Theoretical predictions and observational data indicate a class of sub-Neptune exoplanets may have water-rich interiors covered by hydrogen-dominated atmospheres. Provided suitable climate conditions, such planets could host surface liquid oceans. Motivated by recent JWST observations of K2-18 b, we self-consistently model the photochemistry and potential detectability of biogenic sulfur gases in the atmospheres of temperate sub-Neptune waterworlds for the first time. On Earth today, organic sulfur compounds produced by marine biota are rapidly destroyed by photochemical processes before they can accumulate to significant levels. Domagal-Goldman et al. suggest that detectable biogenic sulfur signatures could emerge in Archean-like atmospheres with higher biological production or low UV flux. In this study, we explore biogenic sulfur across a wide range of biological fluxes and stellar UV environments. Critically, the main photochemical sinks are absent on the nightside of tidally locked planets. To address this, we further perform experiments with a 3D general circulation model and a 2D photochemical model (VULCAN 2D) to simulate the global distribution of biogenic gases to investigate their terminator concentrations as seen via transmission spectroscopy. Our models indicate that biogenic sulfur gases can rise to potentially detectable levels on hydrogen-rich water worlds, but only for enhanced global biosulfur flux (≳20 times modern Earth’s flux). We find that it is challenging to identify DMS at 3.4 μm where it strongly overlaps with CH₄, whereas it is more plausible to detect DMS and companion byproducts, ethylene (C₂H₄) and ethane (C₂H₆), in the mid-infrared between 9 and 13 μm.

中文翻译：

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生物硫气体作为温带海王星下水世界的生物特征

理论预测和观测数据表明，一类海王星以下系外行星可能具有富含水的内部，并被以氢为主的大气层覆盖。如果气候条件合适，这些行星的表面可能存在液态海洋。受 JWST 最近对 K2-18 b 观测的推动，我们首次自洽地模拟了温带海王星以下水世界大气中生物硫气体的光化学和潜在可检测性。在当今的地球上，海洋生物群产生的有机硫化合物在积累到显着水平之前会被光化学过程迅速破坏。多马加尔-戈德曼等人。表明可检测的生物硫特征可能出现在生物产量较高或紫外线通量较低的类太古宙大气中。在这项研究中，我们探索了广泛的生物通量和恒星紫外线环境中的生物硫。至关重要的是，潮汐锁定行星的夜面不存在主要的光化学汇。为了解决这个问题，我们进一步使用 3D 大气环流模型和 2D 光化学模型 (VULCAN 2D) 进行实验来模拟生物气体的全球分布，以通过透射光谱研究其终止剂浓度。我们的模型表明，在富氢水世界中，生物硫气体可能会上升到可检测的水平，但前提是全球生物硫通量增加（≳现代地球通量的20倍）。我们发现在 3.4 时识别 DMS 具有挑战性μ_{m 与 CH 4}强烈重叠，而在 9 至 13 之间的中红外区域更可能检测 DMS 和伴随副产物乙烯 (C ₂ H ₄ ) 和乙烷 (C ₂ H _{6 )}μ米。