Max-Planck-Institut für Astronomie, Heidelberg, Germany.
Leiden Observatory, Leiden University, Leiden, The Netherlands.
Nature. 2023 Aug;620(7975):746-749. doi: 10.1038/s41586-023-06232-z. Epub 2023 Jun 19.
Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a unique opportunity to search for atmospheres on small planets outside the Solar System. Thanks to the recent launch of the James Webb Space Telescope (JWST), possible atmospheric constituents such as carbon dioxide (CO) are now detectable. Recent JWST observations of the innermost planet TRAPPIST-1 b showed that it is most probably a bare rock without any CO in its atmosphere. Here we report the detection of thermal emission from the dayside of TRAPPIST-1 c with the Mid-Infrared Instrument (MIRI) on JWST at 15 µm. We measure a planet-to-star flux ratio of f/f = 421 ± 94 parts per million (ppm), which corresponds to an inferred dayside brightness temperature of 380 ± 31 K. This high dayside temperature disfavours a thick, CO-rich atmosphere on the planet. The data rule out cloud-free O/CO mixtures with surface pressures ranging from 10 bar (with 10 ppm CO) to 0.1 bar (pure CO). A Venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6σ confidence. Thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. The absence of a thick, CO-rich atmosphere on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with less than [Formula: see text] Earth oceans of water. If all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system.
七颗类地行星围绕着附近的矮星 TRAPPIST-1 运行，这为在太阳系外的小行 星上寻找大气层提供了独特的机会。由于最近詹姆斯·韦伯太空望远镜（JWST）的发 射，现在可以探测到二氧化碳（CO）等可能的大气成分。最近 JWST 对最内层行星 TRAPPIST-1b 的观测表明，它很可能是一颗没有任何 CO 大气层的裸露岩石行星。在这里，我们报告了在 JWST 的中红外仪器（MIRI）在 15μm 处探测到 TRAPPIST-1c 的昼面热辐射。我们测量到行星-恒星通量比 f/f=421±94ppm，这对应于推断出的昼面亮度温度为 380±31K。这个高昼面温度不利于行星上存在厚的、富含 CO 的大气层。数据排除了无云的 O/CO 混合物，其表面压力范围从 10 巴（含 10ppm CO）到 0.1 巴（纯 CO）。在 2.6σ置信度下，也排除了具有硫酸云的类金星大气。较薄的大气层或裸露的岩石表面与我们测量的行星-恒星通量比一致。TRAPPIST-1c 上没有厚的、富含 CO 的大气层表明其形成历史相对缺乏挥发物，水的含量不到[Formula: see text]个地球海洋。如果系统中的所有行星都是以同样的方式形成的，这将表明该系统中潜在宜居行星的挥发物储量有限。
