Ultracool dwarf stars are abundant, long-lived and uniquely suited to enable the atmospheric study of transiting terrestrial companions with the JWST. Among them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets. While JWST Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here we propose a roadmap to characterize the TRAPPIST-1 system — and others like it — in an efficient and robust manner with JWST. We notably recommend that — although more challenging to schedule — multi-transit windows be prioritized to mitigate the effects of stellar activity and gather up to twice more transits per JWST hour spent. We conclude that, for such systems, planets cannot be studied in isolation by small programmes but rather need large-scale, joint space- and ground-based initiatives to fully exploit the capabilities of JWST for the exploration of terrestrial planets.

超冷矮星数量丰富、寿命长，并且非常适合利用 JWST 对凌日伴星进行大气研究。其中，最突出的是M8.5V恒星TRAPPIST-1及其七颗行星。虽然 JWST 周期 1 的观测已经开始对行星产生初步的了解，但它们也表明，大气层探索需要更好地了解它们的主恒星。在这里，我们提出了一个路线图，通过 JWST 以高效、稳健的方式描述 TRAPPIST-1 系统以及其他类似系统的特征。我们特别建议，尽管安排起来更具挑战性，但应优先考虑多次凌星窗口，以减轻恒星活动的影响，并在 JWST 每小时内收集最多两倍的凌星现象。我们的结论是，对于此类系统，不能通过小型项目孤立地研究行星，而是需要大规模、天基和地基联合举措，以充分利用 JWST 探索类地行星的能力。