Saturn's Rings are Younger Than Archaeopteryx

Discussion in 'Astronomy, Exobiology, & Cosmology' started by exchemist, Jan 18, 2019.

  1. exchemist Valued Senior Member

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    https://www.bbc.co.uk/news/science-environment-46911945

    Seems the mass of the rings has now been estimated, along with the rate at which they are dispersing. This puts their age at no more than 100m years. So they are very young astronomical objects indeed. But nothing much in the article about what caused them.
     
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  3. Yazata Valued Senior Member

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    I've seen speculation that a comet might have been disrupted somehow. Or a moon. By a collision presumably.

    But the rings seem very finely divided into very small particles.

    I'd always assumed that they were primordial, remains of the 4.5 billion year old accretion disks that newly formed planets presumably had circling them and out of which their families of moons condensed.

    But I guess not...

    We can be pretty sure that the astrophysicists will be aggressively producing new computer models of ring formation and dissipation in hopes of figuring it out.
     
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  5. DaveC426913 Valued Senior Member

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    They almost entirely water-ice, with only trace rocky material.

    Points toward comet.
     
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  7. nebel

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    nebel is in there too, remotely, with his off the beat idea, that, in
    Saturn's equatorial region, in line with rings, particle velocities with respect to the sun cancel at noon and double at night.
     
  8. James R Just this guy, you know? Staff Member

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    Interesting.

    More likely by tidal forces. I believe that Saturn's rings lie within the Roche limit.
     
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  9. nebel

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    To be precise to an asteroid /TNO that has a perihelion of ~ 10 AU like Saturn, then the encounter would have more matched orbital speeds and make capture of the debris, tail easy. make the harvesting of the ice and pebbles last longer. Or perhaps aphelion? a real short period comet. now called rings?
    Kuiper belt objects become comets only when solar influences blast away at their core. possibly Saturn got first call.
     
    Last edited: Jan 19, 2019
  10. exchemist Valued Senior Member

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    Yes it seems they do indeed. So we have the question of what it was that has been disrupted by these tidal forces and how this object arrived in this orbit, comparatively recently. I suppose if the rings are mostly ice that would suggest a comet.
     
  11. sweetpea Valued Senior Member

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    What if the comet was one of these ''peanut'' or'' snowman'' shaped things? How would Saturn's tidal-forces play with that shape?

    I wonder if comet Shoemaker–Levy had not broken up in 1992 before colliding with Jupiter in 1994 there may have been more material to form rings?
    Probably not if all the broken material of the comet did fall to Jupiter.
    https://en.wikipedia.org/wiki/Comet_Shoemaker–Levy_9
     
    Last edited: Jan 20, 2019
  12. nebel

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    there is a thread in alternative theories forum: "Jupiter. Saturn as harvesting machines":
    Jupiter started to prepare the ring work by breaking up shoemaker into bits already before impact. These bodies are collections of water and rubble, mostly, and will shatter easily, For a neat capture you have to have nearly matched velocities or a near miss, not like the serial impact on Jupiter. Even of you deliberately tried, that kind of a structure is not easy to build and maintain. conditions have to be just right.
     
    Last edited: Jan 20, 2019
  13. Janus58 Valued Senior Member

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    Where exactly the Roche limit for a particular object is depends on the relative density between it and the primary body. An object as dense as our Moon would make it as far in as the midpoint of the C ring before breaking up, while Adrastea could get to the inner part of the C ring. The Earth could reach the D ring.
    If we put the midpoint of the major rings at ~105,000 km, then this is the Roche limit for an object with a density approximately equal to that of Phobos. An object that is mainly ice would have a lower density and would break up further out, and an rocky object would tend towards a higher density and would break up further in.
     
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  14. exchemist Valued Senior Member

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    I didn't know that, thanks. Then, given the rings extend out a long way, I presume that argues in favour of a low density object having been responsible. Is that right?
     
  15. nebel

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    Breaking up is one thing, organizing the debris into very thin rings is another. Question : Would the Roche limit also apply in reverse, so that within that radius it would be impossible to assemble an aggregate moon, comet, asteroid body? , metallic ones bring another story altogether.
     
  16. DaveC426913 Valued Senior Member

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    No. That comes naturally by way of orbital mechanics.

    That's not really "in reverse", that's the same thing.

    Any natural body (i.e. held together by its own gravity) will not remain cohesive within another body's Roche limit.

    How it gets there (whether moved there or assembled there) is immaterial.
     
  17. nebel

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    thank you, I did not mean it is magic, just that the same total set of laws that prevent a ball from forming, also would generate, permit such exquisitely proportioned structures to exist for millions of years. and thought that the nearly matching Vo and Vr nearby would be one small contributing factor; for example; rings around Earth? Vo/Vr ratio not ~1:1 like on Saturn, but 1:64.
     
    Last edited: Jan 21, 2019
  18. Seattle Valued Senior Member

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    I believe all the "gas giants" have rings, right? They are just not as pronounced as those around Saturn.
     
  19. exchemist Valued Senior Member

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    I certainly recall a newspaper headline, when I was at school which proclaimed "Rings Around Uranus". We all thought this a great joke.

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  20. nebel

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    10199 Chariklo
    Astronomical discovery

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    Description
    10199 Chariklo is the largest confirmed centaur. It orbits the Sun between Saturn and Uranus, grazing the orbit of Uranus. On 26 March 2014, astronomers announced the discovery of two rings around Chariklo by observing a stellar occultation, making it the first minor planet known to have rings. Wikipedia
    A ring has been found around Haumea, a world more than 2 billion kilometres beyond Pluto. The ring is the most distant ever seen in our solar system. ew scientist 10 11 2017.
     
    Last edited: Jan 24, 2019
  21. Q-reeus Valued Senior Member

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    The 'usual' Roche limit applies to an orbiting self-gravitating fluid body. It does not hold for e.g. a rocky planet held together by a mix of self-gravitation and cohesion. In the latter case, the innermost stable orbital radius will always be less than for a corresponding fluid body of equal size and assumed equal and uniform density. Whats's more, 'usual' Roche limit unrealistically assumes constant density of the orbiting body, whereas for a real body of finite compressibility, density rises towards the core. Just how that effects the net outcome is going to be somewhat complicated and would require a detailed EOS (and maybe more) for the body in question. This article sets out the different Roche limits that are usually considered:
    https://www.cs.mcgill.ca/~rwest/wikispeedia/wpcd/wp/r/Roche_limit.htm
     
    Last edited: Jan 24, 2019
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  22. Michael 345 New year. PRESENT is 69 years old Valued Senior Member

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    I'll see your headline and raise you a QI video



    One for the ignored one Jan

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  23. exchemist Valued Senior Member

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    Nice link.
     

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