A Complicated Web of Warm Fractures
New images and data from NASA's Cassini spacecraft give scientists a unique Saturn-lit view of active fissures through
the south polar region of Saturn's moon Enceladus. They reveal a more complicated web of warm fractures than previously thought.
High Resolution Heat Intensity Mapping
Scientists working jointly with Cassini's composite infrared spectrometer and its high-resolution imaging camera have
constructed the highest-resolution heat intensity maps yet of the hottest part of a region of long fissures spraying
water vapor and icy particles from Enceladus.
Tiger Stripes
These fissures have been nicknamed "tiger stripes." Additional high-resolution
spectrometer maps of one end of the tiger stripes Alexandria Sulcus and Cairo Sulcus reveal never-before-seen warm fractures
that branch off like split ends from the main tiger stripe trenches. They also show an intriguing warm spot isolated from other
active surface fissures.
"The ends of the tiger stripes may be the places where the activity is just getting started, or is winding down, so the complex
patterns of heat we see there may give us clues to the life cycle of tiger stripes," said John Spencer, a Cassini team scientist
based at Southwest Research Institute in Boulder, Colo.
The images and maps come from the Aug. 13, 2010, Enceladus flyby, Cassini's last remote sensing flyby of the moon until 2015.
The geometry of the many flybys between now and 2015 will not allow Cassini to do thermal scans like these, because the
spacecraft will be too close to scan the surface and will not view the south pole. This Enceladus flyby, the 11th of Cassini's
tour, also gave Cassini its last look at any part of the active south polar region in sunlight.
Damascus Sulcus - Hottest Part of the Fissure
The highest-resolution spectrometer scan examined the hottest part of the entire tiger stripe system, part of the fracture
called Damascus Sulcus. Scientists used the scan to measure fracture temperatures up to 190 Kelvin (minus 120 degrees Fahrenheit).
This temperature appears slightly higher than previously measured temperatures at Damascus, which were around 170 Kelvin (minus 150 degrees Fahrenheit).
Spencer said he isn't sure if this tiger stripe is just more active than it was the last time Cassini's spectrometer scanned it,
in 2008, or if the hottest part of the tiger stripe is so narrow that previous scans averaged its temperature out over a larger
area.
In any case, the new scan had such good resolution, showing details as small as 800 meters (2,600 feet), that scientists
could see for the first time warm material flanking the central trench of Damascus, cooling off quickly away from the trench.
The Damascus thermal scan also shows large variations in heat output within a few kilometers along the length of the fracture.
This unprecedented resolution will help scientists understand how the tiger stripes deliver heat to the surface of Enceladus.
Termal and Visible Light Image Pairs
Cassini acquired the thermal map of Damascus simultaneously with a visible-light image where the tiger stripe is lit by sunlight
reflecting off Saturn. The visible-light and thermal data were merged to help scientists understand the relationships between
physical heat processes and surface geology.
"Our high-resolution images show that this section of Damascus Sulcus is among the most structurally complex and tectonically dynamic
of the tiger stripes," said imaging science team associate Paul Helfenstein of Cornell University, Ithaca, N.Y. Some details in the
appearance of the landforms, such as a peculiar pattern of curving striations along the flanks of Damascus, had not previously been
noticed in ordinary sunlit images.
More Data for Saturn's Moon Tethys
The day after the Enceladus flyby, Cassini swooped by the icy moon Tethys, collecting images that helped fill in gaps in the Tethys
global map. Cassini's new views of the heavily cratered moon will help scientists understand how tectonic forces, impact cratering,
and perhaps even ancient resurfacing events have shaped the moon's appearance.
More about Cassini-Huygens Missions
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. 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.
More details are also available at the imaging team's website http://ciclops.org and the composite infrared spectrometer team's website http://cirs.gsfc.nasa.gov .
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This image shows a high-resolution heat intensity map of part of the south polar region of Saturn's moon Enceladus, made from data obtained by NASA's Cassini spacecraft.
The map reveals never-before-seen details of warm fractures that branch off like split ends from the ends of the main trenches of two "tiger stripes." The features nicknamed "tiger stripes" are long fissures that spray water vapor and icy particles. These two fissures, Cairo Sulcus (left) and Alexandria Sulcus (right), extend to the lower right, off the bottom of the image. The map also shows an intriguing isolated warm spot, shown in purple-red in the upper left of the image, that is separated from other active fissures.
The thermal data came from Cassini's composite infrared spectrometer during an Aug. 13, 2010, flyby of Enceladus. Scientists overlaid the data on a background map of that region made from Cassini images taken in July 2005. The intensity of thermal radiation, measured at wavelengths from 12 to 16 microns, is color-coded, with dark blue, purple, red and orange denoting progressively more intense radiation, due to higher temperatures and/or larger expanses of warm material. The pale blue color indicates regions that were mapped but that were too cold to emit significant radiation. Alignment of the thermal map with the underlying base map is approximate. The map shows a region approximately 130 kilometers (80 miles) across.
These data were obtained as winter darkness began to engulf the south polar region of Enceladus. Away from the warm tiger stripes, which reach temperatures up to 190 Kelvin (minus 120 degrees Fahrenheit), Cassini measured surface temperatures near Enceladus' south pole as low as 52 Kelvin (minus 365 degrees Fahrenheit), and still colder temperatures are expected as winter advances. Scientists are still analyzing the data to calculate a temperature for the cross-cutting fractures and the isolated warm spot. Image credit: NASA/JPL/GSFC/SWRI/SSI |
Hot and Narrow Tiger Stripe:
Data from NASA's Cassini spacecraft have enabled scientists to make the highest-resolution heat intensity maps yet for the hottest part of a "tiger stripe" fissure on Saturn's moon Enceladus. The moon's south polar region features several of these long fissures that spray water and icy particles, and the one in this image is called Damascus Sulcus.
The thermal infrared data, shown in color, come from Cassini's composite infrared spectrometer (CIRS). The grayscale background image, which is illuminated by light reflected from Saturn rather than by direct sunlight, is from Cassini's high-resolution imaging camera (ISS). The CIRS scan gives scientists confidence that the peak temperature along Damascus Sulcus, the most active tiger stripe, was about 190 Kelvin (minus 120 degrees Fahrenheit). This temperature is slightly higher than the previous maximum temperatures measured by CIRS at Damascus, which were around 170 Kelvin (minus 150 degrees Fahrenheit).
The intensity of heat radiation, measured by CIRS at wavelengths from 7 to 9 microns, is color-coded, with blue, purple, red, orange and yellow denoting progressively more intense radiation, due to higher temperatures and/or larger expanses of warm material. The image is centered near 80 degrees south latitude and 315 degrees west longitude, and covers a region about 16 kilometers (10 miles) wide. The smallest details seen in the CIRS overlay are about 800 meters (0.5 miles) in size.
The region of peak temperature is sharply bounded by the sides of the trench. Thanks to its high resolution, the CIRS map also shows for the first time that the regions on either side of the central trench are also radiating heat (shown as blue strips flanking the central multicolored strip in this image). CIRS measured temperatures of about 120 Kelvin (minus 240 degrees Fahrenheit) in the flanking regions about 400 to 1,200 meters (a quarter to three-quarters of a mile) away from the central trench.
These data were obtained on Aug. 13, 2010 as the south pole of Enceladus began to go into winter darkness. |
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