Scientists find strongest evidence yet of life on an alien planet
科学家发现外星生命存在的最有力证据
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WASHINGTON, April 16 (Reuters) – In a potential landmark discovery, scientists using the James Webb Space Telescope have obtained what they call the strongest signs yet of possible life beyond our solar system, detecting in an alien planet’s atmosphere the chemical fingerprints of gases that on Earth are produced only by biological processes.
华盛顿，4 月 16 日（路透社）-在一个潜在的里程碑式的发现中，科学家使用詹姆斯韦伯太空望远镜获得了他们所说的太阳系外可能存在生命的最强烈迹象，在外星大气中探测到地球上只有生物过程才能产生的气体的化学指纹。
The two gases – dimethyl sulfide, or DMS, and dimethyl disulfide, or DMDS – involved in Webb’s observations of the planet named K2-18 b are generated on Earth by living organisms, primarily microbial life such as marine phytoplankton – algae.
韦伯 B 对这颗名为 K2-18 b 的行星的观测中涉及的两种气体–二甲基硫醚（DMS）和二甲基二硫醚（DMDS）–是由地球上的生物体产生的，主要是微生物，如海洋浮游植物，藻类。
This suggests the planet may be teeming with microbial life, the researchers said. They stressed, however, that they are not announcing the discovery of actual living organisms but rather a possible biosignature – an indicator of a biological process – and that the findings should be viewed cautiously, with more observations needed.
研究人员说，这表明这颗行星可能充满了微生物。然而，他们强调，他们并不是在宣布发现了实际的生物体，而是一种可能的生物特征–一种生物过程的指标–应该谨慎地看待这些发现，需要进行更多的观察。
Nonetheless, they voiced excitement. These are the first hints of an alien world that is possibly inhabited, said astrophysicist Nikku Madhusudhan of the University of Cambridge’s Institute of Astronomy, lead author of the study published in the Astrophysical Journal Letters.
不过，他们的声音中，却带着一丝兴奋。剑桥大学天文学研究所的天体物理学家 Nikku Madhusudhan 说，这些是外星世界可能有人居住的第一个暗示，他是发表在《天体物理学杂志通讯》上的这项研究的主要作者。
“This is a transformational moment in the search for life beyond the solar system, where we have demonstrated that it is possible to detect biosignatures in potentially habitable planets with current facilities. We have entered the era of observational astrobiology,” Madhusudhan said.
“这是寻找太阳系以外生命的一个转型时刻，我们已经证明，利用现有的设施，有可能在潜在的宜居行星上检测到生物特征。我们已经进入了观测天体生物学的时代，”Madhusudhan 说。
Madhusudhan noted that there are various efforts underway searching for signs of life in our solar system, including various claims of environments that might be conducive to life in places like Mars, Venus and various icy moons.
Madhusudhan 指出，目前正在进行各种努力，寻找太阳系中的生命迹象，包括各种可能有利于火星 、 金星和各种冰冷卫星等地生命存在的环境。
K2-18 b is 8.6 times as massive as Earth and has a diameter about 2.6 times as large as our planet.
K2-18 B 的质量是地球的 8.6 倍，直径是地球的 2.6 倍。
It orbits in the “habitable zone” – a distance where liquid water, a key ingredient for life, can exist on a planetary surface – around a red dwarf star smaller and less luminous than our sun, located about 124 light-years from Earth in the constellation Leo. A light-year is the distance light travels in a year, 5.9 trillion miles (9.5 trillion km). One other planet also has been identified orbiting this star.
它在“可居住区”–行星表面存在液态水的距离，液态水是生命的关键成分–围绕着一颗比我们的太阳更小、更暗的红矮星星星运行，位于狮子座，距离地球约124光年。一光年是光在一年中传播的距离，5.9万亿英里（9.5万亿公里）。另一颗行星也被确认围绕这颗星星运行。
A ‘HYCEAN WORLD’ 一个“海洋世界”
About 5,800 planets beyond our solar system, called exoplanets, have been discovered since the 1990s. Scientists have hypothesized the existence of exoplanets called hycean worlds – covered by a liquid water ocean habitable by microorganisms and with a hydrogen-rich atmosphere.
自20世纪90年代以来，已经发现了大约5,800颗太阳系外的行星，称为系外行星。科学家们假设存在被称为海洋世界的系外行星-被微生物可居住的液态水海洋覆盖，并拥有富含氢气的大气层。
Earlier observations by Webb, which was launched in 2021 and became operational in 2022, had identified methane and carbon dioxide in K2-18 b’s atmosphere, the first time that carbon-based molecules were discovered in the atmosphere of an exoplanet in a star’s habitable zone.
2021 年发射并于 2022 年投入运行的“韦伯 B”探测器此前的观测已经在 K2-18 B 的大气层中发现了甲烷和二氧化碳，这是首次在星星宜居带的系外行星大气层中发现碳基分子。
“The only scenario that currently explains all the data obtained so far from JWST (James Webb Space Telescope), including the past and present observations, is one where K2-18 b is a hycean world teeming with life,” Madhusudhan said. “However, we need to be open and continue exploring other scenarios.”
Madhusudhan 说：“目前唯一能解释迄今为止从 JWST（詹姆斯·韦伯 B 太空望远镜）获得的所有数据，包括过去和现在的观测结果的情况是，K2-18 B 是一个充满生命的海洋世界。”“但是，我们需要保持开放，继续探索其他方案。”
Madhusudhan said that with hycean worlds, if they exist, “we are talking about microbial life, possibly like what we see in the Earth’s oceans.” Their oceans are hypothesized to be warmer than Earth’s. Asked about possible multicellular organisms or even intelligent life, Madhusudhan said, “We won’t be able to answer this question at this stage. The baseline assumption is of simple microbial life.”
Madhusudhan 说，对于海洋世界，如果它们存在的话，“我们谈论的是微生物生命，可能就像我们在地球海洋中看到的那样。“他们的海洋被假设比地球的温暖。当被问及可能的多细胞生物甚至智能生命时，Madhusudhan 说：“我们现阶段无法回答这个问题。基本假设是简单的微生物生命。”
DMS and DMDS, both from the same chemical family, have been predicted as important exoplanet biosignatures. Webb found that one or the other, or possibly both, were present in the planet’s atmosphere at a 99.7% confidence level, meaning there is still a 0.3% chance of the observation being a statistical fluke.
DMS 和 DMDS 都来自同一个化学家族，被预测为重要的系外行星生物特征。韦伯发现，一种或另一种，或者可能两者都存在于行星大气中，置信度为 99.7%，这意味着该观察结果仍有 0.3%的可能性是统计上的侥幸。
The gases were detected at atmospheric concentrations of more than 10 parts per million by volume.
检测到的气体在大气中的体积浓度超过百万分之十。
“For reference, this is thousands of times higher than their concentrations in the Earth’s atmosphere, and cannot be explained without biological activity based on existing knowledge,” Madhusudhan said.
Madhusudhan 说：“作为参考，这比它们在地球大气中的浓度高出数千倍，如果没有基于现有知识的生物活动，就无法解释。”
Scientists not involved in the study counseled circumspection.
没有参与这项研究的科学家建议谨慎行事。
“The rich data from K2-18 b make it a tantalizing world,” said Christopher Glein, principal scientist at the Space Science Division of the Southwest Research Institute in Texas. “These latest data are a valuable contribution to our understanding. Yet, we must be very careful to test the data as thoroughly as possible. I look forward to seeing additional, independent work on the data analysis starting as soon as next week.”
“来自 K2-18 B 的丰富数据使它成为一个诱人的世界，”德克萨斯州西南研究所空间科学部的首席科学家克里斯托弗·格莱因说。“这些最新数据对我们的理解做出了宝贵的贡献。然而，我们必须非常小心，尽可能彻底地测试数据。我期待着看到更多的，独立的，数据分析工作最快从下周开始。”
TRANSIT METHOD 凌日法
K2-18 b is part of the “sub-Neptune” class of planets, with a diameter greater than Earth’s but less than that of Neptune, our solar system’s smallest gas planet.
K2-18 B 是“亚海王星”类行星的一部分，直径大于地球，但小于海王星，海王星是我们太阳系最小的气体行星。
To ascertain the chemical composition of an exoplanet’s atmosphere, astronomers analyze the light from its host star as the planet passes in front of it from the perspective of Earth, called the transit method. As the planet transits, Webb can detect a decrease in stellar brightness, and a small fraction of starlight passes through the planetary atmosphere before being detected by the telescope. This lets scientists determine the constituent gases of the planet’s atmosphere.
为了确定系外行星大气层的化学成分，天文学家从地球的角度分析行星经过其宿主星星的光线，称为凌日法。当行星过境时，韦伯可以探测到恒星亮度的下降，一小部分星光在被望远镜探测到之前穿过行星大气层。这使科学家能够确定行星大气的组成气体。
Webb’s previous observations of this planet provided a tentative hint of DMS. Its new observations used a different instrument and a different wavelength range of light.
韦伯先前对这颗行星的观测提供了 DMS 的初步线索。它的新观测使用了不同的仪器和不同的波长范围的光。
The “Holy Grail” of exoplanet science, Madhusudhan said, is to find evidence of life on an Earth-like planet beyond our solar system. Madhusudhan said that our species for thousands of years has wondered “are we alone” in the universe, and now might be within just a few years of detecting possible alien life on a hycean world.
Madhusudhan 说，系外行星科学的“Holy Grail”是在我们太阳系以外的类地行星上找到生命的证据。Madhusudhan 说，几千年来，我们人类一直想知道“我们在宇宙中是孤独的吗”，现在可能在几年内就能在一个海珊世界探测到可能的外星生命。
But Madhusudhan still urged caution.
但 Madhusudhan 仍然敦促谨慎。
“First we need to repeat the observations two to three times to make sure the signal we are seeing is robust and to increase the detection significance” to the level at which the odds of a statistical fluke are below roughly one in a million, Madhusudhan said.
Madhusudhan 说：“首先，我们需要重复观察两到三次，以确保我们看到的信号是稳健的，并将检测意义提高到统计侥幸的几率低于大约百万分之一的水平。”
“Second, we need more theoretical and experimental studies to make sure whether or not there is another abiotic mechanism (one not involving biological processes) to make DMS or DMDS in a planetary atmosphere like that of K2-18 b. Even though previous studies have suggested them (as) robust biosignatures even for K2-18 b, we need to remain open and pursue other possibilities,” Madhusudhan said.
“其次，我们需要更多的理论和实验研究，以确定是否有另一种非生物机制（不涉及生物过程）在像 K2-18 B 这样的行星大气中制造 DMS 或 DMDS。尽管以前的研究表明，即使是 K2-18 B，它们也是强大的生物特征，但我们需要保持开放，并寻求其他可能性，”Madhusudhan 说。
So the findings represent “a big if” on whether the observations are due to life, and it is in “no one’s interest to claim prematurely that we have detected life,” Madhusudhan said.
因此，这些发现代表了“一个很大的假设”，关于这些观察是否是由于生命，“没有人会过早地声称我们已经探测到生命，”Madhusudhan 说。