Shadows, Plus Navigating the Gap

Equinox at Saturn is only a few weeks away. Shadows cast on the rings are getting lots of press. Many images and some video are up at the Cassini site, including this (above) capture of the shadow of small irregular-shaped moon Epimetheus crossing the rings of Saturn. Shadows of large moon Tethys, small moon Pan, small moon Pandora, and large moon Mimas (in color) are also interesting to see.

The most amazing shadows are those of Daphnis and the rise it gets out of nearby ring boundaries. Check out the link with the one below, as well as here and here. The image below includes a few background stars, including that bright spot, upper right, in the rings.

A Daphnis video is here. Given that the little moon in its gap (the Keeler Gap is about 26 miles wide) is itself about five miles in diameter, and if one assumes the moon is squarely on the ring plane (not above or below it), and the longest of the ripple shadows is about two-thirds the length of the moon’s shadow, the wave heights on the edges of the Keeler Gap might approach a mile-and-a-half, about my commuting distance to work. I like to think about these images and what the scene would be like close-up. It’s interesting to ponder the scale we see in these visuals. The Keeler Gap, for example, is about the distance from one end of a typical Iowa county to another.

You might imagine the sight from the surface of Daphnis would be pretty impressive. And because you’re out in near-Saturn space, indeed it might–big golden Saturn would be part of the backdrop. But I’m thinking the best views are the ones we’re getting from Cassini, from thousands of miles away.

From the moon, yes, you would have a thirteen-mile vantage point for the ring edges. The full wave looks to me to be about 200 miles long, and about the same distance away from Daphnis, so it would stretch off in the distance, up-and down-orbit. I was thinking about running a very long tether from the moon, trailing Daphnis by a few hundred miles. Even then the wave height from the middle of the Keeler Gap would only span a spacesuit’s fist at arm’s length. My sense is you would only see the one wave, so it would be a very gradual curve. Remember: a mile high, but two-hundred miles long. On a sheet of paper, that translates to a millimeter-high ripple. On a tarp-covered baseball diamond, it would be like a forgotten bat–the pitcher’s mound would be way too big.

Zooming in closer could be trouble. There might be a lot of random debris hear the ring edges. Even though it all looks pretty neat from Cassini, a house-sized boulder could do some serious harm to a little spaceship–and objects that size aren’t being resolved by the Cassini images of the rings.

You might wonder: what if we could just hover above the rings, say from fifty miles above the crests and buzz the waves as we pleased? Unless you want to invest in and spend a lot of rocket fuel, no can do. Remember these rings are not like clouds on a planet. Each ring particle from a speck of ice or dust to the stadium-sized boulders and in between are in themselves, moons orbiting the planet. If you were fifty miles above the ring waves, one-quarter trip around Saturn–and less than four hours later–you would find yourself plunging through the ring plane, surrounded by whatever mess Daphnis kicks up.

If I were going to Saturn, plant me on a moon. I’d want to steer clear of the rings–until I know more about what it’s like close up in there.

I’ll leave off this post with a nice color piece of Saturn. The rings cast their own shadow on the planet, plus you can see the blob of the shadow of Mimas. It had just slipped off the rings when this image was captured.

About catholicsensibility

Todd lives in Minnesota, serving a Catholic parish as a lay minister.
This entry was posted in Astronomy. Bookmark the permalink.

1 Response to Shadows, Plus Navigating the Gap

  1. Pingback: Carnival #109 « Catholic Sensibility

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s