Cassini has performed the final close flyby of Enceladus, and the team decided to go back to a mysterious terrain that was glimpsed 10 years ago. The region is peculiar because the dark areas looked similar to the spots on Dalmatians – or at least, that's the simile NASA used.
The new image, seen above in false colors, provides more insights regarding the nature of the spots. The spots are large and they range in size from tens to hundreds of meters. They are believed to be dark protrusions of solid “bedrock” ice likely created by downslope movement or sublimation events. Enceladus has a tenuous exosphere (thin atmosphere) so there is no erosion that could explain how the bedrock become exposed.
The image has a resolution of 67 meters (220 feet) per pixel at the center and it is in a wider range of colors than human vision. The false-color view uses an ultraviolet filter for blue, and a near-infrared filter for red to cover a wider spectrum region than the human eye. The green filter is still used for green.
Enceladus is the sixth-largest moon of Saturn and is mostly covered by fresh, clean ice. Despite its small size, Enceladus has an interesting geology that goes from old cratered areas to young active ones. The region imaged by Cassini is itself tectonically active. The dark spots seem to be aligned in chains parallel to the narrow fractures. Large crevasses can be seen also crossing the area.
This Cassini image shows the dalamation spots as seen in 2005. NASA/JPL/Space Science Institute
Cassini analysis of Enceladus has been very fruitful in the last year, with the probe all but confirming the presence of a global ocean underneath its icy surface. The ocean appears to be warm enough to generate the geological changes seen on the surface as well as producing plumes, which Cassini dived into a few months ago.
Studying the plumes is important to understanding what’s lurking beneath the ice. Organic components could be an indication of biological processes underground, escaping through the plumes, and would allow scientists to estimate the chances of life on Europa. The plumes are also important for Saturn's rings; escaping the moon’s gravity, the material contributes to one of Saturn's rings, the E-ring.
Cassini is a joint mission of NASA, ESA, and the Italian Space Agency. It will conclude in September 2017, when the spacecraft will be sent into Saturn’s atmosphere. This is a precaution to guarantee that there is no contamination of areas that could potentially host life.