Pluto and Charon are not tidally locked in Stellarium

Bug #968738 reported by mpopp on 2012-03-29
This bug affects 2 people
Affects Status Importance Assigned to Milestone
Alexander Wolf

Bug Description

Pluto and Charon are in fact mutually tidally locked. But in Stellarium, Charon simply orbits Pluto.

To reproduce:

* open Stellarium
* find Pluto
* press Ctrl-C to go to Pluto's surface
* find and select Charon
* go forward in time
(same applies to first selecting Charon, then Pluto)

... you will find Charon orbiting around Pluto, while it should remain at pretty much the same spot, just as looking at Earth from the Moon's surface.

Related branches

treaves (treaves) wrote :

That's not what 'tidally locked' means, and the moon certainly orbits the Earth, and does not remain at 'pretty much the same spot.'

mpopp (mpopp75) wrote :

"Pretty much the same spot" as viewed from a specific location on the Moon, of course.

treaves (treaves) wrote :

Yes. :)

Bogdan Marinov (daggerstab) wrote :

A little bit more clear description:

From Pluto's surface, Charon presents one side only, as it should, but rises and sets.
From Charon's surface, Pluto appears to be in the same spot in the sky, but visibly rotates.

Either Stellarium's data on Pluto's rotation and axis is wrong (e.g. not calculated in the same epoch as Charon's orbit), or the culprit is the way natural satellite orbits are modeled in Stellarium, which breaks down with Pluto and Charon, because the barycenter of their system is outside Pluto.

treaves (treaves) on 2012-04-23
Changed in stellarium:
status: New → Incomplete
Launchpad Janitor (janitor) wrote :

[Expired for Stellarium because there has been no activity for 60 days.]

Changed in stellarium:
status: Incomplete → Expired
Bogdan Marinov (daggerstab) wrote :

It's nice I decided to clean up my Inbox, otherwise I wouldn't have remembered this.

Changed in stellarium:
importance: Undecided → Wishlist
milestone: none → 1.0.0
status: Expired → Triaged
Alexander Wolf (alexwolf) wrote :

Pluto and Charon can be tidally locked only if Pluto has non-retrograde rotation or all system has retrograde rotation.

mpopp (mpopp75) wrote :

Here is what I was referring to:

"The system is also unusual among planetary systems in that each is tidally locked to the other: Charon always presents the same face to Pluto, and Pluto always presents the same face to Charon: from any position on either body, the other is always at the same position in the sky, or always obscured. Because of this, the rotation period of each is equal to the time it takes the entire system to rotate around its common centre of gravity."

Alexander Wolf (alexwolf) wrote :
Changed in stellarium:
assignee: nobody → Alexander Wolf (alexwolf)
milestone: 1.0.0 → 0.12.1
status: Triaged → Fix Committed
mpopp (mpopp75) wrote :

Just tried in Beta 3 on Windows. Charon is now correctly tidally locked to Pluto, but Pluto is not correctly locked to Charon in return. In fact they are mutually tidally locked, so both show the same side to each other all the time.

Alexander Wolf (alexwolf) wrote :

Are you updated ssystem.ini?

mpopp (mpopp75) wrote :

Sorry, you're right. I just installed again, removing personal settings (so to have default settings for everything), now they rotate correctly :).

Changed in stellarium:
status: Fix Committed → Fix Released
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