A long-term goal of exoplanet studies is the identification and detection of biosignature gases. Beyond the most discussed biosignature gas O2, only a handful of gases have been considered in detail. In this study, we evaluate phosphine (PH3). On Earth, PH3 is associated with anaerobic ecosystems, and as such, it is a potential biosignature gas in anoxic exoplanets. We simulate the atmospheres of habitable terrestrial planets with CO2- and H2-dominated atmospheres and find that PH3 can accumulate to detectable concentrations on planets with surface production fluxes of 1010 to 1014 cm-2 s-1 (corresponding to surface concentrations of 10s of ppb to 100s of ppm), depending on atmospheric composition and ultraviolet (UV) irradiation. While high, the surface flux values are comparable to the global terrestrial production rate of methane or CH4 (1011 cm-2 s-1) and below the maximum local terrestrial PH3 production rate (1014 cm-2 s-1). As with other gases, PH3 can more readily accumulate on low-UV planets, for example, planets orbiting quiet M dwarfs or with a photochemically generated UV shield. PH3 has three strong spectral features such that in any atmosphere scenario one of the three will be unique compared with other dominant spectroscopic molecules. Phosphine's weakness as a biosignature gas is its high reactivity, requiring high outgassing rates for detectability. We calculate that tens of hours of JWST (James Webb Space Telescope) time are required for a potential detection of PH3. Yet, because PH3 is spectrally active in the same wavelength regions as other atmospherically important molecules (such as H2O and CH4), searches for PH3 can be carried out at no additional observational cost to searches for other molecular species relevant to characterizing exoplanet habitability. Phosphine is a promising biosignature gas, as it has no known abiotic false positives on terrestrial planets from any source that could generate the high fluxes required for detection.

中文翻译：

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膦作为系外行星大气中的生物签名气体。

系外行星研究的长期目标是识别和检测生物特征气体。除了讨论最多的生物特征气体O2外，仅详细考虑了几种气体。在这项研究中，我们评估了膦（PH3）。在地球上，PH3与厌氧生态系统有关，因此，它是缺氧系外行星中潜在的生物签名气体。我们模拟了以CO2和H2为主的宜居行星的大气，发现PH3可以在表面产生通量为1010至1014 cm-2 s-1的行星上积累到可检测的浓度（对应于10s ppb的表面浓度）至100s ppm），具体取决于大气成分和紫外线（UV）辐射。虽然很高 表面通量值可与甲烷或CH4的全球陆地生产速率（1011 cm-2 s-1）相比较，并且低于最大本地陆地PH3生产率（1014 cm-2 s-1）。与其他气体一样，PH3可以更容易地积聚在低紫外线的行星上，例如，绕着安静的M矮星运行的行星或带有光化学产生的紫外线防护罩的行星。PH3具有三个强大的光谱特征，因此在任何大气情况下，与其他主要光谱分子相比，这三个之一将是唯一的。膦作为生物签名气体的弱点在于其高反应性，需要较高的除气率才能进行检测。我们计算出可能需要数十小时的JWST（詹姆斯·韦伯太空望远镜）时间来潜在地检测PH3。然而，由于PH3在与其他大气上重要的分子（例如H2O和CH4）相同的波长区域内具有光谱活性，因此可以免费搜索PH3以寻找与表征系外行星可居住性相关的其他分子种类。磷化氢是一种很有前途的生物特征气体，因为在任何可能产生检测所需高通量的来源中，它在陆地行星上都没有已知的非生物假阳性。