When you ponder all the amazing vistas in our universe, colorful visions of distant nebulae and galaxies likely come to mind. But you don't need to vicariously travel millions of light-years to get an eyeful of wonderment. As NASA's Cassini spacecraft has shown time and time again, spectacular views can be found right in our own planetary backyard.This past week, Cassini scientist Carolyn Porco and her imaging-team colleagues released a clutch of "holiday treats" featuring Saturn and its largest moon, Titan. I found the one shown here particularly beautiful, but you can jump over to the team's CICLOPS website to see the rest.
Titan is an amazing place, not only because it's larger than the planet Mercury but also because it's the only satellite with a substantial atmosphere. The air around Titan is dense and mostly nitrogen, as is this case on Earth, but comparisons to our atmosphere end there. Titan's mix contains no free oxygen, containing instead methane and ethane that create dense photochemical hazes when exposed to sunlight and space radiation.
All that haze is manifest in Titan's dingy coloration and as a dirty-looking layer suspended above the moon's disk all the way around. Also, as Porco points out, "The day-night terminator is real and gradual, as you might expect on a very hazy atmosphere." Note how the disk darkens around its sunlit outer edge, another consequence of countless microscopic haze particles.
Titan's gauzy disk is star of this scene, but there's a lot more going on. Seemingly latched on at right is the bright disk of Dione. It's only one-fifth as large as Titan, but it looks smaller because when Cassini recorded this view last May 11th, Titan was 1.4 million miles (2.3 million km) from the camera and Dione was more than half again farther away. Fascinating in its own right, Dione reflects about 60% of the sunlight striking its icy surface, whereas Titan reflects only 20% and consequently looks darker.
Meanwhile, the planet Saturn creates the dramatic backdrop for the satellites. We see the planet's rings edge-on, projected as a horizontal ribbon that neatly bisects Titan. At bottom is the black shadow cast by the opaque B ring onto Saturn's creamy-colored clouds, and above that are a nest of dark stripes cast by closely spaced ringlets in the inner C ring.
So many of the cosmic scenes released by NASA's Hubble and Spitzer space telescopes often include unseeable infrared channels to enhance the visual impact. But this and many other vistas from Cassini are taken through a simple combination of red, blue, and green filters to reproduce, as closely as possible, the view that you'd see while looking through the porthole of a visiting spaceship.