地球人移居火星？

塞巴斯蒂安·埃切韦里

Inspired by science fiction and a strange phenomenon on the Martian surface， researchers have discovered a way that Earth life could survive on the red planet.

A team of scientists at Harvard University， the University of Edinburgh， and NASAs Jet Propulsion Laboratory have found that a material called aerogel1 can trap enough heat from sunlight to create regions of liquid water and Earth-like temperatures on Mars. This technology， they say， could be adapted to build human habitats in the not-so-distant future.

In a new study， the researchers show that placing a thin layer of a translucent aerogel—just a few centimeters thick—atop Mars surface could heat the ground by up to 50 degrees Celsius， or 90 degrees Fahrenheit， or more. This would be enough to thaw2 water previously frozen underground， providing the crucial ingredient to support life.

Just like carbon dioxide and other greenhouse gases， the aerogel allows visible light to pass through and warm up the ground， but makes it harder for infrared light—which humans cannot see， but experience as heat—to escape. Thanks to its unique structure， aerogel produces a much more efficient greenhouse effect than carbon dioxide.

“Jelly3 [is] a structure [made] of a solid filled with [tiny pockets of] liquid. If you suck out all the liquid and replace it with air， you get an aerogel，” said Laura Kerber， a research scientist4 at the Jet Propulsion Laboratory.

These air pockets are the key to heating up Mars. “Air is really bad at conducting heat， but it usually moves around and brings heat from place to place. But since [in the aerogel] its trapped in all these tiny pockets， then [the air] cant mix around， and that makes it a great insulator，” she said. A similar type of aerogel is used to insulate the Curiosity rover currently exploring Mars， as well as deep sea pipes， firefighting equipment， and even houses here on the Earth.

Scientists could deploy the aerogel on a small-scale first and then work up to5 more ambitious projects. “The simplest one... is to make [an aerogel] blanket and allow algae and microbial life [from Earth] to grow. Habitats for humans—it would still absolutely work， but youd have to combine [the aerogel] with other materials，” said Robin Wordsworth， an associate professor of environmental science and engineering at Harvard.

“In its current form， [the aerogel] is pretty brittle，” Kerber said. Mars atmosphere is very thin and toxic to most Earth life， so any habitable structure would have to be airtight. She explained that in the future， tiles made of aerogel sandwiched between strong plexiglass could be used to make a pressurized6 dome for humans.

Because these Earth-life environments would be self-contained7， they would also preserve whatever Martian life that might exist. “Nobody wants to go to Mars and kill the only other life we find by out-competing8 it with Earth life. This is a nice solution; piece by piece， little contained island of habitability， we can live there and [not] mess it up，” Kerber said.

“This， we think， for the first time， is a local and scalable9 way to approach achieving Martian habitability. There are many challenges. But we think it is very exciting that this is now a possibility in our lifetime，” Wordsworth said.

This finding， exciting as it is， is only the latest in a story that began far before humans even walked on the moon.

“The science fiction I started my life with [is] coming true，” said Edward Guinan， a professor of astrophysics and planetary science at Villanova University. For more than a century， science fiction authors have been writing about human settlements on the red planet， depicted as having breathable air， liquid water， and advanced alien life.

Humanitys understanding of Mars took a leap forward in 1965， when the Mariner 4 probe took the first close-up photos and found that Mars was entirely inhospitable to humans—deserted， dry， and with a dangerously thin atmosphere.

But writers and scientists—many inspired by their favorite novels—didnt give up. Instead， they focused on terraforming10： using technology to radically transform Mars into a place where people could survive.

In 1971， Carl Sagan11 proposed vaporizing all of the frozen water12 and carbon dioxide of Mars ice caps. The resulting gas would then heat the planet by the same greenhouse effect behind Earths own global warming crisis. But in 2018， NASA discovered that there was not enough frozen water and carbon dioxide on Mars for this plan to work without incredibly advanced technology.

Harvards Wordsworth felt pushed13 to think practically about terraforming. “[We asked] what actually could work and what couldnt in our lifetime， as opposed to far in the future，” he said.

The direct inspiration for the aerogel project， however， came from Mars itself.

The same heating process “already happens on Mars right now， but with [frozen carbon dioxide]. Its pretty transparent， and accumulates on dunes. The sun shines through， and gas starts forming. And it finally explodes， and you get these geysers14 of [carbon dioxide] that leave black spots. Happens every spring，” said Kerber.

Having studied the Martian surface， Kerber has already discovered the ideal spot to build a human settlement.

“I know where all of the subsurface water is on the planet. Theres this place called Deuteronilus Mensae15. If you want to do this， this is where Id put your domes; this is where theres water close to the surface，” she said.

As for what those living in aerogel-heated habitats on Mars might eat， Guinan and his astrobotany students are working on it. “We have a greenhouse in Villanova. We are growing plants in Martian simulated soil， [and] under the light conditions we get on Mars，” he said.

Guinan already plans for his students to experiment with growing their “Mars Garden” in an aerogel-based greenhouse. “I already bought [aerogel]. We are actually going to try it，” he said.

Having worked in astrophysics for over 50 years， Guinan is hopeful that this new technology will see humans living and growing food on Mars within his lifetime.

Kerber believes that solving the remaining challenges—the largest of which is the trip to Mars itself—is only a matter of funding. “If someone said， ‘Heres a bunch of money， and go do it， wed do it. People think its so far out of reach， or something from a sci-fi film—its not. Let us try，” she said.

受科幻小說和火星表面奇观的启发，研究人员发现了一种能让地球生命在这颗红色行星上生存的方法。

来自哈佛大学、爱丁堡大学和美国国家航空航天局喷气推进实验室的科学家组成的团队发现，一种叫作气凝胶的材料能从阳光中捕获足够的热量，在火星上形成液态水区域并达到与地球相近的温度。他们认为，在不久的将来，就可采用这项技术建设人类栖息地。

在一项新的研究中，研究人员表明，在火星表面铺上薄薄一层半透明气凝胶，只要几厘米厚，就能使地表升温50摄氏度（90华氏度）甚至更高。这足以融化之前封冻在地下的水，提供维持生命必需的要素。

就像二氧化碳等温室气体一样，气凝胶允许可见光通过并使地表升温，但阻碍红外线逃逸，人类看不见但会感到热。凭借其独特的结构，气凝胶产生温室效应的效率可远胜二氧化碳。

喷气推进实验室的研究员劳拉·克贝尔说：“液凝胶是一种充满微小液囊的固体结构。如果把所有液体抽干，并用空气代替液体，就得到了气凝胶。”

这些气囊是加热火星的关键。克贝尔说：“空气导热性极差，但通常可以流动，能把热量带到各处。而气凝胶中的空气被束缚在这些微小的气囊中，所以无法相互混合，因而成为极好的隔热材料。”类似的气凝胶已经应用到目前正在执行火星探索任务的好奇号火星车上，此外还可以应用到深海管道、消防设备乃至地球上的房屋。

科学家可以先小规模应用气凝胶材料，然后逐步开展更宏大的项目。哈佛大学环境科学与工程副教授罗宾·沃兹沃思说：“最简单的一种……是制作气凝胶毯，让来自地球的藻类和微生物在上面生长。对于人类的栖息地——它也照样保证能工作，但一定要把气凝胶和其他材料结合使用。”

“目前这种形态的气凝胶还相当脆弱。”克贝尔说。火星大气非常稀薄，而且对大多数地球生命来说都有毒，所以任何宜居建筑都必须建成密闭的。她解释道，未来，可以把气凝胶夹在结实的有机玻璃中间制成砖瓦，用来建造供人居住的密封圆顶房屋。

因为地球生命生活的这些环境会自给自足，它们也会保护火星上可能存在的任何生命。克贝尔说：“谁也不想登陆火星后，就让地球生命凭借竞争优势杀死我们发现的唯一地外生命。这个解决方案不错，逐步建成基本自足的宜居小岛，我们就能住在那里而不至搞得一团糟。”

“还是头一次，我们认为这是一种可能实现火星宜居的方式，范围虽小但可以扩展。困难是很多，但我们认为非常鼓舞人心，因为在我们有生之年很可能实现。”沃兹沃思说。

这一发现虽然令人振奋，但也不过是在人类已开始的一个故事的最新进展踏上月球之前就开始了。

维拉诺瓦大学的天体物理学和行星科学教授爱德华·吉南说：“我从小就喜欢的科幻小说要变成现实了。”一个多世纪来，科幻小说作者不断讲述人类在这颗红色星球上定居的故事，将火星描绘为有能呼吸的空气、液态水，甚至还有高级外星生命。

1965年，水手4号火星探测器第一次拍摄到特写照片，发现火星完全不适宜人类生存——荒凉，干燥，大气极为稀薄。人类对火星的认识因此发生了一次飞跃。

但是作家和科学家——很多是受到他们喜爱的小说的启发——没有放弃。不仅如此，他们还专注于地球化：用技术手段把火星彻底改造成人类能够生存之地。

1971年，卡尔·萨根建议把火星冰盖所有水冰和二氧化碳都蒸发掉。就像导致地球自身全球气候变暖危机的温室效应一样，蒸发产生的气体会引起同样的效应让火星变暖。但在2018年，美国国家航空航天局发现，如果没有非常先进的技术支持，火星上水冰和二氧化碳数量不足以实现这个蒸发计划。

哈佛大学的沃兹沃思感到形势紧迫，要实事求是地思考地球化的问题。他说：“我们问的是，在我们有生之年而非遥远的未来，什么是切实可行的，什么又是行不通的。”

然而，就气凝胶项目而言，直接的灵感来自火星本身。

克贝尔说，同样的加热过程“目前已在火星上发生，不过借助的是固态二氧化碳（干冰）。它非常透明，在沙丘上积聚。阳光穿透干冰，气体开始形成。最后气体喷发，产生这些二氧化碳间歇喷泉，留下黑点。这种现象每年春天都会发生”。

通过对火星地表的研究，克贝尔已经发现了建造人类定居点的理想之地。

她说：“我知道火星所有的地下水在哪里。就在那个名叫亚尼罗桌山群的地方。如果想建人类定居点，这就是我推荐建房的地方;这里的地下水离地表很近。”

至于火星上那些住在气凝胶加热定居点的居民吃什么，吉南和他的天文植物學学生正开展此项研究。他说：“维拉诺瓦大学有座温室，我们用模拟的火星土壤栽种植物，光照条件也模拟火星。”

吉南早就计划让学生在利用气凝胶的温室里开展他们建造“火星花园”的实验。他说：“我早买好了气凝胶，实际上我们就要做实验了。”

吉南已在天体物理学领域工作了50多年，他希望在有生之年，这项新技术能见证人类移居火星并在火星上种植粮食。

克贝尔认为，解决剩下的挑战——其中最难的是通往火星的旅程——只是资金的问题。她说：“要是有人说‘钱有的是，放手去做吧，我们就会去做。人们认为这实在遥不可及，或者只是科幻电影里的东西——其实不然。我们共同努力吧。”     □

（译者为“《英语世界》杯”翻译大赛获奖者）