Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Tilt of uranus and its moons

  1. Feb 17, 2010 #1
    One of the leading theories that explains Uranus' tilt is that it was hit early in its lifetime by a protoplanet, which disrupted its rotation axis and caused its unusual tilt. How does this hypothesis explain Uranus' moons as well? Most of them are aligned to the equator, and some are also retrograde as well. If Uranus was hit by a protoplanet, how would that have changed the orbits of its moons to match its new rotation axis as well? Could the moons have been fragments of whatever protoplanet that hit it?
  2. jcsd
  3. Feb 17, 2010 #2
    I think that's the general presumption... But, it's not certain.
  4. Feb 18, 2010 #3

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

    Planets are not spherical bodies, particularly so the rapidly-spinning gas giants. The non-spherical nature of the planets gravity fields coupled with perturbations from the Sun, nearby planets, and other moons causes the orbits of the inner moons to migrate toward being equatorial orbits.
  5. Feb 21, 2010 #4
    If so, then is the presumption that they are from before or after the moon hit it? ie, formed from the debris of the protoplanet that broke up before impact, or formed from the debris that was knocked off the planet from the impact?

    How long would this typically take? Millions of years, hundreds of millions, longer? Also, how much of an effect would the perturbations from the Sun and other planets and such have on equatorializing the moons? ie, is it mostly from the bulge of Uranus, or from the perturbations?
  6. Feb 22, 2010 #5
    I know that many scientists believe that an Earth-sized planet collided with Uranus early on in its life, which they in turn believe is what knocked the planets onto its akward axis. As far is the moons go, there seems to be a definite lack of information about why they rotate the way that the do. Some astronomers think that the moons are peices of the planet that collided with Uranus. There are astronomers out there that believe that the axial tilt of Uranus and its moons is due to some sort of phenomina that we've yet to discover.

    I guess what I'm saying is that we've yet to find a real answer.
  7. Feb 22, 2010 #6

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    Wouldn't that imply that they share the same composition? Miranda and Titania certainly have different internal compositions, and whatever composes the surface of Oberon, it's not whatever composes the surface of Miranda.
  8. Feb 22, 2010 #7
    Yes, you're correct. At least in my mind. This is one of the reasons why I find it hard to accept this theory.

    The main point of contention for me is that even if Uranus' moons were splintered off of some larger object post-collison, it still wouldn't explain their rotations. Yes, it's acceptable that a collision could knock Uranus on its side, but if the other object shattered, where in the laws of physics does it say that the peices of such an object would than follow the same, albeit strange, rotation? I'm just not convinced... Furthermore, I can't seem to find any information about the rotations of the moons anywhere. Not online (at least not from credible sources) and not in texts. If anyone has some solid information, I'd love to hear it.

    Another point of interest worth mentioning, I think it was Voyager 2 that observed that Uranus had a very unique magnetic field; the tail of it seemed to be cork screwed. One can only wonder if maybe this was caused by the planet's rotation or maybe even had an influence on the planet's rotation...

    I'm engaging purely in hypotheticals, though. Just my wandering mind.
  9. Feb 22, 2010 #8

    D H

    User Avatar
    Staff Emeritus
    Science Advisor

  10. Feb 22, 2010 #9
  11. Feb 24, 2010 #10
  12. Mar 14, 2010 #11
    How exactly would a tilted magnetic core affect the entire rotation of the planet?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook