Battlestar Galactica TV show was based on the original 1970s series, it took a very different approach to the sci-fi genre while airing between 2003 and 2009. Six years later, The Expanse arrived as a spiritual successor, bringing the same ethos to science fiction and an equally philosophical outlook on humanity.

While Battlestar Galactica enjoyed more mainstream attention, both shows were lavished with critical acclaim before earning cult followings that have lasted long after each show's respective finale. The Expanse and Battlestar Galactica are similar enough that you could bet your last slice of space lasagna that fans of one will enjoy the other, but each series also feels unique enough to stand apart in a crowded arena. Curiously, one strict rule unites these titans of modern sci-fi - a rule that proved as instrumental to Battlestar Galactica as it later did to The Expanse.

The Expanse & Battlestar Galactica Both Avoid Introducing Aliens Outright

The Expanse Inherited Battlestar Galactica's Strict Policy On Alien Invaders

For a long time, the presence of aliens was a near-certainty in any self-respecting sci-fi franchise, with the twin juggernauts of Star Trek and Star Wars popularizing the notion that every corner of space is crammed with pointy-eared logicians or little green mentors with terrible syntax. Even the original 1978 Battlestar Galactica submitted to the trope by introducing a selection of otherworldly species and creatures during its run.

This allowed The Expanse to deal with the remnants of an alien species, not the species itself.

When Battlestar Galactica returned in the 2000s, it took the exact opposite route, placing a "No Aliens Allowed" sign firmly on the studio door. Adama actor Edward James Olmos expressed open disdain for the idea of extra-terrestrials on Battlestar Galactica (via NBC), and while suggestions of an "anti-alien" clause in his contract remain unconfirmed, the sentiment behind it was very real. As such, Battlestar Galactica adhered staunchly to a landscape composed of only humans and their robotic creations.

As Ronald D. Moore expanded his cyclical mythos, it became apparent that humans/Cylons/human-Cylons existed on other planets in centuries long past. Fortunately for Olmos, these fallen civilizations ultimately belonged to the same species as Battlestar Galactica's main characters, and the rule against aliens remained unbroken.

Edward James Olmos as Adama looking serious in Battlestar Galactica and the Ring Gates from the Expanse.

Battlestar Galactica's Spiritual Successor Was This Underappreciated Sci-Fi That Ended Too Soon

Battlestar Galactica changed sci-fi forever, and found a spiritual successor in another series that was not as widely known and ended far too soon.

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The Expanse adopted a very similar philosophy. Taking place predominantly in Earth's solar system kept the focus on humanity during the early stages, but when the sci-fi weirdness eventually arrived in The Expanse courtesy of the Protomolecule, it was revealed that the ancient empire responsible for creating it had been wiped out thousands of years prior. This allowed The Expanse to deal with the remnants of an alien species, not the species itself, keeping the tone more grounded than if Holden and co. had been chased around the Belt by blue, phaser-toting aliens looking to steal their Protomolecule back.

How Aliens Would've Ruined The Expanse

Holden's Life Was Difficult Enough Without UFOs Showing Up

Chrisjen Avasarala looks worried in The Expanse.

The Expanse thrived due to its strong characterization, amazing visuals, and compelling story based on the book by James S.A. Corey. A few tentacle-covered creatures would not have suddenly turned The Expanse into an unwatchable mess, but aliens would still have put a big dent in the show's appeal.

The Expanse wouldn't be a terrible show with an added spoonful of alien, but it would cease to be The Expanse.

Plausibility was a not-insignificant strand in The Expanse's formula, and at the core of that formula sat one question: "How does humanity react to a discovery it fundamentally doesn't understand?" The entirety of seasons 1-6 revolved around various human factions attempting to exploit the Protomolecule for political or personal ends, then inevitably failing in a variety of spectacular ways. Toss aliens into the mix, and the story stops being about humans' infinite capacity for self-destruction and becomes an "us vs. them" scenario.

Show	Tomatometer Score
Battlestar Galactica	95%
The Expanse	95%

More problematically, the Protomolecule would cease to matter as a plot device. Right up until The Expanse's ending, the Protomolecule was a holy grain of a MacGuffin - the gift left behind by a technologically superior race. If the Protomolecule's creators were actually present, the blue goop would lose all relevance because the alien species itself becomes the big discovery capable of changing humanity's future. The Expanse wouldn't be a terrible show with an added spoonful of alien, but it would cease to be The Expanse in any recognizable form.

How Aliens Would've Ruined Battlestar Galactica

Not A Frakking Alien In Sight

The presence of aliens would have damaged Battlestar Galactica too, albeit for different reasons. With his reboot, Ronald D. Moore sought to move away from the fantastical world of Star Trek, but with its story set elsewhere in the galaxy and Cylons making themselves a nuisance as early as episode 1, Battlestar Galactica required slightly more suspension of disbelief than The Expanse. Still, that extra leeway was nowhere near enough to accommodate aliens.

Cylons either looked exactly like humans, or took the form of metallic robots with weapons attached - hardly a far cry from current technology in the real world.

The issue wasn't one of aliens being implausible, since Battlestar Galactica covered far more space miles than The Expanse ever did. A third species might have even made sense within the context of humanity's battle against the Cylons. Perhaps the robotic allied themselves with another race looking to overthrow the Twelve Colonies, for example. The problem would purely be the stark change of tone an alien presence inevitably triggers for Battlestar Galactica.

Battlestar Galactica was the antithesis of Star Trek. Adama never had a central command chair because it made more sense for him to stand in the thick of the CIC giving orders, meaningless technological jargon was kept to a minimum, and ships like Galactica and Pegasus fired warheads instead of futuristic lasers. Alas, all of that grounding and grit would have been meaningless if aliens got involved, not because Galactica encountering an alien civilization during its journey was beyond the realms of scientific possibility, but simply due to how movies and TV shows typically present aliens onscreen.

Thomas Jane as Miller looking inquisitive in The Expanse.

Rewatching The Expanse Today, Season 1 Almost Feels Like A Totally Different Show

Rewatching The Expanse today, it becomes apparent that season 1 stands apart from the rest of the sci-fi show in of its tone and style.

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Covering actors in prosthetic attachments and dressing them in outlandish costumes always brings with it a new level of fantasy - exactly what Battlestar Galactica was desperately trying to avoid. There is no realistic way to portray civilizations from other planets because writers, directors, and costume designers have no real-world comparison to reference. Everything ends up looking more "fi" than "sci," and that's before the impossible-to-answer questions begin, like "why is this mysterious alien civilization speaking perfect English?"

With the Cylons, Battlestar Galactica avoided such obstacles. They either looked exactly like humans, or took the form of metallic robots with weapons attached - hardly a far cry from current technology in the real world. And since Cylons were made by humans, speaking the same language was never a plot hole.

Battlestar Galactica & The Expanse Both Broke The "No Aliens" Rule (Sort Of)

Both Shows Had Aliens Of A Sort

While the banning of alien life forms was a rule that served Battlestar Galactica and The Expanse well, the two shows would both bend it to breaking point in their own unique ways. Every sentient being in Battlestar Galactica traced back to Kobol one way or another, but the series did include a handful of angelic beings whose origin was never established. The presence of some higher entity, whether that be a god or an alien race, was very strongly hinted at, especially in Battlestar Galactica's tantalizing final scene.

The dark gods would have become far more prominent if The Expanse season 7 and beyond had happened.

Whether this constitutes alien involvement is left to the viewer's discretion, and The Expanse pulled a very similar trick. While the Protomolecule's creators died eons prior to the story, The Expanse's later seasons introduced an unseen threat from beyond the known galaxy - a force of dark gods who were both powerful enough to wipe out entire empires and annoyed enough to try. Just like Battlestar Galactica, The Expanse refused to drop the "A" word outright, wisely letting the audience decide what to call these villains. And because the dark gods never materialized physically, any issues of alien silliness were skillfully dodged.

Ultimately, however, there was an undeniable element of humans vs. aliens to The Expanse's story, even if only as a background plot. The dark gods would have become far more prominent if The Expanse season 7 and beyond had happened, but as far as seasons 1-6 are concerned, Battlestar Galactica's "no aliens" legacy is kept alive. Just.

Sources: NBC