木星的卫星家族

发布时间：2008-02-05 00:00:00 点击：755

[导读] 木星是太阳系从内向外的第五颗行星，是太阳系中体积最大、自转最快的行星，同时也是拥有最多卫星的星球，木星的卫星总数达到了67颗。让我们跟随本文一起了解木星的卫星们。

中国科技网8月21日报道（张微 编译）木星是由罗马人命名的，他们选择众神之王的名字来命名它。它除了是我们太阳系中最大的行星之外——它的质量是所有其他行星总和的2.5倍，它还是太阳系行星中拥有最多卫星的星球。到目前为止，已经确认了67颗天然卫星在围绕着这个巨大的气体巨人运转，可能还会有一些卫星陆续被发现。

木星的卫星数量众多，种类多样，可以将它们分成几类。第一，个头最大的卫星群被称为伽利略卫星或主群。以及个头较小的内群，它们由木星的规则卫星组成。除了它们之外，还有许多不规则卫星在围绕着木星运转，以及它的环状碎片。下面，让我们深入地了解这些卫星。

规则卫星：

木星的规则卫星如此命名是因为它们有着顺行轨道——它们在同一个方向上围绕它们的行星运转。这些轨道接近圆形并且低倾角，这意味着它们的轨道接近木星的赤道。其中，伽利略木星(又名主群)是最为人们熟知，也是体型最庞大的卫星。

主群：

这些都是木星最大的卫星，也分别是太阳系中第四，第六，第一和第三大卫星。它们占据了木星轨道上99.999%的总质量，轨道距离卫星400,000到2000,000公里之间。它们也是太阳系中除了太阳和八大行星之外最大的天体，半径比任何一颗矮行星都要大。

它们包括，艾奥(木卫一)、欧罗巴(木卫二)、加尼未(木卫三)、卡利斯托(木卫四)，都是由伽利略发现的，并命名为伽利略卫星来纪念他。以希腊神话宙斯的情人的名字命名的卫星，在1610年伽利略发现它们之后不久，由西门 马里乌斯对它们命名。其中，最靠近木星的卫星是艾奥(木卫一)，它是以宙斯情人女祭司赫拉的名字命名的。

它的直径3642公里，是太阳系中第四大卫星。在这个天体上有400多座活火山，也是太阳系中地质活动最活跃的星球。它的表面遍布了超过100座山脉，其中一些比地球上的珠穆朗玛峰还要高。

不同于外太阳系的大多数卫星(表面被冰覆盖)，艾奥(木卫一)主要由被熔铁或硫化铁芯包围的硅酸盐岩石组成。木卫一的大气层主要由二氧化硫组成，而且非常稀薄。

从最里层向外数的第二个伽利略卫星是欧罗巴(木卫二)，它得名于神话中被宙斯爱慕的腓尼基公主，后来成为克里特岛女王。它的直径3121.6公里，是伽利略卫星中体积最小的，比月亮略小。

欧罗巴(木卫二)的地表由一层100公里厚的水构成。最上面的部分是固体冰而底部是液态水，有引潮力带来的热量保持液态。如果假设成立，那么有可能有外星生命可能存在于这个地下海洋中，也许在一系列的深海热液喷口附近。

欧罗巴(木卫二)地表是太阳系所有星球中最光滑的一个，支持地表下存在液态水的想法。它的表面缺少陨石坑，这表明地表是一个年轻而活跃的地质构造。木卫二主要由硅酸盐岩石组成，可能还有铁芯，存在一个主要由氧气组成的稀薄的大气层。

接下来是加尼未(木卫三)。它是太阳系中最大的卫星，直径有5262.4公里。它的直径比水星大，质量却只是水星的一半，而且它是一个冰冷的世界。它也是太阳系中已知的唯一拥有磁圈的卫星，这可能是其内部液态铁对流造成的。

加尼未(木卫三)主要由硅酸盐岩石和冰体构成，科学家们推测有一个咸水海洋存在于木卫三200公里的地下。加尼未(木卫三)上有大量的陨石坑，其中大部分都被冰覆盖，并拥有一个稀薄的含氧大气层，主要包括原子氧、氧气、和臭氧，以及一些氢原子。

卡利斯托(木卫四)是第四个也是最远的伽利略卫星。直径4820.6公里，它也是第二大的伽利略卫星和太阳系中第三大卫星。木卫四是以吕卡翁(阿耳卡狄亚国王)女儿，阿特米斯女神的狩猎同伴的名字命名的。

由大致等量的岩石和冰组成，卡利斯托(木卫四)也是伽利略卫星中密度最小的星球。调查显示，木卫四上也有液态水构成的地下海洋，位于地表下100公里的深处。

卡利斯托(木卫四)是太阳系中陨石坑最多的星球，其中最大的一个是3000公里宽的盆地，被称为沃尔哈拉。它有一个非常稀薄的大气层，主要由二氧化碳构成，成分可能还包括氧气。卡利斯托(木卫四)一直被认为是人类探索木星系统设置基地最合适的地方，因为在木卫四上建立基地的好处在于它的较低辐射(木卫四离木星较远)。

内群：



内群(或木卫五组)是四颗直径不到200公里、轨道半径小于200,000公里而且轨道倾斜度小于0.5度的小卫星，这个群包括木卫十六、木卫十五、木卫五、木卫十四。

木卫十六是最接近木星的卫星，距离12.8万公里。它的直径大约40公里，潮汐锁定而且形状高度不对称。旅行者1号太空探测器在1979年发现它。在1983年以宙斯第一个妻子的名字命名它。

距离木星第二近的卫星是阿德拉斯蒂尔星(木卫十五)，这是一个直径20公里与木星距离12.9万公里。也被称为木卫十五，阿德拉斯蒂尔星距离木星第二远，而且是木星的四个内卫星中个头最小的一个。它是在1979年，旅行者2号探测器在飞跃木星时拍摄到的。

阿玛尔忒亚，也被称为木卫五，是距离木星第三远的卫星。它是在1892年9月，由爱德华 艾默生 巴纳德发现的，并以希腊神话中女神的名字命名。它是由多孔水冰与未知数量的其他材料组成的。其表面特征是大型陨石坑和山脊。

忒拜(又名木星十四)是木星的第四个和最后一个内卫星。它的形状不规则，颜色偏红，与木卫五一样由多孔水冰和未知数量的其他材料组成。其表面特征还包括大型火山口和高山，其中有些与卫星本身的大小差不多。

不规则卫星：

不规则卫星是相比于规则卫星来说，个头相当小而且有着更遥远的距离和偏心的轨道。这些卫星根据轨道和组成特征被分为不同的家族。这些不规则卫星被认为，至少有一部分是木星引力场捕捉到的小行星碰撞形成的。

那些分到不同家族的卫星群都按照它们中间体积最大的卫星来命名。例如，希玛利亚群(木卫六)以希玛利亚(木卫六)来命名，这个卫星平均直径85公里，是围绕木星运转的第五大卫星，据认为，希玛利亚(木卫六)曾经是被木星重力场捕获的小行星，然后经历了碰撞，形成了木卫十三，木卫十和木卫七。这些卫星都有顺行的轨道，意味着它们的运转轨道与木星自转轨道在同一方向上。

加尔尼群平均半径23公里，加尔尼群是木星卫星家族成员中最大的一个，有相似的轨道和外观(均匀的红色)，因此被认为有着共同的起源。这个家族中的卫星都是逆行轨道，意味着它们与木星的旋转方向相反。

阿南克群也是以其中最大的卫星来命名的。它的平均半径14公里，据认为，阿南克群也是一个被木星引力场捕捉的小行星，然后遭受碰撞，形成了大量碎片。这些碎片成为阿南克群中其他15个卫星，这些卫星都是逆行轨道，而且外观是灰色的。

帕西法厄群是一个非常多样化的群，颜色从红色到灰色，代表了多次碰撞结果的可能性很大。用帕西法厄这个名字来命名，平均半径30公里，这些卫星是逆行轨道，也被认为是木星捕获的小行星，由于多次碰撞的碎片形成的。

还有几个不规则卫星不属于任何特殊家族。包括木卫十八和木卫四十六，最内层和最外层的规则卫星，他们都是顺行轨道。S/2003 J 12 和S/2011 J 1是最内层逆行轨道卫星，而S/2003 J 2是木星的最外层卫星。

发现和命名的问题：

在伽利略首次记录发现了主群之后，将近三个世纪的时间没有发现其他卫星，直到巴纳德在1892年观测到了阿玛尔忒娅(木卫五)。实际上，直到21世纪，由于可伸缩望远镜和其他技术改进，大多数类木行星的卫星开始被发现。

1904年发现希玛利亚(木卫六)，1905年发现木卫七，1908年发现木卫八，1914年发现木卫九，1938年发现木卫十和木卫十一，1951年发现木卫十二，1974年发现木卫十三。“旅行者”航天探测器在1979年达到木星的时候，已经发现了13个卫星，“旅行者”航天探测器发现了另外三个，木卫十六，木卫十五和木卫十四。

从1999年10月到2003年2月，研究人员利用敏感的地面探测器发现了后来命名的另外34个卫星，他们中的大多数是Scott S. Sheppard 和 David C. Jewitt领导的研究团队发现的。自2003年以来，又发现了16个卫星，但还没有命名，加上之前已知的，木星的卫星总数达到了67颗。

虽然伽利略卫星在1610年被发现不久就得到了命名，但是艾奥(木卫一)，欧罗巴(木卫二)，加尼未(木卫三)和卡利斯托(木卫四)的名字直到21世纪才被广泛接受。阿玛尔忒娅(木卫五)直到1892年一次非正式会议上才如此命名，法国天文学家卡米伊·弗拉马利翁是首位建议将木卫五命名为阿玛尔忒娅的人。

直到20世纪70年代，其他的卫星，在大多数的天文学文献中，依然仅仅通过罗马数字进行简单的标记。1975年国际天文学联合会对太阳系卫星用V–XIII进行命名，由此为未来发现的卫星建立了一个正式的命名程序。

以宙斯的情人或喜欢的神来命名新发现的木星卫星;而且2004年开始，命名规则扩大到以上人物的后代。由于不断的天文发现，用不了多长时间，发现新的木星卫星已经不足为奇了。命名方式就是第68颗然后接着向下数。

英文原文：

The moons of Jupiter

Jupiter was appropriately named by the Romans, who chose to name it after the king of the gods. In addition to being the largest planet in our Solar System – with two and a half times the mass of all the other planets combined – it also has the most moons of any Solar planet. So far, 67 natural satellites have been discovered around the gas giant, and more could be on the way.

The moons of Jupiter are so numerous and so diverse that they are broken down into several groups. First, there are the largest moons known as the Galileans, or Main Group. Together with the smaller Inner Group, they make up Jupiter's Regular Satellites. Beyond them, there are the many Irregular Satellites that circle the planet, along with its debris rings. Here's what we know about them…

Regular Satellites:

Jupiter's Regular Satellites are so named because they have prograde orbits – i.e. they orbit in the same direction the rotation of their planet. These orbits are also nearly circular and have a low inclination, meaning they orbit close to Jupiter's equator. Of these, the Galilean Moons (aka. the Main Group) are the largest and the most well known.

Main Group:

These are Jupiter's largest moons, not to mention the Solar System's fourth, sixth, first and third largest satellites, respectively. They contain almost 99.999% of the total mass in orbit around Jupiter, and orbit between 400,000 and 2,000,000 km from the planet. They are also among the most massive objects in the Solar System with the exception of the Sun and the eight planets, with radii larger than any of the dwarf planets.

They include Io, Europa, Ganymede, and Callisto, and were all discovered by Galileo Galilei and named in his honor. The names of the moons, which are derived from the lovers of Zeus in Greek mythology, were prescribed by Simon Marius soon after Galileo discovered them in 1610. Of these, the innermost is Io, which is named after a priestess of Hera who became Zeus' lover.

With a diameter of 3,642 kilometers, it is the fourth-largest moon in the Solar System. With over 400 active volcanoes, it is also the most geologically active object in the Solar System. Its surface is dotted with over 100 mountains, some of which are taller than Earth's Mount Everest.

Unlike most satellites in the outer Solar System (which are covered with ice), Io is mainly composed of silicate rock surrounding a molten iron or iron sulfide core. Io has an extremely thin atmosphere made up mostly of sulfur dioxide (SO2).

The second innermost Galilean moon is Europa, which takes its name from the mythical Phoenician noblewoman who was courted by Zeus and became the queen of Crete. At 3121.6 kilometers in diameter, it is the smallest of the Galileans, and slightly smaller than the Moon.

Europa's surface consists of a layer of water surrounding the mantle which is thought to be 100 kilometers thick. The uppermost section is solid ice while the bottom is believed to be liquid water, which is made warm due to heat energy and tidal flexing. If true, then it is possible that extraterrestrial life could exist within this subsurface ocean, perhaps near a series of deep-ocean hydrothermal vents.

The surface of Europa is also one of the smoothest in the Solar System, a fact which supports the idea of liquid water existing beneath the surface. The lack of craters on the surface is attributed to the surface being young and tectonically active. Europa is primarily made of silicate rock and likely has an iron core, and a tenuous atmosphere composed primarily of oxygen.

Next up is Ganymede. At 5262.4 kilometers in diameter, Ganymede is the largest moon in the Solar System. While it is larger than the planet Mercury, the fact that it is an icy world means that it has only half of Mercury's mass. It is also the only satellite in the Solar System known to possess a magnetosphere, likely created through convection within the liquid iron core.

Ganymede is composed primarily of silicate rock and water ice, and a salt-water ocean is believed to exist nearly 200 km below Ganymede's surface – though Europa remains the most likely candidate for this. Ganymede has a high number of craters, most of which are now covered in ice, and boasts a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone), and some atomic hydrogen.

Callisto is the fourth and farthest Galilean moon. At 4820.6 kilometers in diameter, it is also the second largest of the Galileans and third largest moon in the Solar System. Callisto is named after the daughter of the Arkadian King, Lykaon, and a hunting companion of the goddess Artemis.

Composed of approximately equal amounts of rock and ices, it is the least dense of the Galileans, and investigations have revealed that Callisto may also have an interior ocean at depths greater than 100 kilometers from the surface.

Callisto is also one of the most heavily cratered satellites in the Solar System – the greatest of which is the 3000 km wide basin known as Valhalla. It is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen. Callisto has long been considered the most suitable place for a human base for future exploration of the Jupiter system since it is furthest from the intense radiation of Jupiter.

Inner Group:

The Inner Group (or Amalthea group) are four small moons that have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree. This groups includes the moons of Metis, Adrastea, Amalthea, and Thebe.

Metis is the closest moon to Jupiter at a distance of 128,000 km. It is roughly 40 km in diameter, tidally-locked, and highly-asymmetrical in shape (with one of the diameters being almost twice as large as the smallest one). It was not discovered until the 1979 flyby of Jupiter by the Voyager 1 space probe. It was named in 1983 after the first wife of Zeus.

The second closest moon is Adrastea, which is about 129,000 km from Jupiter and 20 km in diameter. Also known as Jupiter XV, Amalthea is the second by distance, and the smallest of the four inner moons of Jupiter. It was discovered in 1979 when the Voyager 2 probe photographed it during a flyby.

Amalthea, also known as Jupiter V, is the third moon of Jupiter in order of distance from the planet. It was discovered on September 9, 1892, by Edward Emerson Barnard and named after a nymph in Greek mythology. It is thought to consist of porous water ice with unknown amounts of other materials. Its surface features include large craters and ridges.

Thebe (aka. Jupiter XIV) is the fourth and final inner moon of Jupiter. It is irregularly shaped and reddish in colour, and is thought like Amalthea to consist of porous water ice with unknown amounts of other materials. Its surface features also include large craters and high mountains – some of which are comparable to the size of the moon itself.

Irregular Satellites:

The Irregular Satellites are those that are substantially smaller and have more distant and eccentric orbits than the Regular Satellites. These moons are broken down into families that have similarities in orbit and composition. It is believed that these were at least partially formed as a result of collisions, most likely by asteroids that were captured by Jupiter's gravitational field.

Those that are grouped into families are all named after their largest member. For example, the Himalia group is named after Himalia – a satellite with a mean radius of 85 km, making it the fifth largest moon orbiting Jupiter. It is believed that Himalia was once an asteroid that was captured by Jupiter's gravity, which then experienced a impact that formed the moons of Leda, Lysithea, and Elara. These moons all have prograde orbits, meaning they orbit in the same direction as Jupiter's rotation.

The Carme group takes its name from the Moon of the same name. With a mean radius of 23 km, Carme is the largest member of a family of Jovian satellites which have similar orbits and appearance (uniformly red), and are therefore thought to have a common origin. The satellites in this family all have retrograde orbits, meaning they orbit Jupiter in the opposite direction of its rotation.

The Ananke group is named after its largest satellite, which has a mean radius of 14 km. It is believed that Ananke was also an asteroid that was captured by Jupiter's gravity and then suffered a collision which broke off a number of pieces. Those pieces became the other 15 moons in the Ananke group, all of which have retrograde orbits and appear gray in color.

The Pasiphae group is a very diverse group which ranges in color from red to grey – signifying the possibility of it being the result of multiple collisions. Named after Paisphae, which has a mean radius of 30 km, these satellites are retrograde, and are also believed to be the result of an asteroid that was captured by Jupiter and fragmented due to a series of collisions.

There are also several irregular satellites that are not part of any particular family. These include Themisto and Carpo, the innermost and outermost irregular moons, both of which have prograde orbits. S/2003 J 12 and S/2011 J 1 are the innermost of the retrograde moons, while S/2003 J 2 is the outermost moon of Jupiter.

Issues of Discovery and Naming:

After Galileo made the first recorded discovery of the Main Group, no additional satellites were discovered for almost three centuries – not until E. E. Barnard observed Amalthea in 1892. In fact, it was not until the 20th century, and with the aid of telescopic photography and other refinements, that most of the Jovian satellites began to be discovered.

Himalia was discovered in 1904, Elara in 1905, Pasiphaë in 1908, Sinope in 1914, Lysithea and Carme in 1938, Ananke in 1951, and Leda in 1974. By the time Voyager space probes reached Jupiter around 1979, 13 moons had been discovered, while Voyager herself discovered an additional three – Metis, Adrastea, and Thebe.

Between October 1999 and February 2003, researchers using sensitive ground-based detectors found and later named another 34 moons, most of which were discovered by a team led by Scott S. Sheppard and David C. Jewitt. Since 2003, 16 additional moons have been discovered but not yet named, bringing the total number of known moons of Jupiter to 67.

Though the Galilean moons were named shortly after their discovery in 1610, the names of Io, Europa, Ganymede and Callisto fell out of favor until the 20th century. Amalthea (aka. Jupiter V) was not so named until an unofficial convention took place in 1892, a name that was first used by the French astronomer Camille Flammarion.

The other moons, in the majority of astronomical literature, were simply labeled by their Roman numeral (i.e. Jupiter IX) until the 1970s. This began in 1975 when the International Astronomical Union's (IAU) Task Group for Outer Solar System Nomenclature granted names to satellites V–XIII, thus creating a formal naming process for any future satellites discovered.

The practice was to name newly discovered moons of Jupiter after lovers and favorites of the god Jupiter (Zeus); and since 2004, also after their descendants. Given the discovery process, and how long it has taken us, it would not be surprising if there more satellites around Jupiter just waiting to be discovered. Sixty-seven and counting!

来源：中国科技网 2015年08月21日　10:59

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