论文标题

一种地质强大的程序,用于观察岩石系外行星,以确保检测大气氧是一种类似地球的生物签名

A Geologically Robust Procedure For Observing Rocky Exoplanets to Ensure that Detection of Atmospheric Oxygen is an Earth-Like Biosignature

论文作者

Lisse, Carey M., Desch, Steven J., Unterborn, Cayman T., Kane, Stephen R., Young, Patrick R., Hartnett, Hilairy E., Hinkel, Natalie R., Shim, Sang Heon, Mamajek, Eric E., Izenberg, Noam R.

论文摘要

在接下来的几十年中,天文学界将辩论系外行星中对氧气的首次观察是否表示生命,因此现在建立程序以收集和解释此类数据至关重要。我们提出了一种逐步观察策略,用于使用氧气作为强大的生物签名,以优先考虑系外行星目标并设计未来的观察结果。它的前提是避免缺乏大陆的地下风化的行星,这意味着地球化学循环与地球$'$ s截然不同,从而排除了氧气用作生物签名。该策略始于最容易获得的数据:半高轴和出色的发光度,以确保居住在可居住区;恒星XUV通量,确保系外行星可以保留二次(超出)气氛。接下来,高精度质量和半径信息应与高精度恒星丰度数据结合使用,以限制外部球星$'$ s的水含量;那些与小于0.1 wt%h $ _ {2} $ o不兼容的人可以被剥夺。然后,反射率光度法或低分辨率传输光谱应确认光学上的薄气。随后的长期长期,高分辨率传输光谱应搜索氧气,并确保水蒸气和Co $ _ {2} $仅在低处出现(10 $^{2} $ -10 $ -10 $^{4} $ ppm lacte)。假设发现氧气,归因于生命需要很难获得外部球星的详细的,多光谱的光曲线,以确保表面土地和水。失败的某些步骤的系外行星可能是可居住的,甚至具有可观察到的生物氧,但应该剥夺,因为氧气不能明确地归因于生命。我们展示了太阳系,55 CNC系统和Trappist-1系统的情况,在这种情况下,只有地球和Trappist-1E才能成功地通过我们的程序。

In the next decades, the astrobiological community will debate whether the first observations of oxygen in an exoplanet$'$s atmosphere signifies life, so it is critical to establish procedures now for collection and interpretation of such data. We present a step-by-step observational strategy for using oxygen as a robust biosignature, to prioritize exoplanet targets and design future observations. It is premised on avoiding planets lacking subaerial weathering of continents, which would imply geochemical cycles drastically different from Earth$'$s, precluding use of oxygen as a biosignature. The strategy starts with the most readily obtained data: semi-major axis and stellar luminosity to ensure residence in the habitable zone; stellar XUV flux, to ensure an exoplanet can retain a secondary (outgassed) atmosphere. Next, high-precision mass and radius information should be combined with high-precision stellar abundance data, to constrain the exoplanet$'$s water content; those incompatible with less than 0.1 wt % H$_{2}$O can be deprioritized. Then, reflectance photometry or low-resolution transmission spectroscopy should confirm an optically thin atmosphere. Subsequent long-duration, high-resolution transmission spectroscopy should search for oxygen and ensure that water vapor and CO$_{2}$ are present only at low (10$^{2}$-10$^{4}$ ppm levels). Assuming oxygen is found, attribution to life requires the difficult acquisition of a detailed, multispectral light curve of the exoplanet to ensure both surface land and water. Exoplanets failing some of these steps might be habitable, even have observable biogenic oxygen, but should be deprioritized because oxygen could not be attributed unambiguously to life. We show how this is the case for the Solar System, the 55 Cnc System, and the TRAPPIST-1 System, in which only the Earth and TRAPPIST-1e successfully pass through our procedure.

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