entirely new type of planet. It is quite unlike the planets in our own solar system which are either rocky, ice giants or vast balls of gas.

Astronomer Zachory Berta, of Harvard-Smithsonian Center for Astrophysics (CfA), and colleagues proved that GJ 1214b is mainly made of water and is a world enshrouded by a thick, steamy atmosphere.

It is so close to its own sun, at a distance of 1.3 million miles, a red dwarf star, that it zips round it in a year that is only 38 hours long.

The planet, which lies in the direction of the constellation Ophiuchus, the serpent bearer, and is only 40 light-years away from us, is 2.7 times the diameter of Earth and weighs seven times as much. “GJ 1214b is like no planet we know of,” said Berta. “A huge fraction of its mass is made up of water.”

The internal structure of GJ 1214b would be very different to 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,” said Berta.

GJ 1214b was discovered in 2009 by the ground-based MEarth Project, which is led by CfA’s David Charbonneau. In 2010, CfA scientist Jacob Bean and colleagues reported that their measuremenets of the atmosphere of GJ 1214b showed it was probably composed mainly of water. However, their observations could also be explained by haze throughout the planet’s atmosphere.

Berta and his co-authors used Hubble’s WFC3 instrument to study GJ 1214b when it crossed in front of its host star. They watched the star’s light as it was filtered through the planet’s atmosphere during the transit, revealing information about 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 team found the planet’s spectrum to be featureless over a wide range of wavelengths, suggesting a dense atmosphere of water vapour. Berta said: “The Hubble measurements really tip the balance in favor of a steamy atmosphere.”

The observations also showed that GJ 1214b has much more water than Earth, and much less rock, meaning that its internal make-up must be very different from our world. It is thought that GJ 1214b formed farther away from its star, where water ice was plentiful, and then migrated inwards to its present location.

Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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