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The Star Wars saga currently consists of eight films:
The original trilogy,
the ones the memes come from,
Les Mis in space,
and A New Hope 2: Electric Boogaloo.
Within these films, we're introduced to 28 planets and moons
ranging from the plains of Naboo to the deserts of Tatooine to the lava of Mustafar
to the whatever this is of Felucia.
A lot of these planets are clearly inspired by biomes on Earth, such as
the grasslands of Europe, the Sahara Desert, and the lava of Hawaii.
But scaling up one part of the Earth to a whole planet doesn't always work within the laws of physics.
A lot of the planets that we see in Star Wars could
exist in the real universe though, and we actually have observations of similar
planets around other stars a little closer to home. But yes, some of them are
definitely in the realm of science fiction.
That's the voice of Dr. Hannah Wakeford,
an exoplanet researcher at the Space Telescope Science Institute.
With her knowledge of planetary science, my knowledge of atmospheric physics, and the
Star Wars Wikipedia which is called Wookieepedia because of course it is
We can work out which planets in the Star Wars universe could really exist.
May the Force be with us.
To begin with several planets almost identical to the Earth having lots of
different biomes, polar caps, and a planetary radius of about 6400km.
So Naboo, Takodana, Alderaan, Cato Neimoidia, and Wobani can
definitely exist.
Two more planets which are very similar to the earth are Yavin 4,
the location of the rebel base in A New Hope, and Kashyyyk, the homeworld of the wookiees.
But could they exist?
C3PO: Don't be so sure.
Yavin 4 is a large moon not much smaller than the Earth orbiting the humongous gas giant Yavin.
Yavin is so big that it's either really low density,
which would have to be caused by some strong internal heating,
or it's on the very edge of what we would even call a planet.
We know that brown dwarfs, which are massive objects that are bigger than planets but not
quite massive enough to turn into stars, can orbit other stars,
and we also know that brown dwarfs can host planets.
So the existence of the moon in itself isn't impossible.
The issue here is that orbiting so close to Yavin would cause
humongous amounts of tidal heating.
This is the effect of the near side of the
moon feeling a greater gravitational pull to the planet than the far side.
In addition to this Yavin has several other moons which are similar in size to Yavin 4
which would pull on the moon outwards when nearby.
The combination of these two factors would cause major frictional heating of the moon's interior
which would cause the moon to be extremely geologically active.
This is exactly what we see on Io, the fifth known moon of Jupiter.
It has over 400 active volcanoes and is the most geologically active place in
the entire solar system.
Yavin 4 isn't shown to have any volcanic activity
and though its wiki page suggests that it experienced some in the
past this should continue as the effects of tidal heating will not diminish over time.
So Yavin 4 as it is shown in the movies could not exist so close to such
a large planet.
Ki-Adi-Mundi: What about the droid attack on the Wookiees?
Kashyyyk
Wookiees: [roaring]
Yes, thank you.
Is described as having a perfectly circular orbit,
meaning it stays the same constant distance from its star and also has no
axial tilt, the angle between the planet's rotation and its orbit around the star.
These two combined result in the planet
having one continuous season as all parts of the planet receive constant solar heating year-round.
There are two planets in the solar system which actually exhibit these two characteristics:
Mercury has almost no axial tilt and Venus has an almost perfectly circular orbit.
So while it's possible that these
two characteristics could coincide and they would indeed produce a lack of
seasons this would be very unlikely so Kashyyyk gets a maybe. several other
Chewbacca: [sad grunt]
Several other Star Wars planets are also similar to what we see in the solar system
Tatooine for example is a combination of Mars' dry climate with Earth's thicker atmosphere.
Jakku, Jedha, and Geonosis are also very similar, particularly Jakku
as it once had water which has since frozen or been lost which is exactly what we
currently think happened on Mars.
The interesting thing about Tatooine is that
it's in a binary star system: a planet orbiting two stars which orbit each other.
This gives it its famous twin sunsets. Binary stars are in fact the
most numerous, certainly in our galaxy, and binary stars have been observed to
have planets around them - the first discovered was called Kepler 16b, which
much like Tatooine orbited two stars, one yellow and one red, but you can have
many types of binary systems. Tatooine is likely in what is called a p-type binary
orbit where it goes around both of the stars, but you can also get S type
binaries where the planet orbits one of the stars but not the other.
But you would still often see two suns in the sky in both of these configurations.
This also applies to another planet with two suns: Endor, the home of the Ewoks.
Wicket: Yub Yub.
So Tatooine, Jakku, Jedha, Geonosis, and Endor can all exist. But there's one more
planet which is very similar to a planet in our solar system.
Bespin. It's pretty far but I think we can make it.
A mining colony?
Bespin is a gas giant, about the size of Saturn, where a cloud city floats in a breathable layer of the atmosphere.
From the gas giants in our solar system it's very clear that it's not plausible
for a breathable stratified layer to exist in the planet's
upper atmosphere where cloud city is.
If we move the gas giant close enough to
star we might be able to get some upper parts of the atmosphere hot enough that
everything would not freeze but that's just the first challenge.
Say we have the right temperature at the right pressure in the atmosphere where human lungs could survive.
Next we have to have the material to form breathable air and we have to keep it there.
The air we breathe is mostly molecular nitrogen and oxygen
If we combine this in the 80/20 ratio of the Earth's atmosphere this
would have a mass around 12 times that of hydrogen and helium which would be
making up the majority of the gas in a gas giant planet.
If the atmosphere is then stratified into layers this layer would be much much deeper in the
atmosphere (it's much heavier) where the pressures would be far too high for
humans to survive and temperatures would be much hotter too.
So sadly, Bespin doesn't make the cut.
Lando: It's not my fault!
This still leaves us with plenty of planets though, some of which have parallels
in the Earth's past, or in its future. The frozen planet of Hoth, for example,
is what the Earth is hypothesized to have looked like several times in its past
during periods known as Snowball Earth. During the last of
these hypothesized episodes about 650 million years ago, atmospheric oxygen
would have been at a level which was breathable - so Hoth as it's shown in the
films has historical precedent. Mustafar by contrast is an extremely volcanically
active moon which is covered in lava flows and active volcanoes.
This resembles another period in the Earth's history: the Hadean
The Hadean was an epoch about 4 billion years ago when conditions on the Earth were literally hellish.
Extremely hot, with molten rocks covering the surface and the planet
being hit by a huge number of meteorites. The difference between the Hadean Earth
and Mustafar, however, is that while Anakin and Obi-Wan are able to breathe
perfectly normally on Mustafar, the atmosphere of Earth during the Hadean
was very dense an almost entirely carbon dioxide,
which isn't exactly breathable even to a Jedi.
So Mustafar as shown in the movies just doesn't really make any sense
Darth Vader:NOOOOOOOOOO
I mean, of all the people of Darth I thought you'd be happy about that.
Felucia is a planet that briefly features in episode III but is
completely distinct from all of the others, being a multicolored jungle of huge plants.
The planet itself is a bit smaller than the Earth and so has a
surface gravity about 75% of the Earth's - this would help the plants to grow to
greater sizes, and apart from the colors this is pretty similar to Earth during
the Cambrian about 500 million years ago. So assuming the atmosphere of Felucia
can mix nutrients and water around the planet with strong circulation it could exist.
Two planets which resemble what the Earth might look like in the future are
Coruscant and Hosnian Prime, both being densely populated planets about the same size as Earth.
Coruscant is actually listed on Wookipedia as having a
population of 1 trillion beings and judging by the cities shown in the film
this also seems about right for Hosnian Prime.
The issue here is that Earth, with a population of just seven billion people,
is becoming hotter and hotter due to the buildup of gases like carbon dioxide and methane in its atmosphere.
The effect of one trillion people on a similarly sized planet doing similar industries would be absolutely devastating.
So either Coruscant and Hosnian Prime are doing some serious geoengineering
- not impossible given the technology in Star Wars -
or they should be substantially hotter than they are shown to be, so they get a maybe.
Obi-Wan: I hate it when he does that
A planet with a similar issue is Eadu, which is shown to be covered in dense clouds and storms.
Water vapor is actually a tremendously powerful greenhouse gas, strongly absorbing
thermal wavelengths of radiation, so assuming that Eadu is orbiting a star
similar to our own at a similar distance it should actually be boiling hot.
But it of course could be orbiting a weaker star or further away so it could still exist.
Two planets from the newer films which are very similar are D'Qar and Lah'mu:
relatively small, terrestrial planets which have rings similar to Saturn.
We think of rings as being around gas giants like Saturn and Uranus
but it's always been theoretically possible for small
terrestrial planets like Earth to maintain a ring system.
And recently in October 2017 it was discovered that there's a ring system around the dwarf planet Haumea,
which orbits in our solar system just outside of Neptune.
So it's been shown to be possible for small terrestrial planets - even weird tiny
elongated ones like Haumea - to have rings.
There are differences between the rings though: D'Qar has rings which are composed of loose rocks,
consistent with a disintegrated moon or two: that could definitely exist.
Lah'mu on the other hand looks to have rings like Saturn made of tiny ice and dust grains.
The ice suggests that the planet formed much further out in the star system than the habitable zone
(the range of orbits where liquid water can exist on the surface of a planet)
This is kind of possible if the habitable zone of the star moved over time
to allow that planet to then become habitable, or possibly there's a very
strong greenhouse effect on Lah'mu, but this still would probably impact the
composition of the rings that we see. So it's a tentative maybe for Lah'mu.
This leaves seven planets which don't have direct analogs either in our solar system
or in the Earth's past, and...
Librarian: If an item does not appear in our records, it does not exist!
Sheesh.
However for the past 30 years or so
we've observed planets around other stars or exoplanets some of which are
similar to planets in our solar system but many more are truly weird.
There are a number of techniques we use to observe exoplanets. The first was called radial velocity.
This simply measures the pull the planet has on the starlight over time,
causing a Doppler shift in the light as it moved towards us and away from us due to the pull of its planet.
But the most prolific method being used is the transit method.
This measures the change in the amount of light seen of a star as the planet passes in front of it
and blocks out some of that light.
From observations of thousands of exoplanets in our region of the galaxy alone,
we know that the most common type of planets are ones we don't actually see in our own solar system:
Ones in between the size of our rocky earth and the icy giants Uranus and Neptune.
One class of planets in Star Wars are the water worlds:
Kamino, Ahch'To, and Scarif.
These are planets which are almost completely covered in ocean with only small islands jutting above the water.
We know that several bodies in the solar system contain water,
including the moons Europa, Enceladus, and Ganymede, but only earth has liquid water on the surface
and while we can't directly observe liquid surface water on exoplanets
we can use other measurements as proxies, like the amount of water vapour in the atmosphere of an exoplanet.
Using these proxies we've discovered several objects which could potentially be ocean planets
such as the mini Neptune GJ 1214b. Observations of GJ 1214b so far suggest that it's a
world shrouded in optically thick clouds which would block out most of the star's light,
making the surface, if there is one, very eerie and dark.
So while we don't have direct observations of ocean planets there's nothing in planetary science that says they couldn't exist
and we have pretty good evidence that they should.
So Kamino, Ahch'to, and Scarif are quite possible.
Lama Su: Magnificent.
Another planet which is almost a water world is Dagobah, where Master Yoda makes his home
The whole planet is one massive swamp teeming with life, which implies that the planet is almost completely flat, and waterlogged.
In fact the Wookieepedia page for Dagobah says that the planet is volcanically dead,
with only small remnants of any tectonic activity remaining, such as the smoothed down remains of Mount Yoda.
Really?
Yoda: [laughs]
We think of planets as being geologically active because that's what the Earth is like:
constantly shifting and changing thanks to continental drift and new land
being formed by volcanic action. But that tectonic activity can just stop.
Similar to Jakku this is what we think happened on Mars. There are plenty of features
such as the huge Valles Marineris and Olympus Mons which indicate that there
was tectonic activity in the past, but as the planet cooled the molten rock
between the tectonic plates solidified and the planet became volcanically dead.
It seems like the same thing happened on Dagobah so it could exist.
This leaves us with three final planets which are truly weird:
Utapau, Mygeeto, and the invitingly named Starkiller base
Utapau is a really odd one.
It's very similar to Earth in terms of the composition and size but all the oceans
have drained through holes which used to be magma chambers leaving the planet
barren and covered in sinkholes with subsurface oceans
There are a few problems with this.
I actually got a friend of mine with a PhD in geology to
look at Utapau and he sent me a very long, angry message about how, quote
'geologically and physically wrong it is'
Firstly the water wouldn't be able to drain through holes that used to be magma chambers,
because magma chambers either erupt and have the rocks above them collapse, forming a caldera,
or as is more likely have their contents solidify and freeze into very hard rock
Secondly even if all the water in the oceans were to drain subsurface if Utapau
is anything like Earth then temperatures will increase below the
surface by about 30 Celsius per kilometer that you go down
So a subsurface ocean would exist either a steam or a supercritical fluid and
because either would be less dense than the surrounding rock it would rise to
the surface as geysers or other geothermal activity
Which would make for a really cool planet
but not what we're shown in the films
So in short there are a number of problems with Utapau
Tion Medon: Thousands
Next, Mygeeto is a freezing planet similar to Hoth but the interior has completely
cooled and left the planet volcanically dead
The surface is covered with huge crystals of all different kinds
We've already seen with Hoth and Dagobah that planets can be extremely cold and can be geologically inactive,
so those features on Mygeeto are fine
The massive crystals are one of those cases where we might have to allow artistic license
We know that huge crystals can form on Earth under the right conditions
such as the cave of crystals in Mexico
So given exactly the right set of conditions Mygeeto could probably exist
Then lastly we have Starkiller base: a planet that was hollowed out and turned into a
weapon that keeps the power of a star inside itself
In terms of the laws of physics...
Han Solo: that's not how the force works
Chewbacca: [I'm cold]
I think we just have to give them some creative license with that one
So of the 28 planets and moons, we reckon that only five
couldn't exist in the real world, with some big uncertainties on some of the others
But none of the worlds in Star Wars come even close to real
planets we've seen around other stars
Out of the thousands of exoplanets that have been discovered
none surprised people like the planets we now called hot Jupiters
They're gas giants the size of Jupiter that orbit their stars closer than mercury does to the Sun
and almost all orbiting in under five days
These giant planets are so close to their stars that they're often
hotter than you would be sitting under a rocket as it took off
and that does funky things to an atmosphere
One such hot Jupiter has high speed winds
whipping around over 5000 miles an hour with cloud droplets made of molten glass
Another has clouds that are likely formed at the same substance that makes up rubies and sapphires here on Earth
But it's not just the giant planets that have surprised us
The planetary system around the star Trappist-1 has seven earth sized planets
orbiting it in such a tight configuration that if life were
to exist there and reached our level of technology,
planet hopping would be an easy holiday destination
So while science fiction might be strange,
it's got a long way to go before it becomes even stranger than science fact
Thank you for watching this video! In making it Dr. Wakeford and I have
made use of very real science to tackle science fiction including tools from
astrophysics, atmospheric physics, and the study of exoplanets
Now that I've submitted my thesis I have more time to make science videos like this one which is
hopefully piqued your interest in the science of planets and of atmospheres
But if you really want to understand those concepts the only way to do that
is to tackle some problems yourself
During my PhD I found that I didn't
understand the topic fully until I'd actually tried it myself and done some problems
If you'd like to support science videos on this channel then
go to Brilliant.org/SimonClark (and I'll put that down in the description)
where you can sign up for brilliant for free, and in addition to that
the first 200 people to use that link will get 20% off their annual premium subscription
Huge thanks to Dr. Wakeford for agreeing to be in this video
If you'd like to check out her research or the card game about
female scientists through history which we made together then check the links in the description
Sheev: Do it.
Thanks also must go to my friends Tom Dowling, and newly Dr. David Arnold
for their help with the script
As well as checking out Brilliant.org/SimonClark
if you'd like to learn more about the science of ice on Earth
and indeed other planets then check out the link on the screen
and in the description to the Crash Course which Dr. Dowling and I are currently making on this channel
Lastly though thank you again for watching
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Thank you for watching, I'll see you next time