Why is Ike so large compared to Duna? How could Ike have formed?

[skylifeplays]

Ike is almost half the size as Duna, it is infact so large that Ike does not orbit around Duna, but both orbit around a common center of mass. It is hard to notice, but it is relevant. How did Ike become so large compared to Duna? Also, could this make Ike and Duna a binary planet system?

[magnemoe]

Its not unique, Pluto and its large moon has an similar setup.  Earth's moon is also large compared to the planet. 
I guess an impact like the Moon or a capture, 

[kerbiloid]

Spoiler

 

[mikegarrison]

22 hours ago, skylifeplays said:

Ike does not orbit around Duna, but both orbit around a common center of mass.

That's true of everything that shares an orbital relationship with something else.

[Dafni]

1 hour ago, mikegarrison said:

That's true of everything that shares an orbital relationship with something else.

Indeed.  But to be fair to the OP,  the common center of mass being outside the parent body might be considered unusal... at least in the context of KSP.

[sevenperforce]

On 4/1/2023 at 4:08 PM, Dafni said:

Indeed.  But to be fair to the OP,  the common center of mass being outside the parent body might be considered unusal... at least in the context of KSP.

Does Duna actually orbit a common center of mass with Ike outside of its own surface? I thought it was on rails.

Or are you just saying that the bodies WOULD orbit a common center of mass outside of Duna IF the physics were correct?

[Dafni]

4 hours ago, sevenperforce said:

Or are you just saying that the bodies WOULD orbit a common center of mass outside of Duna IF the physics were correct?

Yes, this. While I never actually checked, it was always my assumption that Duna is on a rail around the Sun and Ike is on a rail around Duna.

If it WERE in the game, it could explain encounters going amiss when you timewarp and such things.

How could one properly check this anyway??

[sevenperforce]

1 hour ago, Dafni said:

Yes, this. While I never actually checked, it was always my assumption that Duna is on a rail around the Sun and Ike is on a rail around Duna.

If it WERE in the game, it could explain encounters going amiss when you timewarp and such things.

How could one properly check this anyway??

Depends on how far above Duna's surface the physical barycentre would actually be. That would tell you how much variation in Duna's position you could expect relative to its rail around the Sun. 

[LunarMetis]

Ike is about 6% the mass of Duna, which makes Ike a really massive moon compared to its parent planet. For comparison, the Moon is about 1% the mass of the Earth, and Charon is about a tenth of Pluto's mass.

In that case, Duna and Ike would technically be a binary planetary system, since the barycenter would be noticeably distant from Duna's center of mass. I made a little graphic below on MS Paint (not perfectly to scale so bare with me) that shows some math and helps to visualize the two-body problem as applied to Duna and Ike. The common barycenter would be inside Duna's radius, but it's far enough from the center to make Duna appear to wobble as Ike orbits it.

I don't think KSP simulates barycenters, aside from modders' attempts to do so, but I feel like it'd be a cool feature to have for the Duna-Ike system, especially if it would present new challenges to exploring Duna.

Edited April 24, 2023 by LunarMetis
moved image up a line