Overview

Margaret is an outer, irregular satellite of Uranus notable for being the only known prograde non-spherical moon among that planet's irregular satellites. It was first reported in 2003 and later received a permanent number and the name Margaret, following the convention of naming Uranian moons after characters from the works of William Shakespeare and Alexander Pope.

Discovery and name

The object was discovered in 2003 by a team including Scott S. Sheppard and colleagues using ground-based telescopes. Initially designated S/2003 U 3, it was subsequently confirmed and numbered Uranus XXIII before being given the name Margaret. The name honors the servant Margaret from William Shakespeare's play Much Ado About Nothing, in keeping with the tradition for Uranian satellites.

Orbit and physical characteristics

Margaret orbits far beyond the regular moons of Uranus on a distant, inclined and notably eccentric path. Unlike the majority of Uranus's irregular moons, which move on retrograde orbits, Margaret travels in a prograde direction relative to the planet's rotation. It is small and irregularly shaped rather than spherical, implying that it lacks the mass needed to pull itself into hydrostatic equilibrium; observations suggest a modest diameter on the order of tens of kilometres.

Origin and dynamical behavior

As an irregular satellite, Margaret is generally interpreted as a captured object rather than having formed in situ with Uranus's large regular moons. Its prograde motion and unusual orbital parameters make it dynamically distinct among Uranian satellites and mean it may be subject to complex gravitational interactions and secular perturbations. These dynamical features are of interest to researchers studying capture processes and long-term orbital stability.

Significance and observations

Margaret provides a valuable counterexample within the population of Uranian irregular satellites, helping astronomers test models of satellite capture and evolution. Because it is small and distant, detailed physical characterization requires large telescopes and careful observation campaigns; photometric and astrometric data remain the primary sources of information about its size, shape, and orbit.

Key facts