Can a Natural Satellite Have Its Own Natural S…

Can a Natural Satellite Have Its Own Natural Satellite?

In all known planetary systems, natural satellites occur in a restricted dynamical phase space: planets orbit stars and moons orbit planets. It is natural to ask, can submoons  orbit moons? If so, why don’t any of the known moons of the Solar System have their own submoons? One possibility is that the formation mechanism of planetmoon systems precludes their formation. Another possibility, is that these bodies are dynamically unstable and are rapidly scoured from their system after formation. Here, we investigate the latter hypothesis. 

What are the requirements for stability of a submoon?  To ensure dynamical stability, the host moon must have a  Hill sphere that is larger than its physical radius as well  as its Roche limit. The submoon must also survive any  long-term dynamical effects such as tidal evolution.

Only large moons on wide-separation  orbits can host long-lived submoons. This is mainly because  massive, distant moons have larger Hill radii that  provide more stable real estate for submoons

The researchers calculated that in the Solar System, 4 natural satellites could have their own natural satellite.

Our Moon, Callisto of Jupiter, and Titan and Iapetus of Saturn.

These satellites are relatively large, are relatively distant from their planets, ie there is a small area around them that could have a natural satellite and that satellite would not be stolen by the planet.

Recalling that this is a theoretical exercise, to date no natural satellite around another natural satellite has been detected. source, article.