Thanks to Masterworks for sponsoring today’s video.
Is a world like Pandora possible? This question was buzzing in my head as I left a recent
screening of the movie Avatar: The Way of Water. I’m sure a lot of you have seen Avatar or its
sequel, or at the very least heard about them. But in case you’ve been living under a rock, or there
weren’t any cinemas on the desert island where you were shipwrecked, here’s the short version.
Both Avatar movies are set on Pandora, an Earth-like moon in the Alpha Centauri A system.
After Earth exhausts nearly all of its natural resources, humans set their sights on colonizing
Pandora, which hosts highly developed ecosystems of interconnected lifeforms, among them, a species
of technologically primitive but physically evolved humanoids called the Na’vi. There is,
of course, a lot more to it – interstellar travel, genetic engineering and memory implants, all of
which are really interesting. But this video is concerned with the science of Pandora itself.
How much is based on real science? What did director James Cameron and his team get right?
What did they get wrong? And, although it might sound farfetched, could there theoretically
be a world like Pandora out there? I’m Alex McColgan, and you are watching Astrum. Join
me today for a fun thought experiment, as we turn our telescopes to the fictional world of Pandora,
and analyse the moon’s complex geology, orbital mechanics, biosphere and atmosphere.
Let’s start by looking at the Alpha Centauri A system where Avatar is set.
Alpha Centauri is a three-star system in the Milky Way Galaxy, comprised of 2 sun-like stars (Alpha
Centauri A and B) and a small red dwarf (Alpha Centauri C, also known as Proxima Centauri).
As the closest neighbouring star system to our own, it’s a convenient place to visit. Of course,
in interstellar terms, convenience is relative.
Alpha Centauri is 4.37 light years away from Earth, meaning it would take a spaceship
travelling at the speed of Voyager 1 over 70 thousand years to get there. But let’s
assume humanity develops technology capable of interstellar spaceflight, as it has in the
Avatar movies (even though the original’s start date of 2154 still might be a bit optimistic).
Alpha Centauri A actually has a few things going for it as far as habitability is concerned. Its
star is only a bit bigger and brighter than our Sun, meaning it has a Goldilocks Zone – not too
hot, not too cold – around 1.2 Astronomical Units from its centre, where liquid water could exist on
rocky worlds orbiting it there. A good start for the science of the film. But despite Pandora’s
Earth-like appearance, one notable difference is that it isn’t a planet. It’s a moon orbiting the
hypothetical gas giant Polyphemus. Here, too, the films are on a pretty sound scientific footing.
There are most likely many more moons than planets in the Milky Way Galaxy,
meaning the chances of finding a moon with the right conditions for life are that much greater.
And even within our own Solar System, we know of several moons that could be hospitable to life.
Two of those, Europa and Ganymede, orbit Jupiter, a gas giant like Polyphemus.
Enceladus, which orbits Saturn, is another. But on all these moons, any potential life would
exist in the oceans that we think lie underneath their frozen surfaces. Pandora, on the other hand,
has Earth-like oceans on its surface, which are on full glorious display in Avatar:
The Way of Water. And any surface life would likely face significant challenges. Gas giants
have intense radiation belts made of electrons and ions trapped by their strong magnetic fields. So,
any life on Pandora’s surface had better be up to the task of dealing with some serious radiation.
There might be offsetting factors, though, such as a buffer from its atmosphere. Pandora could
also have its own magnetic field for protection, and there’s some evidence for this explanation.
We see indirect evidence in the form of aurorae and the film’s floating Hallelujah Mountains
(both of which I’ll discuss in a bit, so hold that thought!) Avatar’s fan wiki proposes the alternate
explanation that Pandora resides outside the main radiation belt, except for one week when it passes
through Polyphemus’s night side. Allegedly, this is when the aurora occurs on Pandora. Whether or
not this was James Cameron’s intention, it seems that Pandora’s life has evolved to survive in a
particularly harsh environment, and I, for one, wouldn’t question the toughness of the Na’vi!
In real life, we have yet to confirm a gas giant orbiting any of the Alpha Centauri stars,
although there is some debate as to whether a possible giant dubbed Candidate 1 might be
orbiting Alpha Centauri A. Candidate 1 was first spotted using mid-infrared imaging technology in
2021, which is over a decade after the first Avatar movie came out.
Incredibly, scientists believe it would orbit right in Alpha Centauri A’s habitable zone. But
before you get too excited about the discovery of a real-life Polyphemus, be aware that scientists
still aren’t sure if it’s really an exoplanet or just an artefact caused by a cloud of dust.
If it is a planet, it would likely have at least the mass of Neptune – in other words, a gas giant.
We’ll have to await further evidence to evaluate this one. But in 2016,
scientists discovered something just as cool orbiting in Proxima Centauri’s habitable zone:
a planet that is Earth-like in size! Seeing as Proxima Centauri is a really old and tiny star,
there is, however, debate surrounding how habitable this world really is.
Our ability to detect exoplanets has gotten way better in recent years and continues to improve,
so it’s likely we’ll continue to find exoplanets that are potentially habitable. Regardless,
whether or not Alpha Centauri A has a planet like Polyphemus isn’t crucial to this exercise.
Polyphemus could exist anywhere in the universe as far as we’re concerned.
One of the more unusual aspects of the Avatar movies is how they handle Pandora’s day-night
cycle. In both movies, there is a night-like phenomenon referred to as “eclipse” by the Na’vi.
This is showcased spectacularly, as Pandora’s inhabitants experience an ethereal twilight when
the moon enters the shadow of its parent planet, Polyphemus. This is a rather beautiful bit of
world-building, as Pandora would likely experience a regular darkening event, like our rarer total
solar eclipses on Earth, which would coincide with the eclipse of Alpha Centauri A behind its parent
planet. These eclipses would probably be experienced as a relatively short darkening,
while a second, longer night phenomenon would occur due to the moon’s rotation.
I also love how night on Pandora takes on a twilight appearance. This makes sense,
given the relative proximity of Alpha Centauri B, which would still be an extremely bright star when
Alpha Centauri A is occluded. When you factor in the bioluminescence of Pandora’s many florae and
fauna, what you get is a shimmering, twilit world with enough scientific grounding to pass muster.
As for how long night lasts on Pandora, James Cameron has yet to spill the beans,
but there’s some interesting speculation among the film’s devoted fan base.
Avatar’s fandom wiki conjectures that Pandoran eclipses are 100 minutes long , and nights are
34 to 35 hours . Since Pandora is probably tidally locked to Polyphemus, it might take just 60 or 70
hours to complete its orbit. (Remember, when a moon is tidally locked to its parent, like ours
is, its orbital period and rotation are the same duration, which is why we always see the same side
of the moon from our standpoint on Earth.) Io orbits Jupiter in 1.8 Earth days, for instance,
so a 60-hour Pandoran orbit isn’t out of the question. This leads to a fascinating inference:
if you are on the side of the moon that sees Polyphemus, it will always be in the same place
in the sky, whereas on the far side of Pandora, you won't see the planet at all – or any eclipses.
So, any natives living on the far side might not even know they’re orbiting a planet!
If any of you have your own theories about Pandora’s day-night cycle,
please let me know in the comments. Your guesses might be better than the ones I was able to find!
Next, let’s talk about Pandora’s atmosphere. According to the films, it is a mix of nitrogen,
oxygen, carbon dioxide, xenon, methane, ammonia and hydrogen sulphide. Unfortunately for humans,
the latter three are unbreathable. And the high quantities of carbon dioxide (allegedly 16 to
18%) are also a no-go for humankind. But humans developed under the unique atmospheric conditions
of Earth. Theoretically, life under Pandora’s alien conditions would evolve differently.
I appreciate that the movies put a lot of thought into this. It’s addressed
with the anatomy of the Na’vi, who have special organs called Wichow,
which combine carbon dioxide with water and convert them into oxygen and methane.
Despite Pandora’s high CO2 levels, it also has higher levels of oxygen than Earth’s atmosphere.
Combine this with the oxygen generating wichow and the Moon’s 20% reduced gravity compared to Earth,
and you can see why the fauna on Pandora grows so big and strong. More oxygen in the atmosphere in
the ancient past is why dinosaurs got to grow so tall on Earth, after all.
Another interesting fact is that Pandora’s heavier mix of gases and denser atmosphere at
sea level means acceleration requires more force. Humans would experience this like a wind blowing
against them as they walk, whereas the Na’vi are equipped to overcome this resistance with thin,
muscular frames and tensile toes for gripping the ground. Pandora’s unique atmosphere manifests
in other ways, too. My absolute favourite touch is the aurorae that appear in The Way of Water,
which appear bluish and violet. On Earth, most aurorae are green, which is the product of solar
winds exciting oxygen and nitrogen molecules under a given set of barometric conditions, although we
do rarely get red, violet or even yellow auroras. It’s no surprise that these phenomena might look
different on Pandora. On Jupiter and several of its moons, for example, aurorae are blue,
while on Saturn, they are largely in the ultraviolet and infrared bands of the spectrum.
On Pandora, these different colours could be a result of differences in atmospheric composition,
pressure and the strength of its magnetic field. So far, I’m actually surprised by
how much of Pandora is pretty plausible! But I know there’s a question you’re waiting to ask,
so let’s get down to it: how realistic are the film’s iconic floating “Hallelujah Mountains”?
Well, there’s good news and bad news. The good news is physicists at Yale and Penn
State say floating masses produced by magnetic repulsion could, theoretically, be possible.
Unfortunately, you would expect this phenomenon to require extremely low levels of gravity
incompatible with the locale’s iconic waterfalls and with how gravity is generally represented on
Pandora. But there could be another explanation. After all, the mountains are rich with Pandora’s
iconic precious metal unobtanium, which is described as a powerful superconductor.
In fact, the prospect of mining unobtanium is what brings humans to Pandora in the first place.
In theory, if there were a magnetic bubble on the moon’s surface, this could produce an
effect in the unobtanium-rich mountains similar to how maglev trains float above their tracks.
Given that unobtanium is a theoretical metal, I’ll give this one an incomplete.
Are floating mountains likely? Not exactly, but we should at least leave the door open to such
a phenomenon being possible. Having said that, the Hallelujah Mountains are based closely in
appearance to the mountains of China's Zhangjiajie National Forest Park, minus the floating part,
so if you want to see the closest thing to Avatar’s most spectacular feature,
you might want to book your next ticket to Zhangjiajie. So, there we have it,
a walk-through of some of Pandora’s likely, not-so-likely and seemingly impossible attributes.
Overall, I’m really impressed with how well Avatar held up to this thought experiment.
James Cameron has said on several occasions that Avatar is meant to be a space fantasy,
but for a fantasy, it’s one that clearly has a lot of thought and research put into it. When
you factor in the film’s important message about ecological preservation, there’s a lot for the
scientific community to embrace and appreciate. And who knows, maybe future discoveries will make
some of Avatar’s more outlandish predictions look prescient? I’m looking at you, floating mountains!
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Want to see more deep dives into the science behind other fictional worlds? Let me know
in the comments. A big thanks to my patrons and members for your support, and especially this week
to GDeath for contributing $25, thank you I really appreciate it. If you want to support too and get
access to the new rewards, check the links in the description. All the best and see you next time.