Sun, Aug 05, 2018 - Page 9 News List

Underground lake found on Mars, raising possibility of life
火星地底驚見湖泊 生命存在可能性大增

This image provided by NASA shows the south polar cap of Mars as it appeared to the Mars Global Surveyor on April 17, 2000.
這張由美國太空總署提供的照片顯示出火星的南極冠,是探測衛星「火星全球探勘者號」於二○○○年四月十七日觀測到的景象。

Photo: AFP
照片:法新社

Using a radar instrument on an orbiting spacecraft, scientists have spotted what they said on July 25 appears to be a sizable salt-laden lake under ice on the southern polar plain of Mars, a body of water they called a possible habitat for microbial life. The reservoir they detected — roughly 20km in diameter, shaped like a rounded triangle and located about 1.5km beneath the ice surface — represents the first stable body of liquid water ever found on Mars.

Whether anywhere other than Earth has harbored life is one of the supreme questions in science, and the new findings offer tantalizing evidence, though no proof. Water is considered a fundamental ingredient for life. The researchers said it could take years to verify whether something is actually living in this body of water that resembles a subglacial lake on Earth, perhaps with a future mission drilling through the ice to sample the water below.

“This is the place on Mars where you have something that most resembles a habitat, a place where life could subsist,” said planetary scientist Roberto Orosei of Istituto Nazionale di Astrofisica in Italy, who led the research published in the journal Science. “This kind of environment is not exactly your ideal vacation, or a place where fish would swim,” Orosei added. “But there are terrestrial organisms that can survive and thrive, in fact, in similar environments. There are microorganisms on Earth that are capable of surviving even in ice.”

The detection was made using data collected between May 2012 and December 2015 by an instrument aboard the European Space Agency’s Mars Express spacecraft that transmits radar pulses, which penetrate the Martian surface and ice caps. “This took us long years of data analysis and struggles to find a good method to be sure that what we were observing was unambiguously liquid water,” said study co-author Enrico Flamini, chief scientist at the Italian Space Agency during the research. The location’s radar profile resembled that of subglacial lakes found beneath Earth’s Antarctic and Greenland ice sheets.

Mars long ago was warmer and wetter, possessing significant bodies of water, as evidenced by dry lake beds and river valleys on its surface. There had been some signs of liquid water currently on Mars, including disputed evidence of water activity on Martian slopes, but not stable bodies of water. Orosei said the water in the Martian lake was below the normal freezing point but remained liquid thanks in large part to high levels of salts. Orosei estimated the water temperature at somewhere between minus 10°C and minus 70°C.

It remains to be seen if more subsurface reservoirs of water will be found or whether the newly discovered one is some sort of quirk, Orosei said. If others are detected and a network of subglacial lakes exists like on Earth, he said, that could indicate liquid water has persisted for millions of years or even dating back to 3 to 0.5 billion years ago when Mars was a more hospitable planet.

The question would be, Orosei added, whether any life forms that could have evolved long ago on Mars have found a way to survive until now. “Nobody dares to propose that there could be any more complex life form,” Orosei said.

(Reuters)

科學家在七月二十五日表示,藉助於一艘繞軌道運行太空船上的雷達儀器,他們在火星的南極平原冰層底下,探測到一片充滿鹽分的大型湖泊,這塊水體被認為是微生物生命可能的棲息地。這個偵測到的天然水庫直徑約二十公里,呈圓弧狀三角形,位於冰層表面下一點五公里處,是火星上第一次發現的穩定液態水體。

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