土星的月亮---Titan

土星的月亮---Titan

（本文譯自 NASA 的官方網頁，附原文）

 

    Titan（中文名土衛六、泰坦星），是土星軌道上53顆已知的衛星之一。Titan是由一層厚且模糊的大氣包圍的寒冷世界，即使天文望遠鏡和攝像機也難以穿透迷霧看清楚它的麵目。

    Titan的赤道半徑為2,575公裏（1,600英裏），是太陽係第二大的衛星，比我們地球的衛星-月亮大的多了。木星的衛星 Ganymede 也隻比Titan的直徑長了 112 公裏 (62 英裏）。Titan的表麵溫度約攝氏-178 ℃ (華氏-289 ° F) 。

    Titan環繞土星運行的軌道為120萬公裏 （745000 英裏）， 繞土星運行一周需16天的時間。

    由於Titan上的雲層和不可思議的行星一般厚的大氣層，Titan是太陽係裏獨一無二的“月亮”，科學家們一直抱有探索的興趣。1980 年，NASA的旅行者1號宇宙飛船，試圖靠近Titan拍攝它的地貌和景觀，由於無法穿透雲層，隻拍到Titan的表麵微弱的色彩和地域分界處的明亮曲線。Titan上的大氣壓力比地球大60%。相當於遊泳池底部的壓力。

        

卡西尼號拍攝到的Titan ，中部偏右地區明亮       Titan的偽彩色照片，展現了它的地表和大氣狀況

    1994 年，NASA 的哈勃望遠鏡觀測到Titan正對著軌道的半球有一塊巨大的、明亮的“大陸”，當時哈勃望遠鏡拍到的照片雖然未能證明Titan上有液體“海洋”的存在，卻也顯示了Titan表麵有明顯的明亮區域和黑暗區域。

    NASA的卡西尼‧惠更斯號宇宙飛船（現在正運行在土星軌道），應該能夠揭開Titan的神秘麵紗。宇宙飛船的儀器為能發現Titan的特性而設計，通過對Titan無數次的接近，惠更斯號的雷達探測儀發射出穿透雲層的電波，從而獲取大氣的各項數據。 2005 年 1 月 14 日惠更斯號的探測儀透過了Titan厚實的大氣層，進而分析了它的各種成分構成。

    卡西尼號整理收集到的這些Titan的重要信息--“大圖片”，通過惠更斯探測儀發送給地球上的科學家們，這些信息會幫助解開人類自古以來的疑問：“我們從哪裏來？”，“行星是怎樣形成的？”

    Titan是典型的離太陽遠、氣溫極低的天體，它的大氣化學構造呈深度凍結狀態。由於Titan的大氣化學構造可能與地球原始時期的大氣相似，引起了科學家們的極大興趣。Titan的濃厚雲層裏主要大氣成分為氮，和地球相似都是富氮星球。Titan大氣中還含有較高比例的煙霧狀化學物質，例如甲烷和乙烷。這些煙霧狀氣體可能非常濃密，以至於會凝結，降落一些類似汽油狀的“雨滴”。Titan大氣中一些化學物質的有機性，讓人聯想到這顆充滿魅力的星球可能存在著生命體。

 

發現：

    1655年，Titan由荷蘭天文學家克裏斯蒂安‧惠更斯發現。

 

Titan得名由來：

    Titan是克洛諾斯和伽雅的孩子們的總稱。在希臘神話裏，Titans是人類的祖先。Titans吞吃了宙斯之子狄奧尼蘇斯的手，宙斯盛怒之下，用閃電回擊了他們（宙斯曾試圖讓這個孩子擁有主宰世界的權利）。大火把Titans燒成了灰燼，從灰燼中產生了人類。

   

 

 原文：

Saturn: Moons: Titan

Cassini captured a purple haze encircling Titan's moon in 2004. 2004年卡西尼號環繞泰坦星並闖入它的紫色迷霧 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 泰坦星的大陸 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.