Issue |
A&A
Volume 695, March 2025
|
|
---|---|---|
Article Number | A26 | |
Number of page(s) | 12 | |
Section | Planets, planetary systems, and small bodies | |
DOI | https://doi.org/10.1051/0004-6361/202451044 | |
Published online | 28 February 2025 |
A closer look at LTT 9779b:The ESPRESSO endeavour to pierce the atmospheric veil
1
Departamento de Astronomía, Universidad de Chile,
Camino el Observatorio 1515, Las Condes,
Santiago,
Chile
2
Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales,
Av. Ejército 441,
Santiago,
Chile
3
Centro de Astrofísica y Tecnologías Afines (CATA),
Casilla 36-D,
Santiago,
Chile
4
European Southern Observatory (ESO),
Av. Alonso de Córdova 3107,
763 0355
Vitacura, Santiago,
Chile
5
Instituto de Astrofísica de Canarias (IAC),
Calle Vía Láctea s/n,
38200
La Laguna,
Tenerife,
Spain
6
Main Astronomical Observatory of the NAS of Ukraine,
27, Akademik Zabolotny Str.,
Kyiv,
03143,
Ukraine
7
Deptartamento de Astrofísica, Universidad de La Laguna (ULL),
38206
La Laguna,
Tenerife,
Spain
8
Space Telescope Science Institute,
3700 San Martin Drive,
Baltimore
MD
21218,
USA
9
Instituto de Astronomía, Universidad Católica del Norte,
Angamos 0610,
1270709,
Antofagasta,
Chile
10
Las Campanas Observatory, Carnegie Institution of Washington,
Colina El Pino S/N,
La Serena,
Chile
★ Corresponding author; rramirez@das.uchile.cl
Received:
9
June
2024
Accepted:
7
November
2024
Context. The proliferation of exoplanet discoveries, particularly within such exotic environments as the Neptune desert, challenges our understanding of planetary atmospheres undergoing intense irradiation. The unexpected discovery of LTT 9779 b, an ultra-hot Neptune deep within this desert offers a prime opportunity for in-depth atmospheric studies. This research builds upon previous observations of LTT9779b from space-based telescopes, including the Transiting Exoplanet Survey Satellite (TESS), Spitzer Space Telescope, and CHaracterising ExOPlanet Satellite (CHEOPS), while incorporating new observations from the Very Large Telescope’s (VLT) Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations (ESPRESSO) instrument to delve deeper into the atmospheric dynamics of this intriguing exoplanet. Preliminary analyses suggest a metal-rich atmosphere alongside a notably high day-side geometric albedo that may imply the existence of silicate clouds. Furthermore, there appears to be minimal atmospheric escape, presenting intriguing contrasts to existing models of planetary evolution and atmospheric behaviour under extreme irradiation.
Aims. We aim to contribute to the broader understanding of atmospheric compositions and the mechanisms behind the survival of atmospheres in the Neptune desert through detailed spectroscopic analysis. We started by obtaining the transmission spectrum of LTT9779 b between 0.4 and 0.78 micrometres with ESPRESSO on the VLT.
Methods. Our analysis addressed systematics in ESPRESSO data across three distinct transit events, focusing on the sodium doublet and hydrogen alpha (Hα). We also used the cross-correlation method with models that contain Na, K, FeH, TiO, and VO
Results. No statistically significant atmospheric signal was detected, with lower limits placed on the atmospheric metallicity established at [Fe/H] ≥ 2.25, which is ≥ 180× solar. The non-detection is aligned with a high metallicity atmosphere scenario in a cloud-free model, suggesting a high mean molecular weight and a reduced atmospheric scale height.
Conclusions. We interpret the lack of any detection as evidence to support a very high metallicity for the planet’s atmosphere. This would give rise to a high mean molecular weight and, hence, a low atmospheric scale height, rendering any signal too weak to be detected. Another possibility is the presence of high-altitude clouds or hazes that would suppress any signal from elements deeper in the atmosphere. These findings are consistent with recent consistent with recent James Webb Space Telescope (JWST) observations, which also report muted spectral features and suggest a high-metallicity atmosphere with clouds at high altitudes. Our results, together with those from JWST, support the hypothesis of a metal-rich atmosphere possibly obscured by clouds or hazes.
Key words: methods: observational / techniques: spectroscopic / planets and satellites: atmospheres / planets and satellites: individual: LTT 9779b / planetary systems
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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