The Expanse: Season 3 Ending & Protomolecule Origin Explained

The season 3 finale of The Expanse took the science fiction series into bold new territory and finally revealed the origins and intentions of the Protomolecule. Over the course of 3 seasons, The Expanse has constructed a tensely intriguing mystery involving political conspiracy, hybrid super-soldiers and a lone Martian gunship fighting the good fight. However, it appeared that the long-awaited answers to The Expanse‘s many questions would go unanswered, when the Syfy network cancelled the series. Fortunately, The Expanse was swiftly snapped up by Amazon Prime, and season 4 is expected to air later this year.

Based on the series of novels by James S. A. Corey, The Expanse is set in a future where Earth has colonized most of the solar system. Predictably, this conquest has given rise to much conflict, with relations between Earth, Martian colonists and the asteroid-dwelling citizens known as “Belters” at an all-time high. Over this disharmonious backdrop, the real story of The Expanse begins with the discovery of something known as the Protomolecule – a substance of unknown origin that appears in Earth’s Sol system, triggering a series of monumental and unprecedented events.

While the Protomolecule has remained at the core of The Expanse‘s narrative since the beginning, the season 3 finale cleared up many of the questions surrounding the alien substance, including its purpose and intentions and the fate of those who originally created it. Typically, however, these answers only gave rise to further mysteries, leaving plenty to explore in season 4. Before then, here’s what happens and what is learned about the Protomolecule in the season 3 finale of The Expanse.

What We Know About The Protomolecule From The Expanse Seasons 1 & 2

The first two seasons of The Expanse fed viewers information about the Protomolecule very slowly, and much of what is revealed relates more to how humans can manipulate the substance for their own ends than the inherent qualities of this technology. The audience does, however, get a very clear idea of what the Protomolecule is capable of. Released into the atmosphere, the Protomolecule acts similarly to any other contagion, finding and infecting nearby hosts and, more often than not, bringing about their deaths, as detailed in season 1’s Eros scenes.

The Protomolecule is different from regular viral infections in the sense that it appears to have some level of intelligence and although it may be a stretch to say that the Protomolecule should be considered a life form in its own right, it certainly has sentient qualities. When the Protomolecule does find a host, whether that be man, machine or even an entire asteroid, the substance is capable of adapting, absorbing and cannibalizing whatever it comes into contact with. Examples of this include Julie Mao, who became some kind of Protomolecule avatar, and the Arboghast research ship.

In The Expanse‘s second season, it’s revealed that the Protomolecule can be fused into the bodies of children to create near-invulnerable super-soldiers, but this experiment was done entirely at the behest of Jules Pierre Mao and his team, and isn’t part of the natural Protomolecule life cycle. Indeed, much of the Protomolecule usage showcased in The Expanses‘s first two seasons comes about due to the actions of human factions, and very little is revealed about the actual intentions behind the Protomolecule’s presence.

The Expanse Season 3 Ending & Protomolecule Reveal

In The Expanse season 3, joint efforts from the Rocinante crew and Chrisjen Avasarala mostly put an end to Mao’s experiments with the Protomolecule, and focus instead moves to Venus. After being released on Eros in season 1, the Protomolecule spread over the entire asteroid, absorbing the technology and lifeforms residing there, and then turned the entire rock into a ship, careering through space and crashing on Venus. It later deconstructed and recycled the Arboghast research ship into parts for an unknown construction the Protomolecule was undertaking on the planet’s surface.

This construction eventually leaves Venus under its own steam, and is revealed to be a giant circular space gateway that leads to an entirely separate physical plane referred to at the Slow Zone, and this is where the finale of season 3 largely takes place. As the name implies, the laws of physics are different within the Slow Zone and, in the form of Detective Miller, the Protomolecule mentally reaches out to Holden on board the Rocinante, drawing him towards a station at the center of the gate. Once inside, Holden is made to trigger the station’s function, transforming the gate into a passageway from Earth’s solar system to an array of faraway galaxies, allowing for rapid interstellar travel.

A conversation between Holden and “Miller” reveals that this was the intention of the Protomolecule all along, although it didn’t exactly act out of a philanthropic desire to help mankind spread throughout the universe. As Miller, the Protomolecule reveals itself to be the creation of an ancient race of aliens, who used it to construct interstellar gateways throughout the universe. Everything was going well for this highly advanced alien race, until a currently unknown enemy appeared and wiped them all out over a billion years before the start of the series. A second function of the Protomolecule is to fight back against these aggressors using the ring gates as a weapon (similarly to how antibiotics target and wipe out infections in the human body) and, as a result of this, the Protomolecule has destroyed entire worlds attempting to eradicate the mysterious beings that wiped out its creator.

This very motivation has been behind the Protomolecule’s actions since the beginning of The Expanse‘s story. “Miller” explains that the Protomolecule took the parts it needed to construct a ring gate and manipulated Holden into activating the structure. While this allows mankind to travel to previously unexplored worlds, the Protomolecule’s true intention has been to find the unknown alien race that wiped out its creators centuries ago.

Questions After The Expanse’s Season 3 Finale

Although viewers finally discover the Protomolecule’s origin and intentions, there are plenty of questions left unanswered, and a host of fresh mysteries created. This new information forces a reevaluation of the Protomolecule’s first appearance on Phoebe. Was the introduction of this technology to the Sol System intentional, or did the moon simply stumble across the remnants of an ancient alien race? Secondly, how benevolent (or otherwise) were the Protomolecule’s creators? The season 3 finale strongly suggests that the Protomolecule’s various attacks on human life were not malicious, but part of a grander plan. Was this attitude shared by those who created it and, if so, were their destroyers acting in self-defense?

Perhaps the biggest questions from The Expanse‘s season 3 finale, however, concern the unknown aggressive race that decimated the creators of the Protomolecule. Are these aliens outright villains, or were their actions justified? Perhaps a more pressing question ahead of season 4 is whether Holden activating the Sol System ring gate will draw the ire of these aliens towards Earth, if they’re even still in existence.

Specifically regarding the Protomolecule, The Expanse has sufficiently answered many of the most important questions, including where it came from, what it can do and what it wants. As a result, the focus in Amazon Prime’s season 4 will likely shift to the ramifications interstellar travel will have on the solar system and whether Earth’s budding space tourists will run into an angry group of extra-terrestrials that are none too happy at the appearance of a new ring gate in the universe.

The Expanse season 4 is expected to premiere later this year on Amazon Prime Video.

About The Author

Craig Elvy
(3630 Articles Published)

Craig first began contributing to Screen Rant in 2016, several years after graduating college, and has been ranting ever since, mostly to himself in a darkened room. Having previously written for various sports and music outlets, Craig’s interest soon turned to TV and film, where a steady upbringing of science fiction and comic books finally came into its own.
Craig has previously been published on sites such as Den of Geek, and after many coffee-drenched hours hunched over a laptop, part-time evening work eventually turned into a full-time career covering everything from the zombie apocalypse to the Starship Enterprise via the TARDIS.

Since joining the Screen Rant fold, Craig has been involved in breaking news stories and mildly controversial ranking lists, but now works predominantly as a features writer.
Jim Carrey is Craig’s top acting pick and favorite topics include superheroes, anime and the unrecognized genius of the High School Musical trilogy.

More From Craig Elvy