The Star Wars franchise always has been long on imagination. Fantastic creatures, giant spaceships, man-made death moons—the galaxy far, far away has them all. It also contains a rich array of planets, each with a unique environment. But one thing about those celestial bodies always stood out: the singular adjective—desert, ice, etc.—describing each of them.
Whereas Earth hosts a wide diversity of biomes, the planets of Star Wars boast far fewer climates and topographies. The ice planet Hoth never thaws. The desert planet Tatooine seems to never see rain or cold. Meanwhile, the forest moon Endor orbits the temperate zone of a gas giant and a diminutive Jedi master trains in a world covered by an unchanging bog.
While a world of sorcerers, faster-than-light travel, and fussy robots may not meet the standards of the hardest of hard sci-fi (why was the T-65 X-wing starfighter a long-range vehicle but the TIE Fighter wasn't?), seeing the mono-ecosystem worlds of Star Wars raises the question: Is a world with a single, homogenous weather pattern the exception or the rule? Earth has many environments, but does the rest of the universe look more like our home or Luke Skywalker's?
The first thing we should point out: In many cases, no one knows for sure. Scientists know there are more than 1,800 confirmed exoplanets out there, but in many cases, that's all they know. While that could change sooner rather than later, for now, science must speculate on their attributes based upon our solar system, what is known about planetary formation, and a few educated guesses.
"It's amazing that we've found all these extrasolar planets, but we know virtually nothing about them," says Greg Laughlin, professor of astronomy and astrophysics at the University of California, Santa Cruz and an exoplanet expert. "So there's still license to do whatever you want when it comes to fictional representation of habitable worlds. And I think there's no way to know if monolithic worlds are the rule, or if a planet is bouncing around between a lot of climatic patterns."
Just how much license does the Star Wars galaxy take with its many worlds? We talked to some planetary scientists to find out.
Monosystem: Desert
Climate: Hot, arid
The first planet we "visit" in the original Star Wars trilogy is the desert world of Tatooine, a harsh planet where the surface has been scorched by binary stars and moisture must be farmed from the air. The idea of a desert world (seemingly) is revisited in Star Wars: The Force Awakens, but J.J. Abrams says the world seen in the teasers isn't Tatooine, but Jakku, which may or may not be an all-desert world.
Most coverage, however, points to Jakku being a desert planet. It certainly looks Tatooine-esque in the trailer; and the upcoming Star Wars Battlefront videogame promises a DLC for the "Battle of Jakku," which EA says occurs on a "remote desert planet." We'll have to wait and see the game—and The Force Awakens—to know whether Jakku is a desert world or one of more varied terrain.
But if Jakku and Tatooine end up being twin—or nearly twin—worlds, they wouldn't be alone. Most astronomers agree desert worlds might be quite common. However, whether those desert planets would be viable places to live, as they are in the Star Wars universe, is another story. Is a planet without much water capable of sustaining indigenous life like Jawas, Tusken Raiders, and wamp rats?
"I don't remember seeing a lake or oasis on Tatooine, and maybe I missed it but it seems like an awfully dry place for people to live and it wasn't clear to me if they were growing crops," says Andrew Johnston, a geoscience researcher at the National Air and Space Museum. "And where were the crops and how were they irrigating them?"
Johnston says moisture-farming situations are certainly possible; they're used in the Atacama Desert in South America, for instance. But to sustain a population of Jawas, Tuskens, farm boys, and bounty hunters, the planet would need some bodies of water. Otherwise it would be harsh, unforgiving, and all but lifeless.
We even have an example of it in our solar system, albeit one that's a little colder than Tatooine. "Mars is largely a desert world, but having an all desert world that has creatures that have grown up there and walk around is somewhat unusual," Johnston says. (And anyone who has read The Martian knows Mars isn't exactly an easy place to survive.)
However, with sufficient water, Laughlin thinks organisms on a planet like Tatooine might not only survive, but thrive.
"If I had to guess, and this is based not on science but just a hunch, I'd have to say that [Tatooine] is the most realistic depiction of a world in our galaxy," he says.
A desert world might have an advantage over a verdant planet, as desert worlds are more resistant to the harmful effects of global warming. As the stars they orbit grow hotter, the worlds are better able to rebound from increased luminosity.
That brings us to the most striking feature of Tatooine: its binary stars. But while the planet's double noon is striking, it's also plausible. We know of planets orbiting binary stars. Some orbit the common center of mass between pairs of stars, while others spend their time around just one of the stars in the system.
"The inference is that they were quite close together, and the planet was quite distant from the stars," Laughlin says. "That posts zero problems for habitability. As far as the planet is concerned, it's just getting mixed light from the two stars."
Could It Exist? Yes
Monosystem: Ice
Climate: Frigid
At the beginning of The Empire Strikes Back, we're taken to Hoth. It's a frozen wasteland, a remote and inhospitable planet the Rebellion chose because it was out of the way, far from where the Empire might look for them. It's a barren hellscape that looks like it will remain that way. But in reality, Hoth has more in common with Earth than you might think.
"We know that there's been several times in the Earth's history where the Earth looked like that---in Snowball Earth phases, when the whole planet gets glaciated," Laughlin says. "When that happens, the whole planet is like a reflective cue ball. … It only eventually gets unlocked when the CO2 levels get so high that the melting starts, and within 100 years you have a crazy, crazy increase in temperature."
As Johnston notes, we have similarly barren ice worlds in our solar system, and they might be capable of supporting life. But life on Europa or Enceladus wouldn't be on the surface, as on Hoth, but deep under the ocean. During the latter Snowball Earth phase, life on Earth was found under the ice shell, near hot vents on the ocean floor, or in temperate undersea regions.
That also means there was nothing like the megafauna we see today. Instead, there were primitive worms and arthropods, some species of jellyfish and sponges, and a smattering of multicellular microscopic life. Creatures like wampas and tauntauns certainly couldn't roam the surface, and with good reason---there's an almost complete lack of vegetation.
"There would have to be a whole ecosystem, something for the apex predator to eat," says Bruce Betts, director of Science and Technology at the Planetary Society, adding that the lack of liquid water means less plants for wampas etc. to eat. "It does seem more challenging to have enough thriving life to support a large apex predator in a Hoth-like environment."
Could It Exist? Yes, but probably without wampas.
Monosystem: Asteroids
Climate: Vacuumous
As the Rebels flee Hoth in Empire Strikes Back, the Millennium Falcon finds itself navigating the Anoat Asteroid Belt to evade the Empire. It's a rocky, dangerous obstacle course, far from our solar system's asteroid belt. Whereas asteroids in the Anoat belt were separated by a few feet, the average distance between those between Mars and Jupiter is 600,000 miles.
The Falcon lands ** in a cave on an asteroid, where Han and the rest of them find a humid environment—only to realize they're in the belly of an asteroid beast, from which they narrowly escape. It's good dramatic tension—and terrible science. Without an atmosphere, life on the scale of a spaceship-swallowing space slug simply couldn't exist.
"Asteroids anywhere near the scale of those shown in the Star Wars movies with large creatures do not have sufficient gravity to support any atmosphere," Betts says.
There is a chance of microbial life, however. Betts says an asteroid formed from material ejected from a planet with life could harbor bacterial survivors for awhile. But there would be nothing on the scale of mynoks or exogorths.
And there's another problem with the scenario, too.
"Large lizard creatures seem unlikely, not to mention the very large question of what, pray tell, do they eat when spacecraft don't fly into their mouths," Betts says.
Could It Exist? As seen? Nope. (And definitely no space slugs.)
Monosystem: Breathable gas giant
Climate: Cold
The Millennium Falcon next arrives at Cloud City, a human habitat tucked amongst the clouds of a gas giant and home base to a mining operation.
When Han Solo, Chewbacca, Leia Organa, and C-3PO arrive, Lando Calrissian greets them on an outdoor landing pad. When Luke falls during his fight with Vader later in the film, he's also seen outdoors. This suggest a layer to the atmosphere that's breathable, which is all but impossible on a gas giant.
"Nothing that we've seen so far matches that description. And what are they mining?" Johnston says.
There are many problems with the Bespin planet model. Every known gas giant is composed chiefly of hydrogen and helium, the most abundant elements in the universe. They would be a poor source of the heavier elements humans typically mine, and an even poorer source of breathable air. Jupiter's atmosphere is around 90 percent hydrogen, for example, and approximately 10 percent helium. A tiny remaining margin is a handful of trace gasses. The most abundant of them, methane, constitutes about 0.3 percent of Jupiter's atmosphere, and any remaining compounds or elements constitute less than a tenth of a percent. There's no oxygen to speak of, and the gasses that are present are noxious to humans.
"Nothing that we've seen right now suggests there'd be a zone there where people could live on a gas giant. Certainly nothing with oxygen," Johnston says. "The density of the gasses of Jupiter increases the lower you go. The point where the pressure there equals what we have here is much too cold for us to survive because we're further from the sun."
Then there's the problem of finding the right mix of pressure and temperature. If you could overcome the breathability issue, you'd still need to build Cloud City in an atmospheric layer temperate enough to not freeze. Given the position of Cloud City seemingly within the upper atmospheric layers, it's far too high to have the atmospheric pressure necessary for humans to breathe. Also, it would be crazy cold.
"If you aren't closer in to the habitable zone you may get to rather large pressures, and certainly would not be seemingly pretty high in the atmosphere as Cloud City is," Betts says.
Could It Exist? Nope.
Monosystem: Forest
Climate: Temperate
In Return of the Jedi, the epic final battle with the Empire takes place above a forest moon orbiting a gas giant.
Endor is theoretically possible, provided the gas giant is close to its sun's habitable zone. With a Sun-like star, Endor's host planet would have to be in the "Goldilocks Zone" of its host star for a moon to be habitable in the way displayed in Return of the Jedi.
"It all depends on the size of the star you have, because some would be brighter or dimmer," says Johnston. "But if it's a sun like ours and if you're at roughly the same distance away, it's theoretically possible you could have things like trees."
Less likely, though, would be a planet-covering forest, Betts says. Every polar region except those on Venus is colder than the rest of the planet, even on Mercury. And again, Venus and its runaway greenhouse effect aside, the other planets still show variability of climate in the clouds.
"Even in the case, like Uranus in our solar system, where a planet is tilted on its side relative to its orbit, there will be huge climate variations over years to tens of years, causing its own kind of variability and instability," Betts says.
What that means for Jupiter's moon Europa, for example, is a climate that, even with the briefly-glimpsed series of rivers and lakes, couldn't support a globe-spanning forest. You'd likely have a more varied terrain of multi-ecosystems. In other words? You'd have Yavin IV, the moon around a gas giant where the rebels take refuge at the end of A New Hope just before their successful run on the first Death Star.
Could It Exist? No
A few other planets are shown in the original trilogy. Not much is known of Alderaan, as it's destroyed almost as quickly as it's introduced in A New Hope. There's also Dagobah, home of Yoda and a swampy world, though it's never described as "the swamp world of Dagobah."
Assuming it is a swamp world, Johnston says that would require a planet with few, if any, geographical features, where all water would hang in low, inert bogs. A swampy planet like Dagobah would be exceedingly rare, as it doesn't align with what we know of swamp formation. Swamps typically exist in "lowlands." But Dagobah seems entirely submerged in a swamp, with plants and trees enveloping it in a humid thicket, and no mountains peaking above its cloud cover.
"It would be unlikely you'd get a planet so uniformly spherical that you'd have complete uniform vegetation all over," Johnston says.
Finally, one monosystem world is seen in the prequel trilogies. The cloning facilities for the new troopers are on the water world of Kamino. All that's necessary to turn the Earth into a water world, Laughlin says, is another ocean's worth of water.
"If you dumped another ocean's worth of water on Earth, there would be really limited land area," he adds. "The oceans would cover the Earth to 12,000 feet."
The only land surface would be the tops of the highest mountains on Earth, which would jut just above the new sea level. But other continents would be submerged.
Then there are other unspoken problems with the world-building of Star Wars. Betts notes that the planets all seem to have the same gravity, a highly unlikely scenario. And the atmospheres of these planets appear to have little variability, as the only time a character needs a breathing mask (outside of Vader) is in the asteroid belt.
But the heart of Star Wars and its enduring legacy isn't in the science It's the visuals, the characters, and the wonder.
"What they got right more than any of the science was really engaging plots and characters," Betts says, adding "there are also, of course, lots of things that are scientifically plausible."
In other words, while some of the worlds of Star Wars look fun and exotic, they're probably not realistic—and we might want to hold off on looking to colonize worlds like them. Could we ever go logging on a moon like Endor? Probably not. Not because we couldn't get there or it wouldn't have good wood, but because it wouldn't exist. Tatooine? That planet is a little more plausible, but it might be too scorched to grow a little grass, let alone a womp rat. So while it might seem exciting to go off in search of adventure in a galaxy far, far away, we are better off saving those adventures for cinemas here on Earth.
But hey, at least we don't have to be afraid of hungry wampas.
