Telescopio Nazionale Galileo helps to detect water in the Jovian planets KELT-8 b and KELT-23 Ab

Thanks to infrarred observations taken with the high-resolution spectrograph GIANO-B installed at the Telescopio Nazionale Galileo, a team led by M. Basilicata (University of Tor Vergata, Rome and INAF ‐ Astrophysical Observatory of Turin), detected for the first time water vapour in the atmosphere of two extra-solar planets and suggested a possible formation scenario.

KELT-8 b and KELT-23 Ab are hot Jovian planets, orbiting two Solar-like stars at about 643 and 414 light years away. Similar in size to Jupiter, these gaseous giants have hydrogen- and helium-rich atmospheres and reach temperatures of around 1,000° C due to their close orbits, completing a revolution in under 10 Earth days.

The mechanism behind the formation of gaseous giant planets in close orbits remains unclear, but studying the chemical abundances in their atmospheres can help reconstruct it. The composition depends on the planet's position in the protoplanetary disk and the enrichment of heavy elements during their migration toward the star.

The importance of studying the atmospheres of extra-solar planets lies in the fact that we can use this study to look for possibility of life or probe atmospheres with chemical-physical conditions not found in our Solar System.

M. Basilicata, the lead author of the study, explains: "The atmospheres of these two exoplanets, rich in water vapor and containing more oxygen and less carbon than their stars, may reveal insights into their formation. Specifically, if we define the water snow line (the region in a protoplanetary disk where water is either steam inside and ice outside), it appears both planets likely accreted most of their atmospheres inside this line."

Thus, concludes the author, "thanks to this study we have not only revealed for the first time the atmospheres of the two planets providing a first characterization of their chemical properties, but we have also added an important point to the understanding of the formation of hot Jupiter planets".

Link to the paper: https://doi.org/10.1051/0004-6361/202452733

Figure: (S/N) Kp ‐ Vrest maps. The maps are built by cross-correlating a single-species model of H2O with data of KELT-8 b (left panel) and KELT-23 Ab (right panel), as described in the paper: https://doi.org/10.1051/0004-6361/202452733