Saturn’s magnificent rings


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Saturn's rings

The Cassini science team released two sets of images taken by the spacecraft of Saturn’s rings.

The image above, reduced in resolution to show here, is from the second link. As they note,

The pale tan color is generally not perceptible with the naked eye in telescope views, especially given that Saturn has a similar hue.

The material responsible for bestowing this color on the rings—which are mostly water ice and would otherwise appear white—is a matter of intense debate among ring scientists that will hopefully be settled by new in-situ observations before the end of Cassini’s mission.

The different ringlets seen here are part of what is called the “irregular structure” of the B ring. Cassini radio occultations of the rings have shown that these features have extremely sharp boundaries on even smaller scales (radially, or along the direction outward from Saturn) than the camera can resolve here. Closer to Saturn, the irregular structures become fuzzier and more rounded, less opaque, and their color contrast diminishes.

Check out both. They reveal to me that our understanding of these rings remains essentially nil, even after more than a dozen years of study by Cassini.

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5 comments

  • Edward

    From the first article:
    This view from NASA’s Cassini spacecraft shows a wave structure in Saturn’s rings known as the Janus 2:1 spiral density wave. Resulting from the same process that creates spiral galaxies, spiral density waves in Saturn’s rings are much more tightly wound. In this case, every second wave crest is actually the same spiral arm which has encircled the entire planet multiple times.

    This wave is remarkable because Janus, the moon that generates it, is in a strange orbital configuration. Janus and Epimetheus share practically the same orbit and trade places every four years. Every time one of those orbit swaps takes place, the ring at this location responds, spawning a new crest in the wave. The distance between any pair of crests corresponds to four years’ worth of the wave propagating downstream from the resonance, which means the wave seen here encodes many decades’ worth of the orbital history of Janus and Epimetheus.

    Although Janus and Epimetheus are far from the B ring where the wave resonance is seen (in the first linked article), it seems that the fact of their trading places has a gravitational effect that is unique in our solar system. I looked into this a little bit, because I could not figure out why tiny Janus had an effect greater than giant Titan does. I still do not quite understand, but it seems to be due to the dual effect of Janus’s orbital period relative to the B ring’s orbital period (Janus takes twice as long to orbit) and the effect of Janus and Epimetheus “trading places” every four years.
    https://en.wikipedia.org/wiki/Janus_(moon)#Orbit

    Janus, at 150,000 km, is farther out than the A ring and the outer, F, ring.
    https://en.wikipedia.org/wiki/Rings_of_Saturn#Subdivisions_and_structures_within_the_rings

    Over the years, we have seen many, many strange features in Saturn’s rings and moons.
    http://behindtheblack.com/behind-the-black/points-of-information/looking-down-at-saturns-rings/
    http://behindtheblack.com/behind-the-black/points-of-information/propellers-by-the-dozens/
    http://behindtheblack.com/behind-the-black/points-of-information/cassini-finds-gap-in-saturns-rings-surprisingly-empty/
    http://behindtheblack.com/behind-the-black/points-of-information/the-rings-of-saturn-2/
    The fundamental science question therefore is not how Saturn’s rings behave (though this is certainly important and quite fascinating) but why did those rings end up the way they are.

    What an education this ring phenomenon is giving us.

  • mpthompson

    Would it be possible to put a craft in orbit around Saturn that would slowly lower its orbit until it actually could “swim” among the ring particles? It would probably have to be tough as hell, but moving with the ring particles it may not get too beat up. The pictures from within the ring plane and the particles that comprise it would be fascinating. It would answer a lot of questions as well.

  • Edward

    mpthompson,
    You asked: “Would it be possible to put a craft in orbit around Saturn that would slowly lower its orbit until it actually could “swim” among the ring particles?

    It sounds like you want to rendezvous with individual ring particles at various places in the rings. Yes, this would be possible, but it would limit the scientific studies of Saturn’s moons and of Saturn’s atmosphere. Because planetary scientists only get a limited number of probes to any given planet, almost always only one (Mars being the exception), they get requests to study multiple aspects with that probe, so they send a multipurpose probe rather than one to Titan, another to the rings, another to a low Saturn orbit, another to a high polar orbit, and others to various other moons and points of interest.

    Cassini carried a daughter probe, Huygens, that descended by parachute to the surface of Saturn’s moon, Titan. Thus, it is possible to take multiple probes in order to carry out specific detailed missions, including a detailed study of the rings. The limitations are mostly due to money and weight (including the weight of the propellant needed to rendezvous with the rings). Another limitation, which may be more easily overcome, is the limits of the Deep Space Network.

    With luck and more advanced technologies, our next Saturn probe may be able to carry even more daughter probes in order to more closely study more points of interest, including the many surprising phenomena that we have seen in the rings.

  • mpthompson

    Edward, thanks for the response. I don’t know how much public relations thinking goes into mission planning, but if NASA is looking to inspire future generations of engineers and scientist who will push us further into the solar system, I personally would have a hard time thinking of something as spectacular as a probe that would explore the rings of Saturn. The views near or at the ring plane would be astonishing and unique. It would be something that even laymen, such those who ultimately foot the bill for these missions, could appreciate.

  • Edward

    mpthompson,
    I am rooting for rapid development of smallsats and cubesats, because these may be able to help widen our exploration of each place that we visit.

    Just as Cassini carried a daughter probe to Titan, the Galileo probe to Jupiter carried a probe that plunged into the Jovian atmosphere, in 1995. Rosetta carried a probe to land on comet 67P, although it failed to land properly; Rosetta was an example of good PR.

    Even though we concentrate on Mars, we continue to explore the other planets with occasional probes, and one of these decades we will return to Saturn. Hopefully, the next time that we go, we will have several small daughter probes to do a more complete exploration.

    In the meantime, the planetary scientists have found ways of maximizing the information gleaned from the limited instruments and processes that they have. For instance, it was by analyzing radio waves and light waves that passed through Saturn’s rings that they were able to determine particle sizes, no additional instrumentation necessary — a weight-free experiment.

    It is mostly scientists who work out the mission planning and who choose the missions. There is a decadal survey by scientists that occasionally prioritizes missions and goals. Getting the public excited about each mission seems to be a lower priority and is a task given to NASA’s PR department after a mission is funded.

    I agree that PR needs to be better thought out. For a while, we were going to go back to the Moon (for some, it would be for the first time), but the public did not get excited enough — inadequate PR — to prevent Obama from cancelling that idea and leaving NASA with a lack of direction and an abundance of strategic confusion that persists to this day. Even NASA’s unmanned space exploration program has been left in bad shape, which could result in it taking longer to decide on a time to go back to Saturn.

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