George Clooney will play an astronaut alongside Sandra Bullock in "Gravity", a 3D thriller about a woman stranded on a space station.
The 49-year-old actor's spokesperson confirmed the news to OnTheRedCarpet.com. The movie is to be directed by Alfonso Cuaron and is set for release in 2012.
In "Gravity", Bullock plays a survivor of a botched space mission to repair the Hubble telescope. Her character tries to return to Earth and reunite with her daughter.
Clooney will replace Robert Downey Jr., who left the project in November, The Hollywood Reporter said. Downey Jr., star of the "Iron Man" films, has not commented.
Cuaron has directed movies such as "Harry Potter and the Prisoner of Azkaban" in 2004 and "Great Expectations" in 1998.
Clooney won an Oscar for his role in the 2005 film "Syriana" and was nominated for Academy Awards for his parts in the movies "Michael Clayton" in 2007 and "Up in the Air" in 2009.
Clooney is also a United Nations Messenger of Peace and has appeared on news programs in recent weeks to raise awareness about regional violence in war-torn southern Sudan and the African nation's January referendum on possible secession.