Portia (moon)

Portia is the second-largest inner satellite of Uranus after Puck. The Portian orbit, which lies inside Uranus's synchronous orbital radius, is slowly decaying due to tidal deceleration. The moon will one day either break up into a planetary ring or hit Uranus.

It is the namesake of a group of satellites called the Portia group, which includes Bianca, Cressida, Desdemona, Juliet, Rosalind, Cupid, Belinda, and Perdita. These satellites have similar orbits and photometric properties.

Little is known about Portia beyond its dimensions of about 156 × 126 km, orbit, and geometric albedo of about 0.08.

In Voyager 2 imagery, Portia appears as an elongated object whose major axis points towards Uranus. The ratio of axes of the Portia's prolate spheroid is 0.8 ± 0.1. Its surface is grey in color. Observations with Hubble Space Telescope and large terrestrial telescopes found water ice absorption features in the spectrum of Portia. Observations with James Webb Space Telescope have also found evidence for water ice or hydrated minerals on Portia's surface, and have also confirmed that Portia group members Juliet, Belinda, and Cressida have roughly similar spectra to Portia.