* Astronomy

This image shows the warmest places in the south polar region of Saturn's moon Enceladus. The unexpected temperatures were discovered by Cassini's composite infrared spectrometer during a close flyby on July 14, 2005. The image shows how these temperatures correspond to the prominent, bluish fractures dubbed "tiger stripes," first imaged by Cassini's imaging science subsystem cameras. Working together the two teams were able to pinpoint the exact location of the warmest regions on Enceladus.


Expand

The composite infrared spectrometer instrument measured the infrared heat radiation from the surface at wavelengths between 9 and 16.5 microns within each of the 10 squares shown here. Each square is 6 kilometres across.
The colour of each square, and the number shown above it, describe the composite infrared spectrometer's measurement of the approximate average temperature of the surface within that square.
The warmest temperature squares, at 91 and 89 degrees Kelvin, are located over one of the "tiger stripe" fractures. They contrast sharply with the surrounding temperatures, which are in the range 74 to 81 degrees Kelvin. The detailed composite infrared spectrometer data suggest that small areas near the fracture are at substantially higher temperatures, well over 100 degrees Kelvin.

Such "warm" temperatures are unlikely to be due to heating of the surface by the feeble sunlight striking Enceladus' South Pole. They are a strong indication that internal heat is leaking out of Enceladus and warming the surface along these fractures. Evaporation of this relatively warm ice probably generates the cloud of water vapour detected above Enceladus' South Pole by several other Cassini instruments. Scientists are unsure how the internal heat reaches the surface. The process might involve liquid water, slushy brine, or soft but solid ice.

The imaging science subsystem image is an enhanced colour view with a pixel scale of 122 metres that was acquired at the same time as the composite infrared spectrometer data. It covers a region 125 kilometres across. The spacecraft's distance from Enceladus was 21,000 kilometres.
The broad bluer fractures that can be seen running from the upper left to the lower right of the image are 1 to 2 kilometres wide and more than 100 kilometres long. The fractures are thought to be bluer than the surrounding surface because coarser-grained ice (which has a blue colour just as thick masses of ice, like glaciers and icebergs, do on Earth) has been exposed in the fractures.
The colour image was constructed using an ultraviolet filter (centred at 338 nanometres) in the blue channel, a clear filter in the green channel, and an infrared filter (centred at 930 nanometres) in the red channel.

The 14th July 2005 close flyby of Saturn’s icy moon Enceladus by the Cassini spacecraft confirms that the moon has a significant, extended and dynamic atmosphere. The flyby was Cassini’s lowest altitude flyby of any object to date, a mere 173 kilometres above the surface of Enceladus.

Flybys of Enceladus which took place earlier this year (on February 17th at an altitude of 1,167, and on March 9th, 500 kilometres above the surface) had shown deformation or bending of the magnetic field around the moon, revealing that Enceladus was acting as a large obstacle to the flow of plasma and magnetic field from Saturn by its extended asymmetric atmosphere.

The recent close flyby confirms and extends the observations from the two other flybys.
The magnetic data also suggests that the atmosphere is not symmetric and may be arising from a comet-like jet from the southern hemisphere.

"These latest observations are very exciting, they confirm the existence of an atmosphere which we predicted from the distant earlier flybys and they will also allow us to gain a much better understanding of the processes taking place which are producing this very exotic atmosphere" - Professor Michele Dougherty, Imperial College London, Principal Investigator on the Magnetometer instrument on Cassini.

Cassini spacecraft has obtained new detailed images of the south polar region of Saturn's moon Enceladus. The data reveal distinctive geological features and the most youthful terrain seen on the moon.
These findings point to a very complex evolutionary history for Saturn's brightest, whitest satellite.

Cassini's July 14 flyby brought it within 175 km of the surface of the icy moon. The close encounter revealed a landscape near the south pole almost entirely free of impact craters. The area is also littered with house-sized ice boulders carved by tectonic patterns unique to Enceladus. These features set the region apart from the rest of the moon.


Expand

As white as fresh snow, Enceladus has the most reflective surface in the solar system. Previous Cassini flybys revealed Enceladus, in contrast to Saturn's other icy moons, has lightly cratered regions, fractured plains and wrinkled terrain.
The new findings add to the story of a body that has undergone multiple episodes of geologic activity spanning a considerable portion of its lifetime. The moon's southern most latitudes have likely seen the most recent activity.

These same latitudes may also bear the scars of a shift in the moon's spin rate. If true, this speculation may help scientists understand why Enceladus has a tortured-looking surface, with pervasive crisscrossing faults, folds and ridges. The most remarkable images show ice blocks, about 10 to 100 metres across in a region that is unusual in its lack of the very fine-grained frost that seems to cover the rest of Enceladus.

"A landscape littered with building-sized blocks was not expected. The minimal cover of finer material and the preservation of small, crossing fracture patterns in the surrounding areas indicate that this region is young compared to the rest of Enceladus" - Dr. Peter Thomas, imaging-team member from Cornell University, Ithaca, N.Y.

False colour composites of this region, created from the most recent images, show the largest exposures of coarse-grained ice fractures seen anywhere on the satellite, which also supports the notion of a young surface at southern latitudes. Some of the latest images may hint at the answer. The images revealed additional examples of a distinctive "Y-shaped" tectonic feature on Enceladus. In this unusual element, parallel ridges and valleys appear to systematically fold and deform around the south polar terrains.

"These tectonic features define a boundary that isolates the young, south polar terrains from older terrains on Enceladus. Their placement and orientation may tell us a very interesting story about the way the rotation of Enceladus has evolved over time and what might have provided the energy to power the geologic activity that has wracked this moon" - Dr. Paul Helfenstein, associate of the imaging team also at Cornell University.

The apparent absence of sizable impact craters also suggests the south pole is younger than other terrain on Enceladus. These indications of youth are of great interest to scientists who have long suspected Enceladus as one possible source of material for Saturn's extensive and diffuse E ring, which coincides with the moon's orbit.
Young terrain requires a means to generate the heat needed to modify the surface. Other Cassini instrument teams are working to understand data about temperature, composition, particles and magnetic field. Together with image interpretation, these data can create a more complete picture.

From New Scientist:

Bizarre boulders on Enceladus surface:

On 14 July, Cassini swooped in for an unprecedented close-up view of the wrinkled moon. Its Imaging Science Subsystem (ISS) camera has since returned pictures of a boulder-strewn landscape that is currently beyond explanation. The "boulders" appear to range between 10 and 20 metres in diameter in the highest-resolution images, which can resolve features just 4 m across.

“That’s a surface texture I have never seen anywhere else in the solar system,” says David Rothery, a planetary geologist at the Open University in Milton Keynes, UK.

Cracks crisscross Enceladus's surface - possibly as a result of the moon being repeatedly squeezed and stretched by the gravity of Saturn and other moons nearby. But Rothery points out the boulders avoid - rather than fill - the cracks. This might indicate that the fracturing took place after the boulders had already formed.
Alien landscape

John Spencer, a Cassini team member at the Southwest Research Institute in Boulder, Colorado, US, agrees that the images are puzzling. “You would expect to see small craters or a smooth, snow-covered landscape at this resolution," he told New Scientist. "This is just strange. In fact, I have a really hard time understanding what I’m seeing.”

NASA scientists have been locked in discussions since 15 July and are expected to pass judgment on what they think this peculiar surface might be later on Tuesday.

But Elizabeth Turtle, a Cassini imaging team member at the University of Arizona in Tucson, US, warns there will be no quick answers. “Trying to figure out what is going on is going to take a lot longer than a weekend of swapped emails,” she says.