|Image left: This black & white image of Saturn's irregular moon Hyperion was taken with the ISS camera on Cassini. Superimposed on the image is color information from the Cassini Visible-Infrared Mapping Spectrometer (VIMS) which was processed by Dr. Brad Dalton at NASA Ames Research Center, Moffett Field, Calif. Hyperion orbits Saturn in a tumbling, chaotic orbit influenced by gravitational interactions with other moons.
The dark patches are not simply shadows in craters or low spots - they are actually deposits of material that may be the result of organic chemistry occurring in space. In the color-coded data, blue shows where water ice is most concentrated, while red indicates frozen carbon dioxide (or, "dry ice"). Thus, the magenta areas are a mix of water and carbon dioxide ice. Green denotes an as-yet unidentified, probably organic, material that appears to contain carbon and nitrogen. The yellow patches are where carbon dioxide and this unknown organic material are found together - usually in the dark deposits.
Rather than being made of patches of pure water ice and patches of other materials, Hyperion's surface is composed of a mix of water ice and other contaminants. The dark regions may have begun as impact craters. These regions absorb more sunlight than the bright ice, warming up enough to drive off the nearby ice. This causes the dark material to become more concentrated, while sinking into the surface. The process is called "sublimation degradation" and is believed to be responsible for the bizarre landscapes of many of the icy moons of Jupiter and Saturn.
Organic compounds concentrated in the dark material may have formed on the surface, or been brought in by impacts, or a combination of these. Additional processing of the surface by radiation in space may drive chemical reactions that create a mixture of organic materials - the stuff of life. This proves that at least some of the necessary building blocks for life can persist in the frozen reaches of deep space.
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|Image Left: The close-up of Hyperion's surface was created by overlaying color-coded information from Cassini's Visible-Infrared Mapping Spectrometer (VIMS) onto a black & white image from the Cassini Imaging Science Subsystem (ISS). The colors reveal the surface composition. Blue shows where water ice is most concentrated, while red indicates frozen carbon dioxide (or, "dry ice"). Thus, the magenta areas are a mix of water and carbon dioxide ice. Green denotes an as-yet unidentified material that appears to contain both carbon and nitrogen. The yellow patches are where carbon dioxide and this unknown organic material are found together, without much water ice. This mostly happens in the dark deposits strewn about the surface.
The carbon dioxide is sometimes concentrated around small craters, but the amount of carbon dioxide also increases in other areas. This suggests that the carbon dioxide is unevenly mixed into the surrounding water ice. The dark deposits may have been left behind by impacting comets or icy debris. They may have been further concentrated by a process called "sublimation degradation" in which darker region, being warmer, drives off the surrounding water ice, leaving behind an even more concentrated deposit of contaminants. Scientists are not yet certain whether the material began as contaminants within the ice, or was brought by impacts, or a combination of both. Further processing by ultraviolet radiation may have enriched these deposits with organic chemicals which are relevant to life.
This dark material appears to be similar to that found on two of Saturn's other moons, Iapetus and Phoebe. However, on Hyperion it has been concentrated in these strange deposits. By studying the similarities and differences between Hyperion and these other moons, NASA scientists are learning more about how these worlds form, and how the processes that drive complex organic chemistry can operate, even in deep space.
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