Postcard from Cassini

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Tiassa, Nov 28, 2012.

  1. Tiassa Let us not launch the boat ... Staff Member

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    More on Enceladus, E Ring

    More on Enceladus, E Ring

    Honestly, this is starting to get unhealthy.

    Okay, no, it's not. But I'm developing a sort of fanboy love affair with Enceladus.

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    (NASA/JPL-Caltech/Space Science Institute)

    The image was taken on September 24, 2012, from 452,000 miles away at a phase angle of 170°. According to NASA, the image has been magnified in order to enhance the cryovolcanic jets.

    As the long winter night deepens at Enceladus' south pole, its jets are also progressively falling into darkness. The shadow of the moon itself is slowly creeping up the jets making the portions closest to the surface difficult to observe by the Cassini spacecraft.

    Cassini looks toward the night side of Enceladus (313 miles, or 504 kilometers across) in this image. Enceladus is lit by light reflected off Saturn rather than by direct sunlight.

    This view looks toward the Saturn-facing hemisphere of Enceladus. North on Enceladus is up. The image was taken with the Cassini spacecraft narrow-angle camera on Sept. 24, 2012 using a spectral filter sensitive to wavelengths of near-infrared light centered at 930 nanometers.

    In addition to being spectacular, it is worth mentioning again that these are the ice geysers that are forming Saturn's E Ring.

    Enceladus is fascinating. For now, I just can't help myself.
    ____________________

    Notes:

    Jet Propulsion Laboratory. "Catalog Page for PIA15642". January 7, 2013. Photojournal.JPL.NASA.gov. February 2, 2013. http://photojournal.jpl.nasa.gov/catalog/PIA14642
     
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  3. RoccoR Registered Senior Member

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    Tiassa,

    I wonder if the exhaust (that big) changes the orbit of spin.

    v/r
    R
     
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  5. Tiassa Let us not launch the boat ... Staff Member

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    Best Guess: No

    I'm going to guess that it does not. The cryovolcanic venting is a result of tidal flexing. Spencer et al. note:

    Observations of Enceladus offer a chance to understand the origin of cryovolcanism, and the observed heat flux from the SPT provides a unique opportunity to constrain geodynamical models. The main source of Enceladus' energy is undoubtedly tidal dissipation, maintained over long time scales by Enceladus' 2:1 mean motion resonance with neighbor satellite Dione (e.g., Murray and Dermott 1999). Thus, Enceladus provides a unique natural laboratory for the study of how the interaction between tidal flexing, interior thermal and compositional heterogeneity, and heat transport gives rise to cryovolcanism and resurfacing on icy bodies. In this section we will focus on the interior of Enceladus, addressing its state of differentiation, heat sources, heat transport mechanisms, and the time evolution of its interior structure. The question of whether or not Enceladus has a subsurface ocean is of particular interest, not only because the presence or absence of an ocean strongly affects the generation of tidal heat, but also because its ocean is potentially habitable.

    (8-9)

    To the other, it's a long paper (71 pp. excluding endnotes), and I literally just found it, so I've got some reading to do.

    But my understanding, admittedly inadequate, of how such physical dynamics work would suggest that the forces of orbital relationship cannot create enough force via cryovolcanic venting of crystallized water vapor (i.e., ice geysers) to overcome the orbital forces themselves. Of course, I might be appyling my sketchy awareness of conservation of energy improperly.

    I could easily be wrong, but the theoretical age of Enceladus is four and a half billion years (cf. Taubner et al.); some estimates suggest a surface age of certain features on Enceladus at 100m years. Accepting such an estimate, we can presume that younger surface regions have been affected to some degree by cryovolcanism. Within that constraint, I would suggest that if cryovolcanism was sufficient to foul Enceladus' orbit, it would have done so by now.

    But I'm not a physicist or astrogeologist. My "commonsense" logical presuppositions may well may not be properly commonsense; indeed, they might be unfounded. For now, though, until someone points me to reliable science indicating otherwise, my best guess is that no, cryovolcanic venting is insufficient to alter Enceladus' orbital relationships with Saturn and Dione.

    Additionally, although new data from Cassini Solstice might further alter the scientific community discussion about Enceladus, Sky & Telescope posted on its blog a few years ago a fascinating article under the title, "What's Going on Inside Enceladus?", which also gives a sense of how quickly the discussion is evolving.
    ____________________

    Notes:

    Spencer, John R. et al. "Enceladus: An Active Cryovolcanic Satellite". Revised Version. May 6, 2009. ES.UCSC.edu. February 4, 2013. http://es.ucsc.edu/~fnimmo/website/enceladus_revised_sm.pdf

    Taubner, R.-S. et al. "The Contribution of Radiogens to the Thermal Budget of Enceladus". 43rd Lunar and Planetary Science Conference. 2012. USRA.edu. February 4, 2013. http://es.ucsc.edu/~fnimmo/website/enceladus_revised_sm.pdf

    Beatty, Kelly. "What's Going on Inside Enceladus?" Sky & Telescope. April 21, 2009. SkyandTelescope.com. February 4, 2013. http://www.skyandtelescope.com/community/skyblog/newsblog/43336757.html
     
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  7. Janus58 Valued Senior Member

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    Well, it's not the force that is the issue, any amount of net force would cause some orbital alteration. The key is whether or not there is any net force, and that is determined by the speed of the material in the jets. If it is above escape velocity for Enceladus, then a net action-reaction force will be created. Escape velocity for Enceladus is 239 m/s, so if the jet velocities are greater than this, then yes, you will get some "rocket motor" action and some resultant change of orbit, albeit very, very small.
     
  8. Tiassa Let us not launch the boat ... Staff Member

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    Thank ye

    Thank you kindly. Given that the venting appears to be creating the E Ring, we can accept that some of the output does exceed escape velocity.

    Given that this net force takes place not only within a Saturn-Enceladus orbital relationship, but also includes interaction between Enceladus and Dione, does the additional force of the latter dampen the "rocket motor" effect? Additionally, I recognize that we do not know the volume of material ejected by Enceladan cryovolcanism, which would seem to me an important variable in understanding the orbital effects of the ice geysers.

    Thanks.
     
  9. Janus58 Valued Senior Member

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    2,312
    There's definitely going to be some reduction in the orbital change of Enceladus, but it comes at the expense of some small orbital change for Dione. The gravitational bond between them is mutual. If Dione tugs on Enceladus in order to pull it back to its normal orbit, it can only be partially effective in doing so, and in the process pulls itself into a slightly different orbit.
     
  10. Tiassa Let us not launch the boat ... Staff Member

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    A humble explanation of my incompetence

    Again, Janus, my thanks.

    I suppose the difference 'twixt your simple answer and my grasping after complicated straw matrices has something to do with my interpretation of Roccor's question. Your explanation does, in fact, reconcile with my poor understanding of astrophysics. I was guessing "no" in the context of orbital decay or other denigration. More appropriately, though, given enough time within such astronomical relationships, "something is bound to happen", as such.

    I would inquire about the scale of orbital alteration compared to the time required to observe and document the changes, but I'm aware there are too many variables to do anything beyond speculate until we have certain hard data to assign to a good number of those variables.

    In the end, it is better to offer our neighbor what answers we can assert affirmatively (i.e., your answers) than simply speculate (i.e., my answers).
     
  11. Tiassa Let us not launch the boat ... Staff Member

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    Titan: Up Close and Personal

    Titan: Up Close and Personal

    Over at the Jet Propulsion Laboratory, the Cassini team is preparing for a close encounter with Saturn's largest moon, Titan:

    On Feb. 17, 2013 (Feb. 16, 5:57 p.m. PST), the Cassini spacecraft performs a gravity-measuring flyby of Titan, one of only four in the entire Solstice mission.

    During the Solstice mission, a main science objective is to measure Titan's gravitational field in order to confirm or deny the presence of an underground ocean. Additional radio science (RSS) gravity observations are needed both to answer this question and to help determine if Titan's crust is thick and rigid, or thin.

    The probe will pass at a range of 1,229 miles (1,978 km), traveling some 13,000 miles per hour (5.8 km/s). As holiday snaps go, these ought to be interesting.

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    Because astronomy geeks are still geeks: The IAU names Titan's mountains after Tolkein's Middle Earth.
    (NASA/JPL-Caltech/University of Arizona/USGS)
    ____________________

    Notes:

    Jet Propulsion Laboratory. "Titan Flyby (T-89): Cassini's Continuing Search for Subsurface Oceans". Cassini Solstice Mission. February 14, 2013. Saturn.JPL.NASA.gov. February 14, 2013. http://saturn.jpl.nasa.gov/mission/flybys/titan20130217/

    Jet Propulsion Laboratory. "PIA16598: Mountains of Titan". Photojournal. December 14, 2012. PhotoJournal.JPL.NASA.gov. February 14, 2013. http://photojournal.jpl.nasa.gov/catalog/PIA16598
     
  12. Bells Staff Member

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    24,146
    Yay it's finally here!

    On the 19th of July, we all smiled and waved at Planet Saturn, while Cassini was taking our photo.

    We have all seen the blue dot photos of our planet through Saturn's rings on previous passes. Well NASA has released the latest family portrait, and what a portrait it is!

    Posting a photo of them here would be, well.. meh. Clicking on the images in the link and then zooming in to the points of interest.. Only one word can describe it. Mesmerizing!

    To say that I feel insignificant would be an understatement.
     
  13. Tiassa Let us not launch the boat ... Staff Member

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    Party On, Cassini: Shepherd Moons, an F Ring, and a Couple Good Friends

    Holiday Snaps

    That's no moon ... that's four freakin' moons.

    It occurs to me just how rare that kind of snapshot really is:

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    Clockwise from top left: Epimetheus, Prometheus, Pandora, and Janus.

    No, really. Way, way, way too cool.

    (And remember, this is the public agency budget Congress likes to cut because they think it makes them look smart to do so.)
    ____________________

    Notes:

    NASA, JPL-Caltech, and Space Science Institute. "Four Moons". Cassini Solstice Mission. March 24, 2014. Saturn.JPL.NASA.gov. March 26, 2014. http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4998
     
  14. Arne Saknussemm trying to figure it all out Valued Senior Member

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    1,353
    What's going n here? Is thee a caption available for this photo please?
     
  15. Trippy ALEA IACTA EST Staff Member

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    It's titan, epimetheus and the rings back lit - that much I can tell (believe it or not, yes, just by looking at it).

    I'll see if I can track down the original.
     
  16. Trippy ALEA IACTA EST Staff Member

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    My bad, it's Titan and Janus, not epimetheus.
     
  17. Trippy ALEA IACTA EST Staff Member

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    Epimetheus and Janus are, however, co-orbital, and here's a picture of them side by side:

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    Not an unreasonable error.
     
  18. Trippy ALEA IACTA EST Staff Member

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