APOD: Saturn's Moon Pan from Cassini (2017 Mar 13)

[APOD Robot]

[img]https://apod.nasa.gov/apod/calendar/S_170313.jpg[/img] Saturn's Moon Pan from Cassini

Explanation: Why does Saturn's moon Pan look so odd? Images taken last week from the robotic Cassini spacecraft orbiting Saturn have resolved the moon in unprecedented detail. The surprising images reveal a moon that looks something like a walnut with a slab through its middle. Other visible features on Pan include rolling terrain, long ridges, and a few craters. Spanning 30-kilometer across, Pan orbits inside the 300-kilometer wide Encke Gap of Saturn's expansive A-ring, a gap known since the late 1800s. Next month, Cassini will be directed to pass near Saturn's massive moon Titan so it can be pulled into a final series of orbits that will take it, on occasion, completely inside Saturn's rings and prepare it to dive into Saturn's atmosphere.

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[sillyworm]

Amazing pictures! Pan looks to be made of ice/snow.

[ceelias]

Does the "slab" on Pan have fewer craters than the main body of the moon?

[Ann]

Click to view full size image

Photo: It must be Cassini!

Saturn's moon Iapetus with equatorial ridge.
Photo: Cassini.

Well, what can I say? I'm flabbergasted by Pan! I thought another moon of Saturn's, Iapetus, was the king of equatorial ridges in the solar system. Little did I know!

If Pan isn't a spaceship or a hat, it must be... well, I guess it must be a moon after all.

But goodness me, what does it look like!!!

Ann

[Night eyes]

Wow, very strange, what made it have such an odd shape? A flying saucer left over from an alien space probe? LOL !

[Knight of Clear Skies]

It looks like a prop from an Ed Wood movie. Its thought that equatorial ridge (or lifebelt) is material deposited from Saturn's rings: http://www.planetary.org/blogs/jason-da ... mages.html

[JohnD]

Thank you, Ann! Among the many comments on Pan, no one else has noted the ridge that it shares with Iapetus, previously the only known example. Iapetus is old enough to have craters all over, including its ridge, as you show; Pan is so young (or so frequently remade) as to have almost none, anywhere, so what does this ridge tell us about moon formation?

John

[BDanielMayfield]

[The Underside of] Saturn's Moon[Bed]Pan from Cassini

[BDanielMayfield]

If you don't know what a bedpan is, well then, you've been fortunate.

I'm sorry, butt sometimes things just have to come out.

[ta152h0]

this is going to be my new " pondering rock ". Like pet rocks !

[douglas]

Click to view full size image

Photo: It must be Cassini!

Saturn's moon Iapetus with equatorial ridge.
Photo: Cassini.

Well, what can I say? I'm flabbergasted by Pan! I thought another moon of Saturn's, Iapetus, was the king of equatorial ridges in the solar system. Little did I know!

If Pan isn't a spaceship or a hat, it must be... well, I guess it must be a moon after all.

But goodness me, what does it look like!!!

Ann

Iapetus' walnut ridge was explained as from spin up, but Pan even shows Phobos-like stress grooves. Did its "hat brim" produce the stress?

[Ray-Optics]

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.

[BDanielMayfield]

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.

That makes sense, making Pan one of the weirdest objects in our solar system; the only world with a miles deep permanent equatorial snowpack.

Bruce

[JohnD]

That is a most attractive theory, given the picture of Pan ("Equatorial view of Pan from Cassini, with the rings of Saturn surrounding the moon") on the Wiki entry https://en.wikipedia.org/wiki/Pan_(moon) Sorry to reference Wiki, but it's the onky source of that pic I can find.

But in looking I also find Atlas! This Saturnian moon has not yet been imaged as well as Pan,but appears to have a ridge but is NOT a shepherd moon! http://www.whillyard.com/science-pages/ ... moons.html Unless it has moved away from the rings, there must be another source of the ridge.

John

[BDanielMayfield]

That is a most attractive theory, given the picture of Pan ("Equatorial view of Pan from Cassini, with the rings of Saturn surrounding the moon") on the Wiki entry https://en.wikipedia.org/wiki/Pan_(moon) Sorry to reference Wiki, but it's the onky source of that pic I can find.

But in looking I also find Atlas! This Saturnian moon has not yet been imaged as well as Pan,but appears to have a ridge but is NOT a shepherd moon! http://www.whillyard.com/science-pages/ ... moons.html Unless it has moved away from the rings, there must be another source of the ridge.

John

Good catch to point out Atlas John. It could have a very similar morphology to Pan though. As Ray-Optics noted, Pan has a ring-let that shares its orbit. The second link you provided says that Atlas also shares its orbit with a ring-let. So I stand sit corrected on Pan's one-of-a-kind status.

Bruce

[Ann]

Thomson and Thompson, or Atlas and Pan?
Source: http://tintin.wikia.com/
wiki/Thompson_and_Thomson

Atlas and Pan are two of a kind!

Ann

[Steve Dutch]

Nice real example of a stress ellipsoid. The conjugate shear fractures indicate the maximum compression was oriented vertically and tension roughly horizontally. What's the direction to Saturn? My guess is to the left or right. The equatorial skirt of course is the ring plane.

[Steve Dutch]

John, why are you sorry to cite Wiki? A number of studies have shown it compares favorably with more standard references. Most of the people who bash Wikipedia seem not to want an easily located source capable of calling out their errors.

[bystander]

That is a most attractive theory, given the picture of Pan ("Equatorial view of Pan from Cassini, with the rings of Saturn surrounding the moon") on the Wiki entry https://en.wikipedia.org/wiki/Pan_(moon) Sorry to reference Wiki, but it's the onky source of that pic I can find.

But in looking I also find Atlas! This Saturnian moon has not yet been imaged as well as Pan,but appears to have a ridge but is NOT a shepherd moon! http://www.whillyard.com/science-pages/ ... moons.html Unless it has moved away from the rings, there must be another source of the ridge.

John

http://asterisk.apod.com/viewtopic.php?p=267920#p267920
http://asterisk.apod.com/viewtopic.php?p=267994#p267994

[neufer]

.

[b][color=#80A000][size=150]Le fils de l'homme[/size][/color][/b]

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Thomson and Thompson, or Atlas and Pan?

Atlas and Pan are two of a kind!

<<The Son of Man (French: Le fils de l'homme) is a 1964 painting by the Belgian surrealist painter René Magritte. About the painting, Magritte said: At least it hides the face partly well, so you have the apparent face, the apple, hiding the visible but hidden, the face of the person. It's something that happens constantly. Everything we see hides another thing, we always want to see what is hidden by what we see. There is an interest in that which is hidden and which the visible does not show us. This interest can take the form of a quite intense feeling, a sort of conflict, one might say, between the visible that is hidden and the visible that is present.>>

[JohnD]

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

[Jimbo Jones]

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

[alcor]

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.

[Billy]

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

[neufer]

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

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<<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.>>

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

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