I understand that a “large” moon, like ours, keeps the planet’s axis from being peturbed, because the spin axis and the moon’s orbital plane exchange momentum and tend to stay in the same plane, and the orbital angular momentum is much stronger because of the long lever arm. So, tipping the planet means changing the moon’s orbital plane too, and the peturbations don’t make a significant change to its large value.

So, why is Pluto, along with the orbital plane of its satellites, tipped nearly 90 degrees?

  • 1
    $\begingroup$ This brings up an interesting point to Pluto's so-called heart or Sputnik Planitia. The link is from Scishow Space and explains why Pluto has an axial tilt. $\endgroup$
    – Nafi04
    Nov 20 '16 at 20:54
  • $\begingroup$ There's axial variation and axial tilt. The Moon, keeps Earth mostly within 21-24 degrees axial tilt, which is 3 degrees variation. I don't know by how much Pluto undergoes axial variation. I've never seen that discussed. $\endgroup$
    – userLTK
    Nov 21 '16 at 0:25
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    $\begingroup$ The Pluto/Charon system was almost certainly tipped on its side by the collision that created the two bodies, but we have no way of knowing if there is any axial wandering occurring or not. It's just too distant to observe and measure. $\endgroup$
    – BillDOe
    Nov 21 '16 at 2:50
  • $\begingroup$ short answer: the universe is full of instances of bizarre configurations which depend on 6-sigma event histories :-) $\endgroup$ Nov 23 '16 at 13:12
  • $\begingroup$ Charon is tidally locked to Pluto but since Charon is half the size of Pluto, the tidal force from the dwarf planet and its satellite is more or less equal. This means that Pluto always shows the same side to Charon, and Charon always shows the same side to Pluto. (nineplanets.org/questions/what-is-tidal-locking) $\endgroup$ Oct 4 '20 at 4:25

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