We know know what the famous announcement by the European Southern Observatory is. They found an asteroid with ring! Two of them!

…the remote asteroid Chariklo is surrounded by two dense and narrow rings.

Telescopes at seven locations in South America, including the 1.54-metre Danish and TRAPPIST telescopes at ESO’s La Silla Observatory in Chile were used to make this surprise discovery in the outer Solar System.

This unique finding has sparked much interest and debate since it is the smallest object by far to have rings and only the fifth body in the Solar System — after the much larger planets Jupiter, Saturn, Uranus and Neptune — to have this feature.

Astronomers think that this sort of ring is likely to be formed from debris left over after a collision.

Details here.

Comments

  1. #1 G
    March 27, 2014

    Layperson speculation on a mechanism:

    Object A gets hit by Object B. Large quantity of debris is ejected and goes into orbit around Object A. The debris cloud elongates as it orbits.

    The higher-mass debris ends up falling back to Object A (and depending on Object A being a rocky object, we might observe a band of returned debris around the circumference of Object A). The lower-mass debris ends up escaping Object A’s gravity and dispersing into space.

    The debris that is of intermediate mass continues to orbit Object A. The interaction of angular momentum and gravity confines the debris to a narrow range of distance from the surface of Object A. And the tendency of everything toward dissipation, causes the debris cloud to diffuse as far as possible while staying within that range of distance.

    The result of that interaction and dissipation, is the ring: an evenly-dispersed debris cloud at a particular orbit around Object A.

    OK, feel free to tell me where I screwed up with that.

  2. #2 Greg Laden
    March 27, 2014

    G: I don’t know. What I’ve heard is that the whole thing is a bit controversial, meaning that astronomers may disagree internally about how rings are formed. Perhaps these rings are impossible for some reason, i.e. because of the small size of the asteroid, by one or more major theories of how they form.

    So get the popcorn out!

  3. #3 Eric Lund
    March 27, 2014

    G: Your model would give a single broad ring, rather than two narrow rings as reported. That doesn’t mean the rings aren’t the result of a collision, but rather that there must be something else going on as well. A shepherd moon, for instance (this is how some of the narrower rings at Saturn and Uranus are maintained).

    The dynamical stability of this ring system is also an interesting question. How long does it take for rings like this to form, and how long do they last until something disrupts them? I don’t know the answers to those questions (it’s not my field), but they are important constraints on any theory of how these rings formed.