Astronomers have discovered water on a distant world the size of Neptune.
The planet HAT-P-11b (natty name) is located in the constellation of Cygnus, more than 798 trillion miles from Earth, and is much smaller than other planets where water has been found.
Researchers from the University of Maryland identified water vapour in its atmosphere by combining data from three NASA telescopes.
Planets outside our solar system are generally very hard to detect and study. That is because they are too far away to directly observe.
Instead we rely on tremors in the light reaching Earth from distant stars, created by planets passing in front of the star, to look for clues about their existence and make-up.
To look for water, scientists study how the planet's size appears to change as it passes in front of the star, an effect caused by the planet absorbing the star's light. This information is collated into a 'transmission spectrum' which can be analysed to show which chemicals are present in the atmosphere.
This approach has limits, however, most obviously that it's easier to see large planets than small ones.
The case of HAT-P-11b is unique because it's far smaller than any other planet where water vapour has been discovered. Here are some other key details about this strange new world:
- It's 4 times as large as Earth, but 26 times as dense
- It's very close to its star, and is 1,120 degrees F in temperature on the surface
- It has a rocky core, wrapped in a 90% hydrogen atmosphere
Scientists are interesting in planets with water, because they add weight to the idea that the compound (and maybe life, which as far as we know depends on water) is a regular sight in the cosmos.
"The water molecule is widespread in the universe," said Professor Drake Deming. "Wherever you have hydrogen and oxygen, it naturally forms. Even some sun spots are cool enough to contain water vapor, although obviously it's far too hot for life on the sun."
"Our ideas about the formation of planets have been developed to match our solar system