Kenneth Branagh's "Thor" just got a little more star power.

Marvel Studios announced today that Natalie Portman has been cast as Jane Foster in the company's big screen adaptation of "Thor."  Portman joins newcomer Chris Hemsworth, who has been cast as the title hero, and Tom Hiddleston, who will play the devious Loki.  Branagh will direct.

It's unclear exactly how Foster will relate to the Norse god in the movie, but her comic book origins she was a human nurse who became Thor's true love.

Marvel's official synopsis for "Thor" is as follows:

"Marvel Studios expands its film universe with a new type of super hero: "Thor." This epic adventure spans the Marvel Universe; from present day Earth to the realm of Asgard. At the center of the story is The Mighty Thor, a powerful but arrogant warrior whose reckless actions reignite an ancient war. Thor is cast down to Earth and forced to live among humans as punishment. Once here, Thor learns what it takes to be a true hero when the most dangerous villain of his world sends the darkest forces of Asgard to invade Earth."

Portman, who received an Academy Award nomination for her role in "Closer," recently wrapped production on "Hesher" alongside Joseph Gordon-Levitt and Don Roos' "Love and Other Impossible Pursuits."  She'll begin filming David Gordon Green's "Your Highness" with James Franco and Danny McBride this summer.  Portman will return to the big screen this fall in Jim Sheridan's "Brothers" opposite Tobey Maguire and Jake Gyllenhaal.

Production on "Thor" is set to begin in early 2010.  The film already has a release date of May 20, 2011.