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Giant waterworld planet where year lasts just 18 hrs discovered

October 27, 2011 - London

A planet where a year lasts just 18 hours is a exotic waterworld with a radius about twice the size of Earth, astronomers say.

55 Cancri E is the innermost planet in orbit around a sun-like star known as 55 Cancri A that is around 40 light years from Earth.

Now a team from The University of Liege in Belgium have revealed further details about the planet after conducting a new study.

The team, led by Michael Gillon, observed the planet using both NASA's Spitzer space telescope and Canada's MOST space telescope, reports the Daily Mail.

The use of the telescopes is significant as the astronomers could analyse the amount of light the planet blocks from its parent star as it passes.

This allowed them to measure the planet's radius which determined that it was twice that of Earth.

This discovery allowed Gillon and his team to deduce that while the planet is rocky, its size made it too large to be made from rock alone.

The astronomers found that 55 Cancri E must therefore contain volatiles, which are compounds with low boiling points found on the planet's crust. They include water, nitrogen and carbon dioxide.

The presence of volatiles led to the group investigating two possible outcomes.

The first was that the atmosphere was made of hydrogen and helium, rather like the atmospheres of ice giants such as Jupiter or Saturn.

However they ruled this out because such an atmosphere would escape into space in just a few million years.

Instead they concluded that an envelope of water accounting for around 20 per cent of the planet's mass was responsible for its size, making it a waterworld.

Because of its close proximity to its sun the water would be a state where liquid and gas phases become one.

The planet may also be tidally locked so that one side is in permanent sunshine while the other is in permanent darkness.


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