Where is Earth's submoon?

Juna Kollmeier and Sean Raymond kicked off an internet firestorm late last year when they posted a draft of their article about submoons on a preprint server. The online conversation obsessed over the best term to describe such phenomena. But nomenclature was not the point of Kollmeier and Raymond's investigation, who set out to define the physical parameters for moons that would be capable of being stably orbited by other, smaller moons.

from Top Technology News -- ScienceDaily https://www.sciencedaily.com/releases/2019/01/190123153517.htm