The three principal moments of inertia of Earth and Moon are reported, for example, in T. J. Ahrens, Global Earth Physics - A handbook of Physical Constants.

I have found reports of the moment of inertia factor $\dfrac{C}{M R^2}$, where $C$ is the polar moment of inertia, $M$ the mass and $R$ the mean radius, for planets of the solar system.

Are the three principal moments of inertia for the planets of the solar system known?

  • $\begingroup$ I'm voting to close this question as off-topic because questions asking for references are generally undesirable. $\endgroup$ Commented Aug 30, 2017 at 13:15
  • 4
    $\begingroup$ @CarlWitthoft Where is this asking for references? James wants to know if the principle moments of inertia are known. Any good answer will use references, but this question is not specifically asking for someone to provide him with references. $\endgroup$
    – zephyr
    Commented Aug 30, 2017 at 13:47
  • $\begingroup$ @zephyr well, sans references, the answer is either "yes" or "no," neither of which is much help $\endgroup$ Commented Aug 30, 2017 at 17:24
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    $\begingroup$ @CarlWitthoft I still don't see your point. Any answer on here should provide references. If that's your metric for closing a question, all questions should be closed. James' question should only be closed (as it pertains to references) if either (a) it is clear he is asking us to do his own homework/research or (b) he is asking only for resources. As it is, neither seem to be true and this is a perfectly valid question whose answer should reference materials for support. $\endgroup$
    – zephyr
    Commented Aug 30, 2017 at 17:26
  • $\begingroup$ Not sure what to do with questions that can be solved by simply googling the exact same question... $\endgroup$ Commented Sep 1, 2017 at 21:34

1 Answer 1


The planets are very, very close to spherical (the Earth has a variaton of about 0.1% between polar and equatorial radii).

The rotational inertial for a solid sphere is


If you give us details about why you might be interested in looking at the rotational inertia of planets in greater detail, there might be more motivation for putting effort into finding an answer for you.

Just saying.


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