Celestia Forums

Sorry guys a noob question again.
I searched the forum and found a scc file for a double planet system. The problem is, I can't get it to work. The first planet's orbit shows up, but you can't see it. The second planet, which is invisible, and the two planets around it don't show up either in orbits or the system browser. Here is the scc file I am trying to manipulate.
Thanx
Tim



Here is the info I could gather, from canon sources-

Vulcan, also known as T'Khasi, is the class-M desert planet that is home to the Vulcans.

Vulcan has no moon, but does have a sister planet - T'Rukhemai - one feature of which is the Vulcanis Lunar Colony. (TOS episode: "The Man Trap", novel: Sarek; and conjecture from VOY episode "Unimatrix Zero" as per VOY novel Pathways).

and that it would "have the Sun's brightness for a planet 50 million miles away",

Vulcan is likely about 0.61 AU from 40 Eridani A. At this distance the planet would complete a revolution in 203 earth days

My theory is that Vulcan has a twin planet, call it B, and they orbit each other around a common gravitational point. Vulcan and B are almost nearly of equal size but B is slightly larger so if one must be totally truthful Vulcan is more under the gravitational influence of B than visa versa. Therefore Vulcan is more a moon of B than B a moon of Vulcan, so Vulcan has no moon. But that scene in ST:TMP is perfectly explainable, it is simply B rising in Vulcan's sky. As for the third object, let's call it C, that is simply B's moon, and as for Tuvok being raised on a Vulcan Lunar colony, that colony could logically be located on C.

One problem is that some of the values are missing leading 0s: Celestia v1.4.1 requires that numeric values not start with a decimal point.

i.e. use 0.5 not .5

This restriction has been eliminated in v1.5.0

Thanks selden, that fixed that.
Now I want to put a moon around T'Khut. Like the info I gathered. But that's not working either. Is it even possible?
Thanx
Tim

1. T'Khut is defined to orbit around ScyllaCharybdis, so you have to include that in the "path" of its moon, too.

"Moon" "40 Eri A/ScyllaCharybdis/T'Khut"

2. The SemiMajorAxis of the moon is too small: it's orbiting inside T'Khut.

3. Bugs in how Celestia handles invisible class objects causes other problems:
a. its orbit path around 40 Eri A isn't drawn
b. T'Khut isn't listed by the Solar System Browser.

A workaround for problem #3 would be to define ScyllaCharybdis as a Class "planet" instead of "invisible" and use a Mesh for it that is made of a material that is invisible (opacity 0).
p.s. or you could color it black and give it a low but non-zero albedo. (0 albedo causes its "moons" not to be drawn, too.)

A few comments about the moon:

1. The moon has a rather long orbital period for its distance. A moon that is orbiting an Earth-sized planet at a distance of ~5000 km would have a period of a few hours, not 28 days.

2. The moon's orbit isn't stable. At a distance of ~5000 km, it would spiral inward and break up or crash on a timescale of a few million years.

The planets:

At their separation of 44087 km, the two planets are likely to be tidelocked to each other by the time the planets are able to be a home to life of any kind. The planets would take maybe a few tens of millions of years to be tide locked, and the time to develop life is on the order of a few hundred million years.

Another problem for moons is the complicated double gravity well of the double planet. This makes it difficult to capture a moon into orbit around one of the worlds because the other planet would perturb it.

So a moon orbiting one of these planets is unlikely on stability grounds. It's not impossible but the moon wouldn't last long.

For double planets, take a look at the Pluto system for inspiration. Pluto and Charon are tidelocked to each other, and they have two small moons - Nix and Hydra - orbiting at a respectful distance. So a fairly close double planet can have moons, they just can't orbit one of the planets. The moons would have to orbit the barycentre of both planets.

In my Local Space fiction (see link below), I have modelled three double planets. The terrestrial pair have no moon, and the other two are binary gas giants with a few moons orbiting at a relatively great separation.

Scientificly, of course you are correct. To stay with Star Trek canon sources that I have been able to track down, then what I have put together (except maybe for distances) is as close as I can get.

Thanx
Tim