A distant planet with a helium-filled atmosphere that has swollen into the shape of a balloon has been discovered by astronomers.
Researchers who made the breakthrough they discovered the inert gas escaping the planet's atmosphere in a cloud 'just as a helium balloon might escape from a person's hand'.
The planet is 124 light years from Earth and was discovered by an international team of researchers at the University of Geneva, Switzerland.
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A distant planet (artist's impression) with a helium-filled atmosphere that has swollen into the shape of a balloon has been discovered by astronomers
Dr. Jessica Spake, of the University of Exeter's physics and astronomy department, said: "This is a very exciting discovery, especially as helium was only detected in exoplanet atmospheres for the first time earlier this year.
'The observations show helium being blasted away from the planet by radiation from its host star.
'Hopefully we can use this new study to learn what types of planets have large envelopes of hydrogen and helium, and how long they can hold the gases in their atmospheres.'
Neptune has been named HAT-P-11b and is in the Cygnus constellation.
As part of the study, researchers use a spectrograph in Spain.
The instrument then pulled apart the star's light in its component colors, like a rainbow.
The helium absorbs light of a specific wavelength, the researchers said the cloud was much more light than the planet itself.
The exoplanet is 124 light years from Earth and what is discovered by researchers at the University of Geneva, Switzerland (stock, artist's impression)
HOW DO SCIENTISTS STUDY THE ATMOSPHERE OF EXOPLANETS?
Anything we see in our atmosphere. Distant stars and their orbiting planets.
To understand these new worlds, and what they are made of, scientists need to be able to detect what their atmospheres consist of.
They often do this by using a telescope similar to Nasa's Hubble Telescope.
These enormous satellites scan the sky and lock on to exoplanets that NASA think may be of interest.
Here, the sensors on board perform different forms of analysis.
One of the most important and useful is absorption spectroscopy.
This form of analysis measures the light that is coming out of a planet's atmosphere.
Every gas absorbs a slightly different wavelength of light, and in this case a black line appears on a complete spectrum.
These lines correspond to a very specific molecule, which indicates its presence on the planet.
They are often called Fraunhofer lines after the German astronomer and physicist that first discovered them in 1814.
By combining all the different wavelengths of light, scientists can determine the atmosphere of a planet.
The key is that what is missing, provides the clues to find out what is present.
It is vitally important that this is done by space telescopes, as the atmosphere of earth would then interfere.
Absorption from chemicals in our atmosphere would skew the sample, which is why it is important to study.
This is often used to look for helium, sodium and even oxygen in all atmospheres.
This diagram shows the presence of key compounds. Search as sodium or helium
Computer simulations were used to track the trajectories of the helium atoms.
Vincent Bourrier, who led the computer simulation, said: 'Helium is blown away from the daytime side of the planet at 10,000kph (6,000mph).
'Because it is such a light gas, it escapes easily from the attraction of the planet and forms an extended cloud all around it.'
It is this phenomenon that gives it the balloon shape.
The planet's upper atmosphere is 20 times closer to its star than the Earth is from the Sun.
Neptune has been named HAT-P-11b and is in the Cygnus constellation (pictured)
Romain Allart, a University of Geneva's PhD student and first author of the study, said: 'We suspected that this could be the impact of the atmosphere of this exoplanet.
'The new observations are so precise that the exoplanet atmosphere is undoubtedly inflated by the stellar radiation and escapes to space.'
The research team believe the study could lead to a greater understanding of extreme atmospheric conditions around the hottest exoplanets.
Helium was only successfully found in the atmosphere at exoplanet, which is outside the solar system, earlier this year in a study by University of Exeter researchers.