I was reading some papers about Iapetus earlier today and I was once again reminded that it hardly qualifies as a spheroid or even ellipsoid. With a mean diameter of 1500km, this is very odd. One has to wonder why an object the size of Iapetus would have a hard time becoming ellispoidal when other smaller moons are undoubtedly that shape.

Now I also noticed Iapetus orbits very far away from its parent planet...with a semi-major axis of 3,560,820km. The next farthest similar-sized moon is Oberon, and it's semi-major axis is 583,520km...over 6 times closer. So my thought is, perhaps Iapetus's working environment was so much colder that it was more difficult to pull itself into a round shape.

Another less odd example of an irregularly-shaped object is Proteus. I compared Proteus's semi-major axis to Mimas and Miranda, two similar-sized but ellipsoidal objects...Proteus is slightly further away than both of them. However, both Mimas and Miranda may have been tidally heated early on, not to mention Mimas is still apart of an orbital resonance. In Mimas's case, Saturn is also over 5 times more massive than Neptune so it should've bathed its moons in more heat than Neptune. Proteus, on the other hand, is not known to have had any tidal relationships. So all of this...related to heat...could explain its more irregular shape.

I'm also aware that it is easier for an object made of ice to round itself than an object made of rocky material. With that in mind, let's briefly consider Ceres. It's density suggests a good deal of rock, much more so than Iapetus...so one would assume it'd have the harder time to become spheroidal. But Ceres, at 950km in diameter, is the spheroidal one. Could its warmer environment (simply due to its closer proximity to the Sun or some tidal resonance) enabled it to more efficiently reach hydrostatic equilibrium?

Interestingly, note that if this is has any merit, it would be quite a bit more difficult for KBOs to become spheroidal (notwithstanding those tidally heated).

I have yet to take any physics classes, but to me it makes sense that a warmer object could round itself easier since the molecules would be much more relaxed. Or I could be way off and this is all junk. I'm curious to hear what you all have to say...correct me if I'm wrong please.

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