Gas Giant with moons is a moon to an Icy Body with moons

JesusRocks1988

JesusRocks1988
MOONS!

Anyway, just thought I'd post this up here as it's a bit of an oddity. On my recent journey to Colonia, I came across this absolutely huge Icy Body - sadly not landable - with a slightly less massive Gas Giant as a moon. Unfortunately neither of the bodies break any Cartographics records, but taken together it's a bit of a rare find, I'd say. Well, certainly something I've never seen before.

dJK0Bf0.png


The Gas Giant orbits quite a long way out from its parent, so it wasn't possible to get them in a screenie. Strange nonetheless, so I offer it here.
 

marx

marx
It's also the 12th planet from its star, so it could be an interesting-looking system. Also, I like how the ice world even has some rings. Nice find!
Do the gas giant's moons orbit it close, by the way?
 

Redfox

Redfox
That's a really massive Icy Body you found there - congrats!

While hunting for Helium-rich Gas Giants I saw quite a few of those GG-as-a-moon setups. That GG down there isn't a Helium-rich Gas Giant by any chance?
 
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JesusRocks1988

JesusRocks1988
Redfox said:
That's a really massive Icy Body you found there - congrats!

While hunting for Helium-rich Gas Giants I saw quite a few of those GG-as-a-moon setups. That GG down there isn't a Helium-rich Gas Giant by any chance?
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Thanks! No, as far as I recall it's a Class I.

marx said:
It's also the 12th planet from its star, so it could be an interesting-looking system. Also, I like how the ice world even has some rings. Nice find!
Do the gas giant's moons orbit it close, by the way?
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The gas giant's moons are actually at a proportionally "normal" orbital distance. I'll have to head back to this system when I leave Colonia.
 

Pirin

Pirin
Nice find!

I have seen couple of such systems where GG is a moon of icy planet. But none if these icy planets was that large. Surprised it doesnt beat any record for size. What is the record then?
 

malenfant

M
This really should be a double planet system. I can't really fathom the logic that the system map uses to decide whether to show things as moons or as double planets - I've seen massive gas giants shown as double planets with small terrestrial worlds (the latter should just be a moon), and then you get things like this where gas giants are moons of large terrestrials. It doesn't really make any sense.
 

JesusRocks1988

JesusRocks1988
malenfant said:
This really should be a double planet system. I can't really fathom the logic that the system map uses to decide whether to show things as moons or as double planets - I've seen massive gas giants shown as double planets with small terrestrial worlds (the latter should just be a moon), and then you get things like this where gas giants are moons of large terrestrials. It doesn't really make any sense.
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With a binary planet system, the barycentre is outside the planets, whereas for planet/moon systems, the barycentre is inside one of the bodies.

If you have a look at any of the binary pairs you'll see an orbit line outside the "parent" planet, sometimes only just barely. That's the difference in classification and how the system map decides whether it's a binary pair or a moon.

In this example, the barycentre is inside Icy Body.
 

Tychu9

T
If the planets are orbiting a central point of gravity then they are double planets. If one is orbiting another; then you get a moon. That's science!
 

malenfant

M
JesusRocks1988 said:
With a binary planet system, the barycentre is outside the planets, whereas for planet/moon systems, the barycentre is inside one of the bodies.
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I know that's how it *should* be calculated. I'm just not remotely convinced that it's being calculated correctly in a lot of cases. I mean, in this case if the gas giant has similar mass to the large icy body primary and orbits quite a ways out, shouldn't it be a double planet? There's no way the barycentre would be inside the icy body if that was the case.
 

Tychu9

T
malenfant said:
I know that's how it *should* be calculated. I'm just not remotely convinced that it's being calculated correctly in a lot of cases. I mean, in this case if the gas giant has similar mass to the large icy body primary and orbits quite a ways out, shouldn't it be a double planet? There's no way the barycentre would be inside the icy body if that was the case.
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Is the mass somewhat equal? You've only given us the Icy body's mass; and it's at 200x Earths. I've come across MANY gas planets that are in the 2-3x range.
 

JesusRocks1988

JesusRocks1988
Tychu9 said:
Is the mass somewhat equal? You've only given us the Icy body's mass; and it's at 200x Earths. I've come across MANY gas planets that are in the 2-3x range.
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Once I'm on my return trip from Colonia, I'll pass back through this system and post up the details for the Gas Giant. As far as I recall, it is a similar mass, but I could be mistaken.

I'm currently sitting at the lowest possible point of the galaxy directly below the Colonia Nebula, so... it might take a few days.
 

malenfant

M
JesusRocks1988 said:
Once I'm on my return trip from Colonia, I'll pass back through this system and post up the details for the Gas Giant. As far as I recall, it is a similar mass, but I could be mistaken.
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Can you not just bring it up on your galaxy map? you don't need to pass through the system to do that, If you've scanned it the data should all be there (or find it in EDDiscovery if you have that?)
 

Tychu9

T
I'm just doing a little Colonia mapping mop up. Today I found an Ice World (60x mass) with a gas "giant" (3x mass) moon. They aren't uncommon. Last time I checked the physics textbooks (astronomy (I've chosen the social sciences as a career)), it's not impossible for this to happen. It just so happens that in our solar system, the gas Giants are "massive". Our Solar System is a bit of an uncommon configuration as well.
 

malenfant

M
Tychu9 said:
I'm just doing a little Colonia mapping mop up. Today I found an Ice World (60x mass) with a gas "giant" (3x mass) moon. They aren't uncommon. Last time I checked the physics textbooks (astronomy (I've chosen the social sciences as a career)), it's not impossible for this to happen. It just so happens that in our solar system, the gas Giants are "massive". Our Solar System is a bit of an uncommon configuration as well.
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The 60 earth mass ice world is the problem. A world that massive should by all rights be a gas giant, it's more than massive enough to mop up the hydrogen and helium from the surrounding protostellar nebula.
 

JesusRocks1988

JesusRocks1988
Okay, so after consulting the Galaxy Map (which I should have done in the first place, don't know what came over me, thank you malenfant), it appears I was mistaken! The Gas Giant is nowhere near the mass or size of the monstrous ice world. See below:

jjORIOJ.png


As you can see, the Gas Giant is tiny in comparison, a meagre 5.7EM and around a 10Mm smaller in radius. That explains why the barycentre is so firmly rooted inside the Uranus-sized ice planet... There's a joke there somewhere, I'm sure.
 
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