SE setting different mass for custom planets

[keen meteor]

While I was making my mod which adds Adrian (Tau Ceti e) to the game, I noticed that the game is setting its mass to 2.9896 M_Earth even though I've specified its mass in its files as 3 M_Earth...

[pale oracle]

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[keen meteor]

In-game:

In its .sc file:

Here is the .sc file for it if needed

It's also on the workshop too https://steamcommunity.com/sharedfiles/filedetails/?id=3702441501

Someone else who makes custom systems had also pointed out (in a different server) this same bug that I was getting

[verbal glen]

I would think that this would be a rounding error, although that would be pretty weird for this, as you specify an integer for it

Maybe try setting it to different values, like 2 or 4, and see what happens there ?

[twin ridge]

Not exactly a rounding error when it can be a whole Earth mass off on larger planets.

[twin ridge]

(Not my planet, this is PlutonionEmpire's)

I think it's happening to proc gen planets too since my 17.2 me terra is now 16.95me in the beta.

But I'll have to export the script later when I get home.

[teal coral]

Probably relates to this, if I had to guess the generator recalculates the mass based on the smaller mean radius and the normal density after adjusting for oblateness. So for procedural objects this might be fixed in a sense.

[twin ridge]

Yep, exactly what was happening and what me and Mystic were able to confirm.

So yeah the oblateness-density bug is indeed fixed. Just not in an ideal way.

[simple stag]

This is technically "not a bug", but with a softness you could sleep on.
I'm looking into issues related to the density fix, and will add this to my reporting.

[teal coral]

Do not forget about THIS density bug https://discord.com/channels/148933808811409408/1417635339492917278

[twin ridge]

Yeah that one is arguably worse 💀

[teal coral]

This has now produced a different bug where all orbits around oblate planets have inaccurate orbital period, because the new mass after adjusting for oblateness is smaller and the orbits are not recalculated.
Example:
RS 7081-452-2-16-262 3
Mass 40.546 Me
Eq diameter 52824.34km
Density 3.1375 g/cm3
Oblateness 0.033827
Moon: Mass 0.96985 lunar
SMA 140067.11 km
This moon has orbital period of 22h 21m 57s.
Based on Kepler's third law the orbital period based on this mass should be 22m 45m 17s.
For the orbital period shown in SE to be correct, original mass must be 41.969 Me.
If we keep eq radius and density constant but set oblateness to 0:
An oblate spheroid with equatorial radius a and flattening f has volume V = (4/3)πa²b, where the polar radius b = a(1−f). Setting f = 0 restores the full sphere, V = (4/3)πa³, so the volume grows by exactly a factor of 1/(1−f) — about 3.50 % in this case.
With an equatorial radius of 26,716.885 km and a density of 3.1375 g/cm³ (3137.5 kg/m³) held fixed, the spherical volume works out to 7.988 × 10²² m³, and the resulting mass is:
M ≈ 2.5063 × 10²⁶ kg ≈ 41.966 Earth masses. (The same as the original mass for that orbital period)
So this mismatch in orbital period is almost certainly because of this "fix". It affects every single planet and moon orbiting planets with oblateness > 0.
Again, the mass is not what needs recalculating. The mean radius should be kept constant and the equatorial radius increased to keep density the same.

Going to take this opportunity to also bump the bugs about binary stars not using their actual combined mass to calculate orbital period, instead using a fake value, and the bug about multiple star systems only using the dominant partner in the barycenter instead of the combined mass to calculate orbital period/SMA.

[lament geyser]

my 2c: this is a clever solution. we just need a new parameter called MassInfo, similar to OblatenessInfo, that serves the same purpose: mass in the wiki and tooltip.

however, it still doesn’t fix the root problem of equatorial radius being the "main radius" instead of mean radius.

[lament geyser]

very clever.

[lament geyser]

This has now produced a different bug where all orbits around oblate planets have inaccurate orbital period, because the new mass after adjusting for oblateness is smaller and the orbits are not recalculated.
I also wouldn’t consider this a bug beyond it displaying the wrong mass. the actual mass and orbital period of planets cannot be changed anyways after that stage of generation.

[teal coral]

Well the idea is the mass is changed to keep the density constant. If the mass is higher then the density is higher.

[lament geyser]

said recalculcated mass is only ever used in the tooltip and wiki though. it’s unnoticeable if they just display the original mass

the mass is, afaik, only changed after generation is 100% complete.

[teal coral]

The whole bug was that oblateness increased density because it reduced the volume. The fix here was to reduce the planets mass apparently so it does not increase density instead of making it increase the eq radius.

[lament geyser]

that’s why the planet editor and tooltip show different values, the planet editor reads the original mass. it just needs to display that.

[lament geyser]

you’re not getting what I’m saying, sure it’s a hacky fix but it is functionally the same

the only difference is visual, that oblateness still only reduces the poles

that could probably be fixed separately without the refactors I brought up in the original post

[teal coral]

How is it the same? It reduces the mass to keep the density the same. If "internally" it uses the old mass then the planet still has the old mass, which has the higher density. Having two different masses, and a different than the one displayed, makes even less sense than before.

[lament geyser]

density is never used except in the tooltip and, afaik, only ESI, so again, it makes no difference

the idea should be to display the “old” mass and only use this lower mass in functions that are affected by the oblateness bug, they probably just missed that the new mass is used in the tooltip, somehow

[lament geyser]

it’s only ever user-facing, this is never used in generation afaik

[teal coral]

Ok but if old mass is displayed and it displays the new density that's just wrong. The volume is still the same, and the mass is still the same, so how would the density be different? Yes density is just something displayed there but this just makes everything inaccurate to each other.

[lament geyser]

yeah, that is a problem. I still feel like even at this point you’d rather display different, correct radii to the user (where mean radius = what is set in the script) alongside changing the rendering code instead of refactoring the entire generation code. thinking about it from what is feasible for them to do instead of what is ideal. an aside, unfortunately equatorial and mean radii are used so much in the code for planet generation that changing them to be correct now would definitely require a universe reset. it’s why I wished for it to get in before 0.991.

said correct radii will then give it the correct volume, and Radius in a script being mean radius would be a nice change, though would definitely be a breaking one. though they’ve done those in the past anyways, see Chthonias.

[lament geyser]

though I do agree now, that mass is the wrong way to do this.

[twin ridge]

Ugh, can we stop adding new bugs when trying to fix other ones?