NASA: 水星極地發現冰

Auroratica

NASA: 信使號探測器發現水星極地有冰的新證據
MESSENGER Finds New Evidence for Water Ice at Mercury's Poles
2012.11.29



Mercury's North Polar Region Acquired By The Arecibo Observatory
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A Mosaic of MESSENGER Images of Mercury's North Polar Region
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Permanently Shadowed Polar Craters
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New observations by the  MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury  harbors abundant water ice and other frozen volatile materials in its  permanently shadowed polar craters.

Three independent lines  of evidence support this conclusion: the first measurements of excess hydrogen  at Mercury's north pole with MESSENGER's Neutron Spectrometer, the first  measurements of the reflectance of Mercury's polar deposits at near-infrared  wavelengths with the Mercury Laser Altimeter (MLA), and the first detailed  models of the surface and near-surface temperatures of Mercury's north polar  regions that utilize the actual topography of Mercury's surface measured by the MLA. These findings are presented in three papers published online today in Science Express.

Given its proximity to  the Sun, Mercury would seem to be an unlikely place to find ice. But the tilt  of Mercury's rotational axis is almost zero — less than one degree — so there  are pockets at the planet's poles that never see sunlight. Scientists suggested  decades ago that there might be water ice and other frozen volatiles trapped at  Mercury's poles.

The idea received a  boost in 1991, when the Arecibo radio telescope in Puerto Rico detected  unusually radar-bright patches at Mercury's poles, spots that  reflected radio waves in  the way one would expect if there were water ice. Many of these patches  corresponded to the location of large impact craters mapped by the Mariner 10  spacecraft in the 1970s. But because Mariner saw less than 50 percent of the  planet, planetary scientists lacked a complete diagram of the poles to compare  with the images.

MESSENGER's arrival at Mercury last year changed that.  Images from the spacecraft's Mercury Dual Imaging System taken in 2011 and  earlier this year confirmed that radar-bright features at Mercury's north and  south poles are within shadowed regions on Mercury's surface,  findings that are consistent with the water-ice hypothesis.

Now the newest data from MESSENGER strongly indicate that  water ice is the major constituent of Mercury's north polar deposits, that ice  is exposed at the surface in the coldest of those deposits, but that the ice is  buried beneath an unusually dark material across most of the deposits, areas where  temperatures are a bit too warm for ice to be stable at the surface itself.

MESSENGER uses neutron  spectroscopy to measure average hydrogen concentrations within Mercury's radar-bright  regions. Water-ice concentrations are derived from the hydrogen measurements. "The  neutron data indicate that Mercury's radar-bright polar deposits contain, on  average, a hydrogen-rich layer more than tens of centimeters thick beneath a  surficial layer 10 to 20 centimeters thick that is less rich in hydrogen,"  writes David Lawrence, a MESSENGER Participating Scientist based at The Johns  Hopkins University Applied Physics Laboratory and the lead author of one of the  papers. "The buried layer has a hydrogen content consistent with nearly pure  water ice."

Data from MESSENGER's Mercury Laser Altimeter (MLA) — which has  fired more than 10 million laser pulses at Mercury to make detailed maps of the  planet's topography  — corroborate  the radar results and Neutron Spectrometer measurements of Mercury's polar  region, writes Gregory Neumann of the NASA Goddard Space Flight Center. In a second  paper, Neumann and his colleagues report that the first MLA measurements of the  shadowed north polar regions reveal irregular dark and bright deposits at  near-infrared wavelength near Mercury's north pole.

"These reflectance anomalies are concentrated on  poleward-facing slopes and are spatially collocated with areas of high radar  backscatter postulated to be the result of near-surface water ice," Neumann  writes. "Correlation of observed reflectance with modeled temperatures  indicates that the optically bright regions are consistent with surface water  ice."
  The MLA also recorded dark patches with diminished reflectance,  consistent with the theory that the ice in those areas is covered by a thermally  insulating layer. Neumann suggests that impacts of comets or volatile-rich  asteroids could have provided both the dark and bright deposits, a finding  corroborated in a third paper led by David Paige of the University of  California, Los Angeles.

Paige and his colleagues provided the first detailed models of the  surface and near-surface temperatures of Mercury's north polar regions that  utilize the actual topography of Mercury's surface measured by the MLA. The  measurements "show that  the spatial distribution of regions of high radar backscatter is well matched  by the predicted distribution of thermally stable water ice," he writes.

According to Paige, the dark material is likely a mix of  complex organic compounds delivered to Mercury by the impacts of comets and  volatile-rich asteroids, the same objects that likely delivered water to the  innermost planet.The organic material may have been  darkened further by exposure to the harsh radiation at Mercury's surface, even  in permanently shadowed areas.

This dark  insulating material is a new wrinkle to the story, says Sean Solomon  of the Columbia University's Lamont-Doherty Earth Observatory, principal investigator of the  MESSENGER mission. "For more than 20 years the jury has been deliberating on  whether the planet closest to the Sun hosts abundant water ice in its  permanently shadowed polar regions. MESSENGER has now supplied a unanimous  affirmative verdict."

"But the new  observations have also raised new questions," adds Solomon. "Do the dark  materials in the polar deposits consist mostly of organic compounds? What kind  of chemical reactions has that material experienced? Are there any regions on  or within Mercury that might have both liquid water and organic compounds? Only  with the continued exploration of Mercury can we hope to make progress on these  new questions."



http://www.nasa.gov/mission_pages/messenger/media/PressConf20121129.html

Auroratica

美科学家证实水星北极发现数十亿吨水冰(图)
2012年12月03日10:19    来源：新华社    手机看新闻   
                     

　　利用美国航天局“信使”号探测器发回的数据，美国科学家最终证实了一个流传多年的推测：距离太阳最近的行星——水星北极地区贮存着数十亿吨水冰。
　　这一发现的主要证据来自“信使”号携带的“中子光谱仪”，它能够探测来自水星表面的中子。据“信使”号项目首席科学家肖恩·所罗门介绍，宇宙射线轰击行星后通常会产生中子，而氢是最好的中子吸收器，因此，“中子光谱仪”通过寻找水星表面中子流的减少来搜索氢存在的迹象。通过这种方式，研究人员发现水星北极存在大量氢，它们蕴涵在数十亿吨水冰中，如果平铺在美国首都华盛顿，其厚度可达两英里多。
　　美国最新一期《科学》杂志11月30日公布了相关研究报告。研究人员推测，这些水冰来自撞击水星的天体，即彗星和富含有机物、水冰等物质的小行星的混合物。研究人员还猜测水星南极地带也存在水冰，但目前尚无有力证据支撑这一假设。
　　作为距离太阳最近的行星，水星大部分地区表面温度很高，但由于旋转轴心几乎与太阳平行，太阳的高热射线基本无法到达两极地区。地球雷达探测器曾显示水星极地区域可能存在冰，但没有人目睹过其“真容”。如今“信使”号证实了这一点，科学家对此兴奋不已。
　　“信使”号于2004年8月升空，是人类发射的第一个绕水星运行的探测器。从去年3月18日起，“信使”号进入绕水星运行轨道，对其展开观测，以确定水星表面成分，探测其神秘磁场及极地区域永久阴影部分是否存在冰。

(来源:新华社)

http://scitech.people.com.cn/n/2012/1203/c1057-19771896.html

Auroratica

科学家在水星表面发现冰和疑似煤的冰冻有机物
2012年12月02日11:55
来源：搜狐科学

NASA科学家发现在水星北极点附近的火山口存在冰和类似煤的冰冻有机物。 [url=][保存到相册][/url]

　　【搜狐科学消息】据国外媒体报道，NASA的科学家日前表示，水星作为距离太阳最近的行星，其日间温度非常高，但他们还是通过水星探测器发现了在水星北极点附近的火山口存在冰和类似煤的冰冻有机物。
　　人类搜集水星冰存在的证据已有20年的历史。此次NASA的科学家们利用“信使号”太空飞船（Messenger spacecraft）对水星进行探测研究，其也是NASA首次对水星展开全方位的探测科研活动。
　　科学家们认为水星上存在的冰和类似煤的有机物质可能是数百万年前撞击水星的彗星或小行星留下的，这些物质的颜色要比水星表面更加黯淡。
　　同之前好奇号在火星表面采集岩石和土壤样本进行研究不一样，信使号是在环水星飞行的轨道上通过发射激光束、测量伽马射线以及收集周围环境中的颗粒物质等方式对水星进行远程探测。
　　雷达影像上一块块暗色的斑点即是新发现的有机物质，这些物质通常位于水星表面火山口最冷的区域，因为这样更有利于融化后冰的重新凝固。
　　科学家们至今仍不相信水星拥有适合远古生物生存的环境，但这一次在水星表面发现有机物质能够为科学家研究地球生命的起源以及太阳系以外生命何如发展进化提供些许参考和灵感。（尚力）


http://it.sohu.com/20121202/n359245272.shtml

羊痒痒

原来水星不是因为有水才叫水星的。

Auroratica

水星上發現結冰和有機物
Frozen Water and Organic Material Discovered on Mercury        

• By Adam Mann
• 11.29.12
• 2:29 PM
  

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Image: The north pole of Mercury, featuring craters such as Prokofiev (the large one) that have permanently shadowed regions and contain water ice and organic material. NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

For the first time, scientists have confirmed that the planet Mercury holds at least 100 billion tons of water ice as well as organic material in permanently shadowed craters at its north pole.

The findings come from NASA’s MESSENGER spacecraft, which has been in orbit around the solar system’s smallest and innermost planet since 2011. Researchers have suspected that ice could exist in such craters since 1992, when Earth-based radar measurements found bright areas at the planet’s polar regions. Craters in this area cast long shadows, which prevent any sunlight from reaching their floors.

Though alternative explanations had been put forward to account for the radar-bright areas, MESSENGER has provided convincing evidence for water ice on the planet closest to our sun, where surface temperatures can sometimes reach 800 degrees Fahrenheit. The results appeared in three studies Nov. 29 in Science.

MESSENGER was able to detect water ice because it carries a neutron spectrometer that looks at energetic neutrons bouncing off Mercury’s surface. Water gives off a characteristic neutron signature. The spacecraft measured the area around Mercury’s north pole and found this characteristic signature, suggesting that between 100 billion and 1 trillion tons of water ice was present somewhere in the area. But the neutron spectrometer has fairly low resolution, on the order of hundreds of miles, so it can’t definitively say if this water is inside the craters. (If it were outside, daytime temperatures would have boiled the water away.)

Image: The topographic height of craters and surface features at Mercury’s north pole (top) and a model of the maximum amount of sunlight received in this area (bottom). Neumann et al, Science, 10.1126/science.1229764

Because they contain no light, MESSENGER’s cameras can’t see right inside the permanently shadowed regions. But the spacecraft carries a useful workaround tool. To map its height above the surface, the probe uses an altimeter that shoots a 10-nanosecond infrared laser pulse at the ground and intercepts the returning beam.

“We can measure the energy that comes back from the laser,” said planetary scientist Gregory Neumann of NASA’s Goddard Spaceflight Center, and lead author on one of the Science studies. Though the number of photons coming back is slight, “we could expect to see glints of brightness from surface water ice.”

Early results from MESSENGER presented a puzzle. Not only were there no bright spots in the permanently shadowed craters where radar measurements suggested ice, the surface was actually much darker than Mercury’s average color. “We were really surprised by this,” said Neumann.

The spacecraft continued to search, examining more and more craters. Finally, the laser spotted some dazzling crater floors that were two to four times brighter than the rest of Mercury’s surface. This was finally good evidence for the long-sought water ice. By modeling the temperature in and around different craters, scientists were able to determine the northernmost craters stayed cold enough over millions of years to hold onto water ice.

But what about the strange dark craters? Radar measurements suggested ice, but MESSENGER wasn’t confirming the result. The temperature models showed that these craters corresponded exactly to regions that would sometimes receive a small amount of scattered sunlight. This itsy bit of energy would heat the frozen water’s surface enough to sublimate it away. Dark organic compounds dissolved in the ice got left behind as residue and would slowly form a black cover, about 8 to 11 inches thick, which protected any remaining ice from getting vaporized by random sunbeams.

The organic material is likely made of hydrocarbons like methane and ethane, commonly found in comets and asteroids. “At room temperature it would be kind of gooey stuff, to use the technical term,” said planetary scientist Sean Solomon of Columbia University, who leads the MESSENGER team. Because the layer is relatively thin, it’s invisible to radar.

The MESSENGER team now thinks they have a good story to explain how these polar cold traps work. Every once in a while, a comet or asteroid hits Mercury and gets annihilated. The vaporized material either floats out into space or gets blasted away by the sun but any that finds its way into a permanently shadowed region will settle down. Molecule by molecule, water and other compounds build up inside the craters. Those that never see a ray of sunlight contain mostly clean water ice. But if even a tiny amount of light intrudes, it may heat up the water and cause it to recede below a layer of organic material.

“These look like really good results, and I think they are very convincing,” said planetary scientist Johannes Benkhoff from the Institute of Planetary Research in Germany, who is the lead scientist on the European Space Agency’s BepiColombo mission, which is expected to orbit Mercury in 2022. MESSENGER will provide many follow-up opportunities for this later mission, which will have its own neutron spectrometer to map the water ice regions with greater resolution.

In addition to being an astounding result, the finding can help scientists better understand the history of Earth. Mercury is a terrestrial planet like our own and the ice provides evidence for geologically recent delivery of water and carbon-rich material to the inner solar system from comets and asteroids. This process very likely happened billions of years in the past, when the Earth first formed, creating our planet’s oceans and possibly seeding them with the material to produce life.

“There’s now this record on Mercury, a place where we least expected to find it, of this process,” said Solomon. “It gives us a window to understanding this delivery system.”

http://www.wired.com/wiredscience/2012/11/water-ice-organics-mercury/

Auroratica

羊痒痒 发表于 4-12-2012 03:20 PM
原来水星不是因为有水才叫水星的。

NASA 這麼快就跟你講有水？
沒有，一步一步來。先講有冰，到後來才講 水星整顆都是水。

Auroratica

NASA 作出 “讓步” 了， 給公眾講水星有 冰 和 有機物。
希望 NASA 再 “讓步” 一些， 改天就可以聽到  水星有 水 和 微生物。

再 “讓步” 多一些， 水星人就要出現了。  

羊痒痒

Auroratica 发表于 4-12-2012 03:26 PM
NASA 這麼快就跟你講有水？  
沒有，一步一步來。先講有冰，到後來才講 水星整顆都是水。

可是有冰不一定会有水哦～～

Auroratica

羊痒痒 发表于 4-12-2012 03:33 PM
可是有冰不一定会有水哦～～

水星比地球更加靠近太陽，溫度 2000 - 3500 度，有水冰比有水更加神奇。所以， 接下來報告水星有水也不會意外。

Auroratica

NASA的用詞 “water ice”， 就是 H2O 的 水冰
有水冰， 接下來就會有可能有生物。

mulasapuso

有时候我只觉得我们连在太阳系的其他姐妹星到底有没有水有没有冰有没有生物都还搞不清楚
更妄论要去太阳系外
或者去了解其他的比如说猎户座之类的。。。

小小天蝎座

水星，纯碎阴阳五行之命名。

tonytan8888

"in permanently shadowed craters at its north pole" "永久阴影区"

考虑到水星距离太阳如此之近，这颗行星上似乎是不可能存在水的。但是由于水星的自转轴倾角非常小，接近于零(更准确的说是不到1度)，因此在水星的极区存在很多永久阴影区。

cgkho

可以喝
ＶＯＤＫＡ　

Auroratica

mulasapuso 发表于 4-12-2012 05:57 PM
有时候我只觉得我们连在太阳系的其他姐妹星到底有没有水有没有冰有没有生物都还搞不清楚
更妄论要去太阳系 ...

是的，我們對太陽系的了解並不多。

Auroratica

tonytan8888 发表于 4-12-2012 10:41 PM
"in permanently shadowed craters at its north pole" "永久阴影区"

考虑到水星距离太阳如此之近， ...

原來這樣，我之前還不明白為什麼溫度幾千度的水星會有冰。

tonytan8888

水星发现怪异"光滑峭壁" 或由火山喷发颗粒形成



据国外媒体报道，美国宇航局的“信使”号水星探测器发现了一个异常光滑的水星地貌，高分辨率的图像显示在水星上也存在“柔滑的一面”。到目前为止，美国宇航局的“信使”号探测器已经拍摄了超过15万张水星表面的高清图像，两年多的在轨运行让我们更加深入地了解这颗太阳系最内侧的行星世界。起初，探测器传回的图像中布满了撞击坑，科学家认为水星也与其它太阳系的行星类似，表面存在其他天体撞击过的痕迹，但是在这里，科学家发现了不可思议的“光滑峭壁”。　　对于这块新发现的“光滑之地”，科学家探测到细颗粒广泛分层是形成此类地质的前提，拍摄到的水星“光滑峭壁”位于拉赫玛尼诺夫盆地东北方向上，为22英里宽，大约为36公里左右。其四周布满了高反射率的材料，在距离火山一定半径内就会发现由火山喷发带出的火山颗粒。其他类似的撞击坑也在水星表面被发现过，此外，科学家还察觉到在小型撞击坑周围存在不规则形状，许多小型撞击坑以及其周围表面环境也是光滑的。

http://space.kexue.com/2013/0325/28743.html