The staring eye of a crescent moon

By Phil Plait | February 10, 2012 10:39 am

Sometimes, the images from the Cassini Saturn probe are so cool it’s tempting just to post them and say, "Look at THAT!"

See what I mean? [Click to gigantesenate.]

But of course, I can’t just leave it at that. This image, taken on January 4, 2012, is a bit different than most. Sure, we see Saturn’s magnificent rings, nearly edge on from this perspective. And we’ve seen this icy moon Enceladus many, many times (see Related Posts below for tons more pictures). Look at the bottom of the moon: see those fuzzy streaks? Those are geysers of water spewing from cracks in the moon’s south pole! Cassini has been studying them intently ever since they were discovered; they are proof that liquid water exists under the surface of Enceladus, though it’s still being argued over whether it’s in pockets, like lakes, or the whole moon has an ocean of water under the surface.

Despite all that, I keep getting drawn to the crescent shape itself. We can never see that from Earth. Saturn is much farther out from the Sun than we are, and geometry demands that from home we always see these worlds nearly fully lit by the Sun. The only way to see them like this is to go there.

But also, that giant circular feature is really interesting. It’s big, maybe 200 km (over 100 miles) across, and a bit darker than the surrounding surface. I tried locating it on an atlas of Enceladus, but it wasn’t obvious at all. I thought it might be an impact basin, but a little scrounging online led me to a paper by Cassini imaging team leader Carolyn Porco, which says there are no large impact basins on Enceladus! So what is it?

Well, why not go to Dr. Porco herself? I sent her a note, and she kindly replied. That region is called Diyar Planitia, and it stands out among the surrounding terrain because it’s much smoother. It does have narrow surface features, but they’re too small to be seen at this resolution. At the low angle at which we’re seeing it here, it looks a little bit darker than the rougher terrain around it, so it’s easier to see (which is why on an atlas it’s harder to find). It is roughly circular, but that may simply be coincidence. Enceladus has been massively resurfaced, with some areas much older than others, due to various forces under the surface — looking this all up I learned a new one, called diapirism, where lower density material underneath higher density material can rise up and break through. That’s one process that’s helped change the surface of Enceladus over the eons.

That’s pretty nifty. And think about that! Today I learned of what is to me a new region of the solar system, one that has an interesting and complicated history, molded by vast forces over long-stretched times, one of which was also new to me. How wonderful to get all that from what’s otherwise just a pretty picture!

But of course, in science, there’s no such thing as just a pretty picture. Science is a tapestry, a vast complex fabric interwoven with countless threads. Each of those threads is amazing, each important, and each leads to another. And that’s where the true beauty of science lies.


Related posts:

- Enceladus sprays anew!
- Enceladus fires on Alderaan
- Saturn weather forecast: rings, with light rain from Enceladus
- Icy moon and distant rings

Comments (17)

  1. George Kopeliadis

    Who stole Saturn?

  2. Diaparism – not to be confused with Diaperism, which has something to do with baby poop.

  3. saphroneth

    Diapirism used to be the most parlous explanation for the emplacement of granite batholiths, but now the picture is a bit more complex. It’s still the driving force behind salt domes, which show up a lot in oil geology. So it happens here on Earth, too.

  4. persnickydietz

    “But of course, in science, there’s no such thing as just a pretty picture. Science is a tapestry, a vast complex fabric interwoven with countless threads. Each of those threads is amazing, each important, and each leads to another. And that’s where the true beauty of science lies.”

    What a beautiful, magnificent paragraph. I love this. Jebus couldn’t've said it better himself.

  5. Grand Lunar

    Given your title of this post, it’d be even better if this was Iapetus. :)

    Still, this is way cool!
    And nice to see we can make out the geysers as well.

  6. Dragonchild

    Ah, Enceladus. . . the moon that never stops farting.

    Not as bad as Io though. . . Enceladus may rip wet ones, but Io are eggy.

  7. Awesome image, wonderfully written-up. Seconding (#4.) persnickydietz. :-)

    @5. Grand Lunar – February 10th, 2012 at 5:08 pm :

    Given your title of this post, it’d be even better if this was Iapetus.

    Or even the “death star moon” Mimas? ;-)

    BTW. Diyar Planitia is named for a land in ‘The Arabian Nights’ and has a wiki-page – linked to my name here – if folks are interested. Its among the most youthful and least cratered regions of Enceladus. :-)

  8. some_moron

    Is there a high-res available? This would look awesome on my desktop.

  9. bkallee

    Your last paragraph is one of those quotable quotes. You should have that on your BA T-shirts.

    “But of course, in science, there’s no such thing as just a pretty picture. Science is a tapestry, a vast complex fabric interwoven with countless threads. Each of those threads is amazing, each important, and each leads to another. And that’s where the true beauty of science lies.”

  10. @ ^ bkallee : Yep – BA T-shirts : *WANT.* 8)

    That quote on a T-Shirt : *WANT.* 8)

    Ever thought about getting into some merchandising BA? :-D

    PS. When’s your next book coming out? Please tell me there will be one – please!

    PPS. I’d love a collection of the best BA blog items you’ve published here printed in book form y’know if you’re short on ideas… (Hint, hint!)

  11. Bob

    I also loved the quote, and thought the T-shirt idea was cool. I took the liberty of setting it up on Zazzle. Phil, email me and I’ll send you a link for approval, or just tell me and I’ll just post it here. Zazzle forces you to take a commission, which I’m happy to donate if you like.

    Of course, if you think it’s a bad idea, let me know and I’ll take it down.

  12. Bob (11): Wow, I’m honored. Sure, go ahead and open that up. As long as you credit me. :) And if you make money, so be it!

  13. ginckgo

    More proof that all the planets and moons are expanding, amiright!

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