液态水“河”在火星上被揭示

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研究人员已经在火星上发现了大量现存的液态水域的证据。

他们相信,这是一个坐落在这颗行星南极的冰冠底下的湖泊,它大概有20公里(12英里)宽。

以前的研究发现了在火星地表漂浮着的、断断续续的、液态水的可能迹象,但是这是当今在火星上的第一个持续出现的水域的迹象。

那些如被NASA好奇号探测器发现的河床显示,在过去,水在火星的地表上是存在的。

不过,后来这个星球的气候由于它薄薄的大气层已经变冷了,使大部分水封锁在冰里。

这个结果特别令人兴奋,因为科学家已经用了很长时间来寻找火星上现有的液态水的迹象,可是它们亦或没有寻找到液态水,亦或产生了不明确的发现。它也将会使那些正在研究地球以外生命的可能的人们感兴趣——虽然这个结果还没有提高寻找生命的堵住。它将会激起那些正在研究地外生命可能性的人们的兴趣 – 虽然它对寻找生命还没有真正的贡献(还没发挥作用)。

这个发现是通过使用欧洲航天机构的火星快捷轨道飞行器的雷达系统Marsis去完成的。

“它有可能不是一个非常大的湖泊。”来自意大利国家天体物理学机构的罗伯特·奥罗赛教授说,他领导这个研究。

Marsis不能够确定那层水有可能有多厚,但这个研究队估计它最小有1米。

“这真的称得上是一个水域。一个湖泊,而不是在地球特定的冰川上充溢在岩石和冰之间的融水”奥罗赛教授补充道。

火星上的水域是怎么被找到的呢?

诸如Marsis这样的雷达系统通过发出一个信号并且检查什么东西反射了回来,去检测这颗行星的地表和附近的次表层。

雷达上部持续的白色线条

在白线底下,研究人员在冰下面1.5公里处发现了不同寻常的东西。

“在浅蓝色中你可以看到从底部来的反射比从表层来的反射要强烈。对我们而言,这对水的存在来讲,是能够说明问题的迹象。”奥罗赛教授说道。

这对生命而言意味着什么?

现在来讲还没有确切的东西。

来自开放大学的马尼什·帕特尔博士解释道:“我们早已经知道,火星的地表对生命是不适于居住的,就如我们知道的一样。因此,现在在火星上寻找生命是在次表层。”

“这是我们不被有害的射线照到的地方。这里能够让我们得到足够的保护。这里的温度和压强上升到更有利的高度。最重要的是,这使得对生命来讲至关重要的液态水的存在成为可能。”

“跟踪水”这个原则是太空生物学的关键——太空生物学是对地球以外潜在的生命的研究。

所以,尽管这个调查发现说明水是现在就有的,它们没有证明任何更深入的东西。

“我们没有更加接近于真正的探测到生命,”帕特尔博士告诉BBC新闻。“但是这个调研结果所能做的,是给予我们在火星上寻找水的位置范围。这就像是一个宝藏地图——除了在这种情况下将会有大量在点上做X的记号。”

水的温度和化学性质也能对任何潜在的火星生物造成一定的困难。

为了在如此冷的条件下保持着液体的状态(研究团队估计在它接触上边的冰的地方温度有零下30摄氏度到零下10摄氏度)这里的水很有可能含有大量溶解进里面的盐。

“可信的是,这里的水有可能是极其寒冷的、浓缩的盐水。这对生命而言是很有挑战性的。”一位来自英国圣安德鲁斯的天体物理学家克莱尔博士的表兄解释说。

我们接下来要做什么?

虽然它的存在为那些对火星上过去或现在生命的可能性感兴趣的人们提供了令人激动的设想,这个湖泊的特征必须先通过进一步的研究来被核实。

“现在需要做的”来自开放大学的玛特·巴尔梅博士解释道,“是在其他地域重复这个测量出来的尺寸,用来寻找相似的信号,如果可能,为了使其他的解释方法被解释——可以指望——把一些解释方法排除掉。”

科学家们在之前已经宣布,他们在南极洲的沃斯托克湖被埋藏的深处里发现了细菌的生命,但是在火星上挖掘的确会促进并形成一个既耗资也耗时的工程。

“到达那里并且得到最终的证据去说明这的确是一个湖泊,这将不是一个简单的任务。”奥罗赛教授说道。

“它将会需要在那里飞行一个能够向1.5公里厚的冰里挖掘的机器人。这一定将会需要一些科技的发展,而此时此刻这是无法得到的。”

Researchers have found evidence of an existing body of liquid water on Mars.

What they believe to be a lake sits under the planet’s south polar ice cap, and is about 20km (12 miles) across.

Previous research found possible signs of intermittent liquid water flowing on the martian surface, but this is the first sign of a persistent body of water on the planet in the present day.

Lake beds like those explored by Nasa’s Curiosity rover show water was present on the surface of Mars in the past.

However, the planet’s climate has since cooled due to its thin atmosphere, leaving most of its water locked up in ice.

The result is exciting because scientists have long searched for signs of present-day liquid water on Mars, but these have come up empty or yielded ambiguous findings. It will also interest those studying the possibilities for life beyond Earth – though it does not yet raise the stakes in the search for biology.

The discovery was made using Marsis, a radar instrument on board the European Space Agency’s (Esa) Mars Express orbiter.

“It’s probably not a very large lake,” said Prof Roberto Orosei from the Italian National Institute for Astrophysics, who led the study.

Marsis wasn’t able to determine how thick the layer of water might be, but the research team estimate that it is a minimum of one metre.

“This really qualifies this as a body of water. A lake, not some kind of meltwater filling some space between rock and ice, as happens in certain glaciers on Earth,” Prof Orosei added.

How was it found?

Radar instruments like Marsis examine the surface and immediate subsurface of the planet by sending out a signal and examining what is bounced back.

The continuous white line at the top of the radar results above marks the beginning of the South Polar Layered Deposit; a filo pastry-like accumulation of water ice and dust.

Beneath this, researchers spotted something unusual 1.5km under the ice.

“In light blue you can see where the reflections from the bottom are stronger than surface reflection. This is something that is to us the telltale sign of the presence of water,” says Prof Orosei.

What does this mean for life?

Nothing definitive. Yet.

Dr Manish Patel from the Open University explained: “We have long since known that the surface of Mars is inhospitable to life as we know it, so the search for life on Mars is now in the subsurface.

“This is where we get sufficient protection from harmful radiation, and the pressure and temperature rise to more favourable levels. Most importantly, this allows liquid water, essential for life.”

This principle of following the water is key to astrobiology – the study of potential life beyond Earth.

So while the findings suggest water is present, they don’t confirm anything further.

“We are not closer to actually detecting life,” Dr Patel told BBC News, “but what this finding does is give us the location of where to look on Mars. It is like a treasure map – except in this case, there will be lots of ‘X’s marking the spots.”

The water’s temperature and chemistry could also pose a problem for any potential martian organisms.

In order to remain liquid in such cold conditions (the research team estimate between -10 and -30 Celsius where it meets the ice above), the water likely has a great many salts dissolved in it.

“It’s plausible that the water may be an extremely cold, concentrated brine, which would be pretty challenging for life,” explained Dr Claire Cousins, an astrobiologist from the University of St Andrews, UK.

What next?

While its existence provides a tantalising prospect for those interested in the possibility of past or present life on Mars, the lake’s characteristics must first be verified by further research.

“What needs to be done now,” explained Dr Matt Balme from the Open University, “is for the measurements to be repeated elsewhere to look for similar signals, and, if possible, for all other explanation to be examined and – hopefully – ruled out.

“Maybe this could even be the trigger for an ambitious new Mars mission to drill into this buried water-pocket – like has been done for sub-glacial lakes in Antarctica on Earth,” he added.

Scientists have previously claimed to find bacterial life in the buried depths of Antarctica’s Lake Vostok, but drilling on Mars would make for an ambitious project indeed.

“Getting there and acquiring the final evidence that this is indeed a lake will not be an easy task,” said Prof Orosei.

“It will require flying a robot there which is capable of drilling through 1.5km of ice. This will certainly require some technological developments that at the moment are not available.”

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