The Cassini
spacecraft captures Saturn's glow, represented in hues of electric blue,
sapphire and mint green, as it flies over the unlit side of Saturn's rings. The
planet itself casts a wide shadow on the rings.
This false-color mosaic incorporates 25 images taken by Cassini's
visual and infrared mapping spectrometer over a period of 13 hours, and
captures Saturn in nighttime and daytime conditions. Data at wavelengths of
2.3, 3.0 and 5.1 microns were combined in the blue, green and red channels of a
standard color image, respectively.
This image was acquired on Feb. 24, 2007, while the
spacecraft was 1.58 million kilometers (1 million miles) from the planet and
34.6 degrees above the ring plane. In this view, Cassini was looking down on
the northern, unlit side of the rings, which are rendered visible by sunlight
filtering through from the sunlit, southern face.
On the night side (right side of image), with no sunlight,
Saturn's own thermal radiation produces a reddish glow. This light, at 5.1
microns wavelength (seven times longer than the human eye can see), is
generated deep within Saturn and works its way upward, eventually escaping into
space. Typically, thick clouds deep in the atmosphere block that light. Here,
dark streaks, spots, and globe-encircling bands are visible instead. These
phenomena are ever-shifting in the planet's strong winds.
The northern hemisphere is about twice as bright as the
southern hemisphere, because high-level, fine particles are about half as
prevalent in the northern hemisphere as in the south. These particles block
Saturn's glow, making Saturn look brighter in the north.
At 2.3 microns (shown in blue), the icy ring particles are
highly reflecting, while methane gas in Saturn's atmosphere strongly absorbs sunlight
and renders the planet very dark. At 3.0 microns (shown in green), the
situation is reversed: water ice in the rings is strongly absorbing, while the
planet's sunlit hemisphere is bright. Thus the rings appear blue in this
representation, while the sunlit side of Saturn is greenish-yellow in color.
-- NASA/JPL/University of Arizona and SPACE.com Staff
Credit: NASA/JPL/University of Arizona
