Starship Asterisk*

by **neufer** » Fri Mar 31, 2017 1:40 pm

: [b][color=#0000FF][size=150]Prometheus's ridge ring with a prominent peak[/size] [size=125][i]on the opposite side[/i] of Prometheus from the F ring.[/size][/color][/b]

JohnD wrote:
As Pan is tidally locked, it will also have the same radial relationship to its adjacent rings. So if the ridge is the result of ice deposited on its equator as it draws particles from the adjacent rings, why is it all around? Either end, or where the moon is nearest to the rings might be more expected. Or would particles spiral down onto the surface, to land and augment the ridge?

The only active accretion of ring material currently taking place is on Atlas's neighbor Prometheus which collides with the F ring every 15 hours knocking out particles which then go into some sort of orbit around Prometheus eventually landing in a ridge ring with a prominent peak on the opposite side of Prometheus from the F ring.

by **neufer** » Fri Mar 31, 2017 12:33 pm

geckzilla wrote:
Would the Coriolis effect still cause horizontal banding for clouded planets tidally locked with a parent star? This is one of those things that bothers me a lot. I wonder if the heat gradient would cause some unusual cloud patterns that would be more apparent than what the Coriolis effect would cause—for both gaseous and terrestrial planet types.

Venus is virtually tidally locked and its cloud structure defies all common sense.

Cloud structure in Venus's atmosphere in 1979,
revealed by ultraviolet observations from Pioneer Venus Orbiter.

I, for one, would be extremely hesitant to suggest what the cloud structure on a rapidly rotating tidally locked planet might look like (if different from this example).

by **JohnD** » Fri Mar 31, 2017 10:08 am

As Pan is tidally locked, it will also have the same radial relationship to its adjacent rings. So if the ridge is the result of ice deposited on its equator as it draws particles from the adjacent rings, why is it all around? Either end, or where the moon is nearest to the rings might be more expected.

Or would particles spiral down onto the surface, to land and augment the ridge?
John

by **geckzilla** » Fri Mar 31, 2017 8:19 am

Would the Coriolis effect still cause horizontal banding for clouded planets tidally locked with a parent star? This is one of those things that bothers me a lot. I wonder if the heat gradient would cause some unusual cloud patterns that would be more apparent than what the Coriolis effect would cause—for both gaseous and terrestrial planet types.

by **NESLON** » Fri Mar 31, 2017 6:18 am

ah so they are tidally locked. they don't spin in the way i was imagining, in that these moons will always have a particular side facing Saturn.

by **Chris Peterson** » Thu Mar 30, 2017 3:47 pm

neufer wrote:
Chris Peterson wrote:
neufer wrote: As in the case of almost all moons they are tidally locked.
So to answer the question, yes, both moons spin.
Just not in relationship to their immediate surrounds.

That seems like a confusing way to put it. I'd just say that their rotation period and orbital period are the same. Their "day" and "year" are the same length.

by **neufer** » Thu Mar 30, 2017 3:30 pm

Chris Peterson wrote:
neufer wrote:
NESLON wrote:
Do we know if Pan or Atlas spin ?
As in the case of almost all moons they are tidally locked.
So to answer the question, yes, both moons spin.

Just not in relationship to their immediate surrounds.

(Although Coriolis forces still apply.)

by **Chris Peterson** » Thu Mar 30, 2017 2:13 pm

neufer wrote:
NESLON wrote: Do we know if Pan or Atlas spin ?
As in the case of almost all moons they are tidally locked.

So to answer the question, yes, both moons spin.

If you are a moon and your planet subtends an angle of 2º or more
(as in the case of the Moon & Earth) then you are tidally locked.

Assuming, of course, they've had ample time to become locked. AFAIK that applies to all the satellites we know of that meet your rule, but if not, we could assume they represented either recent captures or bodies disrupted by recent collisions or near collisions.

by **neufer** » Thu Mar 30, 2017 12:05 pm

NESLON wrote:
Do we know if Pan or Atlas spin ?

As in the case of almost all moons they are tidally locked.

If you are a moon and your planet subtends an angle of 2º or more
(as in the case of the Moon & Earth) then you are tidally locked.

by **NESLON** » Thu Mar 30, 2017 8:29 am

Fascinating. Do we know if Pan or Atlas spin ? On an axis perpendicular to the ring plane presumably? perhaps their little equatorial sand dune is being manicured by saturns gravity as they rotate, sort of scouring loosely attracted grains on the moonlet into such a center ridge??

by **neufer** » Fri Mar 17, 2017 1:01 pm

Click to play embedded YouTube video.

BDanielMayfield wrote:
JohnD wrote:
Art's erudition and polytemporalistic tendency (no doubt the result of residence on Tralfamadore) has led him astray.
My reference was not to Bo-peep (Fool, King Lear, Act 1, Scene 4, Page 8) but to Jeremiah 50:6 (qv)
Very nice John. I had to look it up. It fits.

by **BDanielMayfield** » Fri Mar 17, 2017 11:41 am

JohnD wrote:Art's erudition and polytemporalistic tendency (no doubt the result of residence on Tralfamadore) has led him astray.
My reference was not to Bo-peep (Fool, King Lear, Act 1, Scene 4, Page 8) but to Jeremiah 50:6 (qv)
John

Very nice John. I had to look it up. It fits.

Bruce

by **JohnD** » Fri Mar 17, 2017 9:12 am

Art's erudition and polytemporalistic tendency (no doubt the result of residence on Tralfamadore) has led him astray.
My reference was not to Bo-peep (Fool, King Lear, Act 1, Scene 4, Page 8) but to Jeremiah 50:6 (qv)
John

by **Ann** » Thu Mar 16, 2017 10:58 pm

neufer wrote:.
You’ve met Saturn’s ravioli-shaped moon, Pan.

Ann

by **neufer** » Thu Mar 16, 2017 9:53 pm

.
You’ve met Saturn’s ravioli-shaped moon, Pan.
Now learn how it was discovered.

by **Boomer12k** » Tue Mar 14, 2017 12:37 am

Ray-Optics wrote:Since Pan orbits in the Encke gap along with an irregular ringlet, a hypothesis for the hat brim occurs to me: It is picking up "snow" from this ringlet along its "equator" of spin. Pan's gravity must be very low, so ring snow could pile high. An overall snow layer may also account for the relatively young-looking surface.

My guess too... like Enceladus ejecting the Ice in the first place... only a matter of time a moon would, or at least MIGHT, pick up a good deal... it is like a planet, clearing out its orbit, it gathers debris. Maybe that is WHY it is the Encke Gap???? It has cleared much of its orbit.

:---[===] *

by **ccnield27@outlook.com** » Mon Mar 13, 2017 11:45 pm

that's not Pan. It's Kyle from South Park!

by **douglas** » Mon Mar 13, 2017 11:21 pm

Astronymus wrote:This moon is the weirdest thing.

Its brim appears to indicate it does not tumble.

by **Astronymus** » Mon Mar 13, 2017 9:36 pm

This moon is the weirdest thing.

by **douglas** » Mon Mar 13, 2017 7:18 pm

Daphnis, bump this up to high magnification, very instructive
https://saturn.jpl.nasa.gov/resources/7589/

"You can also see the vertical waves caused by the moon’s feeble pull. Each wave corresponds to one up-and-down bob of the moon relative to the rings. Eventually, tides from Saturn pull the particles back down, but that takes a while, and the ripples extend for a long way around the ring."
http://www.slate.com/blogs/bad_astronom ... rings.html

"What causes those ripples? The orbit of Daphnis is not a perfect circle, but instead is very slightly elliptical. That means it’s sometimes closer to the inner edge of the Keeler gap, and sometimes closer to the outer one. The change is small, only about nine km, but that’s enough. When it’s closer to one edge it pulls on the ring particles a bit harder, creating the wave.

But there’s more to it. The orbit of Daphnis is also tipped a bit to the ring plane, a mere 0.0036° from being exactly aligned. That means it bobs up and down out of the ring plane by about 17 km. When it does it drags the ring particles at the gap edges as well. Those waves you see in the image go in and out of the gap, but also up and down by a kilometer or so."

by **neufer** » Mon Mar 13, 2017 6:18 pm

JohnD wrote:
The Wilyard site does refer to a "faint" ring associated with Atlas, but also says definitely that it is not a shepherd moon.

https://en.wikipedia.org/wiki/Rings_of_Saturn#Roche_Division wrote:
<<The separation between the A Ring and the F Ring has been named the Roche Division in honor of the French physicist Édouard Roche. Lying at the outer edge of the main ring system, the Roche Division is in fact close to Saturn's Roche limit, which is why the rings have been unable to accrete into a moon. Like the Cassini Division, the Roche Division is not empty but contains a sheet of material. The character of this material is similar to the tenuous and dusty D, E, and G Rings. Two locations in the Roche Division have a higher concentration of dust than the rest of the region. These were discovered by the Cassini probe imaging team and were given temporary designations: R/2004 S 1, which lies along the orbit of the moon Atlas; and R/2004 S 2, centered at 138,900 km from Saturn's center, inward of the orbit of Prometheus.>>

JohnD wrote:
Maybe the shepherd has lost his sheep,
or other shepherds have led them astray.

by **Billy** » Mon Mar 13, 2017 6:13 pm

The 'slab' kind of reminds me of a cornice. Maybe it's an accumulation of ring material?

by **alcor** » Mon Mar 13, 2017 5:43 pm

I just enjoy todays comments. They are so dead-pan witty.

The comparison you make, with two other of Saturn's moons is very interesting: Atlas and Iapetus. I am also looking forward to better images of Atlas. Perhaps the Cassini team will deliver something in the future.

by **Jimbo Jones** » Mon Mar 13, 2017 5:38 pm

OK...fantastic new pics...what is the dark spot on the right side at 4:00 ? Looks like a shadow? Gonna miss Cassini...

by **JohnD** » Mon Mar 13, 2017 5:10 pm

The Wilyard site does refer to a "faint" ring associated with Atlas, but also says definitely that it is not a shepherd moon. Maybe the shepherd has lost his sheep, or other shepherds have led them astray.
I don't think we understand the dynamics of Saturn's ring system well enough to say, perhaps three ridged moons, with different sizes and associations may point to new ideas.
Wiki? It's a secondary reference source. I hoped to find where that Pan picture was from
John

Starship Asterisk*

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