Artist impression of the exoplanet 51 Pegasi b. Credit: ESO/M. Kornmesser/Nick Risinger (

Water detected in the atmosphere of hot Jupiter exoplanet 51 Pegasi b

Water detected in the atmosphere of hot Jupiter exoplanet 51 Pegasi b

February 1, 2017 by Tomasz Nowakowski

(—Astronomers have detected the presence of water molecules in the atmosphere of a nearby hot Jupiter exoplanet known as 51 Pegasi b (51 Peb b for short). The discovery sheds new light on the nature of the exoworld’s atmosphere and indicates that the star-planet system is a double-lined spectroscopic binary. The findings were presented Jan. 25 in a paper published on

Located some 50 light years away, 51 Pegasi b is the first exoplanet discovered orbiting a main-sequence star and the first known hot Jupiter. It was classified as a hot Jupiter because it has orbital period of less than 10 days (4.23 days) and is similar in characteristics to the solar system’s biggest planet, with a mass of about 0.47 Jupiter masses. It has high surface temperature, as it orbits its parent star 51 Pegasi very closely—at a distance of about 0.05 AU.
To better characterize this planetary system, a team of astronomers led by Jayne Birkby have observed 51 Pegasi and its planet with the CRyogenic high-resolution InfraRed Echelle Spectrograph (CRIRES) at the Very Large Telescope (VLT) in Chile. They obtained a total of 42 spectra allowing them to observe the radial-velocity shift of the water features in the planet’s day side atmosphere. …