CRIRES$^+$ transmission spectroscopy of WASP-127b. Detection of the resolved signatures of a supersonic equatorial jet and cool poles in a hot planet (2404.12363v2)

Abstract: General circulation models of gas giant exoplanets predict equatorial jets that drive inhomogeneities in the atmospheric physical parameters across the planetary surface. We studied the transmission spectrum of the hot Jupiter WASP-127\,b during one transit in the K band with CRIRES$^+$. Telluric and stellar signals were removed from the data using SYSREM. The planetary signal was investigated using the cross-correlation technique. After detecting a spectral signal indicative of atmospheric inhomogeneities, we employed a Bayesian retrieval framework with a 2D modelling approach tailored to address this scenario. We detected strong signals of H$2$O and CO, which exhibited not one but two distinct cross-correlation peaks. The double-peaked signal can be explained by a supersonic equatorial jet and muted signals at the planetary poles, with the two peaks representing the signals from the planet's morning and evening terminators. We calculated a jet velocity of $7.7\pm0.2$ km~s$^{-1}$ and derive distinct atmospheric properties for the two terminators as well as the polar region. Our retrieval yields a solar C/O ratio and metallicity and challenges previous studies of WASP-127b's atmosphere. It provides tentative evidence for the morning terminator to be cooler than the evening terminator by $-175^{+133}{-117}$K and shows that the muted signals from the poles can be explained by either significantly lower temperatures or a high cloud deck. The presence of a clear double-peaked signal highlights the importance of taking planetary 3D structure into account during interpretation of atmospheric signals. The supersonic jet velocity and lack of signal from the polar regions, representing a detection of latitudinal inhomogeneity in a spatially unresolved target, showcases the power of high-resolution transmission spectroscopy for the characterisation of global circulation in exoplanet atmospheres.

• The paper used CRIRES$^+$ transmission spectroscopy on the VLT to detect resolved signatures of a supersonic equatorial jet and cool polar regions in the atmosphere of exoplanet WASP-127b.
• The study measured the equatorial jet velocity at $7.7\pm0.2$ km~s$^{-1}$, significantly higher than expected from simple tidally locked rotation, indicating complex atmospheric dynamics.
• Using a two-dimensional atmospheric model, the researchers found solar C/O ratios and metallicity, and suggested the muted polar signals are due to lower temperatures or cloud cover, highlighting heterogeneous conditions.

Insights from CRIRES$^+$ Transmission Spectroscopy of WASP-127b

The paper presented in "CRIRES$^+$ transmission spectroscopy of WASP-127\,b" investigates the atmospheric dynamics and composition of the exoplanet WASP-127b, a hot Jupiter, through high-resolution transmission spectroscopy. Utilizing CRIRES$^+$ on the VLT, this research delineates a supersonic equatorial jet and cooler polar regions, providing significant advancements in understanding atmospheric circulation in exoplanets.

WASP-127b, characterized by its low density and high potential for atmospheric paper, was observed across the K band during a full transit event. Through meticulous data reduction involving the removal of telluric and stellar contaminations using the SYSREM algorithm, and subsequent analysis with a cross-correlation technique, the paper identifies robust signals from H$_2$O and CO. Notably, the detection of two distinct cross-correlation peaks aligns with theoretical predictions of a super-rotating equatorial jet, moving at $7.7\pm0.2$ km~s$^{-1}$, a velocity substantially higher than any anticipated from simple tidally locked rotation. This phenomenon implies atmospheric dynamics not previously resolved at such detail in exoplanet studies, demonstrating the need to consider multi-dimensional atmospheric models.

The methodological framework incorporated in this paper emphasizes a Bayesian retrieval approach, using a two-dimensional model to account for latitude-dependent atmospheric variations. The researchers successfully retrieved solar C/O ratios and metallicity for the atmosphere, aligning with equilibrium chemistry expectations under solar conditions. The model further proposes muted spectral signals from the poles, attributing these to either significantly lower temperatures or obscuring cloud decks, indicating heterogeneous temperature and cloud coverage across the planet's atmosphere.

This paper's implications extend both practical and theoretical understanding. Practically, the identification of a double-peaked velocity profile in the atmospheric transmission signals suggests advanced methodologies for interpreting high-resolution spectra, acting as a potential blueprint for future studies of other hot Jupiters or similarly dynamic exoplanetary atmospheres. The detection of H$_2$O and CO, particularly with the unprecedented details of the atmospheric dynamics, challenges prior non-detections and calls for a reevaluation of atmospheric compositions modeled for WASP-127b.

The spectral and dynamical insights present opportunities for further interpretation of exoplanet atmospheric data, emphasizing the importance of considering three-dimensional circulation patterns in analyses. The results advocate for theoretical models incorporating such circulatory dynamics, which can influence observed spectral features. Future advancements in instrumentation and observational techniques will likely build upon studies like this, refining our understanding of atmospheric processes in various exoplanetary environments.

Overall, the research positions high-resolution transmission spectroscopy as a critical tool in exoplanet science, providing granular insights into atmospheric dynamics previously not detectable. The consistent detection of high-velocity equatorial jets opens pathways for exploring weather patterns in extra-solar environments and their influence on atmospheric chemistry and structure, shaping the future trajectory of atmospheric characterization of exoplanets.