Blake Lively and Scarlett Johansson are both eyeing the role of the title character in Warner Bros.' outer space thriller Gravity, starring Robert Downey Jr..

According to Heat Vision, Alfonso Cuarón is directing from a script that he co-wrote with his brother Jonas.

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During the past two weeks, Johansson and Lively tested for the lead role of a female astronaut lost in space. A decision is expected within the next week or two.

The movie's plot revolves around astronauts repairing the Hubble telescope who are hit with an avalanche of satellite junk. In a plot akin to Cast Away, the surviving astronaut must fight her way back to Earth, where she hopes to reunite with her daughter.

The project originally was set up at Universal as a vehicle for Angelina Jolie, who left the project, partially because of Warner Bros.' balking at paying her $20 million fee.

Filming would begin early next year.