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

Vol. 692
10. Planets, planetary systems, and small bodies

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

by L. Nortmann, F. Lesjak, F. Yan, et al. 2025, A&A, 693, A213 alt

One of the most powerful methods for exploiting the high-resolution spectroscopy transit of exoplanets is the cross-correlation technique. With this method, model spectra of different atmospheric components, usually based on physically based abundance models (e.g., chemical equilibrium), are employed as templates and cross-correlated with in-transit ratioed spectra as a function of velocity. The method has not only permitted the detection of tens of atomic and molecular species in the atmosphere of hot and ultra-hot Jupiters, it has also yielded a wealth of information on atmospheric dynamics (day-to-night winds, super-rotation, vertical winds, etc.) and spatial variability (e.g., morning-to-evening asymmetries associated with condensation or cloud effects) based on the precise velocity and strength of the correlation peak. Nortmann et al. present a study of WASP-127b, a hot Jupiter orbiting a solar-type star on a 4.2-day orbit, conducted with CRIRES+/VLT in the near-IR. A strong detection of H2O and CO is achieved, with the cross-correlation signal exhibiting a remarkable two-peaked structure. This is interpreted as the combination of a supersonic equatorial jet with ~8 km/s speeds -- with the two peaks representing the signals from the planet’s morning and evening terminators, respectively -- and muted signals at the planetary poles -- due to either significantly lower temperatures or a high cloud deck -- and explains the lack of a correlation peak at the planet's orbital velocity. This study therefore features a detection of latitudinal inhomogeneity in WASP-127b, opening the field to a 3D characterization of exoplanets, as routinely achieved for Solar System planetary atmospheres.