JWSTによるTRAPPIST-1惑星の最初のスペクトル(JWST’s first spectrum of a TRAPPIST-1 planet)


2023-09-25 ミシガン大学

◆TRAPPIST-1という太陽から40光年離れた恒星系には、寒冷な恒星の周りを7つの地球サイズの惑星が公転しています。研究者は、TRAPPIST-1 bと呼ばれるこの系の最も恒星に近い惑星に関する新たなデータをJames Webb Space Telescope(JWST)から得ました。これらの観測結果により、液体の水が惑星の表面に存在できる生息可能ゾーンにおいて、星が観測にどのような影響を与えるかについての洞察が提供されました。
◆この研究は、TRAPPIST-1 bの特性に関する重要な洞察を提供し、将来の観測プログラムに貢献するもので、太陽系外の惑星の大気とその生息可能性に関する幅広い理解に寄与します。


JWST/NIRISSによるTRAPPIST-1 bの大気探査:透過スペクトルにおける恒星の強い汚染の証拠 Atmospheric Reconnaissance of TRAPPIST-1 b with JWST/NIRISS: Evidence for Strong Stellar Contamination in the Transmission Spectra

Olivia Lim, Björn Benneke, René Doyon, Ryan J. MacDonald, Caroline Piaulet, Étienne Artigau, Louis-Philippe Coulombe, Michael Radica, Alexandrine L’Heureux, Loïc Albert, Benjamin V. Rackham, Julien de Wit, Salma Salhi, Pierre-Alexis Roy, Laura Flagg, Marylou Fournier-Tondreau, Jake Taylor, Neil J. Cook, David Lafrenière, Nicolas B. Cowan, Lisa Kaltenegger, Jason F. Rowe, Néstor Espinoza, Lisa Dang, and Antoine Darveau-Bernier
The Astrophysical Journal Letters  Published:2023 September 22

Figure 1.


TRAPPIST-1 is a nearby system of seven Earth-sized, temperate, rocky exoplanets transiting a Jupiter-sized M8.5V star, ideally suited for in-depth atmospheric studies. Each TRAPPIST-1 planet has been observed in transmission both from space and from the ground, confidently rejecting cloud-free, hydrogen-rich atmospheres. Secondary eclipse observations of TRAPPIST-1 b with JWST/MIRI are consistent with little to no atmosphere given the lack of heat redistribution. Here we present the first transmission spectra of TRAPPIST-1 b obtained with JWST/NIRISS over two visits. The two transmission spectra show moderate to strong evidence of contamination from unocculted stellar heterogeneities, which dominates the signal in both visits. The transmission spectrum of the first visit is consistent with unocculted starspots and the second visit exhibits signatures of unocculted faculae. Fitting the stellar contamination and planetary atmosphere either sequentially or simultaneously, we confirm the absence of cloud-free, hydrogen-rich atmospheres, but cannot assess the presence of secondary atmospheres. We find that the uncertainties associated with the lack of stellar model fidelity are one order of magnitude above the observation precision of 89 ppm (combining the two visits). Without affecting the conclusion regarding the atmosphere of TRAPPIST-1 b, this highlights an important caveat for future explorations, which calls for additional observations to characterize stellar heterogeneities empirically and/or theoretical works to improve model fidelity for such cool stars. This need is all the more justified as stellar contamination can affect the search for atmospheres around the outer, cooler TRAPPIST-1 planets for which transmission spectroscopy is currently the most efficient technique.