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The surface of Mars is etched with ancient river valleys and lake basins. Which makes researchers think that liquid water once flowed on the Red Planet. But how? Today, Mars is too cold for much, if any, liquid water to exist. And 3.8 billion years ago, when the flowing water features formed, the sun was fainter than it is today, making it even harder to imagine a balmy Martian climate. That’s why many researchers think Mars may have gone in and out of deep freezes.

火星表面有着古老河谷和湖泊盆地,这使得研究人员认为液态水曾经在火星上流动。然而它又是怎样流动的呢?今天的火星太冷了,如果有液态水的话,是怎样一种存在状况呢。38亿年前,水的流动特征形成时,太阳比今天更弱一点,很难想象在火星上会有温暖气候。这就是为什么许多研究人员认为火星可能已经进入过,并走出了深冻结时期。

“The real questions have been: for how long was it warm, and what was the mechanism for warming it up.”

“真正的问题是:温暖气候持续了多久,它的温暖机制是什么。”

James Kasting, a geologist at Penn State University. He shared his take on the problem at the December meeting of the American Geophysical Union in San Francisco, and in the journal Earth and Planetary Science Letters. [Natasha E. Batalha et al., Climate cycling on early Mars caused by the carbonate–silicate cycle]

James Kasting是宾夕法尼亚州立大学的一位地质学家。他在美国地球物理联合会12月会议和《行星与科学》杂志上分享了他对这个问题的看法。[ Natasha E. Batalha等人,气候循环对火星早期碳酸盐–硅酸盐循环的影响]

Some researchers have suggested that early Mars only thawed out when large asteroid impacts or volcanic eruptions temporarily warmed the planet. But Kasting and others think warm windows from such dramatic events would have been too brief to carve the vast canyons that exist on Mars. Now, Kasting and his colleagues have come up with an alternative explanation: they think Mars may have experienced a series of climate cycles caused by changes in the strength of the greenhouse effect.

一些研究人员认为,早期火星只有在大行星撞击或火山喷发时暂时变暖才得以解冻。但Kasting和其他人认为,从剧烈变化中吸取热量会在火星上留下短暂的印记如形成巨大的峡谷。现在,Kasting和他的同事们提出另一种解释:他们认为火星可能经历了由温室效应引起的一系列气候变化循环。

The idea goes like this: when Mars was cold and frozen, volcanoes continued to belch out the greenhouse gases carbon dioxide and hydrogen into the atmosphere. There, the gas blanket trapped heat and warmed the planet up until liquid water began to flow, forming Mars’ rivers and lakes. However, warm temperatures and abundant water would also have sped up certain chemical reactions that consumed carbon dioxide, reducing the greenhouse effect and cooling the planet back down again. Then the cycle would repeat.

这一想法是这样的:当火星寒冷和冰冻时,火山持续喷出的温室气体——二氧化碳和氢气进入大气层。在大气层里,热度上升并温暖起来,以致液态水开始流动,从而形成了火星上的河流和湖泊。然而,温暖的气候和充足的水也会加速某些化学反应,这样就消耗了二氧化碳,也会减少温室效应,从而使地球温度下降,这样循环周期不断地重复起来。

“Which is similar to what the impact people have been arguing, except that when it gets warm, it can stay warm for millions of years instead of thousands of years.”

“这类似于人们一直争论不休的话题,不过除这一点:但变得温暖时,它可以保持温暖数百万年而不只几千年。“

So far, Kasting’s team has only shown that such an explanation is possible, according to climate models. But the researchers say NASA’s Curiosity rover and other future Mars missions could help test the idea by looking for evidence of multiple warm events, and their durations. Perhaps, hidden in the dry Martian dust lie clues to a surprisingly soggy past.

到目前为止,Kasting的团队只有表明这样的解释根据气候模型来推断是可能的。但研究人员说,美国宇航局的好奇号探测器和其他未来的火星任务,通过寻找多个温暖现象及其持续时间的证据,或许可以帮助测试这些想法是否属实。也许,干燥的火星尘埃背后隐藏着一个非常潮湿的旧时线索。