Manheim, best known for her role on The Practice, will play Sam Barton, the best friend and closest confidante of Berry's main character, Molly.
Extant is a mystery thriller about a female astronaut (Berry) who tries to reconnect with her family after spending a year in outer space. Steven Spielberg is an executive producer on the show, which is set to premiere this summer.
Manheim is currently guest-starring on CBS' Person of Interest.
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