Syfy’s space drama “The Expanse” has added cast members Chad Coleman (“The Walking Dead,” “The Wire”) and Jared Harris (“Mad Men”). They join Thomas Jane and Steven Strait in the galaxy-spanning story of a hardened detective (Jane) and rogue ship captain (Strait) who team up to find a missing girl, and find themselves in an interplanetary conspiracy.

Coleman will play Fred Johnson, a former Marine caught in a power struggle between Earth and Mars. Harris plays the “strangely terrifying” Anderson Dawes, who comes into conflict with Jane’s Detective Miller. Kristin Hager (“Being Human”) and Shawn Doyle (“Big Love”) joined Coleman and Harris in new cast announcements Thursday, with Hager playing strong-willed navigation officer Ade Nygaard and Doyle playing “consummate politician” Secretary Errinwright.

The 10-episode drama is written by “Children of Men” and “Iron Man” scribes Mark Fergus and Hawk Ostby, who serve as showrunners and executive producers along with “CSI” vet Naren Shankar. The series is based on the bestselling book series by Daniel Abraham and Ty Franck, who also serve as producers on the show.

“The Expanse,” which is produced by Alcon Television Group and the Sean Daniel Co., is set to premiere in 2015.

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