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CalliArcale
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<blockquote><font class="small">In reply to:</font><hr /><p><i>>Iapetus has a very odd orbit around Saturn!</i>Precisely what is odd about the orbit? Can you tell me?<p><hr /></p></p></blockquote><br /><br />I was curious about this claim, so I looked up Iapetus as The Nine Planets (which, lest anyone claim conspiracy, is unaffiliated with NASA, except in that like all Americans above a certain income level, the site maintainers do pay taxes, which fund NASA).<br /><br />The orbit of Iapetus is greatly inclined with respect to the plane of Saturn's ecliptic -- approximately 14.72 degrees. Most of the other moons are closer to 0, with the notable exception of Phoebe, which has an even weirder orbit. Phoebe has an inclination of 175.30 degrees, which means you could think of it as being inclined 4.70 degrees but going around Saturn backwards. It orbits retrograde. The fact hat these *two* moons have unusual orbits, combined with the fact that Phoebe is very dark and Iapetus has a coating of dark material on its leading face, have led some to speculate whether there is some kind of connection between the two. But the dark material on Iapetus doesn't seem to have the same spectra as the surface of Phoebe, and Phoebe's odd orbit is consistent with it being a captured asteroid, so this may simply be coincidence.<br /><br />Of course, it's also possible that Iapetus is a captured object. It's radius is only 780 km; it may be a captured Centaur. However, its orbit is pretty circular (eccentricity of 0.03; our Moon's orbit is more eccentric, at 0.05) and it rotates synchronously, so it is reasonable to think that it may have been around Saturn for a very long time indeed.<br /><br />One other thing to consider -- it is not all that unusual for a moon to have an orbit not directly in the plane of the ecliptic. Our own Moon does not orbit in the plane of the Earth's equator, which is part of the reason why the Apollo astronauts di <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>