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Cassini 'tastes' organic brew at Saturn’s geyser moon
26 March 2008
| New structure, density and composition measurements of Enceladus’ water plume were obtained when the Cassini spacecraft’s Ultraviolet Imaging Spectrograph observed the star zeta Orionis pass behind the plume on 24 October 2007, as seen in this animation.
Changes in the starlight as it dimmed while passing through the plume allowed the spectrograph to identify the plume’s physical and chemical composition. The spectrograph detected four high-density gas streams composed of water vapour. The density of the water vapour is twice that of the broad plume of gas that surrounds each jet.
This measurement confirms the theoretical analysis performed prior to the flyby that showed it was safe for Cassini to fly very closely past Enceladus, even through part of the plume, during the 12 March 2008 flyby.
Credits: NASA/JPL/University of Colorado | |  |  | |
| | | | | Jets of high-density gas detected by Cassini’s Ultraviolet Imaging Spectrograph on Saturn’s moon Enceladus match the locations of dust jets determined from Cassini images, labeled here with Roman numerals. The spectrograph pinpointed the locations of individual gas streams in the plume in a stellar occultation –the technique involves measuring the light of a star (in this case, zeta Orionis), as it passed behind the plume from Cassini’s viewpoint.
The blue line in this projection shows the path of the starlight through the plume, over the south polar region of Enceladus. The instrument looked at the star across this path in the direction indicated by the short blue lines.
Some of the dust jets appear to merge together in stellar occultation data. The dimming of starlight labeled ‘a’ was caused by dust jets V and VII. The dimming of starlight marked as feature ‘b’ may be associated with dust jet I if the jet is not perfectly vertical. Dimming of starlight labeled ‘c’ corresponds to dust jet VI, and ‘d’ is dust jet III, with dust jet II in between. The individual jets come from sources with an area of less than 300 by 300 m - about the size of half a tennis court - probably stretched out rectangularly along the tiger stripes. The new data indicate that the water molecules are blasting off from Enceladus at faster than 600 m/s.
Credits: NASA/JPL/University of Colorado | | | | |
| | | | | The lower panel is a mass spectrum that shows the chemical constituents sampled in Enceladus’s plume by Cassini’s Ion and Neutral Mass Spectrometer during its fly-through of the plume on 12 March 2008. Shown are the amounts, in atomic mass per elementary charge (Daltons [Da]), of water vapor, methane, carbon monoxide, carbon dioxide, simple organics and complex organics identified in the plume.
Credits: NASA/JPL/SwRI | | | | |
| | | | | Enceladus’s plume was found to have a comet-like chemistry by Cassini’s Ion and Neutral Mass Spectrometer during its fly-through of the plume on 12 March 2008. Water vapor, methane, carbon monoxide, carbon dioxide, simple organics and complex organics were identified in the plume. The graph shows the chemical constituents in percentage of abundance found in comets compared to those found in Enceladus’s plume.
Credits: NASA/JPL/SwRI | | | | |
| | | | | Cassini’s 12 March 2008 flyby of Enceladus provided the best view yet of the heat radiation from the active south pole of the satellite. These images summarize what was learned about the south polar landscapes and heat radiation during the previous close flyby on 15 July 2005.
The left panel shows a map of the south pole constructed from images taken by the spacecraft’s imaging system. Four prominent fractures, informally called "tiger stripes," cut diagonally across the south polar region. In the right-hand panel, a July 2005 map of the south polar heat radiation, obtained by Cassini's Composite Infrared Spectrometer, is superimposed in false colour on the visible images. The observations revealed a prominent warm region centered on the south pole, appearing yellow and orange in this view, which coincides with the locations of the tiger stripes. However, these data were taken from too far away from Enceladus (about 80 000 km) to distinguish the fine details of the heat radiation. The July 2005 flyby also included some scattered close-up snapshots by the Composite Infrared Spectrometer; these showed that the heat radiation was concentrated along the tiger stripe fractures, but those snapshots covered only a small fraction of the south polar region.
The white lines enclose the area covered by the much more detailed view of the south pole obtained by the spectrometer during the 12 March 12 2008 flyby. Numbers on the map show latitude and longitude.
Credits: NASA/JPL/GSFC/SwRI/SSI | | | | |
| | | | | Heat radiating from the entire length of 150 km-long fractures is seen in this best-yet heat map of the active south polar region of Saturn's ice moon Enceladus. The warmest parts of the fractures tend to lie on locations of the plume jets identified in earlier images, shown in the annotated version with yellow stars. The measurements were obtained by the Cassini spacecraft’s Composite Infrared Spectrometer from the spacecraft’s close flyby of the moon on 12 March 2008.
Remarkably high temperatures, at least 180 Kelvin were registered along the brightest fracture, named Damascus Sulcus, in the lower left portion of the image. For comparison, surface temperatures elsewhere in the south polar region of Enceladus are below 72 Kelvin.
Heat is escaping from Enceladus' interior along these warm fractures, dubbed "tiger stripes," which are also the source of the geysers that erupt from the polar region. The infrared radiation was mapped at wavelengths between 12 and 16 micrometres. The infrared data, shown in false colour, are superimposed on a greyscale image mosaic of the south pole obtained by Cassini's cameras on 14 July 2005, during the previous close Enceladus flyby. Numbers on the map indicate latitude and longitude.
This new view shows that at least three of the south polar fractures are active along almost their full lengths - the fourth one, on the right, was only partially covered by this scan. The level of activity varies greatly along the fractures. The warmest parts of the fractures tend to lie on locations of the plume jets identified in earlier images. The main ‘tiger stripe’ fractures are not the only sources of heat, however; additional warm spots are seen in the upper right part of the scan. The warm regions are probably concentrated within less than a few hundred meters (a few hundred yards) of the fractures, and their apparent width in this image results from the relatively low resolution of the infrared data.
This map was made by scanning the south pole during the period from 16 to 37 minutes after closest approach to Enceladus, at a distance between 14 000 and 32 000 km as Cassini rapidly receded from its close, 50-km flyby.
Credits: NASA/JPL/GSFC/SwRI/SSI | | | | |
| | | | Notes for editors:
| The number of water particles in Enceladus’s plume peaked over the area highlighted by the circle in this image of Enceladus, which is overlain by data from Cassini’s Ion and Neutral Mass Spectrometer, and the spacecraft’s trajectory, during its fly-through of the plume on 12 March 2008.
Credits: NASA/JPL/SwRI/SSI | | | | |
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