Cassini visits a foamy moon

By Phil Plait | August 26, 2011 11:40 am

I’ve said it before: Saturn’s moon Hyperion is seriously freaky. New images from the Cassini spacecraft flyby of the tiny moon don’t change my mind one bit:

[Click to enchronosenate.]

What a weird place! Hyperion is a lumpy chunk of ice only about 270 km (170 miles) across on average, but yesterday (August 25, 2011) Cassini passed about 25,000 km away from it, so it got a lot of high-resolution shots.

As you can see, it’s saturated with craters. But they look funny! The overwhelming impression I get is that Hyperion is made of resilient foam, like a packing peanut. I’m also fascinated by the ginormous crater that dominates this face of the moon. If Hyperion were made of stiff rock, an impact that size would’ve shattered it like a bullet hitting a pebble. But if the composition of the moon is able to compress and compact — like foam, or something with lots of pockets of empty space inside it — the impact would do pretty much what we see here. Lots of asteroids appear to be "rubble piles" — chunks of material held together by their own gravity, possibly due to impacts that produced myriads of cracks inside the body, or events that just barely shattered the rock, letting it re-accumulate under its own gravity. I’m not saying Hyperion is like that (it’s still not well-understood what it’s like), but that’s one way to bet.

Note also all the dark spots in the bottoms of the craters. Those are from hydrocarbons, complex organic molecules formed when ultraviolet light from the Sun hits simple molecules like methane, rearranging the atoms into bigger molecules. Even under the weak gravity of the moon they flow to the bottoms of the craters, giving Hyperion that decidedly odd black-eyed pea look.

The image here, and the others released today, are raw: that is, they haven’t been processed yet to remove camera artifacts and the like. I imagine they’ll be cleaned up pretty soon, and no doubt my pal Emily Lakdawalla is working on an animation of the flyby right now even as I write this. One was made for a 2010 flyby and it’s awesome. This new flyby is pretty dramatic, showing Hyperion full as well as shadowed, so I can’t wait to see what a Cassini’s eye-view animation will look like!


Related posts:

Hyperion
You’re as cold as ice, but less dense
Raw hypermoon
The stark beauty of Cassini’s Saturn

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Cassini, Hyperion, Saturn

Comments (27)

Links to this Post

  1. La Contextura de Hyperion. | Pablo Della Paolera | August 26, 2011
  1. kevbo
  2. BigBadSis

    It looks like an Oklahoma rose rock!

  3. ruidh

    It has to be a captured comet.

  4. Anon

    Enchronosenate? Seriously? Saturn was named after Jupiter’s father – Cronus, king of the Titans and the god of agriculture. Not Chronos, the god of time. I can’t stand when people confuse the two.

  5. Chronuss

    Anon, does that topic come up a lot? Like ever? Lighten up. Phil likes to make up synonyms for “make bigger.”

  6. Georg

    The staggered small “craters” especially within that ginormous crater
    look to me like something from below boiled/sublimated vigorously,
    and blew the ice away.
    Georg

  7. uudale

    Spongemoon Squarepants!

    “Whooooooooo…. Lives in a pineapple under the rings…”

  8. JT

    This image instantly reminded me of the “penitente” formations I’ve seen climbing in high-altitude, sunny areas. As I understand it they are formed by a feedback mechanism where a small dimple in the snow creates a reflector which increases the radiation on the surrounding snow and melts it. Maybe a similar process could be responsible here?

    http://en.wikipedia.org/wiki/Penitentes

  9. JohnW

    I half expect to see a swarm of angry space yellow jackets come boiling out of that thing.

  10. Jafafa Hots

    An overly cold slushie that got shook up.

    Seriously, ever since I was a kid I’ve had this mental image of icy space things (mostly comets) as being similar to the stuff that accumulates around car tailpipes in snowy towns like Buffalo. A crusty combination of ice and dark gunk that falls off and sits in the gutter until mid-April. That stuff is the very last stuff to melt even though it’s mostly ice.

    (Why would blackened ice take longer to melt?)

    Sorry for the tangent.

  11. Digital Atheist

    That’s not a moon… It’s a living being. ;-)

  12. KC

    I dunno what it is about Hyperion – but when I look at pictures of it I get the heebee-jeebies! Makes the hair on the back my neck stand up. Weird!!

  13. Chief

    Don’t know why but I have a taste for Corn Pops.

  14. lunchstealer

    Woo hoo! It’s stuff like this that makes me wish I’d gone into planetary geology. The downside of dealing with publish-or-perish and the live-by-proposal-die-by-proposal lifestyle that is required for academic success is still something I’m poorly suited for, but hoo-boy would playing with a mystery – suite of interwoven and interconnected mysteries – be just a hell of a lot of fun!

    I’m imagining those weird ice cubes you sometimes get that have too much air trapped in them or something, and so when you bite down on them they’re softer than they should be, and kinda squeak when you bite them. I’m imagining biting down like that on Hyperion.

    Also, I’m having to fight the urge to examine this image of Hyperion for the Time Tombs and the Tree of Pain and Sad King Billy’s City of Poets.

  15. un malpaso

    I think we should rename it “SpongeBob.” :)

  16. VinceRN

    First thing I thought of looking at that was coral. I’ve seen similar shapes while diving. How cool would space coral be?

    I look forward to the processed image and to our host’s thoughts on it.

  17. Messier Tidy Upper

    Excellent image. Cassini never fails. :-)

    Hyperion does seem coral-like in appearance – yes. It also reminds me of the “ever-growing” crystalline hydrogen molecule in the Christmas special of ‘Eureka’ which I saw on TV the other night. :-)

    Hyperion also makes me think of pumice – the volcanic rock – too. :-)

  18. Mekhong Kurt

    @JohnW (# 9) — “I half expect to see a swarm of angry space yellow jackets come boiling out of that thing.” Cracked me right up! I took another look and have to agree! LOL! :-)

  19. James H. (south of Dallas)

    I agree with a lot of the posters here about what Hyperion looks like. To me it does look like the craters were made from the inside out.

  20. John Baxter

    Cheese. Not green. Swiss.

  21. andy

    One question about Hyperion’s rotation… it is well-known that the rotation of Hyperion is chaotic, but just how chaotic is it? What is the timescale before which the orientation cannot be predicted to any reasonable degree of accuracy (even in a chaotic system you can predict the behaviour fairly reliably for a certain amount of time) – is the orientation essentially unknown before each Cassini flyby, or what?

  22. TM Mayyy

    “But they look funny!”

    I like cake!………..

  23. Messier Tidy Upper

    @21. John Baxter : Cheese. Not green. Swiss.

    Couldn’t it be both? Green swiss cheese? Yuuummm! ;-)

  24. Messier Tidy Upper

    @ 22. andy :

    One question about Hyperion’s rotation… it is well-known that the rotation of Hyperion is chaotic, but just how chaotic is it? What is the timescale before which the orientation cannot be predicted to any reasonable degree of accuracy (even in a chaotic system you can predict the behaviour fairly reliably for a certain amount of time) – is the orientation essentially unknown before each Cassini flyby, or what?

    Good question.

    See :

    http://www.youtube.com/watch?v=tk8r85lM3SY

    for a brief animation of Hyperion a-tumbling. :-)

    See :

    http://www.peymanparsa.com/pdf/Hyperion%20Rotation-Saturn-Nov-2010.pdf

    For pdf full of formulae for it & see :

    http://nineplanets.org/hyperion.html

    which notes pertinently to this :

    .. [Hyperion’s] axis of rotation wobbles so much that its orientation in space is completely unpredictable. There is only one other known body in the solar system (asteroid 4179 Toutatis) that rotates chaotically but simulations seem to indicate that other irregular satellites may have done so in the past. Hyperion is unique in that it is very irregularly shaped, has a highly eccentric orbit, and is near another large moon (Titan). These factors combine to restrict the set of conditions under which stable rotation is possible. The 3:4 orbital resonance between Titan and Hyperion may also make chaotic rotation more likely.

    Not sure that helps but hope so.

  25. andy

    Ah-ha, according to Harbison et al. (2011) the Lyapunov timescale is of order 100 days (roughly 5 orbits). It’s bad enough on Earth with the weather being unpredictable over a few days, imagine if the time of day was that unreliable…

  26. Ian Regan

    This colorized movie of the Hyperion flyby was produced using 85 frames taken with Cassini’s narrow angle camera (NAC):

    http://youtu.be/ARyY7BJhzhs?hd=1

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