托福閱讀：火星上可以住人嗎？

　　自古以來，我們對移民外星球的想法從未停歇?；鹦堑淖赞D(zhuǎn)周期與地球幾乎相等，晝夜交替、季節(jié)更迭與地球的情況十分類同，重力和溫度條件雖然稍惡劣些，但并不是極端難耐的程度......種種這些相似點(diǎn)讓浪漫的人類不禁暢想：火星上，可不可以住人呢？

　　19世紀(jì)，美國天文學(xué)家Percival Lowell讓我們知道在火星表面有縱橫交錯的水道，然而火星上酷寒的溫度加上稀薄大氣層帶來的低氣壓，讓其表面任何液態(tài)水都無法存在太久。

　　2006年，火山坑里的氣候變化讓天文學(xué)家猜測少量的液態(tài)水也許會在火星的夏季短暫地冒出來，但一直未被證實。

　　In the 19th century Percival Lowell, anAmerican astronomer, popularised the idea that there were canals criss-crossingthe Martian surface, carrying water from the poles to feed a thirsty desertcivilisation. Better telescopes, and the arrival of space probes in the 1960s,revealed the canals as a mirage. Mars’s frigid temperatures, and the feeblepressure exerted by its wispy atmosphere, mean that no liquid water couldsurvive on the surface for long. Nevertheless, in 2006 seasonal changes in apair of Martian craters led astronomers to speculate that small amounts ofliquid water might be bubbling briefly to the surface in the Martian summer.Over a decade later, though, the case remains unproven.

　　然而最近，一項研究卻讓不少外星迷們振奮不已—意大利天體物理研究學(xué)家Roberto Orosei稱，在火星表面靠近南極冰蓋1.5km以下，發(fā)現(xiàn)一個寬20km的液態(tài)湖泊。

　　Now the question seems to have been settled in spectacular style. In a paper published in Science on July 25th, Roberto Orosei of the National Institute for Astrophysics in Italy, and his colleagues, report the discovery of a lake of liquid water 20km across, buried 1.5km beneath Mars’s surface, close to its southern polar ice cap. The lake seems to be a Martian cousin of familiar Earthly features such as Lake Vostok, a subterranean lake in Antarctica.

　　The team used radar waves to peer beneath the planet’s surface. Different materials reflect the radar waves with different intensities, allowing scientists to detect what is there. The team used a radar sensor on Mars Express, an orbiting probe, to survey a 200km-wide area of Planum Australe, the planet’s southern polar plain. The sensor lacked the sensitivity of those used on Earth, but after more than three years of collecting data Dr. Orosei felt confident enough to claim that water was the only explanation for the team’s readings.

　　該小組利用雷達(dá)波窺探火星表面之下。不同的物質(zhì)會以不同的強(qiáng)度反射雷達(dá)波，使科學(xué)家可以探測出下面是什么。他們通過火星快車號，一種探測器上面的雷達(dá)傳感器來勘測火星南極高原200km寬面積的地區(qū)。這種傳感器并不像地球上的那些傳感器那么靈敏，但是經(jīng)過三年多的數(shù)據(jù)收集，Orosei博士有足夠信心認(rèn)為數(shù)據(jù)解讀的解釋是水。

　　That the lake is underground is key to its survival, says Susanne Schwenzer, a planetary scientist at the Open University, in Britain, who was not involved with the work. As in Antarctica, the thickness of the ice sheet insulates the water from the sub-freezing temperatures on the planet’s surface. At the same time, the pressure exerted by the ice lowers the water’s melting point below 0°C. “And if the water is spiced with salts of sodium, magnesium and calcium—all of which have been found on Mars—its melting point could drop still further.

　　Susanne Schwenzer，英國開放大學(xué)行星科學(xué)家，并未參與到研究中，他說湖泊在地下是它能存在的關(guān)鍵。就像是在南極洲（的湖泊），冰蓋的厚度將湖水與星球表面的零下溫度的水隔離開來。同時，冰所施加的壓力將湖水的融點(diǎn)降低至零度以下。如果水中摻雜鈉鹽，鎂還有鈣的話—這些已經(jīng)在火星上發(fā)現(xiàn)，那么融點(diǎn)將下降的更多。

具體研究方式如下：

　　發(fā)現(xiàn)了湖泊，能否說明有生命呢？火星過去更暖和濕潤，已經(jīng)成為化石的河流三角洲還有湖床在火星表面依稀可見。如果微生物確實在遙遠(yuǎn)的過去出現(xiàn)過，那么這些微生物有可能附著在這片星球地表之下與世隔絕的水洼中。

　　The discovery is exciting from a purely geological point of view. But the biggest question is whether anything might be “alive down there. There is plenty of life in Lake Vostok, even though it has been cut off for tens of millions of years. Mars was much warmer and wetter in the past. Fossilised river deltas and lakebeds are visible on the planet’s surface. If microbial life did arise on Mars in the distant past, it might be clinging on in just such an isolated pocket of water below the planet’s surface.

　　火星已經(jīng)干旱30億年了，這對于能保存生命的湖泊來說很漫長。火星中是否存在、能否存在生命，科學(xué)家們一直在探索中，或許將來有24小時，我們真的能像去美國一樣，去火星。

　　Perhaps. Mars has been dry for around 3.8bn years. That is a long time for a life-preserving lake to have endured. Dr. Schwenzer points out that Mars’s axis has wobbled sufficiently over the planet’s history that the polar caps have wandered widely over its surface. On the other hand, the existence of one such lake suggests there may be more. Alien hunters have, in recent years, been shifting their attentions to the icy moons of Jupiter and Saturn, which sport oceans beneath their surfaces. The discovery of liquid water on Mars will shift some of that attention back.

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