Starship Asterisk*

VictorBorun wrote: ↑Tue Jul 06, 2021 6:31 am the plane of Iapetus' orbit is 15.47° to the plane of Saturn's equator, rings, Titan's orbit and most satellites' orbits.
And it really shows in the posted pic!

MarkBour wrote: ↑Tue Jul 06, 2021 6:20 pm I wonder if there was ever a time when Titan was a planet.

VictorBorun wrote: ↑Tue Jul 06, 2021 8:59 pm

MarkBour wrote: ↑Tue Jul 06, 2021 6:20 pm I wonder if there was ever a time when Titan was a planet.

the first alien suspect should be Iapetus. Why does it orbit in the wrong plane?

MarkBour wrote: ↑Thu Jul 08, 2021 4:41 pm

VictorBorun wrote: ↑Tue Jul 06, 2021 8:59 pm

MarkBour wrote: ↑Tue Jul 06, 2021 6:20 pm
I wonder if there was ever a time when Titan was a planet.

the first alien suspect should be Iapetus. Why does it orbit in the wrong plane?

Yes, that does make it look like a "tourist".

https://en.wikipedia.org/wiki/Iapetus_(moon)#Orbit wrote:

Click to play embedded YouTube video.

<<The orbit of Iapetus is somewhat unusual. Although it is Saturn's third-largest moon, it orbits much farther from Saturn than the next closest major moon, Titan. It has also the most inclined orbital plane of the regular satellites; only the irregular outer satellites like Phoebe have more inclined orbits. Because of this distant, inclined orbit, Iapetus is the only large moon from which the rings of Saturn would be clearly visible; from the other inner moons, the rings would be edge-on and difficult to see. The cause of this highly inclined orbit of Iapetus is unknown; however, it is not likely to have been captured. One suggestion for the cause of Iapetus's orbital inclination is an encounter between Saturn and another planet.>>

https://en.wikipedia.org/wiki/Laplace_plane wrote:
The Laplace plane or Laplacian plane of a planetary satellite is a mean or reference plane about whose axis the instantaneous orbital plane of that satellite precesses. The axis of this Laplace plane is coplanar with, and between, (a) the polar axis of the parent planet's spin, and (b) the orbital axis of the parent planet's orbit around the Sun. The Laplace plane arises because the equatorial oblateness of the parent planet tends to cause the orbit of the satellite to precess around the polar axis of the parent planet's equatorial plane, while the solar perturbations tend to cause the orbit of the satellite to precess around the polar axis of the parent planet's orbital plane around the Sun. The two effects acting together result in an intermediate position for the reference axis for the satellite orbit's precession.

In most cases, the Laplace plane is very close to the equatorial plane of its primary planet (if the satellite is very close to its planet) or to the plane of the primary planet's orbit around the Sun (if the satellite is far away from its planet). Examples of satellites whose Laplace plane is close to their planet's equatorial plane include the satellites of Mars and the inner satellites of the giant planets. Examples of satellites whose Laplace plane is close to their planet's orbital plane include Earth's Moon and the outer satellites of the giant planets. Some satellites, such as Saturn's Iapetus, are situated in the transitional zone and have Laplace planes that are midway between their planet's equatorial plane and the plane of its solar orbit.>>

https://iopscience.iop.org/article/10.1088/0004-6256/148/3/52 wrote:
EXCITATION OF THE ORBITAL INCLINATION OF IAPETUS DURING PLANETARY ENCOUNTERS
David Nesvorný1, David Vokrouhlický1,2, Rogerio Deienno1,3, and Kevin J. Walsh1

Published 2014 August 13 • © 2014. The American Astronomical Society.
The Astronomical Journal, Volume 148, Number 3

ABSTRACT: Saturn's moon, Iapetus, has an orbit in a transition region where the Laplace surface is bending from the equator to the orbital plane of Saturn. The orbital inclination of Iapetus to the local Laplace plane is ~ 8°, which is unexpected because the inclination should be ~ 0 if Iapetus formed from a circumplanetary disk on the Laplace surface. It thus appears that some process has pumped up Iapetus's inclination while leaving its eccentricity near zero (~ 0.03 at present). Here, we examined the possibility that Iapetus's inclination was excited during the early solar system instability when encounters between Saturn and ice giants occurred. We found that the dynamical effects of planetary encounters on Iapetus's orbit sensitively depend on the distance of the few closest encounters. In 4 out of 10 instability cases studied here, the orbital perturbations were too large to be plausible. In one case, Iapetus's orbit was practically unaffected. In the remaining five cases, the perturbations of Iapetus's inclination were adequate to explain its present value. In three of these cases, however, Iapetus's eccentricity was excited to >0.1–0.25, and it is not clear whether it could have been damped to its present value (~ 0.03) by a subsequent process (e.g., tides and dynamical friction from captured irregular satellites do not seem to be strong enough). Our results therefore imply that only 2 out of 10 instability cases (~20%) can excite Iapetus's inclination to its current value (~30% of trials lead to >5°) while leaving its orbital eccentricity low.