Celestia: creating asteroids

Celestia is a cool piece of free software that can be downloaded here (https://celestia.space/) to fly around the universe and explore planets and stars.

Once you have had a good look around you may decide to add more things into Celestia, such as updating it with the latest space mission images or add in planets around other stars. You can find a library of add-ons that have been created here (http://www.celestiamotherlode.net/).

But maybe, like me, you want to make your own objects to visit.

I decided I wanted to create some more asteroids that were discovered by Pam Kilmartin and Alan Gilmore on Mount John Observatory in Tekapo NZ. This is how I did it.

asteroid 2432 Bateson one of the asteroids I created in Celestia. Photo credit: Holly

The first thing is to get familiar with the types of files that Celestia uses. For solar system objects .ssc files are used. This is what an asteroid in Celestia looks like from a program file perspective

“2432 Bateson:Bateson” “Sol”

{

Class “asteroid”

Texture “asteroid.jpg”

Color [ 1.000 0.912 0.833 ]

BlendTexture true

SemiAxes [ 145 120 95 ]

Mesh “deimos.cmod”

EllipticalOrbit

{

Epoch 2458200.5

Period 5.41

SemiMajorAxis 3.0800958

Eccentricity 0.1704132

Inclination 15.62897

AscendingNode 27.36701

ArgOfPericenter 247.948

MeanAnomaly 230.80450

}

UniformRotation

{

Period 7.811

Inclination 56

AscendingNode 196

}

Albedo 0.238

}

The first line gives the name of the object with the ‘:’ separating different names in this case “2432 Bateson” and “Bateson” then it states what star it is around in our solar system that the Sun “Sol”. It then goes onto list parameters for the asteroid such as orbit, spin, color, ect. with the imputed values for the object after them. There are even more parameters you can change in a .ssc file see https://en.wikibooks.org/wiki/Celestia/SSC_File#Structure_of_an_object_definition for a full list and explanation.

So to create your own asteroid you would open a text editor (Wordpad will do but Microsoft Word will not work) and copy in the above structure.

Then you would change the parameters for your object. For an asteroid, you need to have Class set to “Asteroid” then find and input the orbital elements needed. To look up the orbital elements I would recommend using the minor planet center https://minorplanetcenter.net/db_search and type in the asteroids catalog number, which will return the orbital data that you need.

This is another one of the asteroids I created 3087 Beatrice Tinsley. This shows the asteroids orbit highlighted in red in reference to the other inner planets. Photo credit: Holly

The next important thing is how you want the asteroid to look. The parameters Texture and Mesh tell Celestia how it will look.

Mech is the 3D shape that celesta will show and Texture is the image put on top of that shape. I chose to use the built-in mesh of Mars’s moon Deimos to give the asteroids a nice irregular shape and then the texture built-in for generic asteroids but these can be customized if you want.

Once you have completed this, it saves your text as a .ssc file. This file should be saved in your Celestia program files under extras with a new folder with the object name. For example, mine is saved in Celestia\extras\ MJ_astorides.

yet another asteroid 3400 Aotearoa with Jupiter in the background. Photo credit Holly.

Then you start up Celestia and see if it worked! If yes congrats. If not, troubleshoot and see where the issue is, maybe is part of coding.

Happy asteroid building.