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As we build towards robustly detecting and characterizing the atmospheres of terrestrial exoplanets with JWST comma we cannot forget to take a close look at the low-mass stars they orbit. Complete coverage of M dwarf ultraviolet spectra are needed to determine the photochemical production rates of molecular species in terrestrial planet atmospheres comma which will alert us to when disequilibrium chemistry comma a sign of surface processes or even life comma is present. High-energy spectra from the UV to X-ray are also needed to calculate mass loss rates from planetary atmospheres comma which can explain the lack of atmospheres around highly-irradiated terrestrial worlds. LTT 1445Ab and GJ 486b are two of the most spectroscopically accessible terrestrial exoplanets we will ever find comma and their M dwarf hosts are similarly at the top of their class in terms of observability. We will use the unique ultraviolet capabilities of HST comma supplemented by X-ray observations comma to provide complete short-wavelength spectral coverage for the stars LTT 1445A and GJ 486. Both planets comma LTT 1445Ab and GJ 486b comma will be observed in JWST Cycle 1 with the aim of detecting their atmospheres. If we do not take the opportunity to make UV measurements of their host stars while HST is still operational comma this crucial input to understanding the atmospheres of these planets will be lost. We request 18 orbits with HST (COS and STIS) to capture complete UV spectra of LTT 1445A and GJ 486.

在借助詹姆斯·韦布空间望远镜（JWST）稳健探测并表征类地系外行星大气的进程中，我们绝不能忽视这些行星所环绕的低质量恒星。获取完整的M型矮星紫外光谱，是测算类地行星大气中分子物种光化学生成速率的必要前提——该参数可帮助我们识别非平衡化学过程的出现，而这类过程正是地表活动乃至生命活动的潜在信号。此外，还需获取从紫外到X射线波段的高能光谱，以计算行星大气的逃逸速率，这一数据能够解释强辐射环境下类地行星大气缺失的现象。LTT 1445Ab与GJ 486b是目前已知最便于光谱观测的类地系外行星之一，它们的宿主M型矮星同样具备极佳的观测可行性。本研究将依托哈勃空间望远镜（HST）独有的紫外观测能力，并辅以X射线观测，为LTT 1445A与GJ 486两颗恒星获取完整的短波光谱覆盖。LTT 1445Ab与GJ 486b这两颗行星，均已被纳入詹姆斯·韦布空间望远镜第1轮观测计划，核心目标为探测行星大气。若错过哈勃空间望远镜仍处于服役期的窗口，未能对其宿主恒星开展紫外光谱测量，那么理解这两颗行星大气所需的关键基础数据将会永久缺失。我们申请利用哈勃空间望远镜的18个观测轨道（搭载COS与STIS设备），以获取LTT 1445A与GJ 486的完整紫外光谱。