Earlier this year, James Cameron’s Avatar was topped as the highest-grossing movie of all time by Marvel’s big finale, Avengers: Endgame. This gave Cameron faith that the moviegoing public can still be captured by a major release in the streaming era, giving him hope that his upcoming sequel to Avatar can still be a box office success.

RELATED: James Cameron's Movies, Ranked By Rotten Tomatoes

Avatar 2 has been in development for years, but it’s finally on the way – well into production with its cast in place – for a 2021 release. So, here are 5 things that have been confirmed for Avatar 2, plus 5 fan theories!

Confirmed: There are both fresh and familiar faces in the cast

avatar movie

Most of the lead actors from the first Avatar film are returning for the sequel, including Sam Worthington, Zoe Saldana, Sigourney Weaver, and even Stephen Lang, whose character seemingly died in the first film (“I’m not going to say exactly how we’re bringing him back, but it’s a science fiction story, after all,” in James Cameron’s words).

But they’ll also be joined by some exciting new stars, including Kate Winslet, Vin Diesel, Fear the Walking Dead’s Cliff Curtis, David “Lupin” Thewlis, Michelle Yeoh, Flight of the Conchords’ Jemaine Clement, and The Sopranos’ Edie Falco. So, we’ll have a nice mix of fresh and familiar faces.

Fan theory: Eywa brainwashed Jake

In the first movie, pretty much right after Jake plugs his hair into the Tree of Voices to connect with Neytiri, he decides to betray his own race and join the Na’vi in fighting the humans. Now, this could be seen as Jake putting love before reason. This is a common problem in sci-fi stories – Ex Machina, The Terminator, The Hunger Games etc. – and it’s also known as “The Dulcinea Effect.”

But it could also be seen as a terrifying scene in which Jake was brainwashed by Eywa, the Na’vi’s deity, into betraying the humans and reclaiming Pandora for the Na’vi. This would make a heck of a plot twist in Avatar 2 and might be the way to renew audiences’ interest in this story after all these years.

Confirmed: Avatar 2 is the first movie ever to shoot performance-capture scenes underwater

Jake flies in James Cameron's Avatar

The first Avatar film was only made possible by the invention of performance-capture technology. James Cameron couldn’t have made the movie without it. He has faced a similar problem with the sequel. He wanted to explore the unseen ecosystems of Pandora, similar to how George Lucas strived to introduce new and exciting worlds in every Star Wars film.

This involved visualizing sections of the sequels set underwater. Cameron didn’t want to use CGI to create the underwater environments; he wanted to actually shoot them underwater. Performance capture has never been shot underwater before, and new software had to be developed. Ergo, Avatar 2 will be the first movie ever to shoot performance-capture scenes underwater.

Fan theory: The Na’vi themselves were genetically engineered

Pretty much every other species besides the Na’vi that we see populating Pandora in the original Avatar film has six legs. Neytiri and the rest of the Na’vi have two legs, suggesting they’re not really Pandora natives – or, at the very least, they don’t have 100% Pandora native DNA.

The R.D.A. infiltrated the Na’vi when they first arrived on Pandora by putting human soldiers inside Na’vi bodies to create human-Na’vi hybrids as part of the Avatar Program. But it seems like the Na’vi have already been genetically engineered from the DNA of Pandora’s organic life and some other humanoid species. There could be more to the Na’vi’s backstory than we’ve been told.

Confirmed: It’ll (finally!) be released on December 17, 2021

Jake Sully with the glowing bugs in Avatar

Having been first announced with a 2014 release date that was subsequently delayed until 2015, then December 2017, then December 2018, and then December 18, 2020, Avatar 2 will finally – although we’ve heard that before – be arriving in multiplexes on December 17, 2021. A holiday release is a wise idea since the first Avatar film became the highest-grossing movie of all time in this release window.

RELATED: 10 Most Exciting Sequels We Won't See Until 2021

In the Christmas 2021 season, Avatar 2 will face stiff competition from Hotel Transylvania 4, the film adaptation of Broadway’s Wicked, Robert Downey, Jr.’s third Sherlock Holmes film, and Killers of the Flower Moon, Martin Scorsese’s upcoming historical epic starring his two muses, Robert De Niro and Leonardo DiCaprio.

Fan theory: Colonel Miles Quaritch will become half-machine

Miles Quaritch (Stephen Lang) in James Cameron's Avatar

Stephen Lang’s villainous character Colonel Miles Quaritch seemed to die at the end of the first movie, but he’s been confirmed to be returning in the sequel. Quaritch will reportedly remain the primary villain in all of the sequels, and Lang’s portrayal will require performance capture. So, maybe Quaritch will return with mechanical parts.

If his body was mostly destroyed in the first film, but his heart was still beating, maybe he was put into a mostly robotic suit, a little like how Anakin Skywalker became Darth Vader. After all, Deadline did compare the character’s future to Vader after speaking to James Cameron about Lang’s role in the sequel.

Confirmed: The plot involves a second R.D.A. invasion

Sam Worthington as Jake Sully in his Na'vi body in Avatar.

According to the plot details that have been released, Avatar 2 will be set 12 years after the first film. Jake Sully has settled down and started a family with Neytiri following the Na’vi’s victory over the R.D.A. (the invading human military force that brought Jake to Pandora in the first place).

However, their tranquil existence is disrupted when the R.D.A. returns to Pandora to finish what they started. This could be seen as another Starkiller Base plot – it’s the same exact conflict from the first one, repeated – but hopefully, with Jake being in a totally different place now than he was in the original, it’ll still feel fresh.

Fan theory: Humanity will die out on Earth

Sigourney Weaver in Avatar

The whole reason for the humans’ arrival on Pandora in the first Avatar movie is that humanity needs unobtainium (it’s been said before, but that was a really crummy name for a fictional precious material) to survive. In the hypothetical (but also very realistic) future of Avatar, the human race has used up all of Earth’s natural resources and is on the brink of extinction.

RELATED: 10 Most Culturally Influential Movies Of The 2000s

The humans’ mission to extract unobtainium failed when Jake Sully joined the Na’vi’s side and overthrew them. If Avatar 2 picks up 12 years after the original, humanity might have died out. Human extinction could at least be close.

Confirmed: It’s the first of four planned sequels

Jake mounts a flying beast in James Cameron's Avatar

James Cameron is planning for the Avatar saga to span five movies. After the second movie, there are three additional sequels slated for subsequent years. Most major cast members – including Sam Worthington, Zoe Saldana, and Sigourney Weaver – are contracted for more installments.

Cameron has been forthright in saying that if Avatar 2 doesn’t do well at the box office, we probably won’t be seeing Avatar 5 (although Sigourney Weaver and producer Jon Landau have conversely hinted that the fourth and fifth films are in production), but if all goes according to plan, we’ll see Avatar 3 in 2023 (or, if history serves us well, in 2033).

Fan theory: It’ll end with a cliffhanger

Jake Sully (Sam Worthington) in James Cameron's Avatar

While the first Avatar film had to stand on its own, the second will just be the next chapter in an ongoing five-part story arc. Although Bob Iger has suggested that Avatar 4 and 5 are up in the air pending Avatar 2’s box office performance, it seems likely that Avatar 3 will be released regardless, because it’s been shooting back-to-back with Avatar 2.

Often, when the second installment of a franchise is produced with a third in mind – The Empire Strikes Back, The Matrix Reloaded, Back to the Future Part II – it’ll cap things off with a mind-blowing cliffhanger. Maybe Avatar 2 will do the same.

NEXT: The Batman: 5 Things That Have Been Confirmed (And 5 Fan Theories)

Key Release Dates