The first Avatar set records as both the most expensive movie ever (with estimated production costs as high as $310 million) and the most profitable (becoming the first film to gross over $2 billion worldwide). Director James Cameron has been dropping hints about an underwater-set Avatar sequel all year; now, he's confirmed that he'll actually be making two sequels and that he'll be diving in very soon. (Watch star Sam Worthington discuss the Avatar sequels.) Here, a quick guide to the new movies:

So when can we expect the sequels?
Cameron says he'll begin writing in January 2011, with production for the first sequel set to begin at the end of next year. If there's no serious delay (a big if), Avatar 2 is projected to hit theaters in December 2014, according to 20th Century Fox. If Cameron decides to film the two sequels concurrently, as he is thinking of doing, the second sequel would come out in December 2015.

Why is a release date big news?
Because it wasn't clear whether Cameron would make the Avatar sequels first or begin work on one of the other projects to which he's attached — like Battle Angel, which is "about a 26th century female cyborg rescued from the scrapheap." And there's a significant time issue: "With his heavily developed story lines and intensive use of new technology, Cameron can often take a decade or longer between films."

Any hints on what the new movies are about?
Not really. In a statement released by Fox, Cameron was vague on plot and long on platitudes. For instance: "In the second and third films, which will be self-contained stories that also fulfill a greater story arc, we will not back off the throttle of Avatar's visual and emotional horsepower."

But the sequels will be set underwater, right?
Yes. Cameron told the Los Angeles Times in April that Avatar 2 would be focusing on the ocean worlds of Pandora, the fictional planet introduced in the first film. Specifically, Cameron wants to journey into the depths of the the Mariana Trench, almost seven miles beneath the surface of the Pacific Ocean.

Why would he tackle such a difficult location?
For the challenge and also, some say, for a potential $10 million prize that the X Prize Foundation is expected to offer would-be explorers who can successfully descend to the Mariana Trench — something only two people have ever done before. The director wants to film at 36,000 ft. — a depth at which no existing submarine can withstand the enormous pressures. Even the strongest military submersible can only descend to 3,000 ft. 

How will he get down there?
He'll build his own submarine, of course. Cameron has hired a team of Australian engineers to conceive and construct an underwater vessel that can not only handle the fierce conditions but also function as an underwater 3D studio.

What will Cameron be filming at the bottom of the ocean floor?
3D footage that would be incorporated into the Avatar sequel. For "a very basic idea of what Cameron might encounter," suggests Nicholas Jackson at The Atlantic, take a look at this simulated video from the National Oceanic and Atmospheric Administration. If Cameron is expecting the bright blues and greens of Pandora, says Michael Hanlon at The Daily Mail, he won't find them in "this inky world of greys and browns."

Should the Avatar actors be worried?
They're not expected to join Cameron in the Mariana Trench, but Cameron has a history of allegedly tormenting actors underwater. During the filming of 1989's The Abyss, he put those playing deep sea divers through such strenuous paces that one (Mary Elizabeth Mastrantonio) reportedly had a nervous breakdown. After the six month, 70 hour-a-week shoot was finished, Cameron had limited sympathy for his stars. "For every hour they spent trying to figure out what magazine to read, we spent an hour at the bottom of the tank breathing compressed air,'' he told The New York Times.

Sources: Daily Mail, Los Angeles Times, Popular Science, Mashable, The Atlantic, The Independent, Variety

This story was originally published on September 21 and updated on October 28.