I've just googled:

Uranus Portia "Julius Caesar"

...and sites come up indicating that the Portia orbiting Uranus is the one from "Julius Caesar" and not from "Merchant of Venus."

That's curious. I, too, would have thought the Portia from "Merchant"--but Google, at least, takes us elsewhere.

Edit: Here's the listing from one site, similar to Father Steve's above:

"SATELLITES: Cordelia (daughter of Lear in Shakespeare's “King Lear”); Ophelia (daughter of Polonius, fiance of Hamlet in Shakespeare's “Hamlet”); Bianca (daughter of Baptista, sister of Kate in Shakespeare's “Taming of the Shrew”); Cressida (title character in Shakespeare's “Troilus and Cressida”); Desdemona (wife of Othello in Shakespeare's “Othello”); Juliet (heroine of Shakespeare's “Romeo and Juliet”); Portia (wife of Brutus in Shakespeare's “Julius Caesar”); Rosalind (daughter of the banished duke in Shakespeare's “As You Like It”); Belinda (character in Pope's “Rape of the Lock”); Puck (mischievous spirit in Shakespeare's “A Midsummer Night's Dream”); Miranda (the heroine of Shakespeare's “The Tempest”); Ariel (a benevolent spirit in Shakespeare's “The Tempest”); Umbriel (a malevolent spirit in Pope's“ Rape of the Lock”); Titania (the queen of the fairies in Shakespeare's “A Midsummer Night's Dream”); Oberon (the king of the fairies in “A Midsummer Night's Dream”); Caliban (the brutish slave in Shakespeare's “The Tempest”); Sycorax (Caliban's mother in “The Tempest”); Prospero (the rightful Duke of Milan in “The Tempest”); Setebos (a false god worshiped by Caliban in “The Tempest”); Stephano (a drunken butler in “The Tempest”)."

No Google hits for:

Uranus Portia "Merchant of Venice"