Crescent planet, crescent moonrise

By Phil Plait | August 17, 2010 7:00 am

Oh. My.

Another lovely, stunning Cassini image: A thin crescent Enceladus rising over the sunlit cloud tops of Saturn:

cassini_enceladus_crescent

What a sight! As the spacecraft rounded into the dark side of Saturn, it turned back toward the planet (and the far more distant Sun). The top of Saturn’s atmosphere is still lit as seen from Cassini’s vantage point, but also lit was the moon Enceladus. The moon was between Saturn and Cassini, and so the geometry dictates it too was showing almost entirely its dark side to the spacecraft. The result is the thin crescent of the moon just over the (only partially seen) thinly lit crescent of its parent planet.

cassini_craters_tethysThis raw image (meaning it has not been processed to remove camera defects and other artifacts) is one of several available on the CICLOPS site. There are other shots of Enceladus which show its famous string of geysers, and incredible close-ups of craters on the moon Tethys — like the one shown here (click to embiggen).

The average density of Tethys is actually less than that of water, meaning it is mostly ice. Clearly, Tethys has had a rough past; the surface is saturated with craters (the weird lines on the right hand side are one of those camera artifacts I mentioned, and aren’t real). The moon is nearly 1100 km (660 miles) across, so clearly Penelope, the large crater you can see there, is enormous… and old, at least old enough to have suffered multiple peppering impacts in the time since it was created.

The other images on the CICLOPS site are wonderful, and you should look. Also, Emily Lakdawalla took a few of them and made animations which are particularly amazing. Zoom in on Enceladus, or watch it rise in front of Saturn!

CATEGORIZED UNDER: Astronomy, Pretty pictures

Comments (29)

  1. Pete Jackson

    If you download the Enceladus image and crank up the contrast and brightness on the limb of Enceladus, you can see three geysers, including one (the rightmost one) that shoots what appears to be a horizontal jet across to the left to an area of slightly enhanced brightness inside the limb.

    Great pics; this is good, good astronomy!

  2. Messier Tidy Upper

    Thankyou Cassini & thankyou Emily Lakdawalla. :-)

    You never fail to deliver and to awe. I love this image. 8)

  3. Messier Tidy Upper

    Oh & thanks to the BA as well, natch. :-)

  4. MikeMcL

    Like watching C-beams glitter in the dark near the Tannhauser gate.

  5. MikeMcL, that was WIN! Much like the picture itself. Pure win on the intertubes!

  6. AliCali

    “(click to embiggen)”

    Embiggen? I never heard that word before I came to this website.

  7. MT-LA

    AliCali…welcome to the Bad Astronomy blog: Home of made up words and astronomy porn.

  8. Steeev

    A Noble Spirit Embiggens the Smallest Man…

  9. Thespis

    It’s a perfectly cromulent word, AliCali. ;)
    Wallow in the crapulence.

    I like the idea that the moon Tethys might be mostly ice, as the Titan Tethys was a sea-goddess in the mythologies.

  10. Chris A.

    Mmmm. Enchiladas.

  11. Messier Tidy Upper

    @9. Thespis :

    Sedna was named after a sea goddess (the Inuit one) too – & that *very* distant ice dwarf planet is much icier. Well temperature~wise, anyhow. Actually, I’m not sure we know Sedna’s composition but certainly Sedna is an iceball as well although maybe with some rock too. “Ice” here incl. nitrogen and other exotic ices as well as the familiar water variety. Just like the other ice dwarf planets and middle-outer solar system moons some of which (eg., Triton, Phoebe) were probably captured from the cometary disk.

    @6. AliCali :

    Embiggen? I never heard that word before I came to this website.

    Its originally from an episode of The Simpsons but the Bad Astronomer has made it his own. Like it or loathe it, you’ll have to get used to seeing it (& a few other neologisms) here. I’m not sure what’s so wrong with the perfectly good english word ‘enlarge’ myself but it’s Dr Plait’s blog so he gets to choose what words he uses & he has decided on that one. I guess as long as ppl understand what is meant ..

    @4. MikeMcL : Great Bladerunner reference there. :-)

  12. Pepijn

    The CICLOPS people made a very beautiful video with images of Saturn, its rings and its moons here:

    http://www.ciclops.org/view/24

    Unfortunately it has no sound, which I thought it deserved, so I made this remix:

    http://www.youtube.com/watch?v=o1KKXmBnzG0

  13. Interskeptor

    …a little detail made me wonder:

    BA:
    > The moon was between Saturn and Cassini,
    > and so the geometry dictates it too was showing
    > almost entirely its dark side to the spacecraft.

    …wouldn’t it be (nearly) the same geometry lightwise (made that up ;-) ), if saturn would have been on the other side? The proportions might have been a bit different, but the position of both towards the sun wouldn’t change that dramatically…(?)

    just curious…

  14. Chad

    I have a question. How are the pictures taken? Is there someone on earth looking at a video screen and pushing a button? Or is there a set program that it follows and random shots are taken?

  15. Chad: it’s a program. They have to plan out observations about a year in advance (that is, which observations happen when) and then map out exactly what actions (turns, opening shudders, etc.) have to happen about 3 months out. Commands are checked and rechecked, then uploaded for about 1-2 months at a time. The light travel time (90 minutes) means that you can’t be taking the pictures from Earth.

    It’s fun, challenging work, but well worth it.

  16. AliCali

    MT-LA (#7): My comment was a softball pitch – See other comments

    Thespis (#9): That was the response I was looking for; thanks. Although Steeev [sp?] #8 was good.

    Messier Tidy Upper (#11): Embiggen is funnier than enlarge; although I like “craptacular” (in a different context).

  17. @6. AliCali :

    Embiggen? I never heard that word before I came to this website.

    Its originally from an episode of The Simpsons but the Bad Astronomer has made it his own.

    I think that the correct response, Messier Tidy Upper, is “It’s a perfect cromulent word.” AliCali seems to know the reference, or at least has stumbled on the correct wording.

  18. Now that’s a photograph! And all done by a machine far, far away. Amazing.

    “The tasks above are as the flasks below, saith the emerald canticle of Hermes and all’s loth and pleasestir, are we told, on excellent inkbottle authority, solarsystemised, seriolcosmically, in a more and more almightily expanding universe under one, there is rhymeless reason to believe, original sun. Securely judges orb terrestrial. ” (James Joyce, Finnegans Wake)

  19. Anne Verbiscer

    Gordon Ugarkovic has produced a color version of the stunning image of Enceladus and Saturn, upping the “wow” factor even more:

    http://www.unmannedspaceflight.com/index.php?act=attach&type=post&id=22311

  20. jest

    And….. my MBP now has a new desktop background!

  21. Anne Verbiscer — Thanks for that bit of ocular brilliance! Wow

  22. Richard Woods

    @13 Interskeptor

    If Saturn had been between that moon and Cassini, then the side of the moon facing Saturn would’ve been lit up by all the reflected Saturnlight from Saturn’s day side.

    Just a few days ago, BA showed an example of reflected Saturnlight on Enceladus, when Enceladus was between Saturn and the sun, here: http://blogs.discovermagazine.com/badastronomy/2010/08/09/a-moon-skating-in-its-own-ice/

  23. Tethys picture: how can we explain the formation of long furrows in the middle and top left of the crater?
    Complementing these interesting images, I remembered an interesting image so-called “spear” on the surface of Tethys. http://photojournal.jpl.nasa.gov/catalog/PIA07737

  24. Nigel Depledge

    Superb pic!

    Very well done, Cassini, and thanks, Phil, for bringing this to our attention.

  25. Interskeptor

    Richard Woods:
    > If Saturn had been between that moon
    > and Cassini, then the side of the moon
    > facing Saturn would’ve been lit up by
    > all the reflected Saturnlight from
    > Saturn’s day side.

    …of course… X-|
    Got it! Thanx very much!

  26. JohnW

    Pretty amazing how much meaning there is in what is essentially just a fat line and a whisp of a curve.

  27. jojack

    Thats no moon!
    Thats a fully functional death star.

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