Celestia Forums

Is there an addon with the incomplete arcs in Neptune rings system?
Is there a support in Celestia code for such objects?
Thank you.

Celestia generates rings by rotating a ring texture through 360 degrees around the planet, so there is no way to create a partial ring at present, unless someone wants to build a 3ds object to do the job.

Grant

It's easy to fix Celestia to use the entire texture . . . Making the shadows work as well is slightly trickier--mostly a matter of writing an atan2 function in a vertex program.

--Chris

chris wrote:It's easy to fix Celestia to use the entire texture . . .

Oooooh, that'd be nice - then we could build "lumpy" fresh debris rings, too.

Grant

The problem is not really to draw the arcs but to simulate their dynamics, which I think is not well understood and strongly influenced by Neptune's satellites and a little chaotic.

I was looking through the web to find if anyone has come up with a way to tell approximatively for each arc its position, length and thickness at a given time, but haven't found anything yet.

In Solar System Dynamics, there's a description of how Porco reported that a 42:43 resonance with the moon Galatea would produce 42*2 = 84 corotating resonance sites in the Adams ring, each one 360/84 = 4.3 degrees long and 1.2 kilometres wide. Dust in the ring would circulate around these stable points. There are problems with the longterm dynamics of such a system, though.
Here is a paper modifying Porco's original theory so that dust is confined by kilometre-size bodies occupying just some of the resonance sites - improving the longterm stability of the system, and explaining why only some segments contain ring arcs. (In this model, the dust arcs are spread between resonances, rather than being centred on them.) The arcs themselves are ~15km in radial width, embedded in the diffuse Adams ring ~50km wide. Note added later: This paper predicts 86 resonance sites rather than the 84 given in Solar System Dynamics.

The layout of ring arcs (in fact, just dust concentrations within the continuous Adams ring) from Solar System Dynamics is as follows, from leading to trailing:
Courage arc (4.3 degrees, partially filled)
Empty arc (4.3 degrees)
Libert? arc (4.3 degrees)
Empty arcs (8.6 degrees)
Egalit? 1 (4.3 degrees, partially filled)
Egalit? 2 (4.3 degrees)
Empty arc (4.3 degrees)
Fraternit? arc (8.6 degrees, containing two neighbouring librating systems)
(The "empty arcs" contain no noticeable excess dust concentration, but do contain dust at the general background level of the Adams ring.)

To model such a system properly we'd need to be able to rotate the ring texture. Impossible to model more complex systems without being able to introduce several different ring systems, each with its own characteristic orbital period.

Grant

PS added after more reading: I've come back and removed misleading suggestions in my original post that the arcs move in synch with Galatea - in fact, there is a 30km radial "wave" of distortion which sweeps through the arcs in synch with Galatea. I assume that the mean motion of the arc particles must be at the local circular orbital velocity.