Bad Astronomy

A moon skating in its own ice

[IMPORTANT UPDATE: I have been informed that the ring depicted in this image is the G ring, and not the E ring. It was misidentified in the original CICLOPS press release, and an update has been issued. Unfortunately, not being a Saturn expert, I wasn’t able to tell them apart, and they are both diffuse rings - though the E ring is far more spread out than G. I’ll leave the post below as it was published, but bear in mind the one paragraph describing the ring is incorrect.]


There are times I wish I had more than 610 pixels of width to this blog, because then I could display this eerie and wonderful picture in its full glory:

[Click to embiggen]

The full size image isn’t much bigger, but gives you a better idea of the loneliness and blackness of space. Taken by Cassini, it shows the ice moon Enceladus. You can just see the geysers at the moon’s south pole spewing out plumes of frozen water hundreds of kilometers high.


The diffuse swath of light in the background is Saturn’s faint E ring, which is composed of the very ice particles Enceladus has launched into space. The ice is moving rapidly enough to leave the feeble gravity of the moon, but not the far stronger gravity of the solar system’s second largest planet. It settles into orbit, creating the ethereal annulus. A note: look at how the moon is lit. On the far left is the thin bright crescent of the part of Enceladus lit directly by the billion-kilometer-distant Sun. There is a twilight region as you move right, and then ever-brightening landscape as your eyes track even more to the right. That part of Enceladus is being lit by Saturnlight, the glow from the planet 240,000 km (150,000 miles) away. That light is doubly-reflected; once from Saturn to the moon, then from the moon to Cassini’s waiting cameras. Then, of course, it’s translated into radio waves and sent back home, to an Earth a long, long way off, where we can oooh and aaahhhh over the beauty of astronomy and worlds so distant and cold.

Credit: NASA/JPL/Space Science Institute

Related posts:

- Enceladus is erupting!
- A marvelous night for a (Saturn) moon dance
- Seasons E rings!
- What if Earth really did have rings?