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arXiv 2307.08752astro-ph.EP
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高层大气对低质量恒星周围宜居行星上CO/O$_2$失控的重要性

The Importance of the Upper Atmosphere to CO/O$_2$ Runaway on Habitable Planets Orbiting Low-Mass Stars

Sukrit Ranjan, Edward W. Schwieterman, Michaela Leung, Chester E. Harman, Renyu Hu

AI总结:

本文通过多模型方法重新审视M矮星宜居行星上CO$_2$光解生成O$_2$和CO的过程,指出此前预测的丰富非生物O$_2$源于模型顶部过低,实际上O$_2$仍为微量气体,从而强化了O$_2$作为生物标志物的可靠性。

摘要:

利用詹姆斯·韦布空间望远镜(JWST)对围绕M矮星运行的温带类地系外行星大气成分进行光谱表征的工作目前正在进行中。此类搜索的关键分子目标包括O$_2$和CO,它们是潜在的生命指示物。最近有研究提出,在富含CO$_2$大气的宜居M矮星行星大气中,CO$_2$光解会生成丰富的($\gtrsim0.1$ bar)非生物O$_2$和CO,这构成了O$_2$作为生物标志物的强假阳性,并进一步使利用CO作为表面生物学诊断指标的工作复杂化。重要的是,这意味着如果TRAPPIST-1e和TRAPPIST-1f宜居,它们将非生物地积累丰富的O$_2$和CO,而这两颗行星目前正在接受JWST的观测。在这里,我们使用多模型方法重新审视了围绕M矮星运行的行星上光化学O$_2$和CO的积累。我们表明,在宜居的富含CO$_2$的M矮星行星上,光化学O$_2$仍然是一种微量气体,此前对丰富O$_2$和CO的预测是由于大气模型顶部过低,无法准确解析此类行星上异常高的CO$_2$光解峰值。我们的工作加强了O$_2$作为生物标志物气体的论证,并肯定了CO作为光化学O$_2$产生诊断指标的重要性。然而,与观测相关的假阳性可能性仍然存在,尤其是对于O$_2$的光化学产物O$_3$,还需要进一步的工作来可靠地理解O$_2$和O$_3$作为M矮星行星上的生物标志物气体。

英文摘要:

Efforts to spectrally characterize the atmospheric compositions of temperate terrestrial exoplanets orbiting M-dwarf stars with the James Webb Space Telescope (JWST) are now underway. Key molecular targets of such searches include O$_2$ and CO, which are potential indicators of life. Recently, it was proposed that CO$_2$ photolysis generates abundant ($\gtrsim0.1$ bar) abiotic O$_2$ and CO in the atmospheres of habitable M-dwarf planets with CO$_2$-rich atmospheres, constituting a strong false positive for O$_2$ as a biosignature and further complicating efforts to use CO as a diagnostic of surface biology. Importantly, this implied that TRAPPIST-1e and TRAPPIST-1f, now under observation with JWST, would abiotically accumulate abundant O$_2$ and CO, if habitable. Here, we use a multi-model approach to re-examine photochemical O$_2$ and CO accumulation on planets orbiting M-dwarf stars. We show that photochemical O$_2$ remains a trace gas on habitable CO$_2$-rich M-dwarf planets, with earlier predictions of abundant O$_2$ and CO due to an atmospheric model top that was too low to accurately resolve the unusually-high CO$_2$ photolysis peak on such worlds. Our work strengthens the case for O$_2$ as a biosignature gas, and affirms the importance of CO as a diagnostic of photochemical O$_2$ production. However, observationally relevant false positive potential remains, especially for O$_2$'s photochemical product O$_3$, and further work is required to confidently understand O$_2$ and O$_3$ as biosignature gases on M-dwarf planets.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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