Triton

[Matt McIrvin]

The map of Neptune's large moon Triton in Celestia's default database is not very detailed. This is unfortunate, since Voyager 2 got excellent pictures of Triton, and it's an unusual, somewhat mysterious place well worth high-res representation. It even has a tenuous atmosphere with occasional wispy clouds.

I found a good-looking map of Triton in simple cylindrical projection, produced by A. Tayfun Oner from the Voyager pictures:

http://www.star.ucl.ac.uk/~apod/solarsys/cap/nep/trimap1.htm

I haven't tried yet, but it looks as if this could be massaged into an excellent Celestia texture. We'd have to remove the white lines and maybe paint in something for the un-imaged area.

Also, I don't know what the copyright issues are for this particular image.

But it's worth looking into.

[chris]

A better map of Triton would be great . . . it's the only large solar system body for which we have data that isn't properly textured. I'm still too budy bug hunting to do this, so a contribution from someone on the forum would be greatly appreciated.

--Chris

[Matt McIrvin]

Another thing I noticed about Triton while playing around with that texture:

Triton is unique among large moons in that its orbit is retrograde. (This is a bit of a mystery, actually.) Celestia gets this right (in 1.2.2, at least) by using an inclination greater than 180 degrees. However, this defeats Celestia's default synchronous rotation for moons: Triton still rotates as if its orbit were prograde.

Adding

RotationPeriod -141.044496

to the data for Triton solves this problem. Also, if I am interpreting the map captions correctly, I believe that for the texture data mentioned above,

RotationOffset 90

is also necessary to get the sub-Neptune point right.

(Sanity check: I remember from watching TV the night these pictures came back from Voyager 2 that Triton was more or less behind Neptune at the point of closest approach, though not eclipsed. Therefore the best parts of this map should be in the hemisphere that was sunlit at that time, near the sub-Neptune point, which jibes with the above.)

This reminds me to ask: Are the rest of the moon textures oriented correctly as to longitude? I think that the tradition is to put the origin of longitude at the sub-planet point.

[Matt McIrvin]

Triton is unique among large moons in that its orbit is retrograde. (This is a bit of a mystery, actually.) Celestia gets this right (in 1.2.2, at least) by using an inclination greater than 180 degrees.

I meant "greater than 90 degrees," of course. Also, when I say "retrograde," I mean with respect to the parent planet's rotation; the big moons of Uranus and Pluto technically go in the opposite direction to most orbits in the solar system, but really the orbits are mostly sideways, as are the planets themselves.

The other retrograde moons are all tiny.