Cassini and Saturn's moons

[Jerry]

Since the leading side of Iapetus is dark, while the trailing side is bright, the generally accepted belief is that it's a bright moon that has picked up dark material while orbiting.

That would also be consistent with Pheobe forming a dark crust over lighter matter - assuming it is a recent acquisition that was rotating when it was captured.

On the other hand, Rhea looks like it was hit by something white, so if there is also white stuff floating around, a completely dark coat on the leading side is inconsistent with 'white stuff' collisions.

Isn't this a great puzzle?

[ToSeek]

Lots about Iapetus:

Giant landslide

View from the top

Encountering Iapetus

[01101001]

VIMS Shows Iapetus Surface Composition

The different colors represent vastly different surface compositions. The upper bright blue region is rich in water ice, while the lower, dark brown region is composed mainly of a substance rich in organic material. The yellow region consists of a mixture of ice and organics, suggesting a gradual change in composition on the surface. This pattern suggests Iapetus swept up the dark material, which may have come from debris created from meteoritic impacts onto the small, outer satellites of Saturn.

Iapetus Surface Composition

The color composite shows water as blue, carbon dioxide as green, and non-ice minerals as red.

[Ari Jokimaki]

Since the leading side of Iapetus is dark, while the trailing side is bright, the generally accepted belief is that it's a bright moon that has picked up dark material while orbiting.

If that would be the case, then shouldn't we see it in other moons also? Or is Iapetus only moon bright enough to show this effect?

[the_shaggy_one]

Actually, Dione and Rhea have brighter leading hemispheres, but it looks like some other process is at work than what happened at Iapetus.

[01101001]

Stange Hyperion

This unusual view of Saturn's moon Hyperion shows just how strangely shaped this tumbling little moon is. Hyperion is thought to be the largest irregularly-shaped moon in the solar system. Hyperion is 266 kilometers (165 miles) across.

[Kullat Nunu]

I hope they will put the Cassini raw image gallery back online soon, since yesterday (Sunday) Cassini flew past Mimas, Enceladus, and Rhea hopefully taking best pictures of them yet.

Just checked: Here they are!

[Kullat Nunu]

Mimas with Herschell Crater clearly visible (it's surprisingly rough)
Closer view, Herschell at the terminator

Gibbous Enceladus
Crescent Enceladus: this moon is really weird!

Rhea

(There may be even better views, I don't have enough time to check them all.)

[Kullat Nunu]

Now there's only one "classical" moon of Saturn, Hyperion, that lacks better-than-Voyager images by Cassini. Hopefully it'll take some good views of the small satellites too.

[Kullat Nunu]

Cassini Picture of the Day: Rhea and Her Craters



Somehow this view looks dull compared to the new photos. :-?
Well, distance does matter.

[Kullat Nunu]

Race of the Moons

This movie, showing six of Saturn's small ring-region moons as they raced around the planet, was made from images taken by the Cassini spacecraft on Nov. 15, 2004.

[the_shaggy_one]

Am I the only one who noticed the extremely prolate shape of Mimas?

[John Kierein]

Now there's only one "classical" moon of Saturn, Hyperion, that lacks better-than-Voyager images by Cassini. Hopefully it'll take some good views of the small satellites too.

Hyperion looks like it's shaped more like a space station than a moon. Can't wait for a closeup.

It really looks more like a rock though from Voyager.
http://www.solarviews.com/eng/hyperion.htm

[pumpkinpie]

Now there's only one "classical" moon of Saturn, Hyperion, that lacks better-than-Voyager images by Cassini. Hopefully it'll take some good views of the small satellites too.

According to my notes, Cassini will come within 615 miles of Hyperion on September 26th of this year.
=D>

[Kullat Nunu]

Cassini raw images have been updated again; actual high-resolution Rhea pictures are available here (files N00026654.jpg to N00026682.jpg).

[quaternion]

Cassini raw images have been updated again; actual high-resolution Rhea pictures are available here (files N00026654.jpg to N00026682.jpg).

The new images of Enceladus are what really caught my eye:

http://saturn1.jpl.nasa.gov/multimed.../N00026570.jpg

I'm really looking forward to the close flyby on February 17.

--Chris

[AK]

I'm really looking forward to the close flyby on February 17.

I hear ya.

That's a great picture.

[Omicron Persei 8]

Cassini raw images have been updated again; actual high-resolution Rhea pictures are available here (files N00026654.jpg to N00026682.jpg).

The new images of Enceladus are what really caught my eye:

http://saturn1.jpl.nasa.gov/multimed.../N00026570.jpg

I'm really looking forward to the close flyby on February 17.

--Chris

Oh wow!

[Kullat Nunu]

Mimas below the rings:



And yes, the_shaggy_one, Mimas looks very prolate in these images.

[frogesque]

Cassini, Zooming In on Enceladus

The fun continues

[Kullat Nunu]

Mimas, rings and one of the small satellites (Pandora probably)!

[Ian R]

Cassini raw images have been updated again; actual high-resolution Rhea pictures are available here (files N00026654.jpg to N00026682.jpg).

The new images of Enceladus are what really caught my eye:

http://saturn1.jpl.nasa.gov/multimed.../N00026570.jpg

I'm really looking forward to the close flyby on February 17.

--Chris

Enceladus is also displaying a rather prolate shape in this particular picture (you have to increase the brightness a fair amount in order to see the limb on the dark side). It's equatorial diameter is 3% bigger than the north to south polar distance. Can this be attributed to some kind of imaging artifact or are these moons really as flattened as they appear to be in these new pictures?

I certainly don't recall seeing anything like this in the Voyager images.

[01101001]

Enceladus is also displaying a rather prolate shape in this particular picture (you have to increase the brightness a fair amount in order to see the limb on the dark side).

Prolate? Having the shape of a spheroid generated by rotating an ellipse about its longer axis?

[Matt McIrvin]

Enceladus is also displaying a rather prolate shape in this particular picture (you have to increase the brightness a fair amount in order to see the limb on the dark side). It's equatorial diameter is 3% bigger than the north to south polar distance. Can this be attributed to some kind of imaging artifact or are these moons really as flattened as they appear to be in these new pictures?

I certainly don't recall seeing anything like this in the Voyager images.

I know that Mimas, at least really is prolate, stretched tidally in the direction of the moon-Saturn line. The Voyagers did see that, though it wasn't so obvious in the most popular pictures. I'd expect Enceladus to be measurably elongated too.

Of the moons large enough to be roughly spherical, these are the closest to Saturn and experience the most tidal stress.

[Matt McIrvin]

Mimas, rings and one of the small satellites (Pandora probably)!

Here's a colorized version:

http://world.std.com/~mmcirvin/moons_rings_color.jpg

The Saturn-shine effect on the moons' nightsides is lovely.

[Kullat Nunu]

Too cool: Janus, Pandora and one of the larger satellites behind Saturn's rings!



Here's the same moon partially occulted by the rings:

[Manchurian Taikonaut]

Titan info and pictures were great

but here's another moon

http://ciclops.lpl.arizona.edu/media...739_1570_1.jpg

view of the trailing hemisphere of Rhea (1,528 kilometers, 949 miles across) shows the region's bright wispy markings, but also shows off the moon's craters in great detail. Of particular interest to imaging scientists is the distribution and orientation of the many craters with polygonal rims. These are craters with rough, angular shapes, rather than smooth, circular ones.

[Kullat Nunu]

More unusual pictures: two large moons in same view.

[Kullat Nunu]

Cassini Picture of the Day:

January's Moon

[ToSeek]

Natural colour image of Rhea