APOD: Saturn, Tethys, Rings, and Shadows (2022 Jan 23)

[APOD Robot]

Saturn, Tethys, Rings, and Shadows

Explanation: Seen from ice moon Tethys, rings and shadows would display fantastic views of the Saturnian system. Haven't dropped in on Tethys lately? Then this gorgeous ringscape from the Cassini spacecraft will have to do for now. Caught in sunlight just below and left of picture center in 2005, Tethys itself is about 1,000 kilometers in diameter and orbits not quite five saturn-radii from the center of the gas giant planet. At that distance (around 300,000 kilometers) it is well outside Saturn's main bright rings, but Tethys is still one of five major moons that find themselves within the boundaries of the faint and tenuous outer E ring. Discovered in the 1980s, two very small moons Telesto and Calypso are locked in stable along Tethys' orbit. Telesto precedes and Calypso follows Tethys as the trio circles Saturn.

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[Ann]

Saturn, Tethys, Rings, and Shadows. Image Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA

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Composite image comparing the sizes of Saturn and Earth, where the northern hemisphere of Saturn looks bluish. Saturn image: NASA/JPL/Space Science Institute Earth image: NASA/Apollo 17 crew

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Where have I seen the picture that is today's APOD before? And why am I so disappointed that it is not in color?

Oh yes! Today's APOD resembles a beautiful picture of Saturn and the Earth, where the northern hemisphere of Saturn looks blue!

Ann

[VictorBorun]

yeah, Saturn is colorful in a saturated pic

Click to view full size image

Sadly its rings are not.

[orin stepanek]

TethysRingShadow_cassini_1080.jpg

Tethys looking lonely here!

enceladusstripes_cassini_960.jpg

By looking where the cracks are and where they are not. Is it
possible that Enceladus may have continents?

_100729257_photojan0574306am.jpg

Rescue dog saving kitty!

[johnnydeep]

Saturn, Tethys, Rings, and Shadows

Explanation: Seen from ice moon Tethys, rings and shadows would display fantastic views of the Saturnian system. Haven't dropped in on Tethys lately? Then this gorgeous ringscape from the Cassini spacecraft will have to do for now. Caught in sunlight just below and left of picture center in 2005, Tethys itself is about 1,000 kilometers in diameter and orbits not quite five saturn-radii from the center of the gas giant planet. At that distance (around 300,000 kilometers) it is well outside Saturn's main bright rings, but Tethys is still one of five major moons that find themselves within the boundaries of the faint and tenuous outer E ring. Discovered in the 1980s, two very small moons Telesto and Calypso are locked in stable along Tethys' orbit. Telesto precedes and Calypso follows Tethys as the trio circles Saturn.

...are locked in [a] stable Lagrange configuration?

[XgeoX]

A little different view…



So cold and lonely yet so beautiful…

Eric

[revloren]

Fascinating how the shadow of the rings appears as a wavy line. A curved surface projected on another curved surface!

[johnnydeep]

A little different view…



So cold and lonely yet so beautiful…

Eric

I really like this image. Where did it come from?

[XgeoX]

By looking where the cracks are and where they are not. Is it
possible that Enceladus may have continents?

Not in the sense Earth does as Tethys has a active ice mantle but it doesn’t really behave like Earth’s molten mantle and how it generates a separate crust. Scientists are still trying to decode if Enceladus has a “stagnant” or “mobile” lid. If it’s mobile then it could drive movement that looks like Earth’s plate tectonics but is actually quite different.

I got that information from Saturn Cat!



Eric

[XgeoX]

A little different view…



So cold and lonely yet so beautiful…

Eric

I really like this image. Where did it come from?

I do too! I just do web searches for space art. Here is the web site…
https://ralf-schoofs.blogspot.com/2012 ... aturn.html.
Have fun, lots of great stuff out there!

Eric

[johnnydeep]

A little different view…



So cold and lonely yet so beautiful…

Eric

I really like this image. Where did it come from?

I do too! I just do web searches for space art. Here is the web site…
https://ralf-schoofs.blogspot.com/2012 ... aturn.html.
Have fun, lots of great stuff out there!

Eric

Thanks! That link hints at there being a 10000 x 7500 px original, but only seems to show one that's 1024 x 768.

[alter-ego]

Saturn, Tethys, Rings, and Shadows

Explanation: Seen from ice moon Tethys, rings and shadows would display fantastic views of the Saturnian system. Haven't dropped in on Tethys lately? Then this gorgeous ringscape from the Cassini spacecraft will have to do for now. Caught in sunlight just below and left of picture center in 2005, Tethys itself is about 1,000 kilometers in diameter and orbits not quite five saturn-radii from the center of the gas giant planet. At that distance (around 300,000 kilometers) it is well outside Saturn's main bright rings, but Tethys is still one of five major moons that find themselves within the boundaries of the faint and tenuous outer E ring. Discovered in the 1980s, two very small moons Telesto and Calypso are locked in stable along Tethys' orbit. Telesto precedes and Calypso follows Tethys as the trio circles Saturn.

...are locked in [a] stable Lagrange configuration?

Yes.

Telesto (24 kilometers, or 15 miles across) shares the orbit of Saturn's moon Tethys (1,071 kilometers, or 665 miles across), leading the larger moon in its path by 60 degrees. Similarly sized Calypso (22 kilometers, or 14 miles across) trails Tethys by the same amount. These positions, called Lagrange points, are dynamically stable. In being co-orbital moons of Tethys, Telesto and Calypso are like the Trojan moons of Jupiter, which occupy Lagrange points and orbit 60 degrees ahead and behind of Jupiter. The Saturnian moon Dione also has companion moons: Helene, which leads Dione in its orbit, and the Cassini-discovered trailing Lagrange moon, Polydeuces.

[neufer]

Animation of Polydeuces/Dione/Helene orbits relative to Saturn

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Telesto (24 kilometers, or 15 miles across) shares the orbit of Saturn's moon Tethys (1,071 kilometers, or 665 miles across), leading the larger moon in its path by 60 degrees. Similarly sized Calypso (22 kilometers, or 14 miles across) trails Tethys by the same amount. These positions, called Lagrange points, are dynamically stable. In being co-orbital moons of Tethys, Telesto and Calypso are like the Trojan moons of Jupiter, which occupy Lagrange points and orbit 60 degrees ahead and behind of Jupiter. The Saturnian moon Dione also has companion moons: Helene, which leads Dione in its orbit, and the Cassini-discovered trailing Lagrange moon, Polydeuces.

Note that Tethys & Dione are also in 1:2 orbital resonances with the inner moons: Mimas & Enceladus, respectively.

These two orbital resonances helps to maintain the inner moons' eccentricities which result in:

• 1) Mimas clearing out a wide Cassini Division ring gap and
  2) Enceladus spewing out south polar plumes at apoapsis

[Ann]

A little different view…



So cold and lonely yet so beautiful…

Eric

Very beautiful. Please note the Pleiades (and the Hyades) in the background.

Ann

[MarkBour]

Animation of Polydeuces/Dione/Helene orbits relative to Saturn

https://upload.wikimedia.org/wikipedia/ ... _Dione.gif

Telesto (24 kilometers, or 15 miles across) shares the orbit of Saturn's moon Tethys (1,071 kilometers, or 665 miles across), leading the larger moon in its path by 60 degrees. Similarly sized Calypso (22 kilometers, or 14 miles across) trails Tethys by the same amount. These positions, called Lagrange points, are dynamically stable. In being co-orbital moons of Tethys, Telesto and Calypso are like the Trojan moons of Jupiter, which occupy Lagrange points and orbit 60 degrees ahead and behind of Jupiter. The Saturnian moon Dione also has companion moons: Helene, which leads Dione in its orbit, and the Cassini-discovered trailing Lagrange moon, Polydeuces.

Note that Tethys & Dione are also in 1:2 orbital resonances with the inner moons: Mimas & Enceladus, respectively.

These two orbital resonances helps to maintain the inner moons' eccentricities which result in:

• 1) Mimas clearing out a wide Cassini Division ring gap and
  2) Enceladus spewing out south polar plumes at apoapsis

Interesting. I wonder if the three moons, Telesto, Tethys and Calypso also induce some more complex points of stability where other smaller objects are held? Telesto and Calypso are big enough that they're perturbing Tethys as well. Or, perhaps the three are "cleaning out" the rest of the objects in the orbit.

Cassini would be a top contender for "greatest photographer of the solar system" ... even in black-and-white.

[neufer]

Telesto and Calypso are big enough that they're perturbing Tethys as well.

Saturn's mass is ~6 orders of magnitude greater than that of Tethys.

Tethys's mass is ~5 orders of magnitude greater than that of Telesto or Calypso.

[MarkBour]

Telesto and Calypso are big enough that they're perturbing Tethys as well.

Saturn's mass is ~6 orders of magnitude greater than that of Tethys.

Tethys's mass is ~5 orders of magnitude greater than that of Telesto or Calypso.

Okay, so you're suggesting insignificant to the orbital mechanics of Tethys. I see I was misinterpreting your plot, which turns out to be about Helene, Dione, and Polydeuces.