APOD: Saturn and Six Moons (2021 Jul 06)

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APOD Robot
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APOD: Saturn and Six Moons (2021 Jul 06)

Post by APOD Robot » Tue Jul 06, 2021 4:05 am

Image Saturn and Six Moons

Explanation: How many moons does Saturn have? So far 82 have been confirmed, the smallest being only a fraction of a kilometer across. Six of its largest satellites can be seen here in a composite image with 13 short exposure of the bright planet, and 13 long exposures of the brightest of its faint moons, taken over two weeks last month. Larger than Earth's Moon and even slightly larger than Mercury,Saturn's largest moon Titan has a diameter of 5,150 kilometers and was captured making nearly a complete orbit around its ringed parent planet. Saturn's first known natural satellite, Titan was discovered in 1655 by Dutch astronomer Christiaan Huygens, in contrast with several newly discovered moons announced in 2019. The trail on the far right belongs to Iapetus, Saturn's third largest moon. The radius of painted Iapetus' orbit is so large that only a portion of it was captured here. Saturn leads Jupiter across the night sky this month, rising soon after sunset toward the southeast, and remaining visible until dawn.

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azaytsev
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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by azaytsev » Tue Jul 06, 2021 5:18 am

Nicely done!

I tried something similar with Neptune & Triton before, but I only made one step for 1/2 period of rotation of Triton:

Image

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by VictorBorun » Tue Jul 06, 2021 6:31 am

the plane of Iapetus' orbit is 15.47° to Saturn's equator. It really shows!

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by VictorBorun » Tue Jul 06, 2021 6:32 am

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!

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by orin stepanek » Tue Jul 06, 2021 11:42 am

Saturno6luas1024Defavari.png

One of the moons is hard to find! Takes a keen eye!
t8k7f6nvr8j31.jpg
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Orin

Smile today; tomorrow's another day!

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by MarkBour » Tue Jul 06, 2021 6:20 pm

I really love images like this. Great work!
I'm curious as to why all of the objects have "auras" around them (not sure of the best term ... a spread of light around each object). Is it an artifact of the times of the exposures on the camera?

I wonder if there was ever a time when Titan was a planet. According to Wikipedia's article on Titan, modelling of its formation has led to the belief that it most likely formed from an accretion disk around Saturn, rather than that it was captured after a more distant origin.
Mark Goldfain

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by VictorBorun » 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?

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by MarkBour » 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". :-)
Mark Goldfain

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by neufer » Thu Jul 08, 2021 5:55 pm

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.
Art Neuendorffer

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Re: APOD: Saturn and Six Moons (2021 Jul 06)

Post by VictorBorun » Sun Jul 11, 2021 6:07 am

So Iapetus's orbit proves its origin with the eccentricity test.
It's Saturn system's ok, just deformed in an accident.