Astronomers have detected the presence of water molecules in the atmosphere of an exoplanet known as "51 Pegasi b" (51 Peb b for short) located 50 light years away. Known for being the first exoplanet which was discovered orbiting a star and the first known "hot Jupiter", it has a high surface temperature for orbiting its parent star "51 Pegasi" at a distance of only 0.05 AU.

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The discovery, presented in a paper published on arxiv.org, sheds new light on the nature of the exoworld's atmosphere and indicates that the star-planet system is a double-lined spectroscopic binary, reports Phys.

To better study this planetary system, a team of astronomers led by Jayne Birkby observed 51 Pegasi and its planet with the Cryogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) at the Very Large Telescope (VLT) in Chile, obtaining a total of 42 spectra to observe the radial-velocity shift of the water features in the planet's dayside atmosphere.

The researchers have presented in the paper a 5,6σ detection of water molecules in the atmosphere of the original hot Jupiter, 51 Peg b, proving that the 51 Peg Ab system is a double-lined spectroscopic binary. The best-matching model to the planet spectra from their grid contained molecular features from water only, with a volume mixing ratio of VMRH2O = 104.

According to the researchers, the direct detection of water absorption lines in the spectrum of the planet's atmosphere undergoing a change in Doppler shift provides important insights on the nature of this planetary system, particularly showing the true binary nature of the star-planet system revealing it to be a double-lined spectroscopic (non-eclipsing) binary.

Besides water, the researchers also searched for molecular features arising from the expected major carbon- and oxygen-bearing gasses at the observed wavelengths, like water carbon dioxide and methane. But they found no significant hints of presence from these molecules.