Saoirse Ronan has no idea how she will film 'The Host'.

The 17-year-old actress will take on the lead role in the movie about an alien race called Souls who take over Earth and its inhabitants but admitted filming her role - which will see a Soul named Wanderer and a human, Melanie vie for the same body- will be a challenge.

Speaking about the adaptation of 'Twilight Saga' writer Stephenie Meyer's book, Saoirse said: "We're doing 'The Host' at the start of next year. We're figuring out how to film it at the moment. Andrew Niccol the director knows what he's doing, I think it seems incredibly challenging but he knows exactly what to do so I feel very safe."

Saoirse also spoke about the expectations which come with being attached to a project written by the 'Twilight' scribe but said it would be impossible to prepare herself for the reaction from fans.

She exclusively told BANG Showbiz at the UK premiere of 'In Time' at London's Curzon cinema on Monday (31.10.11): "I can see why Stephenie Meyer has such a huge following, she's a great writer. As for preparing myself for the huge level of fame like what the 'Twilight' cast have, I don't know if you could ever prepare yourself for something like that. If it happens I'll just have to deal with it."

Saoirse previously worked with 'Lord Of The Rings' director Peter Jackson on 'The Lovely Bones' and compared the experience to "heaven".

She said: "I loved working with Pete, I loved all of the crew that he had working with him in New Zealand. It was actually kind of like working in heaven for about six months."