@RockDoctor thanks for all the info
More incoming. It's a firehose.
A paper published yesterday described a ring around the Trans-Neptunian Object Haumea. The abstract is available on Nature's website, and the full paper and data at http://sci-hub.cc/http://www.nature.com ... 24051.html
. You'll probably just want the abstract information :
Secondary events observed around the main body of Haumea are consistent with the presence of a ring with an opacity of 0.5, width of 70 kilometres and radius of about 2,287 kilometres. The ring is coplanar with both Haumea’s equator and the orbit of its satellite Hi’iaka. The radius of the ring places it close to the 3:1 mean-motion resonance with Haumea’s spin period ... Haumea’s largest axis (diameter!) is at least 2,322 kilometres
Neglecting the odd shape of Haumea (it's seriously not a sphere, and it's not even an ellipsoid of rotation), that gives you some grounds for your ring opacity figure, and some hints for ring radius - small integer ratios of the 2/3rd power of the radius of the primary (assuming Keplerian dynamics). The presence of close-in satellites does not preclude there being a ring (again, Haumea is really weird - it's satellites are not all in one plane).
I've noticed over the last couple of days flying around that the number of "thin, far out" rings seems to have increased (it may be coincidence though), which from this example and the Uranian example, sounds generally justified.