科学家揭开"火星上是否有水"之迷
科学家们相信，从卫星传回的火星图像中，清晰可见的手指装的图形应该是含盐的溪流流过陨石坑后留下的痕迹。
The puzzling clusters of dark lines fade in winter and reappear in the spring.
这些令人费解的深色线条会在冬天销声匿迹，春季时又重新出现。
Pictures taken by the American space agency Nasa's Mars Reconnaissance Orbiter spacecraft showed the markings on several steep slopes south of the Martian equator.
由美国航天局NASA的火星侦探轨道器拍摄到的照片中，在火星赤道以南的陡峭的山峰出现了这些痕迹。
The features could be the first definitive evidence of present-day liquid water on the Red Planet, say experts.
专家们表示，这一现象有可能成为首个确凿的证据，证明在火星上的确有水的存在。
If this turns out to be the case, the sites may provide a promising hunting ground for signs of life on Mars.
而这一发现有可能成为在火星上寻找生命体存在了有力支撑。
‘The best explanation we have for these observations so far is flow of briny water, although this study does not prove that,’ said co-author Dr Alfred McEwen, from the University of Arizona.
“对于所观察到的这一现象，我们目前最好的解释是有咸水的流经，但这项研究目前还无法全完证明其存在。”美国亚利桑那州的Alfred McEwen教授说。The water may not necessarily be flowing over the ground, according to the scientists.
科学家们认为，水并不一定是在地面以上所流动的。
Some clues suggest it could be buried but affecting the surface to make it appear dark.
有证据表明，水流有可能存在于地表之下，并且使得地表面的颜色变深。
Saltiness lowers the temperature at which water freezes. This means seasonal salty liquid water could exist in mid-latitude regions of Mars, despite the chilliness of the planet's ‘warm’ season.
盐分会使得水凝结成冰的温度降低，这也就意味着，尽管在火星上所谓“温暖”的时期里气温也低得吓人，但在这个星球的中纬度地区，可能有含盐的液态水季节性的存在。
The lines are between around half a metre to five metres wide but extend for hundreds of metres.
这些线条的宽度介于半米到五米之间，有的甚至有几百米。
In some of the sites scientists identified more than 1,000 individual flows reaching down steep slopes such as the rims of impact craters.
在火星的某些区域之内，科学家发现了超过了1000条独立了河流，它们从陡峭的山坡之上流到了陨石坑的边缘。
University of Arizona student Lujendra Ojha, who was the first to spot the features after identifying subtle seasonal changes in the orbiter images, said: ‘I was baffled when I first saw those features ... we soon realised they were different from slope streaks that had been observed before.
亚利桑那州大学的学生Lujendra Ojha是第一个人在卫星图形图片上发现了这一季节性变化的情况，他说：“当我看到了这些情况时百思不得其解，很快地我们就意识到，这与之前所观察到的山坡的线条是不同的。”
‘These were highly seasonal, and we observed some of them had grown by more than 200 metres in a matter of just two Earth months.’
“这些图像的季节性非常之明显，我们观察到了其中的一些在两个月的时间之内，从1米的宽度拓展到超过了200米。”
The lines appear to lengthen and darken on rocky equator-facing slopes from late spring to early autumn.
在春季到初秋的时间里，这些线条长度会变长，在赤道周围的斜坡上所显现的颜色也会变得更深。
They therefore seem to favour warm areas and times, suggesting that they consist of volatile material.
看起来它们在温暖的区域和时节更为明显，这表明其可能是挥发性物质。
However the sites are too warm for frozen carbon dioxide, and in some regions too cold for pure, non-salty water.
然而这些区域由于多余温暖而不可能存在冻结的二氧化碳，然而要有纯净的不含盐分的水出现的话，这里的气温有显得太低。When the scientists turned the orbiter's imaging spectrometer on to the flow-marked slopes, they got a surprise - the instrument, which remotely analyses the chemical composition of materials, failed to confirm the presence of water.
当科学家们用光谱仪分析卫星轨道器获取的图像中河流形的印记，他们惊讶的发现，这种能够远程分析物质化学成分的仪器并不能证实有水的存在。
Dr McEwen said this could be because the water quickly dries on the surface and did not happen to be there when the analysis was carried out.
McEwen说，这也许是因为水在短时间内迅速蒸发掉了，当分析过程正在进行时，星球表面并没有水的存在。
Alternatively, it might exist at shallow depths below ground.
也有可能，水式存在于深色区域的地表之下。
A subterranean flow of briny water could rearrange sand grains or alter surface roughness in a way that darkens its appearance.
地下水流的流动会使得沙粒积累，并使得表面变得粗糙，从而颜色更深。
‘It's a mystery now, but I think it's a solvable mystery with further observations and experiments,’ Dr McEwen added.
“现在这还是一个谜，不过可以通过进一步的观察和试验来解开这个谜”，McEwen说。
Mars has not yet yielded definitive evidence of liquid water active on its surface today.
如今，还没有确凿的证据表面火星表面有液体的水存在。
