美国宇航局(NASA)的科学家们在对土星的卫星土卫二(Enceladus)的研究中发现了新的证据，这些证据表明土卫二上含有对生命早期发展至关重要的物质。这些发现来自于对NASA的卡西尼号(Cassini)探测器收集的数据进行的分析。
卡西尼号探测器在2008年飞越土卫二时，收集了从其冰壳下喷发出来的羽状物样本。科学家们在这些样本中发现了有机化合物，这些化合物携带氮和氧，对于产生氨基酸——蛋白质的构建块——起着关键作用。蛋白质是生命存在的基础，没有它们，地球上的生命形式无法存在。
此外，研究还揭示了土卫二的冰下海洋中存在一种强大的化学能量来源，这种能量来源以多种有机化合物的形式存在。这些化合物在地球上是生命体能量代谢过程的燃料。科学家们将这种能量来源比作“汽车电池”，暗示它可能为土卫二冰下海洋中的任何潜在生命提供大量能量。
这些发现为土卫二可能存在生命提供了进一步的证据，并为研究生命起源和外星生命的可能性提供了新的视角。尽管目前还没有直接证据表明土卫二上存在生命，但这些发现表明土卫二的环境可能支持生命的存在和发展。NASA的这些研究结果发表在《自然·天文学》杂志上，为未来探索土卫二和其他潜在宜居天体提供了宝贵的科学数据。
以下为资料原文：
NASA has discovered new evidence that Saturn's moon Enceladus holds material that is important to the early development of life.
The American space agency said the new evidence came from observations made by its Cassini spacecraft. Cassini spent seven years observing seasonal changes around Saturn. During that time, the spacecraft also collected data on Saturn's moons.
Two of Cassini's discoveries involved Saturn's moons Titan and Enceladus. In its observations of Titan, the spacecraft studied the moon's climate activity and recorded data on rivers, lakes and oceans. Cassini also found evidence of several Earth-like qualities of Titan that could support life.
Another Cassini discovery involved the observation of hydrogen molecules in ice particles and vapor shooting upward from the moon's surface. Researchers announced that finding in 2017, the same year Cassini officially ended its mission.
In announcing that discovery, NASA scientists said the presence of hydrogen molecules could signal deep-sea chemical reactions between water and rock that could create microbial life.
Now, the space agency is sharing a new finding that supports the earlier discoveries. Scientists examining Cassini data said they identified "strong confirmation" of the presence of another molecule seen as important for enabling life.
Evidence of the molecule – hydrogen cyanide – was found in data relating to the same shooting flows of ice and water vapor observed by Cassini on Enceladus.
The team used data collected by an instrument aboard Cassini designed to measure the activity of gas, ions and ice particles around Saturn. The discovery process involved a lot of mathematics aiming to understand the newly examined data.
The new evidence is described in a study in Nature Astronomy by scientists from NASA's Jet Propulsion Laboratory (JPL) in California.
The lead writer of the study, Jonah Peter, is currently a doctoral student at Harvard University. He called the discovery of hydrogen cyanide "particularly exciting," saying the molecule is "the starting point for most theories on the origin of life."
NASA said in a statement that for life to exist in space, there must be collections of the right building blocks. One of the most important of these is amino acids. "Hydrogen cyanide is one of the most important and versatile molecules needed to form amino acids," NASA noted.
The researchers said hydrogen cyanide molecules can join together in many different combinations. They can also serve as a "precursor" for different kinds of amino acids.
In addition, the latest examination of Cassini data suggested the underground ocean on Enceladus "holds a powerful source of chemical energy." The ocean sits beneath the moon's icy surface.
"Unidentified until now, the energy source is in the form of several organic compounds, some of which, on Earth, serve as fuel for organisms," NASA said.
Astronomers involved in the research said that the discovery provides fresh evidence that there may be more chemical energy inside Enceladus than previously thought. The more energy that is available, the team said, the more likely it is that life can form and survive.
"Not only does Enceladus seem to meet the basic requirements for habitability," said JPL's Jonah Peter, "we now have an idea about how complex biomolecules could form there, and what sort of chemical pathways might be involved."
The search for possible life on Titan will continue when NASA launches its Dragonfly exploratory mission in 2026. Dragonfly is a drone, or pilotless aircraft. The vehicle is designed to capture images and also land on Titan to collect data.
Tom Nordheim is a planetary scientist at JPL who helped lead the research. He noted that although NASA purposely sent the spacecraft crashing into Saturn's atmosphere to end its service, Cassini is still proving to be a valuable research tool.
"Our study demonstrates that while Cassini's mission has ended, its observations continue to provide us with new insights about Saturn and its moons..." Nordheim said.
Enceladus - 恩塞拉达斯（土星的一颗卫星）
Cassini spacecraft - 卡西尼号宇宙飞船
observations - 观测
seasonal changes - 季节变化
moons - 卫星
Titan - 泰坦（土星的一颗卫星）
climate activity - 气候活动
rivers - 河流
lakes - 湖泊
oceans - 海洋
evidence - 证据
hydrogen molecules - 氢分子
ice particles - 冰粒子
vapor - 水蒸气
deep-sea chemical reactions - 深海化学反应
microbial life - 微生物生命
molecule - 分子
hydrogen cyanide - 氢氰酸
amino acids - 氨基酸
precursor - 前体
underground ocean - 地下海洋
chemical energy - 化学能量
organic compounds - 有机化合物
fuel - 燃料
habitability - 适居性
Dragonfly exploratory mission - 蜻蜓探测任务
drone - 无人机
valuable research tool - 有价值的研究工具