British scientists say they have found water for the first time in the atmosphere of a planet outside our solar system.
Researchers at University College London said Wednesday they found water vapor in a planet's air 110 light years from Earth that has temperatures suitable for life as we know it.
More than 4,000 exoplanets have been detected, but scientists say it is the only known exoplanet that has water, temperatures needed for life and a rocky surface.
It is not known if the planet, twice the size of Earth, eight times its mass, has water flowing on its surface.
But scientists say the so-called Super Earth is an ideal distance from its sun to conceivably harbor life.
The planet, known as K2-18b, was discovered in 2015 by the U.S. National Aeronautics and Space Administration.
"Finding water in a potentially habitable world other than Earth is incredibly exciting," said Angelos Tsiaras, lead author of the UCL report that was published in the journal Nature Astronomy. "K2-18b is not 'Earth 2.0' but it brings us closer to answering the fundamental question: Is the Earth unique?"
Scientists expect future space missions to detect hundreds of other exoplanets in coming decades.
A new generation of space exploration instruments will be able to describe exoplanet atmospheres in much greater detail.
The European Space Agency's ARIEL space telescope, for example, is scheduled for launch in 2028 and will observe some 1,000 planets, a sampling large enough to identify patterns and outliers.