Some of the trickiest science in 'The Martian' came from the book's biggest fans
His fictional story, which is about astronaut Mark Watney's struggle to survive on Mars after being stranded there, has sold hundreds of thousands of copies and counting, and Hollywood recently turned it into a blockbuster movie.
But Weir's hit sci-fi book didn't start out so glamorously: The story began as a series of self-published chapters on a personal blog.
His few readers loved the story for its attention to scientific accuracy. And that exhaustive research for the book is actually what drove the story forward, he wrote during a recent Reddit "ask me anything":
Weir is a self-described space nerd but says chemistry is not his area of expertise. So his science-minded readers offered their feedback.
"Chemists actually pointed out some problems in early drafts," Weir said during a discussion of "The Martian" at the Humans to Mars Summit in Washington D.C. earlier this year. Thanks to the feedback, he was able to go back and correct some of the chemistry that's crucial for Watney's survival.
The story became more popular, and some readers started asking for an e-reader copy. So Weir made all the individual chapters available in one file. He eventually put it on Amazon.com, and sold it for the lowest possible price - 99 cents.
That's when the floodgates opened. More people downloaded the 99-cent Amazon version than had ever downloaded the free version, Weir said at the summit, and readers started leaving positive reviews (and more factchecking) on the website.
In just a few months it skyrocketed to the top of Amazon's best-selling science fiction list.
Then a book agent got in touch with Weir. Shortly after that, the publishing company Random House called - it wanted to publish a hardcover. Four days later, Hollywood called for the movie rights, Weir said.
So yes, Weir scored a book contract and a movie contract in the same week - both in the low- to mid-six figures, The Washington Post reports.
"It all happened so fast that I really had a hard time believing it," Weir told Tech Insider. "I actually worried it could all be some big scam."
More science, less fiction
You only need to get a couple pages into "The Martian" before it becomes clear that Weir did his homework. He says he's the kind of person who enjoys researching rocket technology, orbital mechanics, and physics for fun.
Creating such a science-heavy plot was a risky move on Weir's part.
"I was afraid it was going to read like a Wikipedia article if I didn't make it really interesting," Weir said during the conference.
But he found a way to weave the heavy science into a gripping plot line with a funny, smart-aleck main character (who Weir says is modeled after his own personality). It strikes a perfect balance between science and fiction, and the fast-paced plot makes it hard to put down.
His earlier attempts at writing pretty much flopped (though he has written some pretty fantastic fan fiction for "Doctor Who" and "Ready Player One"), but "The Martian" took off, partly because it captures Weir's enthusiasm for science and space exploration.
Now he's living the space-nerd dream. Since the book's sudden success, Weir has toured NASA's Jet Propulsion Lab and spent a week at NASA's Johnson Space Center where he got to meet NASA scientists and astronauts.
Weir said he wasn't really involved with the film adaptation.
"My job was basically to cash the check," Weir joked.
However, the writers did send a Weir an early copy of the screenplay and invited him to send notes and feedback.
We've seen the movie, and it definitely incorporates a lot of the hard science that made the book such a big success. And it sounds like Weir thinks so, too:
"It's amazing!" he said during the Reddit AMA. "And it follows the book very closely. They had to pull some plot elements out or it would have been 10 hours long, but they removed the right stuff in my opinion."
The movie is now in theaters everywhere.