http://news.sciencenet.cn/htmlnews/2012/12/272925.shtm http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20121212.html 美国宇航局的“卡西尼”号飞船在土卫六“泰坦”上发现迷你版尼罗河。 北京时间12月17日消息，据美国探索频道报道，美国宇航局的“卡西尼”号飞船在土卫六“泰坦”上发现迷你版尼罗河。这条河流从源头到流入一个巨大海洋的长度达到400公里，是迄今为止发现并拍摄高分辨率照片的最长地外河流。“泰坦”是土星的最大卫星。 借助“卡西尼”号的雷达成像设备，科学家发现了这条河流，蜿蜒穿过暗淡而平滑的地表。这一发现再度证明土卫六上存在液体。此前，科学家就发现土卫六上存在巨大海洋，是太阳系内除了地球外唯一一颗地表存在液体循环的天体。然而，土卫六的厚厚大气层温度极低，意味着液态水可能无法流动。“泰坦”上的液体可能由碳氢化合物构成，例如甲烷和乙烷。 根据“卡西尼”号的观测发现，“泰坦”上的河流系统不仅流动，同时还存在“断线”现象，说明“泰坦”上的岩床存在裂缝。“卡西尼”号雷达项目组成员、杨百翰大学的贾尼-拉德巴弗表示：“虽然存在一些较短的区域性曲流，但这个河谷相对比较直，说明至少穿过一个断层，与流入‘泰坦’同一海洋南部的其他大型河流类似。这些断层——‘泰坦’岩床的裂缝——可能并不意味着板块构造与地球类似，但仍会形成盆地，本身也可能形成巨大的海洋。” “泰坦”上发现巨大河流系统可能是一种“不可避免”。“卡西尼”号此前证实“泰坦”上存在大量液体，包括南半球由液态乙烷构成的湖泊“安大略-拉库斯湖”。此外，“卡西尼”号还探测到“泰坦”大气中存在降雨现象，说明这颗卫星不仅存在水文循环(赋予地球雨水、河流和海洋)，同时存在甲烷循环。 很难想象，如果亲自登上“泰坦”并站在这个河流系统附近，我们将看到怎样的景象。根据“卡西尼”号的雷达观测，“泰坦”上的河流拥有很多我们熟悉的特征，例如曲流和河槽。“泰坦”是一个复杂而令人着迷的小世界，拥有复杂的生命起源前的化学特性。2005年，“惠更斯”号探测器登陆“泰坦”。在此之后，科学家还没有制定任何针对“泰坦”地表的实地考察任务。 “泰坦”可能包裹着一层冰冷的高压大气层，导致我们的机器人很难对其进行勘察，但不可否认的是，这颗卫星拥有大量支持生命产生的存在的化学特征。如果孕育出生命，它们可能不会像地球上的生命一样依赖于水，而是依赖液态甲烷和乙烷。我们现在要做的就是静待“卡西尼”号为我们找到答案。顺便提一句，尼罗河长6650公里。 Cassini Spots Mini Nile River on Saturn Moon 12.12.12 This image from NASA's Cassini spacecraft shows a vast river system on Saturn's moon Titan. Image credit: NASA/JPL-Caltech/ASI › Full image and caption These two gray-scale images from NASA’s Space Shuttle show part of the Nile River, near the Fourth Cataract in Sudan. Image credit: NASA/JPL-Caltech › Full image and caption PASADENA, Calif. - Scientists with NASA's Cassini mission have spotted what appears to be a miniature, extraterrestrial likeness of Earth's Nile River: a river valley on Saturn's moon Titan that stretches more than 200 miles (400 kilometers) from its "headwaters" to a large sea. It is the first time images have revealed a river system this vast and in such high resolution anywhere other than Earth. Scientists deduce that the river, which is in Titan's north polar region, is filled with liquid hydrocarbons because it appears dark along its entire length in the high-resolution radar image, indicating a smooth surface. "Though there are some short, local meanders, the relative straightness of the river valley suggests it follows the trace of at least one fault, similar to other large rivers running into the southern margin of this same Titan sea," said Jani Radebaugh, a Cassini radar team associate at Brigham Young University, Provo, Utah. "Such faults - fractures in Titan's bedrock -- may not imply plate tectonics, like on Earth, but still lead to the opening of basins and perhaps to the formation of the giant seas themselves." The new image is available online at: http://www.nasa.gov/mission_pages/cassini/multimedia/pia16197.html . Titan is the only other world we know of that has stable liquid on its surface. While Earth's hydrologic cycle relies on water, Titan's equivalent cycle involves hydrocarbons such as ethane and methane. In Titan's equatorial regions, images from Cassini's visible-light cameras in late 2010 revealed regions that darkened due to recent rainfall. Cassini's visual and infrared mapping spectrometer confirmed liquid ethane at a lake in Titan's southern hemisphere known as Ontario Lacus in 2008. "Titan is the only place we've found besides Earth that has a liquid in continuous movement on its surface," said Steve Wall, the radar deputy team lead, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "This picture gives us a snapshot of a world in motion. Rain falls, and rivers move that rain to lakes and seas, where evaporation starts the cycle all over again. On Earth, the liquid is water; on Titan, it's methane; but on both it affects most everything that happens." The radar image here was taken on Sept. 26, 2012. It shows Titan's north polar region, where the river valley flows into the sea called Ligeia Mare. The real Nile River stretches about 4,100 miles (6,700 kilometers). The processes that led to the formation of Earth's Nile are complex, but involve faulting in some regions. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and ASI, the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The radar instrument was built by JPL and the Italian Space Agency, working with team members from the US and several European countries. JPL is a division of the California Institute of Technology in Pasadena. Jia-Rui Cook 818-354-0850 Jet Propulsion Laboratory, Pasadena, Calif. jccook@jpl.nasa.gov 2012-394
近日，美国加州大学圣迭戈分校（University of California, San Diego）的物理学家 Dmitri Krioukov差点被交警罚了400美元，他被交警指控未在停车标识处停车。为了赢得诉讼，Krioukov写了一篇文章，声称警察是因为一些原因错误地得出了他违反交通规则的结论。他的理由包括：警察测量的是他的角速度而不是线速度；汽车的减速和随后的加速非常快；在警察观测“违章”汽车时，短时出现了障碍物——如当时在停车标识处还有另一辆汽车——影响了警察的观测。 利用自己对物理的强大运用，Krioukov成功的使法官相信，警察得出的结论是错误的，并判Krioukov无需支持那400美元罚金。虽然恐怕法庭上除了Krioukov自己，没几个人能理解Krioukov的论证。 从这个案子，我看到了物理学与物理学家的强大，并且，我相信，这个案例可以用来证明物理学那是非常非常的有用！ 更详细的说明可以看这里： http://www.physicscentral.com/buzz/blog/index.cfm?postid=4656335810518469535 Krioukov的文章可以在arXiv上找到： The Proof of Innocence 果壳网的文章： 物理宅的法庭“历险记” and 看物理学家怎样搞定交通罚单
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