天体物理学：宇宙の咆哮(Astrophysics: Roaring in the universe)

2025-01-22

2025-01-21 ミュンヘン大学（LMU）

Record
This artist’s visualisation of WASP-127b, a giant gas planet located about 520 light-years from Earth, shows its newly discovered supersonic jet winds that move around the planet’s equator. With a speed of 33 000 km/h, this is the fastest jetstream of its kind ever measured in the Universe. © ESO/L. Calçada

天文学者の国際チームは、地球から約520光年離れた巨大ガス惑星WASP-127bの赤道周辺で、秒速9km（時速約33,000km）に達する超音速の強風を観測しました。これは、惑星の自転速度の約6倍に相当し、これまでに測定された中で最速のジェット気流です。この発見は、チリにある欧州南天天文台（ESO）の超大型望遠鏡（VLT）を用いて行われ、遠方の惑星の気象パターンに関する貴重な洞察を提供します。さらに、惑星の極地域が他の部分よりも低温であり、昼と夜の間にも温度差が存在することが明らかになりました。これらの結果は、WASP-127bが地球や太陽系内の他の惑星と同様に複雑な気象パターンを持つことを示しています。

＜関連情報＞

WASP-127bのCRIRES+透過分光観測高温惑星における超音速赤道ジェットと低温極の分解シグネチャの検出 CRIRES+ transmission spectroscopy of WASP-127 b Detection of the resolved signatures of a supersonic equatorial jet and cool poles in a hot planet

L. Nortmann, F. Lesjak, F. Yan, D. Cont, S. Czesla, A. Lavail, A. D. Rains, E. Nagel, L. Boldt-Christmas, A. Hatzes, A. Reiners, N. Piskunov, O. Kochukhov, U. Heiter, D. Shulyak, M. Rengel and U. Seemann
Astronomy & Astrophysics Published:21 January 2025
DOI:https://doi.org/10.1051/0004-6361/202450438

Abstract

Context. General circulation models of gas giant exoplanets predict equatorial jets that drive inhomogeneities in the atmospheric physical parameters across the planetary surface.

Aims. We studied the transmission spectrum of the hot Jupiter WASP-127 b during one transit in the K band with CRIRES⁺.

Methods. Telluric and stellar signals were removed from the data using SYSREM and 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 two-dimensional modelling approach tailored to address this scenario.

Results. We detected strong signals of H₂O and CO, which exhibited not one but two distinct cross-correlation peaks. The doublepeaked 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 an equatorial jet velocity of 7.7 ± 0.2 km s⁻¹ from our retrieved overall equatorial velocity and the planet’s tidally locked rotation, 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 shows that the muted signals from the poles can be explained by either significantly lower temperatures or a high cloud deck. It provides tentative evidence for the morning terminator to be cooler than the evening terminator by −175₋₁₁₇⁺¹³³ K.

Conclusions. Our detection of CO challenges previous non-detections of this species in WASP-127b’s atmosphere. The presence of a clear double-peaked signal highlights the importance of taking planetary three-dimensional structure into account during interpretation of atmospheric signals. The measured supersonic jet velocity and the 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.