It’s a far cry from the intergalactic exploring of Star Trek or the alien-intermingling of Avatar, but make no mistake, The Martian is futuristic sci-fi. That much is obvious from one key plot component: that NASA botanist Mark Watney (Matt Damon) is among a crew of astronauts inhabiting the fourth planet from the sun when the story begins. Mankind, of course, has never stepped foot on the planet.

When exactly The Martian takes place, however, has been the subject of debate since Andy Weir’s 2011 self-published novel first enthused a wide fanbase. The author deliberately did not include the year Watney’s Ares 3 mission takes place in the original text, though he would tell reporters (like Ars Technica’s Lee Hutchinson last November) that it is a determinable year and that he included Easter eggs within the story for readers to solve the riddle themselves.

“The key,” Hutchinson wrote on Reddit, “was Thanksgiving. ”[Weir] had to find a year where the transfer orbits to Mars worked out such that the crew could spend Thanksgiving on the surface, thus necessitating the potatoes [that Watney relies on growing for survival]. Once he had that figured out, the entire timing of the story flowed backward from that.“ A former computer science student with programming experience at companies like AOL, Weir even developed software that tracked the necessary orbits.

In adapting the novel for the big screen, director Ridley Scott and screenwriter Drew Goddard stayed true to Weir’s space-and-time ambiguity, never mentioning which year the film is set (though Goddard did momentarily muddle the picture with a reference to the year 2047 in answering a goofy question about futuristic pirate-ninjas during a Twitter Q&A).

Related: Let’s Talk About the Marvelous Ending of ‘The Martian’ (Spoilers!)

As it turns out, though, all the message-board speculating is moot: Weir actually revealed which year the story (in book form, anyway) takes place in a Facebook post in January of this year.

Weir awarded Martian fan and "fellow nerd” Kenny Ray with major props (and a signed copy of the book) for being the first reader to crack the code in determining the story’s time setting. “Kenny was able to back-calculate the actual dates from information in the book,” Weir wrote. “He emailed me his findings and he was absolutely right.”

Here’s how Weir breaks down the dates: “Ares 3 launched on July 7, 2035. They landed on Mars (Sol 1) on November 7, 2035. The story begins on Sol 6, which is November 12, 2035.”

And while the idea of an astronaut surviving on Mars for an extended period of time still requires a Hollywood-ized suspension of beliefs, Weir’s choice of year for the Ares 3 mission is not far-fetched in the slightest: According to reports from late 2014, NASA plans to launch a spacecraft that will take humans to Mars in… 2035.

The Martian is now in theaters.

Watch astronaut Tracy Caldwell Dyson share her biggest complaint about space movies: