Jordan Sean, Shorttle Oliver, Rimmer Paul B
Institute of Astronomy, University of Cambridge, Cambridge CB3 0HA, UK.
ETH Zurich, Institute for Particle and Astrophysics, Wolfgang-Pauli-Strasse 27, CH-8093 Zurich, Switzerland.
Sci Adv. 2025 Jan 31;11(5):eadp8105. doi: 10.1126/sciadv.adp8105. Epub 2025 Jan 29.
The circumstellar liquid-water habitable zone guides our search for potentially inhabited exoplanets but remains observationally untested. We show that the inner edge of the habitable zone can now be mapped among exoplanets using their lack of surface water, which, unlike the presence of water, can be unambiguously revealed by atmospheric sulfur species. Using coupled climate-chemistry modeling, we find that the observability of sulfur gases on exoplanets depends critically on the ultraviolet (UV) flux of their host star, a property with wide variation: Most M-dwarfs have a low UV flux and thereby allow the detection of sulfur gases as a tracer of dry planetary surfaces; however, the UV flux of Trappist-1 may be too high for sulfur to disambiguate uninhabitable from habitable surfaces on any of its planets. We generalize this result to show how a population-level search for sulfur chemistry on M-dwarf planets can be used to empirically define the habitable zone in the near future.
恒星周围的液态水宜居带指导着我们寻找可能存在生命的系外行星，但在观测上仍未得到验证。我们表明，现在可以利用系外行星缺乏地表水这一特征来绘制宜居带的内边缘，与水的存在不同，大气中的硫物种能够明确揭示这一特征。通过耦合气候 - 化学模型，我们发现系外行星上硫气体的可观测性主要取决于其主恒星的紫外线（UV）通量，而这一特性变化范围很大：大多数M型矮星的紫外线通量较低，因此可以检测到硫气体作为干燥行星表面的示踪剂；然而，Trappist - 1的紫外线通量可能过高，以至于硫无法区分其任何一颗行星上不适宜居住和适宜居住的表面。我们推广了这一结果，以展示在不久的将来，如何通过对M型矮星行星上硫化学的群体水平搜索来凭经验定义宜居带。
