Even though Neptune is thirty times further
from the Sun than Earth, cold and dimly lit, itās still thousands of times closer to
us than the nearest stars. And yet, it may turn out to be a great place
to live and a gateway to those stars. So today we return to the Outward Bound series
to look at how weād go about colonizing Icy Giants like Neptune. Weāve looked at colonizing gas giants before,
but mostly in the context of colonizing their moons, and not so much the planets. Ice Giants like Neptune and Uranus are very
common in the Universe - as best as we can tell - and arenāt actually that much more
massive than Earth, generally only being 10 to 20 times as massive. Not like the bigger Jovians which are many
hundreds or even thousands of times larger. Indeed their surface gravity, for a given
value of āsurfaceā, is pretty close to Earthās own. Uranus has 89% of the Gravity Earth does,
and Neptune has 114% of Earthās gravity. Only Venus is closer, at 90%, and it is in
some ways harder to colonize than either of these two planets. Akin to the Venusian sky cities, we could
possibly build cities which float in Neptuneās atmosphere; this, however, would be much more
challenging to pull off because the windās on Neptune are murderous. Even on the planet Uranus - which has lower
wind speeds in certain spots due, presumably, to this planet being tilted on its side - high
wind speeds would still be a big problem. They are also potentially a source of massive
power though. Wind is tricky on Earth due to speeds ranging
from useless to hurricane force. You wouldnāt use a classic windmill on places
like Neptune though, youād use something closer to a jet turbine. Power is a pretty big issue for these outer
planets because the sunlight just isnāt strong enough so far from the Sun to be a
viable way to power an entire colony. These planets arenāt dark though, they get
lighting on par with what youād expect in a room lit by normal light bulbs. We have some alternatives though. We could also beam power out as we discussed
in the Power Satellites episode a couple months back. As already mentioned, we can tap the atmosphere
for wind power, as well as the Nuclear Option. But what we really want is fusion, especially
for these two planets as they have large stockpiles of Helium-3, the preferred fusion fuel for
aneutronic fusion. We will discuss why aneutronic fusion is seen
as better than normal fusion in a moment. I mention the other power sources just to
make it clear we have alternatives even if we never achieve portable fusion, but Uranus
and Neptune in particular are both places weād be most likely to hold off fully colonizing
until we either did have it or knew it wasnāt in the cards. So letās follow an intrepid traveller on
a journey to colonize Neptune. It is the year 2400 and while Uranus has some
basic stations on its moons already, Neptune only has a few small scientific outposts in
its atmosphere and on its largest of 14 moons Triton, the coldest object in our solar system. Weāre colonists leaving from Earth on board
a colonization fleet thatās the first to feature fully functional aneutronic fusion
drives, and as those rely on helium-3 for fuel, establishing some big Helium-3 refineries
in the outer solar system is high on everybodyās list. Weāve had fusion technology for a while
but they are big and clunky power plants, and while those improved, they never got too
good at powering ships. The problem with typical neutronic fusion,
like that using deuterium and tritium, is that most of the energy from that fusion event
is in neutrons, and these are hard to tap for energy and do a lot of damage to whatever
containment system you are using. Aneutronic fusion is exactly that, fusion
that doesnāt produce many neutrons, but instead mostly stable and charged particles,
which should be easy to get electricity from. Aneutronic fusion is far harder to do, but
represents probably the best path to relatively compact and lightweight fusion reactors, like
the kind weād like to use in spaceships or small colonies, places where mass and size
matter a lot, and probably maintenance too. Someone went through the difficulties in inventing
one, which opened the gates for us to the outer solar system. Not just Uranus and Neptune, but all of the
Kuiper Belt, which is vastly larger and more massive than the Asteroid Belt, and indeed
it even opens the gates to the Oort Cloud and other solar systems beyond. We now have a ship engine able to produce
a significant thrust for days or even weeks at a time. Our Neptune Colonizing Fleet will burn out
toward Neptune at .2-gee for half the trip, then flip over and burn down, arriving 5 weeks
after our departure from Earth, and reaching a maximum velocity of 1% light speed. Like in the Expanse, we can use constant acceleration
in place of rotating sections to provide gravity, though in this case, just a little better
than Moon gravity. But for a 5 week trip, thatās fine. Now as weāve noted before, this constant
acceleration approach is not usually a good one since it is very fuel wasteful. By preference, youād accelerate faster but
not for as long, cruise, then flip over and burn down to stop. However, in this case it is okay because fuel
and propellant donāt matter too much because thatās the hypothetical maximum acceleration
out of this style of fusion drive, .2-gee, and thatās probably being optimistic. So we just burn the whole time because itās
not that long a trip. And indeed we are quite capable of handling
a much higher acceleration, as we are not exactly human. The fuel is fairly rare but the propellant,
hydrogen in this case, is very common so we can blow it like it was going out of fashion. If we could accelerate faster we would, and
weāll talk about how we might later, but fusion drives and high-thrust donāt work
well, at least not if you want a high final speed. Weād like to be able to do a full-gee, like
we were standing on Earth, and in truth weād like to do more and we could handle a much
higher acceleration. This is the 25th century after all, and weāve
been picked to command this fleet because we are an experienced traveler and colonist. Few people in the solar system have been to
as many of humanityās new worlds as we have and weāve made a career of colonizing planets
over the centuries. And weāve become more than a bit of cyborg
in that time. Long gone are the days of roughing it or making
small outposts to slowly grow. Our fleet is carrying state of the art expandable
rotating habitats with it, huge amounts of colonial gear, and most of those ships will
be immediately departing to either pick up tens of thousands of more colonists from Earth
or race off to the massive factories of the Belt, Titan, and the Jovian Moons to pick
up more equipment. Weāll need it too, because while weāll
be temporarily housing people in those rotating habitats in orbit of Neptune, we are going
to be building massive refining facilities right inside of Neptuneās atmosphere. Indeed, it is going to be the single largest
construct humanity has ever created. It will even outstrip the Orbital Rings of
Earth. After all, those refining facilities are going
to be similar to those rings, but Neptune is a lot bigger than Earth. See thereās a lot of ways to mine gas from
a gas giant. You can dive down and scoop it up for instance. But we are going to do this with the biggest
bucket wheel excavator in the galaxy, namely a giant ellipsoid orbital ring which, incidentally,
looks like a chainsaw, a chainsaw fit for a god like the one the planet is named after. Neptuneās Chainsaw. This is the 25th century we donāt do space
colonization small or on shoestring budgets anymore. Billions of people live and work in space,
and factories the size of small moons convert megatons of ore into products every day. Ships that dwarf the biggest oil supertanker
crawl across the solar system delivering goods and soon they will sprint, not crawl, as superior
engines permit them to race across the void, fueled by the near-endless stockpiles of helium-3
on Neptune and the other gas giants. For now, many of those ships are carrying
out segments of Neptuneās Chainsaw for assembly, and many of our passengers are not colonists
at all, but folks traveling to view the historic event, the colonization of the last planet
in the solar system. Truth be told, we find their presence rather
irritating, standing around gawking and getting in the way, but this mission requires a lot
of resources and backing and spectators were part of the cost for that. One of them, on the younger side, asks us
why it is such a historic event. We explain, until now humanity has been essentially
limited to using either stuff like uranium or thorium for fast ships, or dependent on
powerful energy beams from huge collectors near the Sun. Those work, and energy beaming from the Sun
is actually quite efficient and part of this expedition will be making that system even
more useful, but ultimately we were dependent on those. We couldnāt make massive amounts of power
locally and in a compact way. In a generation or two, a small colony will
be able to buy its own aneutronic reactor, cheaply fill a tank with helium-3 and deuterium,
and have a reliable local power source. With fusion, and some decent local manufacturing
ability, they can set up anywhere they want, even way out in the Oort Cloud, and only need
infrequent refueling. Nobody can threaten to jack up their power
beaming rates or cut them off, a single tanker of what Neptune will soon produce will let
a colony last centuries or even millennia without needing any new fuel. āBut why is the Chainsaw going to be shaped
funny? Elliptical, not circular, like Earthās orbital
rings?ā our passenger asks. Orbits come in many forms, including some
rather peculiar ones, almost every natural orbit is an elliptical one. If you can make a stable orbit, you can make
an orbital ring that matches that orbit. You can even make some that wouldnāt normally
be possible. Our goal, for the Neptunian Chainsaw, is to
have an elliptical one that drops down into the atmosphere on its low portion and rises
high up afterward. We will scoop gases up in big buckets which
will enter the ringās Transport System and be shoved along, refined as it goes for what
we want, and raced up to fill tanker ships. Now we have options like this for Earth too. You could put two big circular rings around
Earth connected by a third elliptical one. Indeed, that would keep the low portion of
the ring just over the atmosphere and lower tethers down to suck up air. But whatās interesting about Neptune is
that its gravity is higher than Earthās, if not by a lot, and on that upper portion
of the ring it will be a bit lower. We can build domes on those sections with
normal gravity and still get protection from micrometeors and radiation by the thinner
atmosphere up there. Meteor protection matters too since all of
the gas giants have rings of debris around them - even though theyāre not as big as
Saturnās - and thus have a lot of meteors. While thereās not enough light there to
grow most natural plants, it is enough to comfortably see by, though Neptuneās day
is only 16 hours long, so you would want supplemental lighting. Fortunately there is an effective near-infinite
power supply right below. And Triton is almost as large as our moon
and can provide plenty of construction and manufacturing materials after weāve consumed
itās tiny siblings. Triton is the last and smallest of the large
moons in our solar system and actually has more mass than all other Neptunian moons smaller
than itself combined. If you head down deeper into Neptuneās atmosphere,
itās got interesting layers of clouds. Clouds on Earth are made of water, but clouds
on some other planets can be made of methane, ammonia or sulfuric acid instead. Neptune though is thought to have many different
layers of clouds made of different things as you go down. Neptune and Uranus - which are small gas giants
but which you can also think of as Ice Giants - have a lot more volatiles proportionally
than Jupiter has for instance. Volatiles, things like nitrogen, water, carbon
dioxide, ammonia, methane and sulfur dioxide, are always of interest to us, and if weāre
willing to dive deeper down, we can find clouds of them for harvesting. We often think of mining space for metals,
precious ones like gold or ones for construction, but these chemicals we need as the basic building
blocks for life itself are very precious. Triton is also a good source for volatiles
and its surface is covered with these ices; but since demand is growing and since mining
that ice is more difficult than just scooping or pumping it up, it would still be advantageous
and indeed preferable to mine such volatiles from Neptuneās atmosphere. Now, we have a few ways to get down to those
deeper levels. The first of course is to suspend yourself
from a tether, hanging from Neptuneās Chainsaw - the orbital ring system that encircles Neptune
which we discussed earlier. The second would be to fly down in some interesting
mixture of plane and submarine. The third would be from a balloon or even
a giant turbine. A problem with using balloons on gas giants,
as opposed to Venus, is that they are mostly hydrogen with a bit of helium, our two preferred
lifting gases. You canāt use something as a lifting gas
inside an atmosphere composed of that, on Venus we can even use oxygen as one because
the atmosphere is made of denser gases. But Neptune is almost 20% helium, so we could
use pure hydrogen, likely in plentiful supply as you refine out the helium and helium-3. And you can heat it too since weāve got
access to power. Or you can just run a giant engine and coast
along with the terrifying winds. But you could also keep yourself pressurized
like a submarine and drop deeper instead, to where youād be buoyant. Hanging down from tethers seems rather neat
though, and since the Sun isnāt really your source of light, thereās no need to build
flat. You donāt have to make your Orbital Ring
wider to support more domes, though you can. Instead you just build up or down from it
or another supported platform. Hanging down is as structurally sound as building
up like a skyscraper; the only difference is that one relies on tensile strength whereas
the other relies on compressive strength. So you could have hanging cities, lighting
themselves, suspended over Neptune and down into its atmosphere. Cities, glowing in the dim dusky light, hanging
down like immense chandeliers. Chandelier cities. A book series Iām fond of, Gregory Benfordās
Galactic Center Saga, references Chandelier Civilizations at one point but I never got
a description of them, Iāve always wondered if this is what he had in mind. I should ask him one day, but regardless we
shall call these Chandelier Cities and theyāre ideal for Ice Giants. I imagine theyād be absolutely stunning
to approach by plane, hanging there among the clouds and storms. But the atmosphere, while it gets much denser
as we go deeper, is not the majority of Neptune. Indeed it has a very large mantle which is
perhaps a dozen times more massive than the entire Earth and which is composed mostly
of the ices that make us call it an Ice Giant. With all that water, ammonia, and methane
ice, it is massively rich in the building blocks we need for artificial ecosystems. Getting down there to mine it would be tricky. But active support, like our orbital rings,
can be used to make stuff much stronger against crushing too. However, itās quite likely it rains diamonds
down there and we could get quite deep just relying on strong materials. Because of this weād be able to harvest
a lot of that diamond and possibly other materials. Or even get to live in diamond hard domes
deep down in Neptune. I should note, though we always hope the future
will be peaceful, that these sort of buried colonies, hidden and shielded by huge atmospheres,
are good places to live during conflicts. For that same reason, you could see a lot
of rotating habitats bury themselves deep under ice or rock in asteroids and comets,
or import a lot of hydrogen and helium not just as a long term fuel supply but additional
shielding, they can wrap their habitat in cheap tanks of gases. Itās hard to drill deep into the Earth not
just because of the pressure but the rising temperature; but itās not as bad inside
Neptuneās mantle as it is in Earthās. Eventually there is a core - which is essentially
a rocky planet all its own down there - but youād probably have to remove that atmosphere
to get to it. Weāll talk more about mining planetary mantles
and cores in our Earth 2.0 series, which will start next month. For Ice Giants in other solar systems, ones
nearer their Sun, as some might well be, you might blow that atmosphere off and use it
like a rocket flame to push the planet into its sunās habitable zone, and be left with
a rocky planet when youāre done which is ready for terraforming. For this we can employ the Fusion Candle we
discussed in Colonizing Jupiter. Weāre not expecting to do that with Neptune
though. The long term plan is just to build more Neptunian
chainsaws and regular circular but wider orbital rings around it till we encompass the whole
planet. This is something we call a Shell World, and
we discussed it in more detail in the Mega Earths episode. Even for an advanced civilization living in
the 25th century, building a shell world around Neptune would take a really long time, but
it can be done incrementally. Just adding more rings and chandelier cities
till you encompass the whole planet, then add dirt and water and lighting, potentially
Sun-Moons orbiting once a day, vast fusion satellites producing light. We have a power supply for that and such an
enormous construction project and as we mine Neptuneās atmosphere and mantle, we can
slowly contract those rings and, therefore, contract the shell world too, keeping it to
a size that provides normal Earth gravity. Incidentally, even if you eventually expanded
your orbital rings to make a complete Shellworld, you could keep those Chandelier Cities we
mentioned earlier hanging down under the shell. They might also work very well on planets
or moons with icy shells over deep oceans, like Europa. Neptuneās own moon Triton might have a subsurface
ocean too. There is a lot of gas on Neptune, and it raises
the question: What would we do with it all? For that matter, with Uranus being closer,
and maybe easier to mine with its lower winds, who is buying our Helium-3? Well, first, the Helium-3 concentration on
Neptune is 19 parts per million which is a little higher than Uranusās 15 parts per
million Helium-3 concentration. But second, in a fusion economy, that extra
distance to Neptune from the inner solar system, as opposed to Uranus, is actually fairly irrelevant. Indeed parts of the asteroid belt will sometimes
be as close to Neptune as Uranus and this difference in distance doesnāt much matter
anyway. Itās a minor amount of delta-v compared
to the energy that fuel contains. Tankers carrying helium-3 and Deuterium would
still move slow. It wonāt spoil and has a high energy density
so there is no reason to move it quickly and waste energy or capital on very large engines. Moreover though, weāll be seeing a lot more
people moving to the outer solar system now, particularly the Kuiper Belt, where land is
cheap and plentiful - but theyād have to bring their own sunlight. And as rarely as one would need to bring in
fusion fuel, folks can wait a couple centuries till Neptune is close to them again on its
own long orbit to refuel themselves. But when asked, our traveler, admiral of this
colonial fleet and figurehead governor of Neptune, says that it is really all about
ships, and not just ones with aneutronic fusion drives. See, you can bounce a laser off a sail and
make it go further away or even off to a side, by tilting the sail to bounce the light at
an angle. But you canāt move just sideways, or inward
toward the Sun, not by bouncing alone. What you can do though is bounce a beam off
something further out, and bounce it back in at your light sail, pushing you back inward
toward the Sun. The problem is, if you stick a mirror further
out than your ship, you will push it away eventually. So it helps to have that mirror on something
that is massive enough for the recoil to be negligibly small. Ice Giants and their Moons are perfect for
this, as are larger icy bodies in the Kuiper Belt. They can also emit their own beams, rather
than bounce, if they have a power source. Had nobody invented good, cheap aneutronic
fusion, we could have gone about colonizing the outer solar system this way. Beaming energy out from massive solar collectors
near the Sun and using those, bounced back, to push ships inward, and to power these cold
lonely pushing stations. Even with fusion though, itās still a nice
path, because it means ships need not rely entirely on onboard fuel and propellant. Indeed, the combination of the two will allow
even better and safer and cheaper interplanetary travel. We said that this sort of fusion drive really
only permitted a maximum acceleration of .2 gee, and there are ways that could perhaps
be boosted, but it could pull that while getting beamed energy, or even beamed propellant,
out to the ship. So youād get laser highways inside a solar
system folks could use to supplement their engine, but they could still operate without
them too. It would be like jumping in the fast lane,
and gives the benefits of both systems while removing many of the limitations of, and dependance
on, each. Our traveler turned admiral turned governor
though has even bigger plans than Chandelier Cities, Planetary Chainsaws, Shellworlds,
and giant mirrors. Indeed even plans beyond colonizing the Kuiper
Belt and Oort Cloud. Our governor plans to colonize the Stars themselves. He tells our young tourist that one day the
Moons of Neptune will be giant shipyards, turning out colonial fleets to head out to
the stars themselves, Armadas that will be built here and launch, not out to the stars,
but in toward the Sun, pushed by beams toward it and then sail past, pushed even faster
by stellasers near the Sun, running up to decent fractions of light speed then back
out again, ever faster, pushed on till they reach the Kuiper Belt and then pushed even
more, from relays and lasers out there. Then they will cruise along ahead, massive
interstellar arks lit and warmed by fusion reactors, sailing off to yet more distant
homes. Neptune, we tell our young passenger, will
be the gateway to the deep ocean of outer space, the last big port of call, and it may
be big indeed. With vastly more size and resources than Earth,
with a near endless source of power, with all those moons and its own rings and Kuiper
Belt nearby, it could become a massive kingdom fit for its namesake. If our young passenger returns to Neptune
when theyāre an adult, theyāll see a growing empire that they can reach in just a couple
weeks travel, and quite cheaply. Itās an empire the governor himself will
never lead. Once itās built up enough to build its own
fleets for interstellar travel, he means to be on one of those, and tells our young passengers
he hopes theyāll join one themselves one day. The solar system is now a much bigger place,
opened up far past the asteroid belt for settlement, but itās just a tiny corner of a vast galaxy. While not the last frontier of our solar system,
Neptune is the last truly big one, and itās fitting it should serve as the gateway to
the stars. So this is not the end of the Outward Bound
series; we still have a lot of solar system to explore, not to mention other systems,
and some places closer to home to revisit like the Moon or Mars. However, while we continue our look at the
ships that will get us to those other star systems, weāre going to take some time to
talk about colonizing a bit closer to home than even our Moon. In the upcoming Earth 2.0 series weāll be
looking at colonizing our oceans and frigid poles and deserts and mountains and how we
can use the technology weāve discussed in this series to do it. We talked a lot about Orbital Rings today
and structures hanging down from them, our Chandelier Cities. A lot of times we suggest structures folks
arenāt used to and can seem less safe as a result, even though they are often more
structurally sound than things we use all the time. Ultimately they use the same structural mechanics
as a Suspension Bridge, so do the rotating habitats we often discuss. Most folks are comfortable with those because
theyāre familiar, but if youāre curious about the mechanics involved, so you can understand
why a city hanging down from an orbital ring is as safe or even safer than a skyscraper
or your house, Iād suggest trying out Brilliant's course āInfrastructureā. As part of their Physics of the Everyday courses,
Infrastructure has some great quizzes on bridges and skyscrapers, and like all their quizzes,
theyāre meant to keep teaching, not just evaluate knowledge. The future is going to be a place of vast,
awe inspiring structures that dwarf anything we have now, and if you want understand them
and the challenges to building them, the Infrastructure course is a great way to do that. If youāre interested in learning more math
and science, and doing so at your own pace, you can go to brilliant.org/IsaacArthur and
sign up for free. And also, the first 200 people that go to
that link will get 20% off the annual Premium subscription
So as mentioned weāll be talking about colonizing Earth soon and weāll start that off with
a look at Seasteading and making artificial islands in two week, then moving on to Colonizing
the Oceans after that. First though, weāll be exploring the human
mind and talking about mind control and brainwashing, and our book of the month, George Orwellās
dystopian classic, ā1984ā Make sure to subscribe to the channel for
alerts when those episodes come out, and since this episode happens to be coming out on my
birthday, I will shamelessly guilt everyone with that before asking you to please like
this video and share it with others, it also happens to be the fourth anniversary of the
channel, and its original pilot episode. If you want to help support the channel on
Patreon, you can find a link to that in the episode description below, along with our
facebook and reddit groups, if you want to discuss this topic more. And should you visit those, Iād be curious
what other places youād like this series to visit, when we return to it. Until next time, thanks for watching, and
have a great week!
Someone make a heavy metal band right now based on Neptune's Chainsaw.
And someone make some Metal Art with Neptune/Poseidon and the Chainsaw (could also be a chain sword like from Space Marines or Chainsaw Warrior).
I really loved the chandelier cities concept, they would look amazing!
Thank you for making this series Isaac, I get so optimistic about our future after watching your videos.
re: specific date, any time you hear me refer to the 25th century, it's usually a Buck Rogers hat-tip :) not an actual time estimate.
Wow. Best one yet. These are becoming almost like mini sci-fi stories.
found this 23 seconds aftr it was published. Yes!
1:23 "Venus is harder to colonize than uranus and neptune" what??
"but neptune is hard due the high winds" what??
Why a floating habitat would have any issue being in the atmosphere of venus or neptune or any other atmosphere? First.. lets define what "wind" is.. We call wind to the speed of gases with respect to something. If we are floating.. this mean that our apparent wind is zero, because we are not anchored to a ground, or using propulsion to generate a speed differential with our medium. That is why you can be in a balloon on earth traveling in the jet stream and feel NOTHING., because there are no winds.
Then, wind speed on gas giants is measured with respect to the rotation speed, they are super slow in comparison to their size, you may have a atmosphere layer or certain latitude of the planet atmosphere is moving a bit faster or slow than other layers, but those layers are hundreds or thousands of km apart, it would be impossible to notice any turbulence or "wind" changing between one to the other.Gas giants had massive atmospheres that dilute any of those variations and they receive almost no energy from the sun, which is what causes winds, another cause of winds is due different light absorption index (soil, water, vegetation, clouds shadows, etc) which produce a pressure differential that generates the wind.. You almost not have that on gas giants or venus.
There are many misconceptions in the Venus video too, but well, I imagine the work it takes you to make each video with all the those 3d animations. So next time, try to think a bit more on the topics and use the common sense before just translate "wind" from wikipedia to what you experiment as wind here on earth fixed to the ground.
How can an elliptical orbital ring be stable? As you get closer/further from the planet, the velocity would be constantly changing. You could have isolated buckets all in the same orbit, but the distance between them will vary wildly between the highest and lowest points such that there is no way to connect them. Some kind of winch that operates at orbital velocities seems unfeasible.
There is a claim in the video that you can't use light to push objects inward from the Sun but I'm not sure it's true.
Orbits are elliptical and when an object is past perihelion and moving closer to the sun you can shine light at an angle that causes the net force to be retrograde. While this is not very efficient it should cause the object to effectively lower it's orbit. Even for perfectly circular orbits it's possible to shine light in a way that has a major retrograde component.
This doesn't even depend on beamed propulsion, it's just the mechanics of solar sails. Aren't there designs for going to the inner planets, like IKAROS?
The timeline is a change. I believe this is the first time we got any dates.
The first Neptune ring is launched in 2400. What year is the first Orca born in the Alpha Centuari system?