Enceladus jets: Surprises in starlight

Posted: May 9, 2016 by oldbrew in solar system dynamics
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Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI

Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI

The text below is the caption to the graphics shown here, taken from a new Phys.org report. It gives some interesting insights into the physics of moons and sets some new puzzles for theorists.

This set of images from NASA’s Cassini mission shows how the gravitational pull of Saturn affects the amount of spray coming from jets at the active moon Enceladus. Enceladus has the most spray when it is farthest away from Saturn in its orbit (inset image on the left) and the least spray when it is closest to Saturn (inset image on the right).

Water ice and organic particles gush out of fissures known as “tiger stripes” at Enceladus’ south pole. Scientists think the fissures are squeezed shut when the moon is feeling the greatest force of Saturn’s gravity. They theorize the reduction of that gravity allows the fissures to open and release the spray. Enceladus’ orbit is slightly closer to Saturn on one side than the other.

A simplified version of that orbit is shown as a white oval. Scientists correlate the brightness of the Enceladus plume to the amount of solid material being ejected because the fine grains of water ice in the plume are very bright when lit from behind. Between the dimmest and brightest images, they detected a change of about three to four times in brightness, approximately the same as moving from a dim hallway to a brightly lit office.

This analysis is the first clear finding that shows the jets at Enceladus vary in a predictable manner. The background image is a mosaic made from data obtained by Cassini’s imaging science subsystem in 2006. The inset image on the left was obtained on Oct. 1, 2011. The inset image on the right was obtained on Jan. 30, 2011. Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI

Phys.org report: Enceladus jets: Surprises in starlight

Just to repeat: the above is only the caption to the graphics, none of the actual linked report has been quoted.

  1. oldbrew says:

    Listed here are details of Saturn’s seven major moons (Titan is 96% of the mass of all Saturn’s moons).

    Looking at the orbital distance (from Saturn) of the first four on the list:
    Mimas:Enceladus ratio = 1:1.2825~
    Tethys:Dione ratio = 1:1.281~

    The ratios are almost the same, and are close to the square root of Phi ( = 1.27202).

    Enceladus:Tethys ratio = 1:1.238165 = about twice the inverse of Phi (= 1.236068)

    Dione:Titan = 1:3.2376~ = about twice Phi (= 3.236068)

    NB all the above ratios are between ‘neighbours’ except Dione:Titan which have Rhea between them.

    The NASA fact sheet includes Hyperion as a major satellite of Saturn.
    Titan:Hyperion orbit ratio = 4:3

    Mimas:Tethys and Enceladus:Dione orbit ratios are both around 2:1

    ‘Dione is currently in a 1:2 mean-motion orbital resonance with moon Enceladus, completing one orbit of Saturn for every two orbits completed by Enceladus. This resonance maintains Enceladus’s orbital eccentricity (0.0047), providing a source of heat for Enceladus’s extensive geological activity, which shows up most dramatically in its cryovolcanic geyser-like jets.’ [bold added]

  2. Paul Vaughan says:

    This simple example won’t help those with closed minds (nothing will), but it might help the sensible few who are able to keep their minds open in the face of oppressive campaigns designed to close.

    We have a 96 year volatility cycle on Earth.

  3. oldbrew says:

    Wikipedia: Tidal heating (also known as tidal working) occurs through the tidal friction processes: orbital and rotational energy are dissipated as heat in either the surface ocean or interior of a planet or satellite. Io, a moon of Jupiter, is the most volcanically active body in the solar system, with no impact craters surviving on its surface. This is because the tidal force of Jupiter deforms Io; the eccentricity of Io’s orbit (a consequence of its participation in a Laplace resonance) causes the height of Io’s tidal bulge to vary significantly (by up to 100 m) over the course of an orbit; the friction from this tidal flexing then heats up its interior. A similar but weaker process is theorised to have melted the lower layers of the ice surrounding the rocky mantle of Jupiter’s next large moon, Europa. Saturn’s moon Enceladus is similarly thought to have a liquid water ocean beneath its icy crust. The water vapor geysers which eject material from Enceladus are thought to be powered by friction generated within this moon’s shifting ice crust. [bold added]