https://solarsystem.nasa.gov/moons/jupiter-moons/io/overview/
Introduction
Jupiter's rocky moon Io is the most volcanically active world in the solar system, with hundreds of volcanoes, some erupting lava fountains dozens of miles (or kilometers) high. Io’s remarkable activity is the result of a tug-of-war between Jupiter's powerful gravity and smaller but precisely timed pulls from two neighboring moons that orbit farther from Jupiter – Europa and Ganymede.
In mythology, Io is a mortal woman transformed into a cow during a dispute between the Greek god Zeus – Jupiter in Roman mythology – and his wife, Hera – Juno to the Romans.
概要
木星的卫星艾奥是太阳系里火山活动最强烈的一个世界，有几百座火山，有些火山喷发熔岩喷泉高达几打英里(几十千米)。艾奥异常的行为是木星强大的引力和两个较小卫星之间精确定时拉锯的结果，这两颗卫星轨道距离木星较远，分别是欧罗巴和伽倪墨得斯。
在古神话里，艾奥是个女凡人被变成了牛，原因是古希腊天神宙斯--罗马神话里是朱庇特(译注:木星的音译)--和他的妻子赫拉之间产生了矛盾--罗马人称朱诺。
Size and Distance
A bit larger than Earth's Moon, Io is the third largest of Jupiter's moons, and the fifth one in distance from the planet.
大小和远近
比地球的卫星月亮稍大，是木星的第三大卫星，距地球远近上位列第五。
Orbit and Rotation
Although Io always points the same side toward Jupiter in its orbit around the giant planet, the large moons Europa and Ganymede perturb Io's orbit into an irregularly elliptical one. Thus, in its widely varying distances from Jupiter, Io is subjected to tremendous tidal forces.
These forces cause Io's surface to bulge up and down (or in and out) by as much as 330 feet (100 meters). Compare these tides on Io's solid surface to the tides on Earth's oceans. On Earth, in the place where tides are highest, the difference between low and high tides is only 60 feet (18 meters), and this is for water, not solid ground.
Io's orbit, keeping it at more or less a cozy 262,000 miles (422,000 kilometers) from Jupiter, cuts across the planet's powerful magnetic lines of force, thus turning Io into a electric generator. Io can develop 400,000 volts across itself and create an electric current of 3 million amperes. This current takes the path of least resistance along Jupiter's magnetic field lines to the planet's surface, creating lightning in Jupiter's upper atmosphere.
轨道和旋转
尽管艾奥始终一面对着木星围绕这个巨大的行星旋转，但是较大的卫星欧罗巴和伽倪墨得斯干扰了艾奥的轨道导致形成了不规则的椭圆形。这样以来，在和木星广远的间距变换中，艾奥受到巨大的潮汐力。
这些力导致艾奥表面忽起忽落(或者进和出)高达330英尺(100米)。对比一下艾奥固态表面的潮汐和地球上海洋的潮汐。在地球上，最高潮汐的地方，高低潮落差不过60英尺(18米)，而且还是水，不是固态的陆地。
艾奥的轨道，使之处于或多或少距离木星262000英里(422000千米) 一个温馨距离，切割这个行星强大的磁力线[译注：木星的磁场是太阳系里最强的，比地球磁场强几十倍，形成原因目前不特别清楚]，致使艾奥成了一个发电机。艾奥自身能产生40万伏的电压，产生3百万安的电流。这些电流沿着木星磁力线流经木星低阻抗表面，在木星高层大气产生闪电。
Surface
The tidal forces generate a tremendous amount of heat within Io, keeping much of its subsurface crust in liquid form seeking any available escape route to the surface to relieve the pressure. Thus, the surface of Io is constantly renewing itself, filling in any impact craters with molten lava lakes and spreading smooth new floodplains of liquid rock. The composition of this material is not yet entirely clear, but theories suggest that it is largely molten sulfur and its compounds (which would account for the varied coloring) or silicate rock (which would better account for the apparent temperatures, which may be too hot to be sulfur). Sulfur dioxide is the primary constituent of a thin atmosphere on Io. It has no water to speak of, unlike the other, colder Galilean moons. Data from the Galileo spacecraft indicates that an iron core may form Io's center, thus giving Io its own magnetic field.
表面
潮汐力在艾奥内部产生巨大的热量，导致它表面下的地壳成为液态，寻找任何到达表面的逃离路径释放压力。这样以来，艾奥表面会得到持续的更新，用岩浆填充任何陨石坑而且会产生光滑的液态熔岩洪泛平原。地质具体成分不太清楚，但理论假说认为大部分是熔化的硫磺及其硫化物(较好的解释了表面不同的颜色构成)或硅酸盐石头(较好的解释了显而易见的表面温度，都硫磺就太热了)。艾奥稀薄的大气主要组分主要是二氧化硫。不得不说，艾奥表面没有水，不像其它较冷的伽利略卫星们[译注：最初古天文学家伽利略发现了一系列的木星卫星，所以后来就有了这种称呼]。伽利略太空船采集到的数据指出，艾奥中心可能存在铁核，于是就拥有了自己的磁场。
Potential for Life
Constant volcanism and intense radiation make Io an unlikely destination for life.
潜在生命
持续的火山活动和强烈的辐射使得艾奥不太可能成为生命的落脚点。
Magnetosphere
As Jupiter rotates, it takes its magnetic field around with it, sweeping past Io and stripping off about 1 ton (1,000 kilograms) of Io's material every second. This material becomes ionized in the magnetic field and forms a doughnut-shaped cloud of intense radiation referred to as a plasma torus. Some of the ions are pulled into Jupiter's atmosphere along the magnetic lines of force and create auroras in the planet's upper atmosphere. It is the ions escaping from this torus that inflate Jupiter's magnetosphere to over twice the size we would expect.
磁圈
伴随着木星自转，木星的磁场包围了艾奥，清扫艾奥，平均每秒从艾奥掠走大约1吨(1千千克)物质。这些物质在磁场里电离，形成面包圈状的离子云，具有强烈的辐射，称之为等离子圆环。一些离子沿着磁力线被拉入木星大气，在木星上空产生极光。这些逃离圆环的离子导致木星磁圈膨胀，比我们预期大小大了一倍不止。
Discovery
Io was discovered on Jan. 8, 1610 by Galileo Galilei. The discovery, along with three other Jovian moons, was the first time a moon was discovered orbiting a planet other than Earth. The discovery of the four Galilean satellites eventually led to the understanding that planets in our solar system orbit the Sun, instead of our solar system revolving around Earth. Galileo apparently had observed Io on Jan. 7, 1610, but had been unable to differentiate between Io and Europa until the next night.
Galileo originally called Jupiter's moons the Medicean planets, after the powerful Italian Medici family and referred to the individual moons numerically as I, II, III, and IV. Galileo's naming system would be used for a couple of centuries.
It wouldn't be until the mid-1800s that the names of the Galilean moons, Io, Europa, Ganymede, and Callisto, would be officially adopted, and only after it became apparent that naming moons by number would be very confusing as new additional moons were being discovered.
In mythology, Io is a mortal woman transformed into a cow during a marital dispute between the Greek god Zeus—Jupiter in Roman mythology—and his wife, Juno. NASA’s Juno mission is named in honor of Juno who could peer through the clouds and expose her husband’s wrongdoings. The spacecraft also peers through clouds to reveal Jupiter’s secrets.
发现史
艾奥在1610年元月8日被伽利略伽利雷发现。和其它三个木星的卫星一起被发现的，这是首次发现地球之外的行星拥有自己环绕的卫星。伽利略四卫星的发现最终导致人类认识到太阳系里的行星们围着太阳转，而不是太阳系围着地球转。伽利略显然于1610年元月7日就发现了艾奥，但是直到第二天晚上才能把它和欧罗巴区分开。
伽利略最初称木星的卫星为美第奇家族行星，意大利美第奇家族之后，这些独立的卫星才被命名为I, II, III和IV。伽利略命名的体系会被沿用几个世纪。
直到18世纪中期伽利略卫星的艾奥，卡利斯托，欧罗巴和伽倪墨得斯几个名字才被官方采纳，因为随着更多卫星被发现，原来以数字命名卫星的做法非常令人费解。
在古神话里，古希腊天神宙斯--罗马神话里称朱庇特--和他的妻子朱诺之间的一次婚姻矛盾导致凡人艾奥[译注：以汉语文化的视角来看，神仙宙斯有婚外情凡人艾奥]变成了牛。美国航空航天局的朱诺之旅为了向朱诺女神表达敬意特此命名，寓意是朱诺能看透云层揭露其丈夫的错误行为。该太空船也能透过云层去揭示木星的秘密。