近日，科学家提出了一种新的探测外星生命的方法，即关注系外行星大气中的二氧化碳含量。这一新思路或为我们探测到更多的宜居或可能宜居的行星，并作为开发下一代太空望远镜的理论基础。
传统的探测宜居行星的方法主要包括探测被海洋反射的光芒、大气中氧含量等。然而，这些方法目前已陷入瓶颈。科学家表示，关注地球上少的东西，如二氧化碳，相较于氧气，是一个更具前景的探测方法。二氧化碳含量低这一特征作为系外行星宜居的标志，这一思路也适用于开发下一代直接成像的太空望远镜。
新研究中，科学家发现詹姆斯·韦布太空望远镜可以对行星的大气二氧化碳含量进行特异性搜查。通过观察凌日过程中，行星大气层对恒星亮度的影响，天文学家可以判断行星的大气成分。相较于氧气，二氧化碳含量更好检测，同时，臭氧的紫外线和可见光波段也比较容易被检测到。
基于二氧化碳，科学家提出了探测系外行星的凌日测光“三步走”策略。首先，在视野最佳的凌日过程（大约10次）中，观测气候温和的岩质行星周围的大气层；其次，根据大约40次凌日过程，评估该行星大气中二氧化碳含量低于其他行星的程度；最后，根据大约40次凌日过程，评估该行星大气臭氧的含量，以确定造成该行星大气中二氧化碳含量低于其他行星的因素中，液态水和生物作用分别造成多大的影响。
此外，科学家认为，行星中二氧化碳含量较低也可以反映这颗星球可能宜居。因为二氧化碳溶解于水，最后沉积形成碳酸盐岩等可以储存碳的岩石，在板块构造运动中，这些岩石被深埋在不易被风化的地方。这些岩石中的碳不返回大气，久而久之，大气中的二氧化碳含量就会下降。一些地球科学家认为，在地球形成最初的十亿年里就有板块构造了，早于生命起源，板块构造是生命起源的一个关键前提条件。
新研究为探索外星生命提供了新的方向，关注二氧化碳含量或成为解锁外星生命之谜的关键钥匙。
Title: New Approach to Detect Extraterrestrial Life: Focus on Carbon Dioxide Content
Keywords: Extraterrestrial life, carbon dioxide, habitable planets
News content:
Recently, scientists have proposed a new method for detecting extraterrestrial life, which is to focus on the carbon dioxide content in the atmospheres of exoplanets. This new idea may help us detect more habitable or potentially habitable planets and serve as the theoretical basis for developing the next-generation space telescopes.
Traditional methods of detecting habitable planets mainly include detecting light reflected by oceans and oxygen content in atmospheres. However, these methods have reached a bottleneck. Scientists suggest that focusing on substances less common on Earth, such as carbon dioxide, is a more promising approach. The low carbon dioxide content in atmospheres can serve as a marker for habitability and is applicable to the development of next-generation direct imaging telescopes.
In the new study, scientists found that the James Webb Space Telescope can specifically search for carbon dioxide content in planetary atmospheres. By observing the impact of planetary atmospheres on starlight during the transit process, astronomers can determine the atmospheric composition of the planet. Compared to oxygen, carbon dioxide is easier to detect, and the ultraviolet and visible bands of ozone are also relatively easy to detect.
Based on carbon dioxide, scientists have proposed a “three-step” strategy for detecting exoplanets using the transit photometry method. First, observe the atmospheres of climate-friendly rocky planets during the optimal transit process (about 10 times); second, assess the degree to which the carbon dioxide content in the planet’s atmosphere is lower than that of other planets based on about 40 transit processes; and third, assess the content of ozone in the planet’s atmosphere based on about 40 transit processes to determine the factors contributing to the lower carbon dioxide content in the planet’s atmosphere, including the influences of liquid water and biological processes.
Additionally, scientists suggest that a lower carbon dioxide content in planets can also reflect the possibility of habitability. As carbon dioxide dissolves in water and ultimately forms carbonate rocks that can store carbon, these rocks are buried in areas less susceptible to weathering during plate tectonic movements. The carbon stored in these rocks does not return to the atmosphere, leading to a decrease in atmospheric carbon dioxide content over time. Some Earth scientists believe that plate tectonics existed in the first billion years of Earth’s formation, preceding the origin of life. Plate tectonics are a crucial precondition for the origin of life.
【来源】https://www.ithome.com/0/743/739.htm
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