Cassini sings Saturn's blues
Saturn's northern latitudes are presently a serene blue, more like Uranus or Neptune, seen in this natural colour view taken by the NASA/ESA/ASI Cassini spacecraft on 14 December 2004.
Light rays here travel a much longer path through the relatively cloud-free upper atmosphere. Along this path, shorter wavelength blue light rays are scattered effectively by gases in the atmosphere, and it is this scattered light that gives the region its blue appearance.
Why the upper atmosphere in the northern hemisphere is so cloud-free is not known, but may be related to colder temperatures brought on by the ring shadows cast there.
Shadows cast by the rings surround the pole, looking almost like dark atmospheric bands. The ring shadows at higher latitudes correspond to locations on the ringplane that are farther from the planet - in other words, the northernmost ring shadow in this view is made by the outer edge of the A ring. Spots of small bright clouds also are visible throughout the region.
The Cassini-Huygens mission is a co-operative project of NASA, ESA and ASI, the Italian space agency.
Credit: NASA/JPL/Space Science Institute