Located at the bottom of the main sequence, ultracool dwarf stars are widespread in the solar neighbourhood. Nevertheless, their extremely low luminosity has left their planetary population largely unexplored, and only one of them, TRAPPIST-1, has so far been found to host a transiting planetary system. In this context, we present the SPECULOOS project’s detection of an Earth-sized planet in a 17 h orbit around an ultracool dwarf of M6.5 spectral type located 16.8 pc away. The planet’s high irradiation (16 times that of Earth) combined with the infrared luminosity and Jupiter-like size of its host star make it one of the most promising rocky exoplanet targets for detailed emission spectroscopy characterization with JWST. Indeed, our sensitivity study shows that just ten secondary eclipse observations with the Mid-InfraRed Instrument/Low-Resolution Spectrometer on board JWST should provide strong constraints on its atmospheric composition and/or surface mineralogy.

超冷矮星位于主序带的底部，在太阳附近广泛分布。然而，它们极低的光度使得它们的行星种群在很大程度上未被探索过，并且迄今为止只有其中一颗 TRAPPIST-1 被发现拥有凌日行星系统。在此背景下，我们介绍了 SPECULOOS 项目对一颗地球大小的行星的探测，该行星位于 16.8 pc 外的 M6.5 光谱类型超冷矮星周围 17 小时的轨道上。这颗行星的高辐射（地球的 16 倍）加上其主星的红外光度和类似木星的大小，使其成为 JWST 详细发射光谱表征最有希望的岩石系外行星目标之一。事实上，我们的敏感性研究表明，利用 JWST 上的中红外仪器/低分辨率光谱仪进行的 10 次次日食观测就应该对其大气成分和/或表面矿物学提供强有力的限制。