Water has been detected in the atmosphere of a planet with a radius four times the size of Earth in the constellation Cygnus about 124 light years away.
The finding brings the hope that scientists will soon be able to detect water in the atmosphere of planets similar in size to the Earth.
This discovery marks the smallest planet for which scientists have been able to identify some chemical components of its atmosphere.
The team was led by University of Maryland Astronomy Professor Drake Deming, an expert in the study of exoplanets, or planets whch orbit suns outside our own solar system.
The finding of water vapour and hydrogen in the atmosphere of the exoplanet HAT P-11b is an astonishing piece of long-distance detective work, based on analyses of observations by three different NASA telescopes.
The scientists used a quirk of light which happens when a planet transits, or passes in front of, its host star.
Material in the planet’s atmosphere absorbs some of the star’s light and that makes the planet appear bigger in the same way our sun seems bigger at sunset when looking to the horizon across a broad swath of Earth’s atmosphere.
By plotting changes in the exoplanet’s size and relating them to the wavelength of electromagnetic radiation the telescope observes, astronomers get a graph showings how much of the star’s radiation the planet’s atmosphere is absorbing.
The shape of that graph, called a transmission spectrum, can reveal which chemicals are present in the atmosphere.
The bigger the planet, the more obvious are the changes in the planet’s size during its transit across its host star.
Water is a precondition for life but its presence alone is not enough for life to arise.
Details of the discovery is published in the journal Nature.
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