Chrisjen Avasarala doesn't appear until the second book in the series, but she has been added earlier to be able to portray the politics of the Expanse universe more deeply, as the politics were explained by internal monologue in the book.
The character of Bobbie Draper, like Chrisjen Avarsarala, is originally debuted in the second book, Caliban's War. However, for the purposes of expediting the political aspects of the different planetary governments, she has also been shown earlier than in the source material.
Tycho Station is likely a nod to Tycho Brahe (1546-1601). Brahe was a Danish nobleman renowned for his accurate and comprehensive astronomical observations. He is considered one of the first competent minds in modern astronomy.
In Season 3, Melba is wearing a jumpsuit branded from "Savage Industries". This has been confirmed by the writers as an in-show nod to Expanse superfan and behind-the-scenes host Adam Savage from Discovery Channel's Mythbusters.
S3, E2. When a ship receives a message from a space suit, the message console displays "TK4.21" a reference to a stormtrooper in Star Wars. "TK 421, why aren't you at your post?". It also has an 1138, a popular Easter egg reference to a George Lucas film THX1138.
Just like today, there are several slang or slur words used to describe the different members of a solar society: Earther: someone from Earth; Duster: Martians; Skinnies/Belters: people from the Asteroid Belt and associated space stations (Tycho, Eros, etc.)
The name of the ship, Rocinante is also the name of the space ship in the song Cygnus X-1 by Rush. In the song Rocinante explores the black hole Cygnus X-1. The song both closes out the album "A Farewell to Kings" and opens the follow-on album "Hemispheres".
Wes Chatham's character Amos has a Hebrew-style tattoo on his left forearm. The tattoo consists of Hebrew letters, except the last one, which is not an actual letter. The tattoo is actually misspelled and does not have a particular meaning "as is" but if you ignore that last letter it can be loosely interpreted as "experience camaraderie" written in female gender. Another option can be "express your views", in female gender but this would require assumption of that non-Hebrew last letter. Character's name Amos is a Hebrew name of Biblical Prophet and is symbolizes leadership and charisma.
In the books, the character Miller is almost a foot taller than the series protagonist Holden. However, the actor playing Holden (Steven Strait) is 8 centimeters taller than the actor playing Miller (Thomas Jane).
Both Thomas Jane and Cas Anvar have ties to the Marvel live action Punisher movies. In the first Thomas Jane played the title character of Frank Castle. In the follow up movie Cas Anvar played a plastic surgeon.
Hugh Dillon(Lt. Sutton) and Mpho Koaho (Private Travis) have appeared on screen together before on an episode of Flashpoint, in which Hugh Dillon was a title character, and Mpho Koaho was a guest lead. Mpho Koaho was later nominated for a Gemini Award for his guest appearance.
The trivia items below may give away important plot points.
The 'Scopuli' is likely named after both the scopuli cliffs on Mars' northern pole, and (which those same cliffs are named after) the 'sirenus scopuli', the islands on which the Sirens of Greek mythology lived. This is fitting, as the Sirens would lure sailors to the cliffs so as to wreck their ships. In The Expanse, the Scopuli lures the Canterbury with the song of Julie Mao's distress beacon which leads to the destruction of the Canterbury and the major subsequent narrative of the show and book series.
The book titles in the Expanse series bear cryptic names in reference to the events in their respective novels. In the first books, "Leviathan Wakes" it refers to the once dormant and powerful alien virus that has 'woken up' to wreak havoc on humanity.
In the Season 2 episode "Pyre," Prax arrives at Tycho Station aboard the freighter "Jefferson Mays." Jefferson Mays is a noted audio book narrator who provided the voice for the audio book editions of several novels in the Expanse series.
Elias Toufexis, who plays Kenzo in the first season, has vast experience in Performance Capture. After his character arc ended in the last scene of season 1, the producers asked him to come back and play the Hybrid creature for season 2 through Performance Capture. He has since been in every season playing the hybrid monsters or even occasionally other soldiers or cast members bodies. The producers have promised to "kill Elias every season in some way"