HAT P-11b
Water vapour has been discovered on a planet trillions of miles away from EarthNASA/JPL-Caltech

Astronomers have found water vapour in the atmosphere of a planet 124 light years away.

The exoplanet, HAT P-11b, is four times the radius of Earth and 26 times the mass, and is located in the constellation Cygnus 729 trillion miles away.

Scientists from the University of Maryland, led by astronomy professor Drake Deming, are hoping to test the hypothesis that other planets in the universe are formed in the same way as ours.

The planets in our system are created by a process called core accretion, which is the mass growth of a large object via gravitational pull. A rocky core forms through the native electrical charges in the particles of dust and ice, which keep sticking together until the core is big enough to accrete a gaseous envelope around it.

Early on in this process, large planets far from the sun were able to attract huge amounts of hydrogen gas to create water.

HAT P-11b Passes In Front of It's Star
An artists rendition of HAT P-11b passing in front of its star in the constellation Cygnus.NASA/JPL-Caltech

However, in large planets the water only occurs at deep levels, where it is hard to observe. Researchers are keen to study small planets because they believe it is more likely there will be heavy molecules, such as water vapour and hydrogen.

"Our ideas about the formation of planets have been developed to match our solar system, and we don't know whether other planetary systems behave the same way," explained Deming. "We want to test the fundamental question of whether small planets are rich in heavy elements, like the oxygen in water vapour."

Smaller planets are much harder to study due to their size and HAT P-11b is the smallest planet where scientists have been able to identify chemical components in the atmosphere.

The discovery of water vapour on exoplanets is important because water is a precondition for life. However, it's not enough to suggest that there is life on HAT P-11b or will ever be. For example, the sun has water vapour in its atmosphere, as it will naturally form wherever there is oxygen and hydrogen.

This discovery "is a key piece of the puzzle," Deming says, and could provide vital information about how planets are formed.