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探索火星新發現 地表夏季有水流動
（中央社紐約28日綜合外電報導）美國國家航空暨太空總署稍後將召開記者會，宣布探索火星的重大發現，根據新公布的研究報告，科學家首度發現證據，顯示火星在夏季幾個月期間，可能有水在地表上流動。
路透社報導，雖然這些水的來源和化學成分仍不明，美國國家航空暨太空總署（NASA）仍發出新聞，宣告「解開了火星的一個謎」，並計畫於美東時間今晨11時30分就此事召開記者會。1040928
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Although the source and the chemistry of thewater is unknown, the discovery could affectthinking about whether the planet that is mostlike Earth in the solar system could supportpresent day microbial life.
Scientists developed a new technique toanalyze chemical maps of the Martian surfaceobtained by NASA's Mars Reconnaissance Orbiterspacecraft.
They found telltale fingerprints of saltsthat form only in the presence of water innarrow channels cut into cliff walls throughoutthe planet's equatorial region.
The slopes, first reported in 2011, appearduring the warm summer months on Mars, thenvanish when the temperatures drop.
Scientists suspected the streaks, known asrecurring slope lineae, or RSL, were cut byflowing water, but had previously been unable tomake the measurements.
"I thought there was no hope," LujendraOjha, a graduate student at Georgia Institute ofTechnology and lead author of a paper in thisweek's issue of the屏東縣清償債務 journal Nature Geoscience,told Reuters.
Mars Reconnaissance Orbiter makes itsmeasurements during the hottest part of theMartian day, so scientists believed any tracesof water, or fingerprints from hydratedminerals, would have evaporated.
Also, the chemical-sensing instrument on theorbiting spacecraft cannot home in on details assmall as the narrow streaks, which typically areless than 16 feet (5 meters) wide.
But Ojha and colleagues created a computerprogram that could scrutinize individual pixels.That data was then correlated withhigh-resolution images of the streaks.Scientists concentrated on the widest streaksand came up with a 100 percent match betweentheir locations and detections of hydratedsalts.
"We're not claiming that we found ...evidence of liquid water. We found hydratedsalts," Ojha said.
Still, that was enough for NASA, whichdeclared a "Mars mystery solved," in a pressadvisory. A press conference on it was plannedfor 11:30 a.m. EDT/1530 GMT on Monday.
"It's a little bit over-the-top announcementby NASA," Ojha said. "There's so many mysteriesto be solved about RSL."
The discovery "confirms that water isplaying a role in these features," added AlfredMcEwen, a planetary scientist with Arizona StateUniversity. "We don't know that it's coming fromthe subsurface. It could come from theatmosphere.'
Whatever the water's source, the prospect ofliquid water, even seasonally, raises theintriguing prospect that Mars, which is presumedto be a cold and dead planet, could support lifetoday. Much more information about the water'schemistry, however, would be needed beforescientists could make that assessment, McEwenadded. "It's not necessarily habitable justbecause it's water - at least to terrestrialorganisms," he said. NASA's ongoing Mars roverCuriosity has found evidence that Mars had allthe ingredients and suitable habitats formicrobial life to exist at some point in itspast. Scientists have been trying to figure outhow it transformed from a warm, wet and likelyEarth-like planet early in its history into thecold, dry desert that exists today. Billions ofyears ago, Mars, which lacks a protective,global magnetic field, lost much of itsatmosphere. Several initiatives are under way todetermine how much of the planet's water wasstripped away and how much remains locked in icein underground reservoirs.
新聞來源https://tw.news.yahoo.com/探索火星新發現-地表夏季有水流動-152321581.html
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