APOD: In Through and Beyond Saturns Rings (2011 Oct 26)

[APOD Robot]

In Through and Beyond Saturns Rings

Explanation: A fourth moon is visible on the above image if you look hard enough. First -- and furthest in the background -- is Titan, the largest moon of Saturn and one of the larger moons in the Solar System. The dark feature across the top of this perpetually cloudy world is the north polar hood. The next most obvious moon is bright Dione, visible in the foreground, complete with craters and long ice cliffs. Jutting in from the left are several of Saturn's expansive rings, including Saturn's A ring featuring the dark Encke Gap. On the far right, just outside the rings, is Pandora, a moon only 80-kilometers across that helps shepherd Saturn's F ring. The fourth moon? If you look closely in the Encke Gap you'll find a speck that is actually Pan. Although one of Saturn's smallest moons at 35-kilometers across, Pan is massive enough to help keep the Encke gap relatively free of ring particles.

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[zerro1]

That is a cool Image! Well Done!

[islader2]

Robot asks us to find a "spec" that is Pan. I found no "spec"==but several specks; which, it turned out to be dirt on my screen and some "floaters" in my vitreous fluid from searching for Pan. Wish I could make a ditty of the search for spec. Well, we have a sci-fi movie 'Search for Spock' with light travel and such.

[Stan Schultz]

And my very first, knee jerk reaction was, "Aha! Darth Vader and the Death Star zero-in on Saturn!" Obviously I've been watching too many sci-fi flicks.

[Ann]

That Pan is everywhere!

Isn't it cold for him out in the Encke Gap, however, considering he is so scantily clad?

On a more serious note, I find the brightness contrast between Titan and Dione fascinating. Is Titan actually so dark? Of course Dione is very bright, with its ice cliffs. But its albedo, reflectivity, still can't match that of Enceladus, which is perhaps my favorite moon in the solar system.

Can the darkness of Titan be explained by the filter used to take this picture? Was it a blue or perhaps an ultraviolet filter? I didn't check out the caption of today's APOD carefully enough to know.

Well, today's APOD is surely striking. What a family of moons and ring Saturn has!

Ann

[starstruck]

Was it a blue or perhaps an ultraviolet filter?

The first link provides some more information; it says they took the picture in visible blue light. I believe that would mean that if Titan has more red hues in it's colouration then it would appear darker in such an image.

These Cassini images are always stunning and this one is no exception. Those razor sharp rings and the way the moons are hanging there . . makes for an impressive composition, they almost look too real, if that's possible . . . sometimes it's easy to forget that we are not looking at computer generated simulations. This beauty really is out there!

[kidvid]

It seems like there is a fifth moon unless it is an artifact.
In the rings below Dione there is a thin ring gap and it appears to have a bright spot just at the outter gap edge.
So with Massive Titan; Bright Dione; Pandora to the far right and Pan to the far left and possibly the other even smaller moon than Pan; maybe Pan's Flute?

[neufer]

I find the brightness contrast between Titan and Dione fascinating. Is Titan actually so dark? Of course Dione is very bright, with its ice cliffs. But its albedo, reflectivity, still can't match that of Enceladus, which is perhaps my favorite moon in the solar system. Can the darkness of Titan be explained by the filter used to take this picture? Was it a blue or perhaps an ultraviolet filter? I didn't check out the caption of today's APOD carefully enough to know.

The first link provides some more information; it says they took the picture in visible blue light. I believe that would mean that if Titan has more red hues in it's colouration then it would appear darker in such an image.

• Titan Albedo: 0.22
  Dione Albedo: 0.998 ± 0.004
  Enceladus Albedo: 1.375 ± 0.008 (geometric)

<<The surface materials (regoliths) of airless bodies (in fact, the majority of bodies in the Solar system) are strongly non-Lambertian and exhibit the opposition effect, which is a strong tendency to reflect light straight back to its source, rather than scattering light diffusely. The geometric albedo of an astronomical body is the ratio of its actual brightness at zero phase angle (i.e., as seen from the light source) to that of an idealized flat, fully reflecting, diffusively scattering (Lambertian) disk with the same cross-section. Diffuse scattering implies that radiation is reflected isotropically with no memory of the location of the incident light source. Zero phase angle corresponds to looking along the direction of illumination. For Earth-bound observers this occurs when the body in question is at opposition and on the ecliptic.

For very bright, solid, airless objects such as Saturn's moons Enceladus and Tethys, whose total reflectance (Bond albedo) is close to one, a strong opposition effect combines with the high Bond albedo to give them a geometric albedo above unity (1.4 in the case of Enceladus). Light is preferentially reflected straight back to its source even at low angle of incidence such as on the limb or from a slope, whereas a Lambertian surface would scatter the radiation much more broadly. The geometric albedo above unity means that the intensity of light scattered back per unit solid angle towards the source is higher than is possible for any Lambertian surface.>>

[tigermsm]

This is an awesome pic of the day!

[nstahl]

Very nice APOD.

[K1NS]

Wow! That's all I can say. Wow. This has my vote for the APOY award, or at least the APOM. Well done, Cassini and APOD.

[K1NS]

it says they took the picture in visible blue light.

They did this so you could see the people on Pandora.

BTW, on my screen Pandora appears oblate rather than spherical. Is it? Or is this an artifact? Or just my screen?

[owlice]

Yes, Pandora is oblate. I was surprised it appeared so in the image; that it does is a tribute to how fine this image is!

[moonstruck]

Just simply WOW! Thanks Cassini Team.

[orin stepanek]

Great black and white!

[Guest]

Gorgeous picture, thank you1

[lazy_ant]

beautiful, it's one of the best APODs recently

[BMAONE23]

Robot asks us to find a "spec" that is Pan. I found no "spec"==but several specks; which, it turned out to be dirt on my screen and some "floaters" in my vitreous fluid from searching for Pan. Wish I could make a ditty of the search for spec. Well, we have a sci-fi movie 'Search for Spock' with light travel and such.

Looking to the left side of the image you see the "Gap" talked about and inside the middle of that Gap you will find Pan

[redskyatnight]

Was this a planned picture or was it just a random photograph?

[Chris Peterson]

Was this a planned picture or was it just a random photograph?

All the Cassini images are planned.

[stowaway]

Was this a planned picture or was it just a random photograph?

Pictures such as this of the moons in alignment are often obtained to verify the exact position of the spacecraft. They frequently turn out to be really neat pictures. In this case it is exceptionally neat. In my opinion, the coolest picture yet from Cassini.

[Anthony Barreiro]

Oh my god. Best apod ever.

[Ray Wilson]

Enlarged, Titan seems to have an atmosphere.

[Tszabeau]

It seems like there is a fifth moon unless it is an artifact.
In the rings below Dione there is a thin ring gap and it appears to have a bright spot just at the outter gap edge.
So with Massive Titan; Bright Dione; Pandora to the far right and Pan to the far left and possibly the other even smaller moon than Pan; maybe Pan's Flute?

I see that too. Maybe it's the relatively empty space at the outermost part of the gap that, doubled back on itself in the 2D space of the photo, looks more solid and substanative than it really is.