全火星地下水系统的首个证据

WatersofMars二十年以前,火星曾经是否有过大量储存的液态水的问题依然备受争议。当前,这个讨论变成了对自然和液态水的体积的评估,例如液态水在哪里以及对于在火星上寻找生命(或生命留下来的物质)的努力有什么暗示。欧洲空间局的科学家们已经公布了火星快车对一些位于火星北半球的封闭的坑洞的观测结果。

作为作家中的领袖和荷兰的乌德勒支大学弗兰克林·萨莱斯说道:“早期的火星是一个充满水的世界,但是当该行星扥气候变化时,这些水从地表退回来了,形成了‘地下水 ’和水池。由于水的规模和角色还存争议,因此在这个研究中,我们记录了这些水,而且我们寻找到了火星上首个全星球的地下水系统的地质的证据。”

在从4000米到4500米深的范围内,被撞击出的坑洞的底部显示了只有水的存在下才会形成的特征。变化的深度的发现说明随着时间的变迁,水的高度改变了,并且渐渐降低。

GlobalGroundwater

坑洞中水的高度与人们所猜想的火星海洋里被提议的水的高度在一条直线,这证明了一个位于北方大平原(显示在上面的图中)的全球性大洋曾经覆盖火星北半球的三分之一。另外一种猜测也是可能的,就是至少两个覆盖全球的大洋在不同时期出现过——一个是连绵而辽阔的,存在于这颗行星早期时,另一个是更小、更浅的、不连续的(或者是河湖系统),有可能在大量火山作用或其他地热的活动加热了受困于地表以下的冰块时短时间地存在过。

火星上的地下水系统的存在可与这些假说兼容。火山口湖通过和我们在地球上看到的相同的地下水系统相互联系在一起。这个共同点是为什么我们相信火星长期地拥有显著的液态水的一个主要因素。我们已经找到了一些岩石,这些岩石在地球上的形成依靠液态水的存在和说明水力驱动侵蚀的地形的大规模特征,而水力驱动侵蚀的地形和液态水的存在曾经对改变火星的地貌景观有显著的作用。

在火星的古代时期转变到赫斯珀里亚时期后,这种活动迅速减少,而赫斯帕里亚时期也是火星被相信已经变得比以前干旱很多的时间。挪亚时代后的亚马逊河时期的特点是寒冷,这是现在仍然影响并支配这个星球的寒冷的火星环境。

已知的是大量的冰仍旧存在于这颗行星的北极,一个湖泊被相信依旧残留在南极的冰盖下面,这个湖泊和地球上南极洲中数英里冰层底下 的液态湖相似。任何依然存在于火星上的液态水在这个时候可能被更好地描述成“在火星里”。液体的痕迹会在地表偶尔出现,但是曾经却没有观测到大量的自由流动的水。

相同的团队也发现了5个特定的坑洞,在这几个坑里含有对于地球上生命的起源很普遍的矿物质,包括各种各样的黏土、碳酸盐与硅酸盐。这种流域有可能成为寻找火星上曾经可能存在的生命的主要位置。

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First Evidence of Global Groundwater System Found on Mars

Twenty years ago, the question of whether Mars ever had large reserves of liquid water was still open to debate. Today, the discussion has shifted to an evaluation of the nature and size of those reserves, where they existed, and what this implies for any effort to find life (or the remains of it) on the Red Planet. Scientists with the European Space Agency have released the results of Mars Express’ observation of some 24 deep, enclosed craters in the northern hemisphere of Mars.

“Early Mars was a watery world, but as the planet’s climate changed this water retreated below the surface to form pools and ‘groundwater,’” says lead author Francesco Sales of Utrecht University in the Netherlands. “We traced this water in our study, as its scale and role is a matter of debate, and we found the first geological evidence of a planet-wide groundwater system on Mars.”

The floor of the impact craters showed features that could only have formed in the presence of water, at depths ranging from 4,000 to 4,500 meters. The various depth findings show that the water level changed and receded over time.

The water level in the craters aligns well with the proposed water level in the Mars ocean hypothesis, which argues that a global ocean situated in the Vastitas Borealis (pictured above) once covered the northern third of Mars. It’s also possible that at least two global oceans existed on Mars at different points — one vast and persistent, during the earliest days of the planet, and a smaller, shallower, and less-persistent ocean (or system of rivers and lakes) that may have temporarily existed when vast amounts of volcanism or other geothermal activity heated ice trapped below ground.

The existence of a groundwater system on Mars is compatible with these hypotheses. Crater lakes would have attached to each other through the same types of groundwater systems we see on Earth. Such commonalities are a major component of why we believe Mars supported significant amounts of liquid water for long periods of time. We’ve found rocks whose formation on Earth depends on the presence of liquid water and large-scale features of the terrain that indicate water-driven erosion once played a significant role in weathering the Martian landscape.

The incidence of such activity drops off sharply after Mars’ Noachian period transitions into the Hesperian, which is also when Mars is believed to have become much drier. The Amazonian period that followed the Noachian is characterized by the cold, arid Martian conditions that still dominate the planet today.

Substantial amounts of ice are known to still exist at the planet’s north pole, and a lake is believed to still remain beneath the south polar ice cap, similar to the liquid lakes under miles of ice in Antarctica on Earth. Any liquid water still existing on Mars might be better described as being in Mars at this point, given the depths at which it would be located. Traces of liquid are occasionally found at the surface, but no significant amount of free-running water has ever been observed.

The same team also spotted five specific craters where mineral ingredients believed to be common to the rise of life on Earth also exist, including various clays, carbonates, and silicates. Such basins could be prime locations for searching for the life that may have existed on Mars.