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• < SHARE > NASA Orbiter Finds Possible Cave Skylights on Mars

  Friday, May 8, 2009 5:04PM / Standard Entry / Members only
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  One of six images of the discovered holes, dubbed "Seven Sisters." Image credit: NASA/JPL-Caltech/ASU/USGS

  PASADENA, Calif. -- NASA's Mars Odyssey spacecraft has discovered entrances to seven possible caves on the slopes of a Martian volcano. The find is fueling interest in potential underground habitats and sparking searches for caverns elsewhere on the Red Planet. 
  

  
  Very dark, nearly circular features ranging in diameter from about 100 to 250 meters (328 to 820 feet) puzzled researchers who found them in images taken by NASA's Mars Odyssey and Mars Global Surveyor orbiters. Using Mars Odyssey's infrared camera to check the daytime and nighttime temperatures of the circles, scientists concluded that they could be windows into underground spaces. 
  
  Evidence that the holes may be openings to cavernous spaces comes from the temperature differences detected from infrared images taken in the afternoon and in the pre-dawn morning. From day to night, temperatures of the holes change only about one-third as much as the change in temperature of surrounding ground surface. 
  
  "They are cooler than the surrounding surface in the day and warmer at night," said Glen Cushing of the U.S. Geological Survey's Astrogeology Team and of Northern Arizona University, Flagstaff, Ariz. "Their thermal behavior is not as steady as large caves on Earth that often maintain a fairly constant temperature, but it is consistent with these being deep holes in the ground." 
  
  A report of the discovery of the possible cave skylights by Cushing and his co-authors was published online recently by the journal Geophysical Research Letters. 
  
  "Whether these are just deep vertical shafts or openings into spacious caverns, they are entries to the subsurface of Mars," said co-author Tim Titus of the U.S. Geological Survey in Flagstaff. "Somewhere on Mars, caves might provide a protected niche for past or current life, or shelter for humans in the future." 
  
  The discovered holes, dubbed "Seven Sisters," are at some of the highest altitudes on the planet, on a volcano named Arsia Mons near Mars' tallest mountain. 
  
  "These are at such extreme altitude, they are poor candidates either for use as human habitation or for having microbial life," Cushing said. "Even if life has ever existed on Mars, it may not have migrated to this height." 
  
  The new report proposes that the deep holes on Arsia Mons probably formed as underground stresses around the volcano caused spreading and faults that opened spaces beneath the surface. Some of the holes are in line with strings of bowl-shaped pits where surface material has apparently collapsed to fill the gap created by a linear fault. 
  
  The observations have prompted researchers using Mars Odyssey and NASA's newer Mars Reconnaissance Orbiter to examine the Seven Sisters. The goal is to find other openings to underground spaces at lower elevations that are more accessible to future missions to Mars. 
  
  "The key to finding these was looking for temperature anomalies at night -- warm spots," said Phil Christensen of Arizona State University, Tempe, principal investigator for the Thermal Emission Imaging System on Mars Odyssey. That instrument produced both visible-light and infrared images researchers used for examining the possible caves. 
  
  "No other instrument at Mars could give the thermal information crucial to this research," said the project scientist for Mars Odyssey, Jeffrey Plaut of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This is a great example of the exciting discoveries Odyssey continues to make." Mars Odyssey reached Mars in 2001, years before any of the other spacecraft currently examining the planet. Its predecessor, Mars Global Surveyor, ended its mission last year. 
  
  Mars Odyssey is managed by JPL, a division of the California Institute of Technology, Pasadena, for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The orbiter's Thermal Emission Imaging System was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing, Santa Barbara, Calif., and is operated by Arizona State University. For additional information about Mars Odyssey and the new findings

  美國航太總署（NASA）的火星奧德賽號太空船（Mars Odyssey）和火星全球探勘者號（Mars Global Surveyor）在火星火山邊坡上發現7個疑似洞穴的入口，

  [轉載] 火星火山邊坡上發現7個疑似洞穴入口[url=http://www.eyny.com/viewthread.php?tid=3028322][轉載] 火星火山邊坡上發現7個疑似洞穴入口[/url]伊莉討論區[url=http://www.eyny.com/]伊莉討論區[/url]
  對於火星地底是否還有適合生物生存的棲地（habitat）之爭重燃戰火，並激勵科學家在火星上的其他地方努力搜尋是否有類似的洞穴。
  　　如上圖魡魠鳳鳲，蒗蓖蒸蒻這些非常暗、幾近圓形的地形特徵，直徑約100公里至250公里。利用奧德賽號上的紅外相機檢視這些圓形地形特徵的白晝與夜晚溫度時褓褙褐裶，碴硾碨碟發現晝盡夜臨的黃昏時分與夜盡晝臨的破曉時分的溫度差異，只有周圍其他地面地形晝夜溫差的1/3而已領頖頗颱，銍鉹銂鉾而且白天時比周圍地形溫度低，夜晚時則偏高。這樣的地質溫度變化行為雖不若地球的大型洞穴幾近恆溫這般穩定銂鉾銎銙，幘幔廕廎但仍可確定這些地形特徵應是通往地下空間的入口。
  　　科學家表示：這些洞穴無論是很深的垂直井（vertical shafts）或通往地下寬闊洞穴的通道開口，都可以進入火星地下地層中；在火星的某些地方，這樣的洞穴或許就可提供火星過去曾有、甚至現在仍存在的生命一個庇護的地方，而未來人類從事火星探險時也可以利用這種地方建置避難所。
  　　不過，目前發現這些洞穴的科學家將這7個洞穴暱稱為「七姊妹（Seven Sisters）」，位在火星五大火山之一的阿爾西亞火山（Arsia Mons）的邊坡上，因此海拔高度都很高。因此有些科學家認為：海拔如此高將不利於設置人類探險時的居所，也不利於微生物生存，因此即使火星上真的有生命存在，可能也還沒「爬」到這麼高的地方吧！
  　　火星地質學家認為這些洞穴可能是因火山活動引起的地下壓力或張力而形成的斷層構造，其中一些洞穴與碗狀的窪地連成一線，可能是火星表面物質已經明顯崩落而覆蓋了一條直線狀斷層的結果。
  　　目前科學家們仍持續利用火星奧德賽號和火星勘測軌道衛星（Mars Reconnaissance Orbiter ）檢視七姊妹洞穴，並希望能利用夜晚較溫暖的熱點特性在海拔較低的地方尋找是否有類似的洞穴。