What is the longest natural bound orbit chain observed? Define a bound orbit chain as a list of successively less massive bodies, each in a bound orbit with the bodies preceding it in the list.
Then an example of a bound orbit chain would be: &lt;Sun, Earth, Moon&gt;, since the Earth orbits the Sun, and the Moon orbits the Earth and the Sun (and they are listed from most to least massive).  This is a chain of length 3.
Question: What is the longest natural bound orbit chain we've ever observed?
Related: Do moons have moons?
Certainly 4 (perhaps 5):
The longest certainly-known chain is &quot;3&quot;:  Sun-Earth-Moon.
Rhea (a moon of Saturn) has been observed to have a ring of orbiting material: That gives Sun-Saturn-Rhea-Ring for four levels (including unresolved dust)
Looking further afield:
DH Tauri and DI Tauri are a binary pair of similarly sized T-Tauri stars (both small red dwarfs); they are in a mutual orbit.
DH Tauri has a large sub-stellar companion.
The companion has an accretion disc of orbiting matter.
So we have DI-Tauri &gt; DH-Tauri &gt; DH-Tauri-b &gt; matter in disc, for four levels of orbit.
Even this isn't very good, because DH Tauri is bigger than DI Tauri, so it is a bit of a stretch to say that DH Tauri orbits DI.  If anything it is the other way round.  There are very few planets found in orbit around the secondary star in a system and none of those have likely moons. Moreover the disc of matter around the sub-stellar object is not known to have actual &quot;moons&quot; embedded in it.
So &quot;4&quot; seems to be the best we can do...
But if we can add in Galaxy - Star - planet -moon - dust/ring? we get 5 levels.