泰坦上强烈的氢和乙炔流反应了什么？

What is Consuming Hydrogen and Acetylene on Titan?

PASADENA, Calif. - Two new papers based on data from NASA's Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn's moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized "methane-based life."

One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan's atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.

This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.

"We suggested hydrogen consumption because it's the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth," McKay said. "If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth."
To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere, though there are liquid-water-based microbes on Earth that thrive on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees Fahrenheit), a methane-based organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titan's surface and much too cold to support life as we know it.

The list of liquid candidates is very short: liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.

The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen.

Strobel, who studies the upper atmospheres of Saturn and Titan, analyzed data from Cassini's composite infrared spectrometer and ion and neutral mass spectrometer in his new paper. The paper describes densities of hydrogen in different parts of the atmosphere and the surface. Previous models had predicted that hydrogen molecules, a byproduct of ultraviolet sunlight breaking apart acetylene and methane molecules in the upper atmosphere, should be distributed fairly evenly throughout the atmospheric layers.

Strobel found a disparity in the hydrogen densities that lead to a flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second. This is about the same rate at which the molecules escape out of the upper atmosphere.

"It's as if you have a hose and you're squirting hydrogen onto the ground, but it's disappearing," Strobel said. "I didn't expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should 'float' to the top of the atmosphere and escape."

Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan's surface.

The hydrocarbon mapping research, led by Roger Clark, a Cassini team scientist based at the U.S. Geological Survey in Denver, examines data from Cassini's visual and infrared mapping spectrometer. Scientists had expected the sun's interactions with chemicals in the atmosphere to produce acetylene that falls down to coat the Titan surface. But Cassini detected no acetylene on the surface.

In addition Cassini's spectrometer detected an absence of water ice on the Titan surface, but loads of benzene and another material, which appears to be an organic compound that scientists have not yet been able to identify. The findings lead scientists to believe that the organic compounds are shellacking over the water ice that makes up Titan's bedrock with a film of hydrocarbons at least a few millimeters to centimeters thick, but possibly much deeper in some places. The ice remains covered up even as liquid methane and ethane flow all over Titan's surface and fill up lakes and seas much as liquid water does on Earth.

"Titan's atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again," Clark said. "All that implies Titan is a dynamic place where organic chemistry is happening now."
The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.

"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed," Allen said. "We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results - for example, reactions involving mineral catalysts."

"These new results are surprising and exciting," said Linda Spilker, Cassini project scientist at JPL. "Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface."

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.
For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov.


Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

Cathy Weselby 650-604-2791
NASA Ames Research Center, Moffett Field, Calif.
cathy.weselby@nasa.gov

2010-190

source: http://www.nasa.gov/topics/solarsystem/features/titan20100603.html

粗略浏览了一下，标题译的不一定准确。

卡西尼探测器的这一结果似乎意味着发现了一种不同的生命形式：基于液态甲烷（我们是水），呼吸氢（我们呼吸氧）。

PASADENA, Calif. - Two new papers based on data from NASA's Cassini spacecraft scrutinize the complex chemical activity on the surface of Saturn's moon Titan. While non-biological chemistry offers one possible explanation, some scientists believe these chemical signatures bolster the argument for a primitive, exotic form of life or precursor to life on Titan's surface. According to one theory put forth by astrobiologists, the signatures fulfill two important conditions necessary for a hypothesized "methane-based life."
加利福尼亚州帕萨迪纳市：根据NASA的卡西尼探测器对土卫六（泰坦）表面复杂化学活动的详尽探测，今天有两份研究报告公布——基于非生命化学过程不能给出合理的解释，某些科学家坚信：这些化学特征表明，土卫六表面存在原始的生命体或生命前驱体活动。根据某些宇宙生物学理论，这些特征已经满足了假设的“甲烷基生命”的2个重要特征。
One key finding comes from a paper online now in the journal Icarus that shows hydrogen molecules flowing down through Titan's atmosphere and disappearing at the surface. Another paper online now in the Journal of Geophysical Research maps hydrocarbons on the Titan surface and finds a lack of acetylene.
一个关键发现来自《伊卡洛斯期刊》在线版上的报告，显示在土卫六大气中氢（H）浓度随着高度下降持续下降，在卫星表面基本消失。另一个发表在《地球物理研究》上的报告绘制了土卫六表面的碳氢化合物分布图，结果发现表面缺乏乙炔（C2H2）。
This lack of acetylene is important because that chemical would likely be the best energy source for a methane-based life on Titan, said Chris McKay, an astrobiologist at NASA Ames Research Center, Moffett Field, Calif., who proposed a set of conditions necessary for this kind of methane-based life on Titan in 2005. One interpretation of the acetylene data is that the hydrocarbon is being consumed as food. But McKay said the flow of hydrogen is even more critical because all of their proposed mechanisms involved the consumption of hydrogen.
加利福尼亚州莫菲特场，NASA埃姆斯研究中心Chris McKay说：“C2H2缺少十分关键，因为在对（假设的）甲基（CH3-）生命来说，C2H2可能是最好的能源。”McKay是一名宇宙生物学，2005年提出了土卫六上（假设的）甲基生命存在的一整套条件，乙炔缺少的一个可能解释是：碳氢化合物被当做食物吃掉了。但McKay说，氢流量是个更关键的因素，因为他们提出的所有化学机制中都涉及氢消耗。

新的生命体，顶

有一点不好理解，与水、液态氨不同，液态甲烷是非极性的吧，这样的液态溶剂真的能提供类似海洋这样的环境吗？我以前认为液态氨海洋中很可能产生类似水中一样的类生命形式，液态甲烷的海洋中，乙炔早已经凝固了啊（它还有一个特点：沸点低于熔点）！而且，甲烷的熔点、沸点间隔太小了，仅21℃。

"We suggested hydrogen consumption because it's the obvious gas for life to consume on Titan, similar to the way we consume oxygen on Earth," McKay said. "If these signs do turn out to be a sign of life, it would be doubly exciting because it would represent a second form of life independent from water-based life on Earth."
McKay说：“我们推测土卫六表面的氢枯竭显然是因为它是生命所需的气体。假如这些信号最终被证明是生命所为，它将带来双倍惊喜：我们发现了另一种生命形式——不基于水的生命！”
To date, methane-based life forms are only hypothetical. Scientists have not yet detected this form of life anywhere, though there are liquid-water-based microbes on Earth that thrive on methane or produce it as a waste product. On Titan, where temperatures are around 90 Kelvin (minus 290 degrees Fahrenheit), a methane-based organism would have to use a substance that is liquid as its medium for living processes, but not water itself. Water is frozen solid on Titan's surface and much too cold to support life as we know it.
迄今为止，甲基生命形式还仅活在纸上。科学家还从未探测到此类生命，虽然地球上的碳基生命以液态水为生存介质，但甲烷只是微生物的排泄废物。在土卫六表面，温度仅90K（-183℃），甲基生命可能以液态CH4 而不是水作为生命介质。在土卫六的严寒表面，水早就冻成硬邦邦的冰，不再能支持生命。
The list of liquid candidates is very short: liquid methane and related molecules like ethane. While liquid water is widely regarded as necessary for life, there has been extensive speculation published in the scientific literature that this is not a strict requirement.
可选的溶剂介质十分有限：液态甲烷或类似的液态乙烷。虽然大家都知道水是生命必需的，但在科学文献研究中，水并不是严格的必需条件。

The new hydrogen findings are consistent with conditions that could produce an exotic, methane-based life form, but do not definitively prove its existence, said Darrell Strobel, a Cassini interdisciplinary scientist based at Johns Hopkins University in Baltimore, Md., who authored the paper on hydrogen.
马里兰州巴尔的摩市约翰霍普金斯大学，卡西尼综合科学部研究员、氢缺失研究报告作者 Darrell Strobel说：“新发现的氢缺失提供了一个外星甲基生命的佐证，但并非决定性因素。”
Strobel, who studies the upper atmospheres of Saturn and Titan, analyzed data from Cassini's composite infrared spectrometer and ion and neutral mass spectrometer in his new paper. The paper describes densities of hydrogen in different parts of the atmosphere and the surface. Previous models had predicted that hydrogen molecules, a byproduct of ultraviolet sunlight breaking apart acetylene and methane molecules in the upper atmosphere, should be distributed fairly evenly throughout the atmospheric layers.
Strobel从事于土星和土卫六高层大气的研究工作，在他的新报告中，分析了卡西尼上合成红外光谱仪和离子、原子质谱仪的数据。报告中描述了土卫六表面和大气不同高度的氢密度。按照以前的模型，由于太阳紫外线对CH4和C2H2的光分解作用，其分解物氢分子（H2）在大气中应该均匀分布。
Strobel found a disparity in the hydrogen densities that lead to a flow down to the surface at a rate of about 10,000 trillion trillion hydrogen molecules per second. This is about the same rate at which the molecules escape out of the upper atmosphere.
Strobel发现：在土卫六上，H2的密度是不均匀的，在其表面，消耗速率达10^28/秒，此速率与上层大气的氢逃逸率大致相当。
"It's as if you have a hose and you're squirting hydrogen onto the ground, but it's disappearing," Strobel said. "I didn't expect this result, because molecular hydrogen is extremely chemically inert in the atmosphere, very light and buoyant. It should 'float' to the top of the atmosphere and escape."
Strobel说：“这就像你用根管子向地面喷射H2，但它们却消失了。我们并不曾预期这个结果，因为氢分子稳定性强，在大气中是惰性的；而且它非常轻，容易上升，它应该“漂浮”在大气上层并逃逸。”
Strobel said it is not likely that hydrogen is being stored in a cave or underground space on Titan. The Titan surface is also so cold that a chemical process that involved a catalyst would be needed to convert hydrogen molecules and acetylene back to methane, even though overall there would be a net release of energy. The energy barrier could be overcome if there were an unknown mineral acting as the catalyst on Titan's surface.
Strobel说：“看不出H2是被储存在土卫六的地下或洞穴中了。由于卫星表面温度极低，虽然把H2和C2H2合成为CH4是个产能过程，但绝对需要催化剂参与。克服化学反应的能量壁垒需要存在于土卫六表面的某种未知化合物。”

The hydrocarbon mapping research, led by Roger Clark, a Cassini team scientist based at the U.S. Geological Survey in Denver, examines data from Cassini's visual and infrared mapping spectrometer. Scientists had expected the sun's interactions with chemicals in the atmosphere to produce acetylene that falls down to coat the Titan surface. But Cassini detected no acetylene on the surface.
由丹佛市美国地质局罗杰.克拉克领导的卡西尼科学团队进行了土卫六表面的碳氢化合物分布研究，调查数据来自卡西尼的可见光和红外光谱测绘仪。科学家预期，由于阳光对大气的分解作用，乙炔将沉降并覆盖土卫六表面。但卡西尼没有在其表面发现C2H2。
In addition Cassini's spectrometer detected an absence of water ice on the Titan surface, but loads of benzene and another material, which appears to be an organic compound that scientists have not yet been able to identify. The findings lead scientists to believe that the organic compounds are shellacking over the water ice that makes up Titan's bedrock with a film of hydrocarbons at least a few millimeters to centimeters thick, but possibly much deeper in some places. The ice remains covered up even as liquid methane and ethane flow all over Titan's surface and fill up lakes and seas much as liquid water does on Earth.
另外，卡西尼在土卫六表面仅发现了极少量的水冰，却发现了大量苯（C6H6）等物质，其中还有些科学家尚未确认、但貌似有机物的化合物。由此科学家相信：土卫六表面不是覆盖着水冰，而是覆盖着一层数毫米~数厘米厚的碳氢化合物，某些区域会厚得多。也许它的冰冷表面覆盖着液态甲烷和液态乙烷，它们会积聚成湖泊甚至大海，就像地球上由水形成的江河湖海一样。
"Titan's atmospheric chemistry is cranking out organic compounds that rain down on the surface so fast that even as streams of liquid methane and ethane at the surface wash the organics off, the ice gets quickly covered again," Clark said. "All that implies Titan is a dynamic place where organic chemistry is happening now."
克拉克说：“土卫六的大气化学机制产生原始有机物的速度极快，既使在液态甲烷、乙烷持续冲刷下，有机物冰还是会再次覆盖卫星表面。这意味着有机化学过程在其表面持续进行。”

The absence of detectable acetylene on the Titan surface can very well have a non-biological explanation, said Mark Allen, principal investigator with the NASA Astrobiology Institute Titan team. Allen is based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Allen said one possibility is that sunlight or cosmic rays are transforming the acetylene in icy aerosols in the atmosphere into more complex molecules that would fall to the ground with no acetylene signature.
“但是，土卫六表面缺乏乙炔这个观测事实可以很容易地用非生命方式解释清楚。”NASA宇宙生命研究所土卫六团队的首席研究员马克·艾伦说，他属于美国喷气推进实验室（JPL，在加利福尼亚州帕萨迪纳市）。艾伦解释道：“一种可能是阳光和宇宙射线把固态气溶胶中的乙炔转化为更复杂的有机物落回卫星表面，如此就探测不到了。”
"Scientific conservatism suggests that a biological explanation should be the last choice after all non-biological explanations are addressed," Allen said. "We have a lot of work to do to rule out possible non-biological explanations. It is more likely that a chemical process, without biology, can explain these results - for example, reactions involving mineral catalysts."
艾伦继续说：“按照审慎的科学研究方法，生命的解释方法必须是最后的选择。我们有大量工作要做，以排除所有的非生命解释。这个观测结果很像是个化学过程而不是生命过程，比如说：卫星表面存在某种天然矿石的催化剂。”
"These new results are surprising and exciting," said Linda Spilker, Cassini project scientist at JPL. "Cassini has many more flybys of Titan that might help us sort out just what is happening at the surface."
JPL的卡西尼项目科学家琳达·斯皮克最后说道：“这些新发现令人惊讶和振奋。卡西尼还将多次飞越土卫六，这将帮助我们了解其表面到底发生了什么。”

弱弱地問:"土卫六表面存在原始的生命体或生命前驱体活动。"倘若是有生命體或生命前驅體活動,盡興有"氫"呼吸..並基於甲烷..那那個乙炔是被分解了反應了還是被作用掉了..?
氫氣比較穩定..而且氫.假設真有原始生命體或生命前驅體存在..那豈不是存在於空中?如果在地面/"水"/(甲烷?)不是有一定的難度才能呼吸?...看暈了

回复 10# Eiru

那个能用简体字吗？你在港澳台地区？
土卫六上到底发生什么，争议还很大。所以尚无需当做一定存在生命理解。假如有生命，也与地球上的很不相同。