中国科技网5月20日报道（张微 编译）研究人员已经查明地球上最干旱的地点是阿塔卡马沙漠，这个位于智利的沙漠已经被确认是世界上最干燥的地区。而且研究人员还在这个地方找到了生命存在的证据，这一发现对寻找火星生命产生了深远影响。

由于阿塔卡马沙漠的永盖地区的环境条件接近地球上生命存在的“干旱极限”，超过十年的时间里，这里一直被认定为极度干旱的阿塔卡马沙漠中最干燥的区域。一些学术论文已经论述了这个地区非同寻常的特点而且天体物理学家将它与模拟火星条件相关联。但是，经过一个更加系统的搜索之后，智利的一个研究团队发现了一个新的地点，María Elena South (MES)，这里比永盖地区更干旱。

西雅图蓝色大理石空间科学研究所的研究员，环境生物学家，也是论文的主要作者Armando Azua-Bustos说，这个团队发现MES地区平均大气相对湿度(RH)17.3%，一米深度的土壤RH是14%。这个土壤数值与火星科学实验室在火星的盖尔陨坑测量的最低RH值相匹配，说明这个地区的现场条件与最近发现的火星表面情况一样干燥。

“值得注意的是，我们利用分子依赖和独立方法的结合，在MES地区的土壤剖面中发现大量的活种细菌，首次揭示了在阿塔卡马沙漠的最干旱地区存在生命，”Azua-Bustos说。

微传感器

这个团队使用了微传感器，包括大气温度和相对湿度记录器，对MES地区的微观环境条件进行了详细测量。微传感器器还显示了这个地区土壤的地理化学组成，揭开了在这样恶劣条件下微生物物种的存在，以及能够生存的微生物物种类型。研究结果以论文的形式发表在3月份出版的《微生物学通报》期刊上，题目是“在极度干旱的智利阿塔卡马沙漠中最干燥地区的发现和微生物物种”。

Azua-Bustos已经花了12年的时间研究阿塔卡马沙漠并发展了天体生物学研究领域，同时由于这项工作获得了“沙漠天体生物学家”的绰号。他对这个区域感兴趣是因为他读了《科学》杂志上的一篇被他成为“关键论文”的文章，这是美国宇航局埃姆斯研究中心的行星科学家Chris McKay领导的一项研究。

这篇论文提出阿塔卡马沙漠永盖地区，由于其极度的干旱，土壤的特征，微量有机物种的存在以及极低水平的可培养细菌，使其可以作为“火星模拟模型”。

作为一个土生土长的阿塔卡马人，Azua-Bustos依据他的经验，确信这里有比永盖地区更干旱的地方，所以他决定把湿度传感器放在有可能更干燥的几个地方。

他说：“在这篇论文中提到，我们发现至少有三个这样干燥的地方。”

天体生物学的含义

对于Azua-Bustos来说，MES地区由于其干燥的特点，是最接近火星环境的，它是地球上模拟火星条件的最佳地点，能够让我们了解和调查火星表面存在微生物以及它们类型的潜在可能性。

“这也意味着，如果你想测试火星环境下工作的下一代机器人、工具和其他检测仪器与技术，这里是你能找到的拥有与红色星球关键特征一致的最佳地点。”

这个地点还能够用来做实验，也许可以了解未来火星科学实验室在盖尔陨石坑搜索火星生命的工作是什么样情况。

根据Azua-Bustos的观点，一个有趣的实验室是火星科学实验室在MES地区测试一个相同的仪器，并与火星的数据进行对比，“由于这个阿塔卡马沙漠的新地点具有正控制的优势，因此可以进一步说明这两个地点在可居住性方面详细的相似性。”

对于Azua-Bustos来说，已经知道了MES地区土壤中存在生命的事实，他更感兴趣的是火星样本分析设备(搭载在火星车上的包括质谱仪，气相色谱仪和可调谐激光光谱仪，一套三个设备))以及将被送到火星上的检测仪器是否能够检测出在这个同样干燥的地方存在生命的可能性。

“知道MES地区土壤中微生物的数量，地点和类型，就能够在这里测试火星样本分析仪器，可以测试它们在一个地点的敏感度。换句话说，如果火星样本分析仪器或其他设备不能检测到MES地区土壤中的生命，那么它们的精确度就不足以探测火星生命，”他补充到。

英文原文：

Driest place on Earth hosts life

Researchers have pinpointed the driest location on Earth in the Atacama Desert, a region in Chile already recognised as the most arid in the world. They have also found evidence of life at the site, a discovery that could have far-reaching implications for the search for life on Mars.

For more than a decade, the Yungay region has been established as the driest area of the hyper-arid Atacama desert, with conditions close to the so-called "dry limit" for life on Earth. Several academic papers have been published reporting on the extraordinary characteristics of the site and its relevance to astrobiologists as an analogue of conditions on Mars. However, following a more systematic search of the desert, a Chilean research team has now found a new site, María Elena South (MES), which it describes as "much drier" than Yungay.

Lead author Armando Azua-Bustos, an environmental biologist and research scientist at the Blue Marble Space Institute of Science in Seattle, says the team discovered that MES has a mean atmospheric relative humidity (RH) of 17.3 percent and a soil RH of a constant 14 percent at a depth of one meter. This soil value matches the lowest RH measurements taken by the Mars Science Laboratory at Gale Crater on Mars, establishing the fact that conditions at the site are as dry as those found recently on the Martian surface.

"Remarkably, we found a number of viable bacterial species in the soil profile at MES using a combination of molecular dependent and independent methods, unveiling the presence of life in the driest place on the Atacama Desert reported to date," Azua-Bustos says.

Microsensors

The team used microsensors, including atmospheric temperature and relative humidity loggers, to take detailed measurements of the microenvironmental conditions at the MES site. It also characterized the geochemical composition of the soils at the site to unveil the presence and type of microbial species able to survive under these conditions. The results are presented in the paper, "Discovery and microbial content of the driest site of the hyperarid Atacama Desert, Chile," published in March in the journal Environmental Microbiology Reports.

Azua-Bustos has spent the last 12 years studying the Atacama Desert and developing the field of astrobiology in Chile, and in so doing earned the nickname "astrobiologist of the desert." He first became interested in the region after reading what he describes as a "pivotal paper" published in the journal Science in 2003 by a research team led by Chris McKay, a planetary scientist at NASA Ames Research Center.

The paper proposed the Yungay region in the Atacama as a "pertinent Mars analogue model," mainly due to its extreme dryness, the characteristics of its soils, the presence of organic species at trace levels and extremely low levels of culturable bacteria.

However, based on his experience as a native of the Atacama who was born and raised in the desert, Azua-Bustos was convinced that there were drier places than Yungay, so he decided to set RH sensors in several places that were potentially drier.

"We found at least three such places, the driest of which we describe in this paper," he says.

Implications for Astrobiology

For Azua-Bustos, the fact that the conditions at MES site, in terms of dryness, are the closest to Mars as it is possible to get means that it is one of the best analogue models on Earth to understand and investigate the potential existence, and type of, microbial life in the Martian subsurface.

"This also implies that if you want to test the next generation of robots, instruments and other detection techniques and technologies in a Mars-like environment, this is one of the best you can find as it possesses many of the key characteristics that you will find on the Red Planet," he says.

The site could also be used to conduct experiments that might inform future work carried out by the Mars Science Laboratory (MSL) at Gale Crater in its search for extant life on Mars. In Azua-Bustos' view, one interesting experiment would be to test the same instruments being used by MSL at the MES site to compare results with the Martian data and to "further detail how similar both sites may be in terms of habitability, having the advantage of this new site in the Atacama as a positive control."

For Azua-Bustos, the fact that we already know that there is life in the soil at María Elena South means that it would also be interesting to test if the sample analysis at Mars (SAM) instrument (a suite of three instruments, including a mass spectrometer, gas chromatograph, and tuneable laser spectrometer carried onboard the MSL rover), as well as similar detection instruments scheduled to be sent to Mars, are also able to detect life at a similarly dry terrestrial site.

"[K]nowing the amount, location in the subsoil and type of microbial life present in María Elena South, it would be of interest to test the SAM instruments here, in order to test its sensitivity in a site which you know is inhabited. In other words, if SAM or any other instrument were not able to detect life in Maria Elena soils, one could argue that SAM would not be sensitive enough to detect life on Mars," he adds.