Portia (moon)

Background

Portia was discovered from Voyager 2 images taken on 3 January 1986 and given the temporary designation S/1986 U 1. It is named after the heroine of Shakespeare's The Merchant of Venice and is also designated Uranus XII. The moon is the second-largest inner satellite of Uranus after Puck, and its orbit lies inside Uranus's synchronous orbital radius, causing it to slowly decay due to tidal deceleration; it will one day either break up into a planetary ring or hit Uranus.

Portia is the largest member and namesake of the Portia group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda, and Perdita, all of which have similar orbits and photometric properties. Little is known about Portia beyond its dimensions of about 156 km × 126 km, orbit, and geometric albedo of about 0.069. In Voyager 2 imagery, Portia appears as an elongated object whose major axis points toward Uranus, with a prolate spheroid axis ratio of 0.8 ± 0.1.

Its surface is grey or slightly reddish in color, and fellow Portia group members Juliet, Belinda, Cressida, Desdemona, and Rosalind have particularly similar spectra to Portia.