问道新水好还是老水好:NASA航空数据间接指出火星上有液态水流动（PIc + Video）

Oblique View of Warm Season Flows in Newton Crater
NASA宣布，火星勘测轨道器(MRO)可能发现了液态水在火星表面季节性流动的证据。报告发表在最新的《科学》期刊上。液体水可能是咸水。
MRO搭载的高分辨率科学实验成像仪器（HiRISE)）在火星南半球多个陨石坑陡峭的边缘拍到一种条纹现象，它们的宽度不过半米到5米，但是延伸超过数百米，数量超过1000条。这种奇怪的暗色条纹每年冬季就会消失，而春季又再度出现。科学家认为，细长条状暗纹可能是地下流出的咸水，这可能是迄今探测到的火星存在液态水的首个直接证据。暗色条纹并不一定意味着水流已经暴露出地面，也有可能水流仍然埋在地表之下，但是它们影响了地表，使之看起来呈现暗色。

August 04, 2011
NASA Finds Possible Signs of Flowing Water on Mars
Suzanne Presto
Photo: NASA
An image combining orbital imagery with 3-D modeling shows flows that appear in spring and summer on a slope inside Mars' Newton crater
A NASA spacecraft that is orbiting Mars has revealed that liquid water might still flow on the Red Planet.  We have more about this new discovery as scientists continue to "follow the water" in an attempt to learn if Mars might be habitable.
Scientists say there is a possibility that there is flowing water on Mars during the planet's warmest months.
Philip Christensen, a geophysicist at Arizona State University, Tempe, focuses his attentions on Mars and Earth.  He spoke to reporters at NASA headquarters in Washington Thursday about a revelation that is exciting the science community.
"We know Mars has a lot of ice, but this is the first time we've seen the potential for liquid water.  It might be salty water, but it still could [be] still liquid, and I think that's the real key here," said Christensen. " It's not that Mars doesn't have a lot of ice, but liquid water - certainly to an organism - is very, very, very different than ice."
And what are the indications that there could be flowing water?  NASA's Mars Reconnaissance Orbiter has revealed dark, finger-like features that extend down some steep mountain slopes in the Martian middle latitudes during late spring and summer.  The features fade in winter, and they return the next Martian spring.
NASA scientists say the flows are not dark because they're wet, but they say there is a chance that a water flow could have changed the surface in such a way to darken the slopes' appearance.
But don't start daydreaming just yet about a summertime in the southern hemisphere of Mars, lolling by a salty Martian shoreline.
Alfred McEwen is the principal investigator for the Mars orbiter's High Resolution Imaging Science Experiment.  He is also the lead author of the new report about recurring flows.
"So we have this circumstantial evidence for water flowing on Mars," said McEwen. "We have no direct detection of water."
And, McEwen cautioned, it might not be water as we know it on our watery blue planet.
"This very salty water can be very different from water in that it is higher in density and higher in viscosity, so it is more like a syrup maybe in how it flows," he said. "We really don't know how salty this water is from these observations, so this is speculation, but it could be rather different from pure water."
Scientists believe water on Mars would be briny because past landers and rovers, as well as Martian meteorites, have shown that the planet's surface is salty.
Lisa Pratt is a biogeochemist at Indiana University, Bloomington, who studies the fate of complex organic molecules on the surface of Mars.  While it's hard to equate Martian territory to places on Earth, Pratt said Siberia is the most similar place where researchers have studied habitability and permafrost.
Pratt compared the possible water on Mars to the contents of a plastic bottle of soda that's been in the freezer.
"You get a block of ice in the middle of it and then this very sugar-syrup around it where all the flavor and the goodies are," said Pratt. "That's because the water that freezes out is quite pure ice, and all of the other things - the sugars and the salts - are in the syrup.  We all know this from experience.  The whole thing doesn't freeze.  The ice freezes and then there's a remaining liquid brine in that plastic bottle."
Pratt told reporters at NASA that the new discovery is eye-opening, and she said it will help scientists plan future missions to look for signs of life on present day Mars.
"The difficulty has been that Mars is simply too large a planet to keep an eye on every place at all times, and we've needed a way to really focus our instruments and think about the engineering decisions that need to be made for future landed missions or for future orbiting missions, and I really think we now have it," she said.
The new report about possible water flows on Mars was published in Thursday's edition of the journal Science.
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