To keep Saturn’s A ring contained, its moons stand united

Posted: October 17, 2017 by oldbrew in Astronomy, moon, research, solar system dynamics
Tags: ,

Saturn’s moon Janus


Cassini maintains its reputation for surprises right to the end. It’s the ‘moon resonances’ that maintain ring stability, but with a new twist.

For three decades, astronomers thought that only Saturn’s moon Janus confined the planet’s A ring – the largest and farthest of the visible rings.

But after poring over NASA’s Cassini mission data, Cornell astronomers now conclude that the teamwork of seven moons keeps this ring corralled, as Phys.org explains.

Without forces to hold the A ring in check, the ring would keep spreading out and ultimately disappear.

“Casini provided detail on the mass of Saturn’s moons and the physical characteristics of the rings, so mathematically speaking, we concluded that the moon Janus alone cannot keep the rings from spreading out,” said Radwan Tajeddine, a research associate in astronomy and lead author of the new research.

“What Confines the Rings of Saturn?” is planned for publication Oct. 18 in the Astrophysical Journal. Tajeddine also will present this research in a poster at the American Astronomical Society’s Division of Planetary Science meeting Oct. 17 in Provo, Utah.

The scientists discovered that confinement of the A ring is shared among the moons Pan, Atlas, Prometheus, Pandora, Epimetheus, Mimas and Janus. “All of these moons work as a group to contain the ring. Together they are strong. United they stand,” said Tajeddine.

Cassini, which crashed into Saturn Sept. 15 at the mission’s end, provided valuable data and detailed images of the planet’s rings. The A ring looks similar to a vinyl record; it has “density waves” that resemble a record’s grooves that are created by what astronomers call moon resonances.

These resonance markers enabled scientists to deduce that the moons’ gravitational influence help to slow and reduce the spreading ring’s momentum.

Continued here.

Comments
  1. angech says:

    What works one way works the other in balancing.
    We might as well say Saturn’s A ring helps keep the 7 moons aligned and stops them dispersing and hitting each other.
    Both comments are trivially true and meaningless.

  2. oldbrew says:

    They already had clues about some of this e.g.:

    A number of features in Saturn’s rings are related to resonances with Mimas. Mimas is responsible for clearing the material from the Cassini Division, the gap between Saturn’s two widest rings, the A Ring and B Ring. Particles in the Huygens Gap at the inner edge of the Cassini division are in a 2:1 resonance with Mimas. They orbit twice for each orbit of Mimas. The repeated pulls by Mimas on the Cassini division particles, always in the same direction in space, force them into new orbits outside the gap. The boundary between the C and B ring is in a 3:1 resonance with Mimas.
    . . .
    Mimas is also in a 2:1 mean-motion resonance with the larger moon Tethys, and in a 2:3 resonance with the outer F Ring shepherd moonlet, Pandora.

    http://en.wikipedia.org/wiki/Mimas_(moon)#Orbital_resonances

  3. JB says:

    @ angech My thoughts also.The title is misleading–as though there was some intelligence inherent in the moons. Really, I don’t think they truly know what keeps them all in the observed orbits. They just know the waves have some important relationship.

  4. oldbrew says:

    The ‘shepherd moon’ concept is well known.
    http://en.wikipedia.org/wiki/Shepherd_moon

    However – the explanations may well be a bit flaky :/
    Wiki refers to ‘interior and exterior shepherds’.
    – – –
    Some say the ‘strange “twisted” deformations’ that are observed are Birkeland currents, or are caused by them.

    Birkeland currents are also one of a class of plasma phenomena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. This can also twist, producing a helical pinch that spirals like a twisted or braided rope, and this most closely corresponds to a Birkeland current. [bold added]

    http://en.wikipedia.org/wiki/Birkeland_current#Characteristics

  5. angech says:

    I don’t think there is a typical solar system or set up of planets, moons rings, belts etc.
    It is all the process of matter derived from previous sun explosions conglomerating and the different and varied effects that evolve.
    Yes there will be a physical explanation that they are all in balance, how else could they be there for so long but as to the particular flukes of composition, size, stability, rotation makes us seem more part of a SIM costruct a universe game than anything else.

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