Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology
Nitrogen Dioxide Pollution as a Signature of Extraterrestrial Technology
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二氧化氮污染是外星技术的标志
DOI：
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发表时间：
2021
影响因子：
4.9
通讯作者：
G. Villanueva
中科院分区：
文献类型：
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作者：
R. Kopparapu;G. Arney;J. Haqq‐Misra;J. Lustig;G. Villanueva
当今地球上的二氧化氮(NO2)有生物来源和人为来源。在新冠肺炎大流行期间，对全球二氧化氮排放的观测显示，城市地区的二氧化氮排放量显著减少。利用工业副产品NO2的这个例子，我们使用一维光化学模型和合成光谱发生器来评估NO2作为系外行星上的大气技术特征的可探测性。我们考虑类地行星围绕类太阳、K矮星和M矮星运行的例子。我们发现，在温度较低的恒星周围的行星上，NO2浓度增加是因为能够光解NO2的短波光子较少。在无云的结果中，当在NO2有强吸收的0.2-0.7LUVOIR米范围内观察时，在10pC时，使用15m类LUVOIR望远镜，在∼400hr内，可以以信噪比μ5探测到目前类地行星上的类太阳恒星上的NO2。然而，云层和气溶胶可能会降低探测能力，并可能模仿NO2的特征。从历史上看，全球NO2水平高出3倍，表明有能力探测到40年前地球文明阶段的文明。在M矮星周围的宜居行星上进行凌日和直接成像观测以探测NO2的红外光谱特征将需要数百小时的观测时间，这既是因为该区域对NO2的吸收较弱，也是因为光谱中占主导地位的H2O和CO2波段的掩蔽特征。这些水平的未检测可以用来对NO2的流行设定上限，作为一种技术特征。
Nitrogen dioxide (NO2) on Earth today has biogenic and anthropogenic sources. During the Covid-19 pandemic, observations of global NO2 emissions have shown a significant decrease in urban areas. Drawing upon this example of NO2 as an industrial byproduct, we use a one-dimensional photochemical model and synthetic spectral generator to assess the detectability of NO2 as an atmospheric technosignature on exoplanets. We consider cases of an Earth-like planet around Sun-like, K-dwarf, and M-dwarf stars. We find that NO2 concentrations increase on planets around cooler stars because there are fewer short-wavelength photons that can photolyze NO2. In cloud-free results, present Earth-level NO2 on an Earth-like planet around a Sun-like star at 10 pc can be detected with signal-to-noise ratio ∼5 within ∼400 hr with a 15 m LUVOIR-like telescope when observed in the 0.2–0.7 μm range where NO2 has a strong absorption. However, clouds and aerosols can reduce the detectability and could mimic the NO2 feature. Historically, global NO2 levels were 3× higher, indicating the capability of detecting a civilization at the stage where Earth’s civilization was 40 yr ago. Transit and direct imaging observations to detect infrared spectral signatures of NO2 on habitable planets around M-dwarfs would need several hundred hours of observation time, both due to weaker NO2 absorption in this region and because of masking features by dominant H2O and CO2 bands in the infrared part of the spectrum. Non-detection at these levels could be used to place upper limits on the prevalence of NO2 as a technosignature.