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In this unique mosaic image combining high-resolution data from the imaging science subsystem and composite infrared spectrometer aboard NASA's Cassini spacecraft, pockets of heat appear along one of the mysterious fractures in the south polar region of Saturn's moon Enceladus. The fracture, named Baghdad Sulcus, is one of the so-called "tiger stripe" features that erupt with jets of water vapor and ice particles. It runs diagonally across the image.
This mosaic, obtained on Nov. 21, 2009, shows a 40-kilometer (25-mile) segment of Baghdad Sulcus and illustrates the correlation between the geologically youthful surface fractures and anomalously warm temperatures recorded in the south polar region. It shows the highest-resolution data yet of the heat leaking from the moon's interior along the tiger stripes.
The image shows that broad swaths of heat previously detected by the infrared spectrometer are confined to a narrow, intense region no more than a kilometer (half a mile) wide along the fracture. The thermal image also reveals that the strength of the thermal radiation varies considerably along the length of this fissure segment. The temperature along Baghdad Sulcus reached more than 180 Kelvin (about minus 140 degrees Fahrenheit).
This mosaic layers temperature data atop of a visible-light image and alignment of the two data sets is approximate. The mosaic is centered near 80 degrees south latitude and 30 degrees west longitude. The V-shaped valleys that distinguish Baghdad are about 500 meters (1,600 feet) deep. The 30-degree slopes that rise along the valleys appear to be coated with smooth-looking particulate deposits that are peppered with large ice blocks that can reach tens of meters (yards) in size. The smooth materials most likely represent ice grain fallout from active jets that erupt along this warm and active section of Baghdad. The ice blocks appear to be icy rubble that may have been exposed by scouring from the eruptions, seismic shaking, and down-slope settling of the finer ice particles.
The moon's south pole lies outside of the frame of the mosaic, in the darkness below what is shown here. The full-length of Baghdad Sulcus, one of the longest tiger stripes, stretches about 175 kilometers (109 miles) all the way across the south polar region. This high-resolution view focuses only on one end of the rift, in the hemisphere that always faces toward Saturn. The other end of Baghdad was in shadow when these images were obtained. See chg111109_02_01 to see all of Baghdad Sulcus and the other tiger stripes.
At the end of the Baghdad Sulcus segment shown here, a distinct branching pattern of fractures can be seen forking away from the central rift. The main fissure and the branching rifts slice through a complex system of quasi-parallel, rope-like, rounded ridges each as large as a kilometer (half a mile) across and hundreds of meters (yards) in height. At scales of tens to hundreds of meters (tens to hundreds of yards), a fine network of small parallel cracks are pervasive, slicing through the valley walls of Baghdad as well as through the ropey ridges. Near the very top of the mosaic, the ropey terrain transitions to a distinctly different zone in which a complicated network of fractures subdivides a broad plain into complex polygonal patterns created by tectonics.
The temperature data shows how the surface glows at 10 to 16 micron wavelength radiation along this segment of Baghdad Sulcus, covering a region about 10 kilometers to 5 kilometers (6 miles to 3 miles) in width, with the smallest features on the thermal map measuring less than 1 kilometer (half a mile) across. The best previous map (chg032608_06_01 and the left-hand side of chg022310_02_01) showed details no smaller than about 5 to 9 kilometers (3 to 6 miles) across.
The brightest colors in the map do not correspond directly to higher temperatures, but rather to a combination of higher temperatures and larger areas of warm surface material. The intensity of heat radiation increases as the color shades from violet to red to orange to yellow. No internal heat was detected in the darkest violet regions. Uncolored regions were not mapped by Cassini's composite infrared spectrometer instrument.
While the heat appears to emanate mostly from the main Baghdad tiger stripe, some of the fractures branching off or parallel to it also appear warmer and active to varying degrees, though this needs to be confirmed by further analysis. The total amount of infrared energy and the relative amounts given off at different wavelengths show that the highest temperatures along Baghdad Sulcus are limited to a region no more than tens of meters (yards) across. Most of the heat measured by the infrared spectrometer probably arises from the warm flanks of the active fractures, rather than their central fissures. The narrow central fissure is probably even warmer than the 180 Kelvin (minus 140 degrees Fahrenheit) detected – possibly warm enough for liquid water in the fractures to be the source of the observed jets.
Four narrow-angle-camera images were re-projected to create the polar stereographic mosaic with a center latitude of 90 degrees south latitude and with the prime meridian, or 0 degrees west longitude, pointing up in the image. The seams in the mosaic are unavoidable due to change in viewing angle from image to image. The visible light images and the spectrometer data were both obtained at distances ranging from approximately 2,000 kilometers (1,200 miles) to 3,000 kilometers (1,800 miles) from Enceladus. The sun-Enceladus-spacecraft, or phase, angles vary between 135 and 90 degrees. The resolution of this mosaic is approximately 12 meters per pixel at the south pole. This view shows the side of Enceladus (504 kilometers, or 313 miles in diameter) that faces toward Saturn.
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. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md., where the instrument was built.
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