Slashdot Mirror
Cassini Confirms New Moon of Saturn
pipcorona writes ""In a spectacular kick-off to its first season of prime ring viewing, which began last month, the Cassini spacecraft has confirmed earlier suspicions of an unseen moon hidden in a gap in Saturn's outer A ring. A new image and movie show the new moon and the waves it raises in the surrounding ring material."
I do believe our own moon is named Luna, which would be where you get the word "Lunar", although you rarely ever hear anybody call the moon by its actual name.
The Rings are inside the Roche limit, which is the point where tidal forces will destroy a satellite. However, the Roche limit assumes a liquid body. A small solid body has enough physical strength to hold itself together even inside the Roche limit.
"Words of wisdom: drop that zero and get with the hero" -- Vanilla Ice
Resolution. Most space cameras work by detecting light falling on a CCD (Charge-Coupled Device); if the camera was full color, then the resolution would be cut by at least 2/3 because you'd have to devote 1/3 of the CCD to each of the primary colors. (It might be even worse than that if your imaging system wasn't 100% efficient at directing the color components to the proper pels on the CCD). You can obtain the effect of a color camera by using different lens filters and taking multiple pictures and then composing them into a single image - this is what's usually done when a color photograph is desired. By doing that you can produce an image that's exactly what you could obtain with a color camera, but at a higher resolution and without having to use a higher resolution CCD. Also, that way your pictures aren't limited to using a selection of color components that are compatible with those the human eye sees - you can use the filters to "see" parts of the spectrum outside the range that's visible to the human eye.
The Roche limit only works for large bodies, when you assume that the moon is only held together by its own gravity.
For very small, rocky moons, the tensile strenght of the rock itselv enabls them to exist nearer than the roche limit. Its nothing extremely longtime-stable, but otoh, the tidal forces on a small moon arent very large.
Also, the roche limit is only a contant (2.xxx*R_bigplanet or so) if the bodies have the same density. If the objects is, for example, a captured iron asteroid, its roche limit can be VERY close to a not very dense saturn.
HI O WISE PRINCE. WHT TOOK U SO DAM LONG?
No good. That name would be for a moon of Jupiter (as they're usually named for his various lovers). Saturnian moons are named for Titans or Titan-like gods from other pantheons.
You nailed it. The ring material inside the S/2005 S1's position is moving faster than the moon, so the waves that the moon excites appear ahead of the moon's present position. (That material just had a close encounter.) The other edge of the gap is orbiting more slowly, so the moon PASSES it, so the waves appear behind the moon.
I'd avoid the word "turning" because it suggests a solid object. The rings are anything but solid.
There are other ways to make asymmetries in these wakes. If the moon isn't well-centered in the gap (although it isn't clear why it wouldn't be) or has a significant orbital eccentricity, you'll get asymmetry as well.