APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Comments and questions about the APOD on the main view screen.
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APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by APOD Robot » Mon Apr 02, 2018 4:06 am

Image Moons, Rings, Shadows, Clouds: Saturn (Cassini)

Explanation: While cruising around Saturn, be on the lookout for picturesque juxtapositions of moons, rings, and shadows. One quite picturesque arrangement occurred in 2005 and was captured by the then Saturn-orbiting Cassini spacecraft. In the featured image, moons Tethys and Mimas are visible on either side of Saturn's thin rings, which are seen nearly edge-on. Across the top of Saturn are dark shadows of the wide rings, exhibiting their impressive complexity. The violet-light image brings up the texture of the backdrop: Saturn's clouds. Cassini orbited Saturn from 2004 until September of last year, when the robotic spacecraft was directed to dive into Saturn to keep it from contaminating any moons.

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heehaw

Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by heehaw » Mon Apr 02, 2018 9:02 am

How I love the rings of Saturn! I first saw them at age 15 with my new SkyScope 3 1/2 inch telescope. They are so thin! Supposedly, a 100 meters or so. And yet so vast. And I've wept before on this forum that we never got a tight closeup of a chunk of ring with Cassini! Billions of big snowballs just There, as far as the eye can see, not moving at all, not bumping one another (or some would be ejected). A stately procession of snowballs around Saturn! Wow!

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by BDanielMayfield » Mon Apr 02, 2018 2:04 pm

heehaw wrote:
Mon Apr 02, 2018 9:02 am
How I love the rings of Saturn! I first saw them at age 15 with my new SkyScope 3 1/2 inch telescope. They are so thin! Supposedly, a 100 meters or so. And yet so vast. And I've wept before on this forum that we never got a tight closeup of a chunk of ring with Cassini! Billions of big snowballs just There, as far as the eye can see, not moving at all, not bumping one another (or some would be ejected). A stately procession of snowballs around Saturn! Wow!
Yes, seeing (real) closeup views of Saturn's rings would be high on many a wish list for solar system sights.

A Ring Explorer mission is called for. Is one in the works?

Bruce
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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by Chris Peterson » Mon Apr 02, 2018 2:13 pm

BDanielMayfield wrote:
Mon Apr 02, 2018 2:04 pm
A Ring Explorer mission is called for. Is one in the works?
It's a huge technical challenge. Spacecraft and small bits of stuff don't mix well. A damaged or uncontrollable spacecraft inside the ring system could be a disaster for future research (which is why they have been careful to avoid the rings, and design orbits such that damaged probes would decay into Saturn, and, of course, to deliberately dispose of probes into Saturn).

Not a mission that couldn't be done, but not an easy one.
Chris

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by JohnD » Mon Apr 02, 2018 2:55 pm

"not bumping one another (or some would be ejected)"
Now I'm no orbital calculator, but is it possible that in the time that the Rings have existed (?10M years?) their particles have settled into perfect orbits that never intersect? Seems unlikely, given their number, and given the Ring's size, a significant number of extra-Saturnian objects must collide with it, causing instability.
And Lo! they haven't become static and stable; they have and do collide, contributing to the dimensions of the Rings:
"collisions between them occur quite often, leading to the dissipation of kinetic energy. The cumulative effect of countless collisions in the past can be seen in the razor-like thinness of the disk and the near circularity of particle orbits." https://sciencing.com/close-rocks-satur ... 13152.html

This has been studied by our astronomers for many years, for instance Cuzzi et al: https://www.sciencedirect.com/science/a ... 3579900848 "the “many-particle-thick” condition ... may be reconciled with ongoing particle collisions."

The Rings are a dynamic evolving system, not a static one.
John

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by BDanielMayfield » Mon Apr 02, 2018 3:32 pm

Chris Peterson wrote:
Mon Apr 02, 2018 2:13 pm
BDanielMayfield wrote:
Mon Apr 02, 2018 2:04 pm
A Ring Explorer mission is called for. Is one in the works?
It's a huge technical challenge. Spacecraft and small bits of stuff don't mix well. A damaged or uncontrollable spacecraft inside the ring system could be a disaster for future research (which is why they have been careful to avoid the rings, and design orbits such that damaged probes would decay into Saturn, and, of course, to deliberately dispose of probes into Saturn).

Not a mission that couldn't be done, but not an easy one.
Thanks for that Chris, which well explains why such a mission hasn't been attempted yet. My thinking was of placing a probe (or, better yet, several small probes) in an (a) orbit(s) inside the rings such that the velocity differences between probe and ring objects would be very small.

Have any planetary missions been easy? Many things worth doing aren't.
"Happy are the peaceable ... "

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by BDanielMayfield » Mon Apr 02, 2018 3:47 pm

JohnD wrote:
Mon Apr 02, 2018 2:55 pm
"not bumping one another (or some would be ejected)"
Now I'm no orbital calculator, but is it possible that in the time that the Rings have existed (?10M years?) their particles have settled into perfect orbits that never intersect? Seems unlikely, given their number, and given the Ring's size, a significant number of extra-Saturnian objects must collide with it, causing instability.
And Lo! they haven't become static and stable; they have and do collide, contributing to the dimensions of the Rings:
"collisions between them occur quite often, leading to the dissipation of kinetic energy. The cumulative effect of countless collisions in the past can be seen in the razor-like thinness of the disk and the near circularity of particle orbits." https://sciencing.com/close-rocks-satur ... 13152.html

This has been studied by our astronomers for many years, for instance Cuzzi et al: https://www.sciencedirect.com/science/a ... 3579900848 "the “many-particle-thick” condition ... may be reconciled with ongoing particle collisions."

The Rings are a dynamic evolving system, not a static one.
John
Excellent post John. The slow speeds of such collisions are what keep the rings from dissapating over time.

DAMGEM

Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by DAMGEM » Mon Apr 02, 2018 11:06 pm

What is the object bottom left of center. It looks to be a giant snowball or baby moon.

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by MarkBour » Tue Apr 03, 2018 12:03 am

BDanielMayfield wrote:
Mon Apr 02, 2018 3:32 pm
Chris Peterson wrote:
Mon Apr 02, 2018 2:13 pm
BDanielMayfield wrote:
Mon Apr 02, 2018 2:04 pm
A Ring Explorer mission is called for. Is one in the works?
It's a huge technical challenge. Spacecraft and small bits of stuff don't mix well. A damaged or uncontrollable spacecraft inside the ring system could be a disaster for future research (which is why they have been careful to avoid the rings, and design orbits such that damaged probes would decay into Saturn, and, of course, to deliberately dispose of probes into Saturn).

Not a mission that couldn't be done, but not an easy one.
Thanks for that Chris, which well explains why such a mission hasn't been attempted yet. My thinking was of placing a probe (or, better yet, several small probes) in an (a) orbit(s) inside the rings such that the velocity differences between probe and ring objects would be very small.

Have any planetary missions been easy? Many things worth doing aren't.
It sounds like such an excellent objective to me. Are the challenges mainly a question of sufficient motion control to navigate this environment? I'm wondering how much harm would be caused by a small space probe, about the size of a car, that has died in the middle of a ring. Particularly if it is constructed out of not-very-offensive materials.

I think a wonderful mission plan would be to try to drop into the Encke Gap, trying to get near to Pan, then to pull out of the rings, and slip down to the Huygens gap and, if successfully inserted into the middle of it, to work inward until good views of ring particles were seen. The main goal would be for close-up observation of ring composition. All the while, I think verification of forces and dynamics would be a second goal. My plan may be trying the wrong approach. If all you want is a good look at the typical composition of the rings, perhaps just flying straight into the middle of the B ring is your best and simplest plan, not pussy-footing around with it like my other strategy.

One question that I'd anticipate immediately if anyone seriously considers this idea, is "What kind of energy would the craft need to expend to maneuver 'out of' the rings?" A spacecraft that was a kilometer above the rings would naturally be in an orbit that would not stay there, but would make it pass through the rings twice per orbit. But no doubt with the exertion of some energy, it should be able to follow a non-natural path away from its natural orbit. I'd love it if someone with better knowledge of orbital mechanics could "school me" in this idea. Feasible or not? I don't know. Have we ever tried to put a spacecraft into an off-center orbit and maintain it for some reason? I kind of doubt that we have, but I also doubt that it is any harder to work out than some of the other amazing flight plans NASA has executed.

I think I like this goal mainly because I am such a tourist at heart. I can't argue that this information cannot be gathered in some other way, nor can I argue that this information is vital. It's just one of the things that has my curiosity aroused.

I note that space.com did an article listing the leading proposals for a return to Saturn just days after Cassini obediently took its suicidal plunge into Saturn's atmosphere. https://www.space.com/38159-future-satu ... ssini.html A ring-exploration mission was not among the list of leading proposals.
Mark Goldfain

Sa Ji Tario

Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by Sa Ji Tario » Tue Apr 03, 2018 1:24 am

Para DAMGEN
If you enlarge the image you see that it is a moon and there are two more objects in the vicinity

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by BDanielMayfield » Tue Apr 03, 2018 3:23 am

MarkBour wrote:
Tue Apr 03, 2018 12:03 am
BDanielMayfield wrote:
Mon Apr 02, 2018 3:32 pm
Chris Peterson wrote:
Mon Apr 02, 2018 2:13 pm


It's a huge technical challenge. Spacecraft and small bits of stuff don't mix well. A damaged or uncontrollable spacecraft inside the ring system could be a disaster for future research (which is why they have been careful to avoid the rings, and design orbits such that damaged probes would decay into Saturn, and, of course, to deliberately dispose of probes into Saturn).

Not a mission that couldn't be done, but not an easy one.
Thanks for that Chris, which well explains why such a mission hasn't been attempted yet. My thinking was of placing a probe (or, better yet, several small probes) in an (a) orbit(s) inside the rings such that the velocity differences between probe and ring objects would be very small.

Have any planetary missions been easy? Many things worth doing aren't.
It sounds like such an excellent objective to me. Are the challenges mainly a question of sufficient motion control to navigate this environment? I'm wondering how much harm would be caused by a small space probe, about the size of a car, that has died in the middle of a ring. Particularly if it is constructed out of not-very-offensive materials.

I think a wonderful mission plan would be to try to drop into the Encke Gap, trying to get near to Pan, then to pull out of the rings, and slip down to the Huygens gap and, if successfully inserted into the middle of it, to work inward until good views of ring particles were seen. The main goal would be for close-up observation of ring composition. All the while, I think verification of forces and dynamics would be a second goal. My plan may be trying the wrong approach. If all you want is a good look at the typical composition of the rings, perhaps just flying straight into the middle of the B ring is your best and simplest plan, not pussy-footing around with it like my other strategy.

One question that I'd anticipate immediately if anyone seriously considers this idea, is "What kind of energy would the craft need to expend to maneuver 'out of' the rings?" A spacecraft that was a kilometer above the rings would naturally be in an orbit that would not stay there, but would make it pass through the rings twice per orbit. But no doubt with the exertion of some energy, it should be able to follow a non-natural path away from its natural orbit. I'd love it if someone with better knowledge of orbital mechanics could "school me" in this idea. Feasible or not? I don't know. Have we ever tried to put a spacecraft into an off-center orbit and maintain it for some reason? I kind of doubt that we have, but I also doubt that it is any harder to work out than some of the other amazing flight plans NASA has executed.

I think I like this goal mainly because I am such a tourist at heart. I can't argue that this information cannot be gathered in some other way, nor can I argue that this information is vital. It's just one of the things that has my curiosity aroused.

I note that space.com did an article listing the leading proposals for a return to Saturn just days after Cassini obediently took its suicidal plunge into Saturn's atmosphere. https://www.space.com/38159-future-satu ... ssini.html A ring-exploration mission was not among the list of leading proposals.
Great ideas Mark, but I don't think ring probes need to be near as large as a car. A mission even with several cubesat sized probes might be able to place them into all the orbits on your wish list and more. No need for a large camera for close ups if you can get up close.

Bruce
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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by Chris Peterson » Tue Apr 03, 2018 5:03 am

MarkBour wrote:
Tue Apr 03, 2018 12:03 am
It sounds like such an excellent objective to me. Are the challenges mainly a question of sufficient motion control to navigate this environment? I'm wondering how much harm would be caused by a small space probe, about the size of a car, that has died in the middle of a ring. Particularly if it is constructed out of not-very-offensive materials.
I think the primary concern is biological contamination, not material contamination. In fact, we don't appear to have figured out how to reliably decontaminate our space probes, and Saturn has moons which might support life.
One question that I'd anticipate immediately if anyone seriously considers this idea, is "What kind of energy would the craft need to expend to maneuver 'out of' the rings?"
Quite a lot, depending how far out of the plane it went. Changing inclination is the most expensive of orbital maneuvers, and all the worse if you're doing it from a low eccentricity orbit, as you'd have if you were inside the rings. Also, missions are usually designed to minimize the number of burns required, because these are always risky.
Chris

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by MarkBour » Thu Apr 05, 2018 9:46 pm

BDanielMayfield wrote:
Tue Apr 03, 2018 3:23 am
Great ideas Mark, but I don't think ring probes need to be near as large as a car. A mission even with several cubesat sized probes might be able to place them into all the orbits on your wish list and more. No need for a large camera for close ups if you can get up close.

Bruce
Good point, Bruce. I guess placing several multiple cubesats sounds much easier than my initial idea. But it still might be nice to try to fly one along above a ring for a while. And I wouldn't want to simplify them so much that the images were not good. Given the expenditure of reaching Saturn, the cost of the finest camera(s) would be negligible. And at least one of them will have to be able to send the info clear back to Earth, so it would need a good antenna for transmission, however bulky that is.
Mark Goldfain

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Re: APOD: Moons, Rings, Shadows, Clouds:... (2018 Apr 02)

Post by Chris Peterson » Thu Apr 05, 2018 10:12 pm

MarkBour wrote:
Thu Apr 05, 2018 9:46 pm
BDanielMayfield wrote:
Tue Apr 03, 2018 3:23 am
Great ideas Mark, but I don't think ring probes need to be near as large as a car. A mission even with several cubesat sized probes might be able to place them into all the orbits on your wish list and more. No need for a large camera for close ups if you can get up close.

Bruce
Good point, Bruce. I guess placing several multiple cubesats sounds much easier than my initial idea. But it still might be nice to try to fly one along above a ring for a while. And I wouldn't want to simplify them so much that the images were not good. Given the expenditure of reaching Saturn, the cost of the finest camera(s) would be negligible. And at least one of them will have to be able to send the info clear back to Earth, so it would need a good antenna for transmission, however bulky that is.
I imagine a mission along those lines would fly a largish probe out to Saturn and place it in a safe orbit well outside the rings, and it would release the cubesats, and act as a buffer/relay for the information they returned. No need for big antennas or lots of power that way.
Chris

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