Margaret (pron.: /ˈmɑrɡrɨt/ MAR-grət) is the only prograde irregular satellite of Uranus. It was discovered by Scott S. Sheppard, et al. in 2003 and given the provisional designation S/2003 U 3.
Confirmed as Uranus XXIII, it was named after the servant of Hero in William Shakespeare's play Much Ado About Nothing.
Irregular satellites of Uranus
Margaret stands out as the only prograde irregular satellite of Uranus. The diagram illustrates the orbital parameters of Margaret, unique among the irregular satellites of Uranus, with inclination on the vertical axis and the eccentricity of the orbits represented by the segments extending from the pericentre to the apocentre.
Margaret's inclination of 57° is close to the limit of stability. The intermediate inclinations 60 < i < 140 are devoid of known moons due to the Kozai instability. In this instability region, solar perturbations at apoapse cause the moons in this region to acquire large eccentricities that lead to collisions or ejection over 10 million to a billion years. Margaret's periapsis precession period (Pw) is almost 1.6 million years long.
In 2008, Margaret's current eccentricity was 0.7979. This temporarily gives Margaret the most eccentric orbit of any moon in the solar system, though Nereid's mean eccentricity is greater.
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