好英语网 - www.HaoEnglish.com


What life might be like in alien oceans

Recent discoveries have led astrobiologists to think that moons are the most promising places for alien life to exist in our Solar System. And now several major space missions are being planned over the next decade to search for hints of life there.


Unlike our neighbouring planets, some of the moons have plenty of liquid water. Jupiter’s moon, Europa, for example, is thought to contain more liquid water than all of Earth's oceans combined. This water – and any life in it – is protected from space radiation and asteroid impacts by a thick layer of kilometers-deep surface ice.


The discovery of plumes of water shooting up from Saturn’s moon Enceladus and Europa have suggested they could have warm interiors that can support liquid oceans, heated not by the Sun, but by an internal dynamo powered by radioactive decay in their cores or by tidal heating generated by the gravitational attraction of the planets that they orbit.

There is now evidence for water oceans on several moons, including Europa, Enceladus, Callisto and Ganymede. One study published this June estimates that the Enceladus ocean is around one billion years old. Others have suggested it may be billions of years old – plenty of time for life to evolve.


These oceans are thought to be salty, containing sodium chloride, like Earth’s oceans, which is another boost for the prospects of Earth-like life.


Also, there is likely to be an interface between the liquid water and the rocky mantle below the oceans – key ingredients for interesting chemistry that scientists think led to the origins of life on Earth. Nasa’s Cassini mission, for example, detected molecules in Enceladus’ water plumes that hint at the existence of hydrothermal vents on the moon’s ocean floor.


Similar vents exist in the deep oceans of the Earth, where magma meets salt water and provides heat, chemicals and a substrate helpful for the complex chemistry some scientists think was needed for life to first evolve on our planet. Deep below the surface of Earth’s ocean, there is practically no sunlight, as would be the case for oceans of Jupiter and Saturn’s moons. But that doesn’t mean there is no life. Indeed, on Earth, such vents are teeming with life.


Some 20 years ago Natural History of an Alien, a BBC documentary, suggested that entire ecosystems could also be based around deep-sea thermal vents on Europa. A team of scientists suggested that bacteria would form the base of the food chain, using chemosynthesis to extract energy from the vents, and building tall tubes of deposits rising many miles above the ocean floor.

大约20年前,英国广播公司(BBC)的纪录片《外星人的自然史》(Natural History of a Alien)指出,整个生态系统也可能以欧罗巴上的深海热泉为基础。一组科学家提出,细菌将形成食物链的基础,利用化学合成从喷口中提取能量,并在海底上方数英里处建造高高的沉淀物管道。

Other creatures, such as fish-like grazers would pierce those tubes to suck in large amounts of bacteria to feed on. They would be territorial, defending their grazing patches against rivals. And, in turn, they would be preyed upon by shark-like animals, streamlined for speed, using echolocation to detect their prey.


This is much more advanced than what most scientists expect to find there.


Even on Earth, for some 90% of our planet’s history, the only life that existed here was microbial, says Andrew Knoll, a professor of earth and planetary sciences at Harvard University. So, if there is life in space, chances are it’s going to be microbial, Knoll says, and in places like Europa or Enceladus it would have to rely entirely on chemosynthesis for energy, so could probably only support a small biomass.

哈佛大学地球和行星科学教授诺尔(Andrew Knoll)说,即使在地球上,在地球90%的历史中,唯一存在的生命也是微生物。因此,如果太空中存在生命,很可能是微生物,而像木卫二或土卫二这样的地方,必须完全依靠化学合成来获得能量,因此只能维持少量生物。

But such an ecosystem might still be possible, says Dimitar Sasselov, an astronomy professor and director of the Harvard Origins of Life Initiative, a centre supporting multi-disciplinary research to discover whether life is abundant in the universe. Just because Europa’s ocean is cold and lacking in energy, doesn’t necessarily rule out complex ecosystems of a smaller size evolving there.

天文学教授兼哈佛生命起源计划的负责人萨斯洛夫(Dimitar Sasselov)说,但这样的生态系统仍然可能实现。该计划支持多学科研究,旨在发现宇宙中是否存在丰富的生命。虽然木卫二的海洋寒冷且缺乏能量,但并不排除在那里进化出规模较小的复杂生态系统。

“Speculating is fun,” Sasselov says. “My gut feeling is that there is a lot of evolutionary innovation space possible there where you can have something which is small and yet predatory and is a multicellular organism rather than just a single cell.”


Another moon we’re planning to visit presents a whole different puzzle.


Saturn’s moon, Titan, is the only world beyond Earth known to have stable bodies of liquid on its surface. When the Huygens probe from the Cassini mission landed there in 2005, it sent back pictures of an Earth-like landscape: river beds and seas.


But rather than water, the clouds, rain and seas of Titan are made up of liquid methane and ethane, components of natural gas on Earth. Any water that does exist there is solidified into rocks and mountains because its surface temperature is around -180C (-292F).


This means that, while its landscape might look familiar, the actual conditions are totally alien. If there is life, it would rely on methane, not water, and would be exotic – life as we don’t know it. True aliens.


It is possible and plausible that life exists on Titan, but with a “completely different, independent biochemistry”, says Sasselov, whose long-term goal is to figure out if there is an alternative biochemistry and how to create it in the lab.


Life on Earth depends on cell membranes made of phospholipids: molecular chains with phosphorus-oxygen heads and carbon-chain tails that bind to each other to form a flexible membrane in water.


Methane-based life would need an alternative way to form cells.


A Cornell University team led by chemical engineer Paulette Clancy showed in 2015 that small molecules made from nitrogen, carbon and hydrogen could build cells fit to survive in Titan’s conditions.

2015年,由化学工程师克兰西(Paulette Clancy)领导的康奈尔大学(Cornell University)研究小组发现,由氮、碳和氢组成的小分子可以构建适合泰坦生存条件的细胞。

Since then, Nasa researchers have confirmed the presence of vinyl cyanide in Titan’s atmosphere, an organic compound that could provide such cellular membranes. So, at least in theory, cells that could form a very different life in Titan’s vast methane oceans could physically exist there.


“In some respects, what we see here on Earth is a matter of chance,” says Theresa Fisher, astrobiologist at Arizona State University, US. There’s an “enormous amount of potential variety” that we could see in life on other worlds, she says.

美国亚利桑那州立大学的天体生物学家费舍尔(Theresa Fisher)说:“在某些方面,我们在地球上看到的是一个偶然的问题。在其他世界的生活中,我们可以看到巨大的潜在的多样性。”

"There might emerge a fluorescence of new and very diverse organisms occupying a range of new niches,” adds Sarah Blaffer Hrdy, a professor emerita in anthropology at the University of California, Davis. "Assuming any of these creatures evolve to be as social, intelligent and communicative as say cetaceans or elephants, and as manipulative, dexterous and clever as chimpanzees or orangutans, I see no reason why they could not eventually evolve more sophisticated technological and cultural capacities.”

加州大学戴维斯分校(University of California, Davis)人类学荣誉教授赫迪(Sarah Blaffer Hrdy)补充道:“可能会出现一种荧光现象,显示出新的、非常多样化的生物体,它们占据了一系列新的生态位。假设这些生物中的任何一种进化到像鲸目动物或大象那样具有社会性、智慧和沟通能力,以及像黑猩猩或猩猩那样善于操纵、灵巧和聪明,它们最终为什么不能进化出更先进的技术和文化能力。”

Lauren Sallan, a palaeontologist at the University of Pennsylvania, thinks alien life will be microbial – and there’re only so many ways to be a microbe.

宾夕法尼亚大学的古生物学家萨兰(Lauren Sallan)认为,外星生命将是微生物,而微生物的存在途径会有很多。

As far as multicellular aliens are concerned, she says, things may get more complicated. “We would recognise that they’re doing the same kind of jobs because everything is focused on either taking in energy or consuming things to get energy,” she says. “But the way that they go about it would be pretty unpredictable.”


“We really don’t know what are the limits of life,” says David Charbonneau, professor of astronomy at Harvard University, who adds that this is why we need to send more probes to examine the moons.

哈佛大学天文学教授夏博诺(David Charbonneau)说:“我们真的不知道生命的极限是什么。这就是为什么我们需要发射更多的探测器来检测卫星。”

So, it’s good news that there are plans to do just that.


Nasa announced this summer that its Dragonfly mission will launch in 2026 and arrive on Titan in 2034. It will land a drone-like craft to explore dozens of promising locations and look for signs of life.

美国宇航局今年夏天宣布,它的蜻蜓计划(Dragonfly mission)将于2026年发射,2034年到达泰坦。并将着陆一架类似无人机的飞行器,探索数10个有希望的地点,寻找生命迹象。

Nasa is also exploring the possibility of sending an autonomous submarine to study Titan’s largest northern sea, Kraken Mare, which is some 1,000 km (621 miles) wide, with depths estimated at 300m (1,000ft), similar in size to North America’s Great Lakes. This would be the first opportunity to explore a sea on another world, and it could inform the design of future submarines to explore the subsurface waters of Europa and other moons. The mission is still in its conceptual stage, some 20 years away, with scientists and engineers starting to investigate how to even build such a submarine.

美国宇航局还在探索能否派遣一艘自主潜艇去研究泰坦最大的克拉肯海(Kraken Mare)的可能性。该海域宽度约1000公里(621英里),深度估计为300米(1000英尺),大小与北美五大湖相仿。这将是探索另一个世界海洋的第一次机会,也将为未来探索木卫二和其他卫星地下水域的潜艇设计提供参考。该任务仍处于概念阶段,大约20年后,科学家和工程师开始研究如何建造这样一艘潜艇。

Intriguingly, Titan is also thought to have a liquid ocean of water deep beneath its icy outer layer, which would mean that in addition to its exotic surface life based on liquid methane, there could exist more Earth-like life under its surface.


Another possibility for layers of different types of life on a single world is Ganymede, Jupiter’s moon. Some scientists think this moon has several different layers of ocean, separated by different types of ice that form at different depths and pressures. If this is the case, each layer could, in theory, host different lifeforms adapted to local conditions at that depth.


Ganymede is set for a visit by the European Space Agency’s 2022 Juice mission, which will also visit two of Jupiter’s other moons – Callisto and Europa – to study their habitability and look for signatures of life.

欧洲航天局(European Space Agency)将于2022年进行果汁计划(Juice mission),访问木卫三,该计划还将访问木星的另外两颗卫星——木卫四和木卫二,研究它们的宜居性,并寻找生命的迹象。

Meanwhile, Nasa’s Europa Clipper is planning to orbit Jupiter and fly past Europa multiple times to investigate whether it could harbour conditions suitable for life, with a take-off date of 2023. Nasa is also discussing sending a lander to Europa, as early as 2025.

与此同时,美国宇航局的“木卫二快船”(Europa Clipper)计划绕木星轨道运行,并多次飞越木卫二,以考察它是否具备适合生命生存的条件。起飞日期为2023年。美国宇航局也在讨论最早在2025年向木卫二发射着陆器。

And, there is a private, Nasa-backed plan for a mission to Enceladus to look for life there that could take off in 2025 if it gets the green light later this year.


But to really figure out what life might exist in these alien oceans, we will need to send a submersible, which will be tricky as such a vehicle would have to drill through several kilometres of ice to even reach the ocean. Nasa is funding some conceptual studies on how to do that.


One concept, for a nuclear-powered “tunnelbot” to search for life on Europa, was presented at a 2018 meeting of the American Geophysical Union in Washington DC, by scientists at the University of Illinois at Chicago and Nasa. Their bot would sample ice and water as it descended, sending information back to the surface through a fibre optic cable.

2018年在华盛顿举行的美国地球物理联盟(American Geophysical Union)会议上,伊利诺斯大学芝加哥分校(University of Illinois at Chicago)和美国宇航局的科学家们提出了一个概念,那就是用核动力“隧道机器人”在木卫二上寻找生命。他们的机器人会在冰层和水面的下降过程中采样,通过光缆将信息传回地面。

But, if lifeforms there turn out to be truly alien, we might struggle to detect them. It’s also possible there simply isn’t any life there yet.


In the distant future, though, some five billion years from now, when our Sun runs out of hydrogen fuel and starts expanding into a red giant phase before it eventually dies, it will melt the ice on these moons and turn them into much more Earth-like places. There should be liquid water on their surface and more temperate climates, perhaps opening up the possibility of life evolving there then – or at least harbouring refugees from the scorched Earth.


In the distant future, if we are to survive, we will all have to become migrants and hope these newly habitable worlds welcome us as our own world gets too hot for life.

上一篇: 返回列表
下一篇: 外太空的幽暗真空处哪里有生命?