Although James Cameron's Avatar stands financially as the most successful movie ever made, many fans were surprised when the director announced that he was making no fewer than four sequels. Production is underway on Avatar 2 and 3, with the first of these set to arrive in 2020. However, Cameron has now admitted that the fate of Avatar 4 and 5 depends on the success of the first two movies.

In an interview with Vanity Fair, Cameron was very honest about the future of the sci-fi series. "If Avatar 2 and 3 don't make enough money, there's not going to be a 4 and 5," he said.

However, the director also explained that while connected, the movies also work as standalone narratives that aren't entirely dependent on each other. "They're fully encapsulated stories in and of themselves," he explained. "It builds across the five films to a greater kind of meta narrative, but they're fully formed films in their own right, unlike, say, The Lord of the Rings trilogy, where you really just had to sort of go, 'Oh, s**t, all right, well I guess I better come back next year.' Even though that all worked and everybody did!"

Last week, Cameron spoke about some of the technical challenges involved with making the Avatar sequels, in particular shooting motion-capture underwater. "It's never been done before and it's very tricky," he said. "Our motion capture system, like most motion capture systems, is what they call optical base, meaning that it uses markers that are photographed with hundreds of cameras. The problem with water is not the underwater part, but the interface between the air and the water, which forms a moving mirror. That moving mirror reflects all the dots and markers, and it creates a bunch of false markers.

"So, we've thrown a lot of horsepower, innovation, imagination, and new technology at the problem, and it's taken us about a year and a half now to work out how we're going to do it."

The first cast image from the Avatar sequel was revealed in September. Although specific plot details about Avatar 2 are scarce, producer Jon Landau did explain that the young cast would help shift the tone of the movie. "We never had this youthful element before, and that brings a different kind of energy to the film," he said. "They represent the future generation of Pandora and play a very significant role--not just in this movie but throughout all the movies."

Avatar 2 is set to hit theaters on December 18, 2020, with the third part arriving on December 17, 2021. If all goes to plan, we'll see Avatar 4 and 5 on December 20, 2024 and December 19, 2025 respectively.