Anthony Horowitz is writing the screenplay with Peter Jackson to direct after The Hobbit is released in 2013:
I can tell you that I think the second film is not going to be Prisoners of the Sun. What it is going to be is still under discussion. I’ve had meetings with the directors and producers and we’ve talked about ideas and action sequences. At the moment I’m trying to put together a story that will please everybody. It’s a very difficult one to do…The good news is if [Prisoners Of The Sun] is not the second film it’ll be the third film so actually I could end up with two Tintins under my belt.
http://www.bbc.co.uk/news/entertainment-arts-15553417
