English: Iapetus as seen by the Cassini probe.

Original NASA caption: Cassini captures the first high-resolution glimpse of the bright trailing hemisphere of Saturn's moon Iapetus.
This false-color mosaic shows the entire hemisphere of Iapetus (1,468 kilometers, or 912 miles across) visible from Cassini on the outbound leg of its encounter with the two-toned moon in Sept. 2007. The central longitude of the trailing hemisphere is 24 degrees to the left of the mosaic's center.
Also shown here is the complicated transition region between the dark leading and bright trailing hemispheres. This region, visible along the right side of the image, was observed in many of the images acquired by Cassini near closest approach during the encounter.
Revealed here for the first time in detail are the geologic structures that mark the trailing hemisphere. The region appears heavily cratered, particularly in the north and south polar regions. Near the top of the mosaic, numerous impact features visible in NASA Voyager 2 spacecraft images (acquired in 1981) are visible, including the craters Ogier and Charlemagne.
The most prominent topographic feature in this view, in the bottom half of the mosaic, is a 450-kilometer (280-mile) wide impact basin, one of at least nine such large basins on Iapetus. In fact, the basin overlaps an older, similar-sized impact basin to its southeast.
In many places, the dark material--thought to be composed of nitrogen-bearing organic compounds called cyanides, hydrated minerals and other carbonaceous minerals--appears to coat equator-facing slopes and crater floors. The distribution of this material and variations in the color of the bright material across the trailing hemisphere will be crucial clues to understanding the origin of Iapetus' peculiar bright-dark dual personality.
The view was acquired with the Cassini spacecraft narrow-angle camera on Sept. 10, 2007, at a distance of about 73,000 kilometers (45,000 miles) from Iapetus.
The color seen in this view represents an expansion of the wavelengths of the electromagnetic spectrum visible to human eyes. The intense reddish-brown hue of the dark material is far less pronounced in true color images. The use of enhanced color makes the reddish character of the dark material more visible than it would be to the naked eye.
This mosaic consists of 60 images covering 15 footprints across the surface of Iapetus. The view is an orthographic projection centered on 10.8 degrees south latitude, 246.5 degrees west longitude and has a resolution of 426 meters (0.26 miles) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope.
At each footprint, a full resolution clear filter image was combined with half-resolution images taken with infrared, green and ultraviolet spectral filters (centered at 752, 568 and 338 nanometers, respectively) to create this full-resolution false color mosaic.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

NASA最初的标题: 卡西尼捕捉到的第一幅高分辨率土卫八明亮的拖尾半球的图像.
这个伪色拼图显示了土卫八的整个半球 (跨越 1,468 km), 
该半球可以在[卡西尼号于2007-09遇到该双色卫星时的伸出去的腿]上看到.
拖尾半球的中心经度是拼图中心向左 24 度.
该图还显示了暗的领头半球和亮的拖尾半球之间的复杂的过渡区域. 
这个区域可沿图像右部看到, 并且在卡西尼接近最近路线时获得的很多图像中都能看到.

这里第一次在细节上显露了拖尾半球标志性的地质学结构. 
这个区域看上去极为多坑, 尤其在北南两个极区. 
接近拼图顶部, 许多撞击面貌可以在NASA的航行者2号飞船1981获得的图像中看到, 包括撞击坑Ogier和撞击坑Charlemagne.
这个视图中最突出的地貌是, 拼图的下半部, 一个 450 km 宽的撞击盆地, 在土卫八上至少有九个这样的大盆地.
实际上, 该盆地覆盖了一个更早的盆地, 即新盆地的东南方的那个尺寸相近的盆地.<br>
在很多地方, 暗的物质看上去覆盖了赤道 斜坡 和 坑底. 
这些暗的物质推测成分是氮轴有机化合物即氰化物 水合矿物 和 其他含碳矿物.
跨越拖尾半球的明亮物质的分布和颜色变化, 将是至关重要的线索, 让我们去理解 
土卫八的罕见的亮暗双重人格的起源. :) 

视图由卡西尼太空船窄角度相机于 2007-09-10 获得, 相机距离土卫八大约 73,000 km . 
此有色视图扩展了人眼视觉电磁波谱可见的波长. 
暗材料的强烈的红褐色调远远不是真色图具有的. 
增强色的采用使得暗材料的红属性比单纯人眼所见更显著.

该拼图来自跨越土卫八的表面的 60 个图像 覆盖了 15 个脚印 (基本测绘区域).
该视图是一个正射投影, 中心位于南纬10.8度, 西经246.5度, 分辨率为 426 米/像素. 
一个正投影视图很像遥远的观察者通过望远镜所看到的情景.
每个脚印上, 全分辨率清晰过滤图由半分辨率图像组合而成, 
这些半分辨率图像以红外 绿 和紫外光谱过滤器拍摄, 
这些过滤器的中心波长分别是 752 nm, 568 nm 和 338 nm.

卡西尼-惠更斯任务是 NASA 欧洲空间局 和 意大利空间局的协作工程. 
JPL喷气推进实验室, 是加利福尼亚技术学院的一部分. 
喷气推进实验室为华盛顿特区的NASA科学任务理事会管理着该工程. 
卡西尼轨道器及其两个相机在喷气推进实验室设计开发和组装. 
图像处理中心建于空间科学研究所(位于 Boulder, Colo).

(译者注: California Institute of Technology in Pasadena, 或者翻译成加州工学院, 但不要翻译成什么 '理工大学' 那样太没谱了. 
名词 '技术学院' 不同于中国大陆的技工职业教育院校专用的 '技术学院'. 
技术一词应该是不分大小的真正的技术 而非中国大陆普遍认为并在传统上轻视的 '小小的技术'.)