• Can small sub-moons orbit large moons that orbit planets?
  • This seemingly innocuous question has been considered by astronomers Juna Kollmeier and Sean Raymond, to get nontrivial answers.
  • Their research published in Monthly Notices of the Royal Astronomical Society reveals details about the physical parameters of moons that can support smaller sub-moons that stably orbit them.
  • Their study shows that only those large moons having a wide orbit around a planet can host sub-moons.
  • If the moon was smaller or had an orbit that was close to the planet, tidal forces that act on the sub—moon from both the moon and the planet would destabilise its orbit.
  • They also found four moons within our solar system that were in principle capable of hosting sub-moons.
  • These are Callisto, Jupiter’s moon; Titan and Lapetus, Saturn’s moons and even Earth’s Moon.