Do The Expanse and The Martian take place within the same universe, or is the crossover merely a fun Easter egg? Currently gearing up for its fourth season, and first on Amazon Prime, The Expanse is based on a series of novels by James S. A. Corey, the writing alias of Daniel Abraham and Ty Franck. The live-action version of The Expanse has been a largely faithful adaptation thus far, and as the book series nears completion, Amazon have recently confirmed The Expanse season 5 will happen.
Like Abraham and Franck's creation, Andy Weir's 2011 novel, The Martian, offers a more grounded and realistic look at space exploration than the usual science fiction fare, and was also translated for the screen - a 2015 movie starring Matt Damon. Set in 2035, The Martian chronicles the misfortunes of an astronaut named Mark Watney, who is stranded on Mars following an expedition. The Expanse is set many years later, at a time when Mars has been fully colonized and is home to a population of billions.
While The Expanse's history and timeline is deliberately vague, one small detail may suggest that Earth's colonization of Mars also began in 2035 - and that Mark Watney himself was the man who started it all. In the world of The Expanse, United Nations spaceships are named after key historical figures, some of which are recognizable (the Nathan Hale is named after an 18th century U.S. soldier and spy), and some of which are less obvious, such as the Agatha King.
The connection to The Martian comes in Babylon's Ashes with the reveal of an Earth colony ship called the Mark Watney, and The Expanse's fans are divided as to what this inclusion actually means. One school of thought suggests that, since Earth ships are named after important Earth figures, The Martian's protagonist must have existed within the world of The Expanse and therefore both stories are set within the same universe. Watney's exploits on Mars in The Martian would have no doubt been revered for centuries and formed a vital chapter in Earth history, even more so in the colonized world of The Expanse. It's only logical that he'd have a ship named in his honor.
Furthermore, the timelines of The Expanse and The Martian line up closely enough to suggest that both could feasibly exist within the same fictional world. The Martian takes place in 2035, and while no exact date is provided for when humans first reached The Expanse's Mars, it would have to be very close to that same period in order for the planet's population to become so vast by the time The Expanse begins.
On the other hand, many fans argue that the existence of the good ship Mark Watney is not a Martian tie-in, but merely a clever nod to a similar work of fiction. While some UN ship names do correlate with known real-life figures, others are obscure references to fellow authors, production staff on the TV series, or are seemingly plucked at random. The reference to The Martian could certainly fall into this category.
All three authors involved have willingly stoked the mystery. Weir, Franck and Abraham have each addressed the connection between The Expanse and The Martian with a positive outlook and admitted that the two works could potentially exist within the same universe, however the two sides have sent mixed messages. In a 2015 tweet, James S. A. Corey revealed that they got together with Andy Weir at SDCC and verbally agreed both stories existed together, including the live-action adaptations. However, in a Reddit AMA with Andy Weir, the author of The Martian stated that the inter-franchise references were "thrown in for fun."
With no definitive confirmation either way, the connection between The Expanse and The Martian is perhaps best considered "very plausible head-canon" at present. As the authors themselves have admitted, there are parallels and crossovers between the two that make perfect logical sense but, at the same time, it's understandable that neither author wants to be restricted by the timeline and events of another writer's work. Certainly don't expect Matt Damon to cameo in The Expanse season 4.
The Expanse season 4 premieres December 13th on Amazon Prime.