Cassini's pentaverate

By Phil Plait | June 2, 2011 9:30 am

I haven’t posted a Cassini picture in quite some time. To make up for that, here’s a stunner of a family portrait showing five worlds!

[Click to enchronosate.]

This shot shows Saturn’s rings nearly edge-on, but dominating the scene is Rhea, 1500 km (950 miles) in diameter, seen here 61,000 km (38,000 miles) distant. Below it is Dione, to the right and just above the rings is Epimetheus, and Tethys is all the way on the right, below the rings.

So what’s the fifth moon? Look to the right of Dione, right at the rings. See that tiny bump? That’s dinky Prometheus, all of 119 km (71 miles) along its longest dimension — it’s basically a spud orbiting Saturn. Prometheus, along with its sister moon Pandora, act like shepherds, keeping Saturn’s F-ring particles entrained.

Saturn is a weird, weird place, and it’s orbited by a diverse collection of weird, weird moons. I forget that sometimes, but images like this really drive it home.

… on the other hand, as we discover more planets orbiting other stars, we see lots of them with masses like Saturn’s. Of course, low-mass planets like Earth are much harder to find, but still. Who knows? It may turn out Saturn’s normal, and we’re the weird ones.


… and if you’re wondering about the post title, this may help. Whoa, man.


Related posts:

Dr. Tongue’s 3D House of Prometheus
- Perspective on four moons
Cassini’s slant on the rings
The bringer of fire, hiding in the rings
The real Pandora and two mooning brothers

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (17)

  1. Prometheus, along with its sister moon Pandora, act like shepherds, keeping Saturn’s F-ring particles entrained.

    That’s a bit ironic, as I always thought it was Prometheus Unbound.

    <GDRFC>

  2. Greg in Austin

    I see 6 worlds… 5 moons and the rings of Saturn!

    8)

  3. Mejilan

    That is a CRAZY image! So cool! :)

  4. It’s kind of surreal the way everything is different sizes and different distances, but you can’t tell how large or small the are relatively due to the distances. The rings almost look like they shouldn’t even be there. Dione kind of looks like it’s skating across them.

  5. Gonçalo Aguiar

    Is there any shot of the stuff inside the rings?

  6. Sam H

    Sweet image!! :cool:

    @4 Endyo: I agree. What gets me with these pics is that, although these worlds are separated by inconceivable distances, there’s no way to tell which is nearer or farther. If we were actually there, floating amongst their orbits in a windowed spacecraft with a wider view angle, would the human eye be able to deduce at least some kind of distance perception?

  7. Quiet Desperation

    The extreme differences between the moons is why I feel that most of these things formed independently in the primordial nebula and were captured later. Does the current thinking still have the larger moons of the gas giants forming along side their parents? All the CGI animations you see on the science shows depict it this way. That always seemed a little too… tidy. Does a captured moon have to have some odd orbit? Can’t a couple billion years of perturbations smooth it out to something that looks like it formed there?

    I’d model this if I had the time.

    It’s kind of surreal the way everything is different sizes and different distances, but you can’t tell how large or small the are relatively due to the distances. The rings almost look like they shouldn’t even be there. Dione kind of looks like it’s skating across them.

    It’s the usual telephoto effect. It flattens the scene making it look like everything is on top of one another. Photographers use it all the time for various effects.

  8. ohai

    This is officially the second time in my life that I have heard the word “pentaverate“. Just fyi.

  9. Thea

    The rings are so insubstantial. In other photos taken of Saturn, the rings look so huge, but they only contain enough material to make a sphere 100 kilometres in diameter. The Universe is an amazing place.

    ‘Penta-‘ means five. What does ‘verate’ refer to? Moons? Spheres?

  10. MarkW

    Enchronosate? Shouldn’t it be enchronosenate? ;)

  11. Nigel Depledge

    Wonderful shot!

  12. Nigel Depledge

    Sam H (6) said:

    If we were actually there, floating amongst their orbits in a windowed spacecraft with a wider view angle, would the human eye be able to deduce at least some kind of distance perception?

    In short, no.

    Human binocular vision is only effective out to about 100 m or so. Beyond that, we must rely on other clues for relative distances of objects (such as knowledge we already have of them, haziness due to atmospheric dust and so on).

    The absence of an atmosphere (combined with the absence of any familiar objects) on the moon made it very hard for the Apollo astronauts to judge distances. However, when they were heading towards the LM (i.e. an object with whose size they were familiar), they found it easier.

  13. TJ Czeck

    Nigel (13) said:

    The absence of an atmosphere (combined with the absence of any familiar
    objects) on the moon made it very hard for the Apollo astronauts to judge
    distances.

    That reminds me of some Apollo footage that I’ve seen (can’t remember where now) where one of the astronauts is bouncing over to a boulder. From the initial shot, it looks to be about the size of a car or so, but when he gets to it, it is the size of a house. Very confusing at first.

  14. Messier Tidy Upper

    Would a pentaverate be a plural of Titans? ;-)

    Oh wait, that’s not among that particular quintuple of Saturnian moons. Drat. Neta new word though.

    My personal top five “pentaverate” of Saturn’s moons would have to be :

    Titan, Enceladus, Iapetus, Mimas & Hyperion. (Or maybe Phoebe?)

    @1. Ken B : “That’s a bit ironic, as I always thought it was Prometheus Unbound.”

    Well, if it helps it is Prometheus that is *doing* the binding in this case! ;-)

  15. Linda

    Absolutely stunning!

    Thanks for sharing this with us. :-)

  16. Matt B.

    It should be “pentavirate”, with an i, like “triumvirate” (“vir” being Latin for “man”). Of course, the word really should have been “quinquevirate”, using a Latin prefix on a Latin suffix.

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