Extreme climatology on Hot Jupiters. The study: “The GAPS Programme at TNG. LXIX.The Dayside of WASP-76b revealed by GIANO-B, HARPS-N and ESPRESSO: Evidence for Three-Dimensional Atmospheric Effects” of G. Guilluy (INAF – OATo) appeared on A&A

Planetary climatology under extreme conditions thanks to GIANO-B, HARPS-N and ESPRESSO observations of the hot Jupiter WASP-76b

Among the 6007 confirmed exoplanets to date (09/22/2025), there exists a class of planets absent in the Solar System but crucial for studying atmospheric physics under extreme conditions: ultra-hot Jupiters.

These are gas giants in very close orbits around their host stars, with orbital periods shorter than 3 days and equilibrium temperatures exceeding 2000 degrees kelvin. Studying such worlds allows us to test our understanding of atmospheric physics, chemistry and models in regimes of temperature, pressure, and dynamics very different from those encountered in Solar System planets.

The team led by astrophysicist G. Guilluy (INAF – Astrophysical Observatory of Turin) analyzed spectroscopic observations of the ultra-hot Jupiter WASP-76b, obtained with the GIANO-B and HARPS-N instruments at the Telescopio Nazionale Galileo, and with ESPRESSO at ESO’s Very Large Telescope. The observations were carried out when the planet was showing its dayside, i.e., just before and just after its passage behind the star from our point of view.

The researchers identified significant signals from carbon monoxide (CO) molecules and neutral iron (Fe I) atoms. The data were then compared with Global Circulation Models (GCMs), originally developed for studying Earth’s atmosphere and more recently adapted to exoplanets. These are three-dimensional models that solve the equations of fluid dynamics and radiative transfer (i.e., how radiation propagates through the atmosphere and deposits energy), thereby providing a 3D description of the atmosphere’s structure, temperature and pressure distribution, winds, and chemical composition.

In particular, the authors observed that the signal associated with iron increased in intensity after the eclipse. This could indicate the presence of an atmospheric “hot spot”: a region of the atmosphere that is hotter than average. In this case, the hot spot is not located exactly at the point facing the star (known as the substellar point, where an observer on the planet would see the star at the zenith), but shifted closer to the nightside due to atmospheric circulation. This configuration means that, from Earth, we are observing a region of the atmosphere with a temperature–altitude profile different from that of the surrounding environment.

The study is presented in the article “The GAPS Programme at TNG. LXIX. The Dayside of WASP-76b revealed by GIANO-B, HARPS-N and ESPRESSO: Evidence for Three-Dimensional Atmospheric Effects”, published in Astronomy & Astrophysics. Among the co-authors are astrophysicists C. Di Maio and G. Micela of INAF – Palermo Astronomical Observatory.

The cover figure (click here to view in full) shows a schematic illustration of the effect underlying the asymmetries observed in the Fe I signal in WASP-76b atmosphere. The white portion represents the dayside of the planet, illuminated by the star (yellow circle at the center). The red area marks the position of the hot spot. From our line of sight (indicated by the arrows), the temperature–altitude profile shows a more pronounced variation (i.e., a steeper gradient) during the post-eclipse phase compared to the pre-eclipse phase.