A team of astronomers who used the European Southern Observatory's 3.6m telescope in Chile to analyse the planet's atmosphere said they have found possible evidence of water in the form of steam shrouding the planet.
Alternatively, the planet, which is orbiting a star in the constellation of Ophiuchus, could have a mostly hydrogen atmosphere hidden beneath high clouds or hazes, as seen on Venus or Saturn's moon Titan, they said.
Codenamed GJ 1214b, the planet hugs its parent star at a distance of only two million kilometres -- 70 times closer than the earth is to the sun, the Daily Mail reported.
That's why conditions on its surface are hot, said the astronomers who carried out their study by analysing light coming from the star as the planet passed in front of it. The planet travels across the disc of its parent star once every 38 hours as it orbits.
Specific wavelengths of the starlight were absorbed by gases in the atmosphere, providing clues to its composition. Before making the observations, scientists had predicted a steam atmosphere, a cloud-obscured hydrogen atmosphere, or a deep hydrogen-rich atmosphere like that of Neptune. But the measurements did not show tell-tale signs of hydrogen, thereby ruling out the third option.
Dr Jacob Bean, from the Harvard-Smithsonian centre for astrophysics in Massachusetts, who led the research team, said, "This is the first super-Earth to have its atmosphere analysed. We've reached a real milestone on the road toward characterising these worlds."
"Although we can't yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy. Follow-up observations in longer wavelength infrared light are now needed to determine which of these atmospheres exists on GJ 1214b," he added.
The number of confirmed exoplanets reached 500 last month and more have been confirmed since.The findings were published in the journal Nature.