GIARPS unveils new clues about the fiery atmosphere of Ultra-Hot Jupiter WASP-76b

A new study carried out with observations at the Telescopio Nazionale Galileo has provided fresh insights into the atmosphere of the ultra-hot Jupiter WASP-76b. Using the powerful GIARPS observing mode - which uniquely combines the GIANO-B (near-infrared) and HARPS-N (optical) spectrographs - researchers successfully detected key chemical species on this extreme exoplanet. This multi-instrument approach marks a major step forward in ground-based exoplanetary science.

WASP-76b, one of the most intensely studied ultra-hot Jupiters, with a mass of 0.894 Jupiter masses and a radius of 1.854 Jupiter radii, orbits its host star (an F7 main-sequence star) every 1.81 days. Due to this proximity to the star, the planet is exposed to an intense stellar irradiation, reaching dayside temperatures over 3000 K which make it an ideal target for atmospheric characterization. Despite its popularity, most previous studies relied on simplified 1D atmospheric models. In contrast, this new research applies a 3D framework, supported by Global Circulation Models (GCMs), to better interpret high-resolution spectra.

The team part of the GAPS project (Global Architecture of Planetary Systems), collected two new dayside emission spectra of WASP-76b using GIARPS at TNG, and re-analyzed four public datasets from ESPRESSO at the VLT. Their goal was to track carbon monoxide (CO) and neutral atomic iron (Fe I), two key tracers of temperature structure and atmospheric dynamics, in order to better understand the complex processes shaping the atmosphere of this ultra-hot Jupiter.

The results reveal a compelling picture of WASP-76b's atmosphere. CO was clearly identified in the GIANO-B data, with a high S/N of 10.4, making it one of the most robust ground-based detections of this molecule so far. Fe I was also detected, with significant signals emerging from both the HARPS-N and ESPRESSO instruments, showing S/N values of 3.5 and 6.2 respectively. In addition, a marginal Fe I signal (S/N 4.0) appeared in the GIANO-B spectra. Although this on its own might be considered tentative, its reliability is reinforced by the consistency with simultaneous HARPS-N observations. Notably, the ESPRESSO dataset also revealed a small but measurable offset of approximately 6 km/s in the planet's orbital velocity (Kp) compared to theoretical predictions, hinting at potentially complex atmospheric or orbital dynamics influencing the signal.

These findings were further compared to outputs from 3D GCMs, which simulate planetary winds and heat redistribution. Both cross-correlation and likelihood analyses showed that models including atmospheric dynamics fit the data significantly better than static ones—especially for the ESPRESSO datasets.

One of the most intriguing features emerged in the Fe I signal, which was found to be asymmetric, appearing stronger after secondary eclipse. This pattern suggests that WASP-76b's atmospheric hotspot is shifted eastward from the substellar point, likely due to fast eastward zonal winds—an effect that only 3D models can fully capture.

This study highlights the instrumental role of the TNG and GIARPS in high-resolution exoplanetary science. The ability to combine optical and near-infrared spectroscopy from a single site provides unique advantages in tracing both atomic and molecular signatures under consistent observational conditions.

Link to the paper: https://ui.adsabs.harvard.edu/abs/2025arXiv250719299G/abstract

Detection S/N maps as a function of vrest and Kp (planet's orbital velocity) for CO in GIANO-B (left panel), Fe I in HARPS-N (central panel), and Fe I in ESPRESSO (right panel) data. These maps were obtained by cross-correlating the observed spectra with 1D atmospheric models. The red (white) dotted lines indicate the expected (measured) planetary velocity position. For each map, the top and right sub-panels show the corresponding 1D cross-correlation functions (expressed in terms of S/N) at the peak location, with the best-fit Gaussian profile overplotted in orange. In the case of ESPRESSO data, the analysis reveals a slight negative offset in the planet's orbital velocity (Kp) of about 6 km/s compared to theoretical predictions. This discrepancy may suggest the need to adopt 3D atmospheric models that more accurately capture the dynamics of WASP-76b's atmosphere. See paper for more details.

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Home General Info News Telescope & Instruments Observing Time Allocations & Schedules Publications Seminars Weather Webcam Outreach Gallery Links	GIARPS unveils new clues about the fiery atmosphere of Ultra-Hot Jupiter WASP-76b A new study carried out with observations at the Telescopio Nazionale Galileo has provided fresh insights into the atmosphere of the ultra-hot Jupiter WASP-76b. Using the powerful GIARPS observing mode - which uniquely combines the GIANO-B (near-infrared) and HARPS-N (optical) spectrographs - researchers successfully detected key chemical species on this extreme exoplanet. This multi-instrument approach marks a major step forward in ground-based exoplanetary science. WASP-76b, one of the most intensely studied ultra-hot Jupiters, with a mass of 0.894 Jupiter masses and a radius of 1.854 Jupiter radii, orbits its host star (an F7 main-sequence star) every 1.81 days. Due to this proximity to the star, the planet is exposed to an intense stellar irradiation, reaching dayside temperatures over 3000 K which make it an ideal target for atmospheric characterization. Despite its popularity, most previous studies relied on simplified 1D atmospheric models. In contrast, this new research applies a 3D framework, supported by Global Circulation Models (GCMs), to better interpret high-resolution spectra. The team part of the GAPS project (Global Architecture of Planetary Systems), collected two new dayside emission spectra of WASP-76b using GIARPS at TNG, and re-analyzed four public datasets from ESPRESSO at the VLT. Their goal was to track carbon monoxide (CO) and neutral atomic iron (Fe I), two key tracers of temperature structure and atmospheric dynamics, in order to better understand the complex processes shaping the atmosphere of this ultra-hot Jupiter. The results reveal a compelling picture of WASP-76b's atmosphere. CO was clearly identified in the GIANO-B data, with a high S/N of 10.4, making it one of the most robust ground-based detections of this molecule so far. Fe I was also detected, with significant signals emerging from both the HARPS-N and ESPRESSO instruments, showing S/N values of 3.5 and 6.2 respectively. In addition, a marginal Fe I signal (S/N 4.0) appeared in the GIANO-B spectra. Although this on its own might be considered tentative, its reliability is reinforced by the consistency with simultaneous HARPS-N observations. Notably, the ESPRESSO dataset also revealed a small but measurable offset of approximately 6 km/s in the planet's orbital velocity (Kp) compared to theoretical predictions, hinting at potentially complex atmospheric or orbital dynamics influencing the signal. These findings were further compared to outputs from 3D GCMs, which simulate planetary winds and heat redistribution. Both cross-correlation and likelihood analyses showed that models including atmospheric dynamics fit the data significantly better than static ones—especially for the ESPRESSO datasets. One of the most intriguing features emerged in the Fe I signal, which was found to be asymmetric, appearing stronger after secondary eclipse. This pattern suggests that WASP-76b's atmospheric hotspot is shifted eastward from the substellar point, likely due to fast eastward zonal winds—an effect that only 3D models can fully capture. This study highlights the instrumental role of the TNG and GIARPS in high-resolution exoplanetary science. The ability to combine optical and near-infrared spectroscopy from a single site provides unique advantages in tracing both atomic and molecular signatures under consistent observational conditions. Link to the paper: https://ui.adsabs.harvard.edu/abs/2025arXiv250719299G/abstract Detection S/N maps as a function of vrest and Kp (planet's orbital velocity) for CO in GIANO-B (left panel), Fe I in HARPS-N (central panel), and Fe I in ESPRESSO (right panel) data. These maps were obtained by cross-correlating the observed spectra with 1D atmospheric models. The red (white) dotted lines indicate the expected (measured) planetary velocity position. For each map, the top and right sub-panels show the corresponding 1D cross-correlation functions (expressed in terms of S/N) at the peak location, with the best-fit Gaussian profile overplotted in orange. In the case of ESPRESSO data, the analysis reveals a slight negative offset in the planet's orbital velocity (Kp) of about 6 km/s compared to theoretical predictions. This discrepancy may suggest the need to adopt 3D atmospheric models that more accurately capture the dynamics of WASP-76b's atmosphere. See paper for more details.
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