Cassini finds plethora of plumes, hotspots at Enceladus

High resolution image

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.

Credit: NASA/JPL/GSFC/SWRI/SSI




High resolution image

Dramatic plumes, both large and small, spray water ice out from many locations along the famed "tiger stripes" near the south pole of Saturn's moon Enceladus. The tiger stripes are fissures that spray icy particles, water vapor and organic compounds. More than 30 individual jets of different sizes can be seen in this image and more than 20 of them had not been identified before. At least one jet spouting prominently in previous images now appears less powerful. The view was obtained at a distance of approximately 14,000 kilometers (9,000 miles) from Enceladus and at a sun-Enceladus-spacecraft, or phase, angle of 145 degrees. Image scale is 81 meters (267 feet) per pixel. Credit: NASA/JPL/Space Science Institute




High resolution image

This wide-angle image shows the south polar region of Saturn's moon Enceladus and outlines the area covered by the high-resolution mosaic combining data from the imaging science subsystem and composite infrared spectrometer aboard NASA's Cassini spacecraft. The outlined area focuses on Baghdad Sulcus, a fracture in the south polar region.

Cassini captured the data for this wide-angle image during the spacecraft's close flyby of the moon Nov. 21, 2009. This image and others from that flyby are among the best visible light images Cassini will capture of the region around the "tiger stripes," -- the fissures that spray icy particles, water vapor and organic compounds -- compounds, before the moon's south polar region enters winter darkness for the coming years.

This wide-angle view shows not only Baghdad Sulcus, but also other nearby fractures. Lit terrain seen here is on the leading hemisphere and Saturn-facing side of Enceladus (504 kilometers, 313 miles across). The south pole lies in shadow near the bottom middle of the image.

The wide-angle view was acquired at a distance of approximately 2,000 kilometers (1,200 miles) from Enceladus and at a sun-Enceladus-spacecraft, or phase, angle of 114 degrees. Scale in the wide-angle view is 116 meters (381 feet) per pixel.

Credit: NASA/JPL/Space Science Institute




High resolution image

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.

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 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. Credit: NASA/JPL/GSFC/SWRI/SSI