Astronomy Picture of the Day
February 22, 2013

Inside the Magnificent Herschel Crater
Inside the Magnificent Herschel Crater

Credits: NASA/JPL/Space Science Institute - Credits for the additional process. and color.: Dr Paolo C. Fienga/Lunar Explorer Italia/IPF

Remarkable color differences on the Saturnian moon Mimas are apparent in this (enhanced) Absolute Natural Color view of Herschel Crater that was captured by the NASA - Cassini Spacecraft during its closest (so far) Fly-By of that Celestial Body which occurred on February 13, 2010. The image shows Terrain-dependent color variations and, in particular, the contrast between the light-gray (with slightly pale blue nuances) Surface Materials which are found in and around Herschel Crater and the brownish cast that, on the other hand, is found on older and more heavily Cratered Terrain elsewhere.

The origin of the color differences between these two types of Terrain is not yet understood, but it is quite logical to assume that it should be caused by the existence of some considerable differences in the Surface Elements which form the Terrains themselves (and a few false color images which were obtained from Cassini's previous closest encounter with Mimas, during the AD 2005, also showed such variations, which are, therefore, something real and NOT a simple optical effect caused, for instance, by the Illumination Geometry existing at the time whan the different pictures were taken). The huge Herschel Crater (approx. 130 Km, or a little more than 80 miles, wide) covers most of the bottom of the image.

To create the original false-color view of Mimas, UltraViolet, Green and InfraRed images were combined into a single picture that was fit to exaggerate the color differences of the photographed Terrains; these data were then combined with a High-Resolution image taken in Visible Light so to obtain a mix between the High-Resolution information coming from the Clear-Filter image and the color information coming from the UltraViolet, Green and InfraRed filter images.

During the Fly-By, the NASA - Cassini Spacecraft came within about 9500 Km (such as about 5900 miles) of Mimas and this view looks toward the Northern part of the Hemisphere that leads the moon in its orbit around Saturn (---> Leading Hemisphere, in contrast with the Trailing Hemisphere). The images were obtained with Cassini's Narrow-Angle Camera at a distance of approximately 16.000 Km (such as 9936 miles) from Mimas. Afterwards, the images were re-projected into an Orthographic Map Projection. Furthermore, a black and white image, taken in Visible Light with the Wide-Angle Camera, was also used to fill in parts of the mosaic. The global scale of the mosaic is 90 meters (295 feet) per pixel.

This frame (which is an Original NASA - Cassini Spacecraft false color image mosaic published on the NASA - Planetary Photojournal with the ID n. PIA 12572) has been additionally processed, contrast enhanced, and then re-colorized in (slightly enhanced) Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Cassini Spacecraft and then looked outside, towards the Surface and Limb of the Saturnian moon Mimas), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements present on the Surface of Mimas, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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