What Could Life on Mars Look Like? This Chilean Desert Holds Some Clues.
If alien life exists below the surface of Mars, it might very well have a thing or two in common with these populations
Popular Science BlockedUnblockFollowFollowing Mar 5
Photo: Pepe Cast Zam
照片：Pepe Cast Zam
By Eleanor Cummins
Mars is a cold, dry hellscape, but that doesn't mean Earth doesn't share some its more inhospitable traits. If you venture out into the Atacama Desert in Northern Chile, you'll find the driest place on the planet (outside of the North and South Poles), where the average rainfall is 0.6 inches per year --- and even less in some locations. That makes it an imperfect, but useful analogue for Mars, so if you need a place to, say, test out a rover designed to investigate extraterrestrial life
火星是一种寒冷干燥的地狱景观，但这并不意味着地球不会分享一些更不适合居住的特征。如果你冒险进入智利北部的阿塔卡马沙漠，你会发现这个星球上最干燥的地方（北极和南极之外），平均每年降雨量为0.6英寸 - 在某些地方甚至更少。这使得它成为火星的一个不完美但有用的类似物，所以如果你需要一个地方来测试一个用于调查外星生命的漫游车somewhere like the red planet, the Atacama Desert is the place to be. An international team of researchers is doing just that, and recently literally unearthed something unexpected.
A robotic rover tasked with testing out an array of instruments in the Atacama Desert managed to dig up subsurface soil samples possessing incredibly specialized and unique forms of microbial life. According to the findings,
一个机器人漫游车的任务是在阿塔卡马沙漠测试一系列仪器，设法挖掘地下土壤样本，拥有令人难以置信的专业和独特的微生物生命形式。根据调查结果，published Thursday in Frontiers in Microbiology, the study is the first ever to drill beneath the surface of an extreme desert soil like Atacama and recover samples for biological analysis. Moreover, it's the first to illustrate the ability of life to adapt to this sort of environment, and leaves the door open for the potential that we could very well find signs of similar life lurking beneath the surface of Mars.
"The results are a cause for optimism that bacterial life could tolerate the conditions of the Martian subsurface," says Stephen Pointing, a researcher based at the Yale-National University of Singapore and a co-author of the new study. "There is nowhere on Earth quite like the surface of Mars [where] the surface has potentially lethal levels of radiation and very little liquid water. A summer's day on Mars might see equatorial temperatures rise to comfortable 20 degrees Celsius but at night they would plummet to -100 degrees Celsius. Just beneath the surface, however, where the mineral soil and rock provide shelter from the extreme conditions, there is a potential habitat for life."
The most Mars-like soils on Earth exist in the Atacama desert. They're dry, nutrient-poor, and extremely salty and alkaline. The purpose of the trial rover mission was essentially to test out the viability of drilling beneath the surface to recover samples that could then be examined for potential Martian "biosignatures," the chemical signs that life once did (or perhaps still does) exist on Mars.
Drilling's not easy. You have to ensure you can go down far enough to recover samples without compromising the integrity of any biosignatures. Before we land a brand-spanking new drill-bot on the red planet, we want to make sure it knows what it's doing. So, in a project funded by NASA's Astrobiology Science and Technology for Exploring Planets program, Pointing and his colleagues deployed a rover into Atacama in 2013 to see whether rover-acquired samples could be used one day to identify biosignatures of microbial life beneath the surface of Mars.
What they found was entirely unexpected. The subsurface soil samples collected by the trial rover did indeed possess bacteria, able to thrive in extremely salty and alkaline soils. But more galvanizing was the fact that those bacteria communities were distributed in clear, zonified formations --- a major sign that these populations were advanced enough to organize themselves in a way that makes the most use of a limited amount of resources. Further down, as deep as 80 centimeters underground, the team found that a specific group of bacteria was able to survive because it learned how to metabolize the greenhouse gas methane.
他们发现的是完全出乎意料的。试验流动站收集的地下土壤样本确实含有细菌，能够在极度咸和碱性土壤中茁壮成长。但更为激动的是，这些细菌群落分布在清澈的分区形态中 - 这是一个主要标志，即这些种群的进展足以组织自己，最大限度地利用有限的资源。再往下，在地下80厘米深处，研究小组发现一组特定的细菌能够存活下来，因为它学会了如何代谢温室气体甲烷。
Pointing finds these findings exciting because bacteria being hardy enough to survive the harsh conditions of the Atacama subsurface, specialized enough to make due with a limited amount of resources and nutrients, and evolved enough to metabolize methane, then extraterrestrial life on Mars could have potentially done the same. "These bacteria clearly survive right at the limit of habitability," he says.
Before we get over-excited about what a future rover mission to Mars might unearth, there's plenty of room for caution. The patchy nature of the bacterial communities suggests a "needle in the haystack" scenario where we're relegated to drilling at random and hoping to feasibly stumble on something. Even more damning, the parts of the soil that containing subsurface bacteria all showed a somewhat recent history of water input --- and most of Mars, for billions of years, has been basically bone dry, as far as we know. Any investigation of Martian life that's informed by these findings would need to have a very good idea of what spots have the best chances of being most recently habitable to life.
在我们对火星未来的火星探测任务可能发生的事情过度兴奋之前，我们有足够的谨慎空间。细菌群落的不完整性质暗示了"大海捞针"的情景，我们将其随机降级为钻井，并希望能够偶然发现某些东西。更为诅咒的是，含有地下细菌的土壤部分都显示出近期的水输入历史 - 据我们所知，数十亿年来，大部分火星基本上都是干燥的。根据这些调查结果对火星生命进行的任何调查都需要非常清楚哪些地点最有可能成为最近适合生活的地方。
Brian Hynek, a planetary scientist at the University of Colorado Boulder who was not involved with the study, believes the study was very useful as a proof-of-concept for the types of technologies we'll need to really understand the history of habitability on Mars. But he points out that the investigation collected a low amount of biomass, and there was no real correlation between finding microbial life on the surface and finding it within the soil. "To me," he cautions, "this study demonstrates that our prospects of finding life on Mars in the shallow subsurface in desert soil environments is quite low."
科罗拉多大学博尔德分校的行星科学家Brian Hynek认为，这项研究非常有用，可以作为我们真正了解可居住性历史所需技术类型的概念验证。火星。但他指出，调查收集了少量的生物量，并且在寻找表面上的微生物生命和在土壤中发现它之间没有真正的相关性。 "对我而言，"他警告说，"这项研究表明，我们在沙漠土壤环境浅层地下火星上寻找生命的前景非常低。"
Moreover, the limitations of using the Atacama Desert to anticipate what we might find on Mars cannot be overstated. "Like all analogs, there are important differences that limit the application of the results to Mars," says Hynek. They give us a starting point, but Atacama is still nowhere near as harsh as the Martian surface is.
Still, the findings add to our general understanding that life, to quote our lord and savior Jeff Goldblum during his role in
尽管如此，这些发现还增加了我们对生活的一般理解，引用了我们的主人和救世主杰夫戈德布鲁姆的角色 Jurassic Park, finds a way. If it's possible on Earth, it may have been possible on a wetter, warmer Mars a long time ago. And it might still be possible on a Martian world today.