科學家揭開"火星上是否有水"之迷
科學家們相信，從衛星傳回的火星圖像中，清晰可見的手指裝的圖形應該是含鹽的溪流流過隕石坑後留下的痕跡。
The puzzling clusters of dark lines fade in winter and reappear in the spring.
這些令人費解的深色線條會在冬天銷聲匿跡，春季時又重新出現。
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.
由美國航天局NASA的火星偵探軌道器拍攝到的照片中，在火星赤道以南的陡峭的山峯出現了這些痕跡。
The features could be the first definitive evidence of present-day liquid water on the Red Planet, say experts.
專家們表示，這一現象有可能成爲首個確鑿的證據，證明在火星上的確有水的存在。
If this turns out to be the case, the sites may provide a promising hunting ground for signs of life on Mars.
而這一發現有可能成爲在火星上尋找生命體存在了有力支撐。
‘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.
“對於所觀察到的這一現象，我們目前最好的解釋是有鹹水的流經，但這項研究目前還無法全完證明其存在。”美國亞利桑那州的Alfred McEwen教授說。The water may not necessarily be flowing over the ground, according to the scientists.
科學家們認爲，水並不一定是在地面以上所流動的。
Some clues suggest it could be buried but affecting the surface to make it appear dark.
有證據表明，水流有可能存在於地表之下，並且使得地表面的顏色變深。
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.
鹽分會使得水凝結成冰的溫度降低，這也就意味着，儘管在火星上所謂“溫暖”的時期裏氣溫也低得嚇人，但在這個星球的中緯度地區，可能有含鹽的液態水季節性的存在。
The lines are between around half a metre to five metres wide but extend for hundreds of metres.
這些線條的寬度介於半米到五米之間，有的甚至有幾百米。
In some of the sites scientists identified more than 1,000 individual flows reaching down steep slopes such as the rims of impact craters.
在火星的某些區域之內，科學家發現了超過了1000條獨立了河流，它們從陡峭的山坡之上流到了隕石坑的邊緣。
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.
亞利桑那州大學的學生Lujendra Ojha是第一個人在衛星圖形圖片上發現了這一季節性變化的情況，他說：“當我看到了這些情況時百思不得其解，很快地我們就意識到，這與之前所觀察到的山坡的線條是不同的。”
‘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.’
“這些圖像的季節性非常之明顯，我們觀察到了其中的一些在兩個月的時間之內，從1米的寬度拓展到超過了200米。”
The lines appear to lengthen and darken on rocky equator-facing slopes from late spring to early autumn.
在春季到初秋的時間裏，這些線條長度會變長，在赤道周圍的斜坡上所顯現的顏色也會變得更深。
They therefore seem to favour warm areas and times, suggesting that they consist of volatile material.
看起來它們在溫暖的區域和時節更爲明顯，這表明其可能是揮發性物質。
However the sites are too warm for frozen carbon dioxide, and in some regions too cold for pure, non-salty water.
然而這些區域由於多餘溫暖而不可能存在凍結的二氧化碳，然而要有純淨的不含鹽分的水出現的話，這裏的氣溫有顯得太低。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.
當科學家們用光譜儀分析衛星軌道器獲取的圖像中河流形的印記，他們驚訝的發現，這種能夠遠程分析物質化學成分的儀器並不能證實有水的存在。
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說，這也許是因爲水在短時間內迅速蒸發掉了，當分析過程正在進行時，星球表面並沒有水的存在。
Alternatively, it might exist at shallow depths below ground.
也有可能，水式存在於深色區域的地表之下。
A subterranean flow of briny water could rearrange sand grains or alter surface roughness in a way that darkens its appearance.
地下水流的流動會使得沙粒積累，並使得表面變得粗糙，從而顏色更深。
‘It's a mystery now, but I think it's a solvable mystery with further observations and experiments,’ Dr McEwen added.
“現在這還是一個謎，不過可以通過進一步的觀察和試驗來解開這個謎”，McEwen說。
Mars has not yet yielded definitive evidence of liquid water active on its surface today.
如今，還沒有確鑿的證據表面火星表面有液體的水存在。
