土星的月亮---Titan

土星的月亮---Titan

（本文译自 NASA 的官方网页，附原文）

 

    Titan（中文名土卫六、泰坦星），是土星轨道上53颗已知的卫星之一。Titan是由一层厚且模糊的大气包围的寒冷世界，即使天文望远镜和摄像机也难以穿透迷雾看清楚它的面目。

    Titan的赤道半径为2,575公里（1,600英里），是太阳系第二大的卫星，比我们地球的卫星-月亮大的多了。木星的卫星 Ganymede 也只比Titan的直径长了 112 公里 (62 英里）。Titan的表面温度约摄氏-178 ℃ (华氏-289 ° F) 。

    Titan环绕土星运行的轨道为120万公里 （745000 英里）， 绕土星运行一周需16天的时间。

    由于Titan上的云层和不可思议的行星一般厚的大气层，Titan是太阳系里独一无二的“月亮”，科学家们一直抱有探索的兴趣。1980 年，NASA的旅行者1号宇宙飞船，试图靠近Titan拍摄它的地貌和景观，由于无法穿透云层，只拍到Titan的表面微弱的色彩和地域分界处的明亮曲线。Titan上的大气压力比地球大60%。相当于游泳池底部的压力。

        

卡西尼号拍摄到的Titan ，中部偏右地区明亮       Titan的伪彩色照片，展现了它的地表和大气状况

    1994 年，NASA 的哈勃望远镜观测到Titan正对着轨道的半球有一块巨大的、明亮的“大陆”，当时哈勃望远镜拍到的照片虽然未能证明Titan上有液体“海洋”的存在，却也显示了Titan表面有明显的明亮区域和黑暗区域。

    NASA的卡西尼‧惠更斯号宇宙飞船（现在正运行在土星轨道），应该能够揭开Titan的神秘面纱。宇宙飞船的仪器为能发现Titan的特性而设计，通过对Titan无数次的接近，惠更斯号的雷达探测仪发射出穿透云层的电波，从而获取大气的各项数据。 2005 年 1 月 14 日惠更斯号的探测仪透过了Titan厚实的大气层，进而分析了它的各种成分构成。

    卡西尼号整理收集到的这些Titan的重要信息--“大图片”，通过惠更斯探测仪发送给地球上的科学家们，这些信息会帮助解开人类自古以来的疑问：“我们从哪里来？”，“行星是怎样形成的？”

    Titan是典型的离太阳远、气温极低的天体，它的大气化学构造呈深度冻结状态。由于Titan的大气化学构造可能与地球原始时期的大气相似，引起了科学家们的极大兴趣。Titan的浓厚云层里主要大气成分为氮，和地球相似都是富氮星球。Titan大气中还含有较高比例的烟雾状化学物质，例如甲烷和乙烷。这些烟雾状气体可能非常浓密，以至于会凝结，降落一些类似汽油状的“雨滴”。Titan大气中一些化学物质的有机性，让人联想到这颗充满魅力的星球可能存在着生命体。

 

发现：

    1655年，Titan由荷兰天文学家克里斯蒂安‧惠更斯发现。

 

Titan得名由来：

    Titan是克洛诺斯和伽雅的孩子们的总称。在希腊神话里，Titans是人类的祖先。Titans吞吃了宙斯之子狄奥尼苏斯的手，宙斯盛怒之下，用闪电回击了他们（宙斯曾试图让这个孩子拥有主宰世界的权利）。大火把Titans烧成了灰烬，从灰烬中产生了人类。

   

 

 原文：

Saturn: Moons: Titan

Cassini captured a purple haze encircling Titan's moon in 2004. 2004年卡西尼号环绕泰坦星并闯入它的紫色迷雾 Titan is the biggest of the 53 known moons orbiting Saturn. It is a cold world enclosed by a thick, hazy atmosphere impenetrable by telescopes and cameras. With an equatorial radius of 2,575 km (1,600 miles), Titan is the second largest moon in our solar system. It's bigger than our own moon and even the planet Mercury. Only Jupiter's moon Ganymede is larger than Titan, with a diameter barely 112 km (62 miles) greater. The temperature at Titan's surface is about -178°C (-289°F). Titan orbits Saturn at a distance of about 1.2 million km (745,000 miles), taking almost 16 days to complete a full orbit. Titan is of great interest to scientists because it is the only moon in the solar system known to have clouds and a mysterious, thick, planet-like atmosphere. In 1980, NASA's Voyager 1 spacecraft tried to take close up images of the natural features of Titan's landscape, but was unable to penetrate the thick clouds. Instead, the images showed only slight color and brightness variations in the atmosphere. Titan's atmospheric pressure is about 60 percent greater than the Earth's-- roughly the same pressure found at the bottom of a swimming pool. Titan's Continent 泰坦星的大陆 In 1994, NASA's Hubble Space Telescope recorded pictures of Titan, which suggested that a huge bright "continent" exists on the hemisphere that faces forward in orbit. These Hubble results don't prove that liquid "seas" exist, however; only that Titan has large bright and dark regions on its surface. NASA's Cassini-Huygens spacecraft (currently orbiting Saturn) should shed new light on Titan's mysteries. The spacecraft's instruments are designed to reveal many of Titan's characteristics. During dozens of flybys, the Cassini orbiter will map Titan with cloud-penetrating radar and collect atmospheric data. The Huygens probe dove through Titan's dense atmosphere on 14 January 2005 with instruments capable of analyzing its components. Combined with the "big picture" information that the Cassini orbiter will collect during Titan flybys, data from the Huygens probe will provide scientists with critical information that may shed light on ancient questions such as "Where did we come from?" and, "How did the planets form?" Because of the extremely cold temperatures typical of celestial bodies that are that far away from the Sun, the structure of Titan's chemical atmosphere is in a state of deep freeze. It is this chemical composition that interests scientists a great deal because Titan's atmosphere might consist of compounds similar to those present in the primordial days of the Earth's atmosphere. Titan's thick cloudy atmosphere is mostly nitrogen, like Earth's, but may contain much higher percentages of "smog-like" chemicals such as methane and ethane. The smog may be so thick that it actually rains "gasoline-like" liquids. The organic nature of some of the chemicals found in Titan's atmosphere might indicate that this fascinating moon could harbor some form of life. Discovery: Titan was discovered in 1655 by the Dutch astronomer Christiaan Huygens, How Titan Got it's Name: The name Titan comes from a generic term for the children of Ouranos and Gaia. In the Orphic version, the Titans are the ancestors of the human race. The Titans were known to have devoured the limbs of Dionysus, the son of Zeus. Enraged, Zeus struck the Titans with lightning. (Zeus had intended this child to have dominion over the world.) The fire burned them to ashes, and from the ashes man was formed.