The right-hand image shows a dramatically improved view of heat radiation from a warm fissure near the south pole of Saturn’s icy moon Enceladus. It was obtained by NASA’s Cassini spacecraft during its Nov. 21, 2009, flyby of that moon. The fissure, named Baghdad Sulcus, is one of four so-called “tiger stripe” features that emit jets of water vapor and ice particles. The tiger stripe runs from the upper left to the lower right of the image. The infrared map, obtained by Cassini’s composite infrared spectrometer, is nearly 10 times more detailed than the image on the left, which was the best previous map of heat from the fissures. That image was obtained in March 2008.
The new data show that broad swaths of heat previously detected by the composite 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 signal varies considerably along the length of this fissure segment. The composite infrared spectrometer data indicate that the temperature along Baghdad Sulcus reached more than 180 Kelvin (about minus 140 degrees Fahrenheit).
The new map shows how the surface glows at 10 to 16 micron wavelengths of radiation along a 40-kilometer (25-mile) length of Baghdad Sulcus. This covers 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 older March 2008 map covered a larger area but showed no details smaller than about 5 to 9 kilometers (3 to 6 miles) across. The approximate area covered by the November 2009 scan is shown on the March 2008 map by a green rectangle.
The brightest colors in both maps do not correspond directly to the 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, and uncolored regions were not mapped by Cassini’s composite infrared spectrometer. The background image is derived from visible-light images taken by Cassini’s imaging science subsystem cameras in July 2005: alignment of the infrared data with the visible-light map is approximate.
Analysis of the total amount of infrared energy and the relative amounts of radiation measured at different wavelengths shows 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 from the fractures themselves. The fractures themselves may be even warmer than the 180 Kelvin (minus 140 degrees Fahrenheit) detected – perhaps warm enough for liquid water to exist under the surface.
Cassini captured the data for this new mosaic during the spacecraft's close flyby of the moon on Nov. 21, 2009, at a distance of approximately 2,000 to 3,000 kilometers (1,200 to 1,800 miles) from Enceladus. The closeness of the flyby and the speed at which the spacecraft swept past the moon meant that Cassini had to use its thrusters to rotate the spacecraft to track Enceladus, rather than using its slower but more accurate reaction wheels.
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 composite infrared Spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md., where the instrument was built.
For more information about the Cassini-Huygens mission visit http://www.nasa.gov/cassini or http://saturn.jpl.nasa.gov.