18 November 2016
Colonizing the Inner Solar System
Inner Solar System
Science fiction has told us again and
again, we belong out there, among the stars.
But before we can build that vast
galactic empire, we've got to learn how to just survive in space.
Fortunately, we happen to live in a Solar System with many worlds,
large and small that we can use to become a space-faring
This is half of an epic two-part article
that I'm doing with Isaac Arthur, who runs
an amazing YouTube channel all about futurism, often about the
exploration and colonization of space. Make sure you subscribe to
This article is about colonizing the
inner Solar System, from tiny Mercury, the smallest planet, out to
Mars, the focus of so much attention by Elon Musk and SpaceX.
other far below article, Isaac will talk about what it'll take to
colonize the outer Solar System, and harness its icy riches. You
can read these articles in either order, just read them both.
At the time I'm writing this, humanity's
colonization efforts of the Solar System are purely on Earth. We've
exploited every part of the planet, from the South Pole to the
North, from huge continents to the smallest islands.
There are few places we haven't fully
colonized yet, and we'll get to that.
But when it comes to space, we've only
taken the shortest, most tentative steps. There have been a few
temporarily inhabited space stations, like,
Our first and only true colonization of
space is the International Space Station, built in collaboration
with NASA, ESA, the Russian Space Agency and other countries. It has
been permanently inhabited since November 2nd, 2000.
Needless to say, we've got our work cut
out for us.
NASA astronaut Tracy
an Expedition 24
flight engineer in 2010,
took a moment during
her space station mission to enjoy
an unmatched view of
home through a window in the Cupola
of the International
Space Station, the brilliant blue and white part of Earth
glowing against the
blackness of space.
Before we talk about the places and ways humans could colonize the
rest of the Solar System, it's important to talk about what it takes
to get from place to place.
Just to get from the surface of Earth into orbit around our planet,
you need to be going about 10 km/s sideways. This is orbit, and the
only way we can do it today is with rockets.
Once you've gotten into Low Earth Orbit, or LEO, you can use more propellant to get to other
If you want to travel to Mars, you'll need an additional 3.6 km/s in
velocity to escape Earth gravity and travel to the Red Planet. If
you want to go to Mercury, you'll need another 5.5 km/s.
And if you wanted to escape the Solar System entirely, you'd need
another 8.8 km/s. We're always going to want a bigger rocket.
The most efficient way to transfer from world to world is via the
Hohmann Transfer. This is where you raise your orbit and drift out
until you cross paths with your destination. Then you need to slow
down, somehow, to go into orbit.
One of our primary goals of exploring and colonizing the Solar
System will be to gather together the resources that will make
future colonization and travel easier. We need water for drinking,
and to split it apart for oxygen to breathe.
We can also turn this water into rocket
fuel. Unfortunately, in the inner Solar System, water is a tough
resource to get and will be highly valued.
We need solid ground to build our bases, to mine our resources, to
grow our food, and to protect us from the dangers of space
radiation. The more gravity we can get the better, since low gravity
softens our bones, weakens our muscles, and harms us in ways we
don't fully understand.
Each world and place we colonize will have advantages and
disadvantages. Let's be honest, Earth is the best place in the Solar
System, it's got everything we could ever want and need.
Everywhere else is going to be brutally
difficult to colonize and make self-sustaining.
We do have one huge advantage, though. Earth is still here, we can
return whenever we like. The discoveries made on our home planet
will continue to be useful to humanity in space through
communications, and even 3D printing.
Once manufacturing is
sophisticated enough, a discovery made on one world could be mass
produced half a solar system away with the right raw ingredients.
We will learn how to make what we need, wherever we are, and how to
transport it from place to place, just like we've always done.
imaged by the MESSENGER spacecraft,
revealing parts of
the never seen by human eyes.
NASA/Johns Hopkins University
Laboratory/Carnegie Institution of Washington
Mercury is the closest planet from the Sun, and one of the most
difficult places that we might attempt the colonize.
Because it's so close to the Sun, it
receives an enormous amount of energy. During the day, temperatures
can reach 427°C, but without an atmosphere to trap the heat, night
time temperatures dip down to -173°C.
There's essentially no atmosphere, 38%
the gravity of Earth, and a single solar day on Mercury lasts 176
Mercury does have some advantages, though. It has an average density
almost as high as Earth, but because of its smaller size, it
actually means it has a higher percentage of metal than Earth.
Mercury will be incredibly rich in metals and minerals that future
colonists will need across the Solar System.
With the lower gravity and no atmosphere, it'll be far easier to get
that material up into orbit and into transfer trajectories to other
But with the punishing conditions on the planet, how can we live
there? Although the surface of Mercury is either scorching or
MESSENGER spacecraft turned up regions of the
planet which are in eternal shadow near the poles.
In fact, these areas seem
to have water
ice, which is amazing for anywhere this close to the Sun.
Mercury's northern polar region,
You could imagine future habitats huddled into those craters,
pulling in solar power from just over the crater rim, using the
reservoirs of water ice for air, fuel and water.
High powered solar robots could scour the surface of Mercury,
gathering rare metals and other minerals to be sent off world.
Because it's bathed in the solar winds, Mercury will have large
Helium-3, useful for future fusion reactors.
Over time, more and more of the raw materials of Mercury will find
their way to the resource hungry colonies spread across the Solar
It also appears there are lava tubes scattered across Mercury,
hollows carved out by lava flows millions of years ago. With work,
these could be turned into safe, underground habitats, protected
from the radiation, high temperatures and hard vacuum on the
With enough engineering ability, future colonists will be able to
create habitats on the surface, wherever they like, using a
mushroom-shaped heat shield to protect a colony built on stilts to
keep it off the sun-baked surface.
Mercury is smaller than Mars, but is a good deal denser, so it has
about the same gravity, 38% of Earth's.
Now that might turn out to be just fine,
but if we need more, we have the option of using centrifugal force
to increase it. Space Stations can generate artificial gravity by
spinning, but you can combine normal gravity with spin-gravity to
create a stronger field than either would have.
So our mushroom habitat's stalk could have an interior spinning
section with higher gravity for those living inside it.
You get a big mirror over it, shielding
you from solar radiation and heat, you have stilts holding it off
the ground, like roots, that minimize heat transfer from the warmer
areas of ground outside the shield, and if you need it you have got
a spinning section inside the stalk.
A mushroom habitat...
spacecraft in 1978.
Venus is the second planet in the Solar System, and it's the evil
twin of Earth.
Even though it has roughly the same
size, mass and surface gravity of our planet, it's way too close to
the Sun. The thick atmosphere acts like a blanket, trapping the
intense heat, pushing temperatures at the surface to 462°C.
Everywhere on the planet is 462°C, so there's no place to go that's
cooler. The pure carbon dioxide atmosphere is 90 times thicker than
Earth, which is equivalent to being a kilometer beneath the ocean on
In the beginning, colonizing the surface of Venus defies our
ability. How do you survive and stay cool in a thick poisonous
atmosphere, hot enough to melt lead?
You get above it.
One of the most amazing qualities of Venus is that if you get into
the high atmosphere, about 52.5 kilometers up, the air pressure and
temperature are similar to Earth. Assuming you can get above the
poisonous clouds of
sulfuric acid, you could walk outside a
floating colony in regular clothes, without a pressure suit.
need a source of breathable air, though...
Even better, breathable air is a lifting gas in the cloud tops of
Venus. You could imagine a future colony, filled with breathable
air, floating around Venus. Because the gravity on Venus is roughly
the same as Earth, humans wouldn't suffer any of the side effects of
In fact, it might be the only place in
the entire Solar System other than Earth where we don't need to
account for low gravity.
Artist's concept of a
Venus cloud city
- a possible future
outcome of the
High Altitude Venus
Operational Concept (HAVOC) plan.
at NASA Langley
Now the day on Venus is incredibly long, 243 earth days, so if you
stay over the same place the whole time it would be light for four
months then dark for four months.
Not ideal for solar power on a first
glance, but Venus turns so slowly that even at the equator you could
stay ahead of the sunset at a fast walk.
So if you have floating colonies it would take very little effort to
stay constantly on the light side or dark side or near the twilight
zone of the terminator. You are essentially living inside a blimp,
so it may as well be mobile. And on the day side it would only take
a few solar panels and some propellers to stay ahead.
And since it is so close to the Sun,
there's plenty of solar power.
What could you do with it?
The atmosphere itself would probably serve as a source of raw
materials. Carbon is the basis for all life on Earth. We'll need it
for food and building materials in space. Floating factories could
process the thick atmosphere of Venus, to extract carbon, oxygen,
and other elements.
Heat resistant robots could be lowered down to the surface to gather
minerals and then retrieved before they're cooked to death.
Venus does have a high gravity, so launching rockets up into space
back out of Venus' gravity well will be expensive.
Over longer periods of time, future colonists might construct large
solar shades to shield themselves from the scorching heat, and
eventually, even start cooling the planet itself.
Earth as seen on July 6, 2015
from a distance
of one million miles
by a NASA
scientific camera aboard
the Deep Space
Climate Observatory spacecraft.
The next planet from the Sun is Earth, the best planet in the Solar
One of the biggest advantages of our
colonization efforts will be to get heavy industry off our planet
and into space. Why pollute our atmosphere and rivers when there's
so much more space… in space.
Over time, more and more of the resource gathering will happen off
world, with orbital power generation, asteroid mining, and zero
gravity manufacturing. Earth's huge gravity well means that it's
best to bring materials down to Earth, not carry them up to space.
However, the normal gravity, atmosphere and established industry of
Earth will allow us to manufacture the lighter high tech goods that
the rest of the Solar System will need for their own colonization
But we haven't completely colonized Earth itself. Although we've
spread across the land, we know very little about the deep ocean.
Future colonies under the oceans will help us learn more about
self-sufficient colonies, in extreme environments.
The oceans on Earth will be similar to
on Europa or Enceladus, and the
lessons we learn here will teach us to live out there.
As we return to space, we'll colonize the region around our planet.
We'll construct bigger orbital colonies in
Low Earth Orbit, building
on our lessons from the
International Space Station.
One of the biggest steps we need to take, is understanding how to
overcome the debilitating effects of microgravity: the softened
bones, weakened muscles and more.
We need to perfect techniques for
generating artificial gravity where there is none.
A 1969 station concept.
The station was to
rotate on its central axis
to produce artificial
The majority of early
space station concepts
gravity one way or another
in order to simulate
a more natural or familiar environment
for the health of the
The best technique we have is rotating spacecraft to generate
Just like we saw in 2001, and The
Martian, by rotating all or a portion of a spacecraft, you can
generated an outward centrifugal force that mimics the acceleration
of gravity. The larger the radius of the space station, the more
comfortable and natural the rotation feels.
Low Earth Orbit also keeps a space station within the Earth's
protective magnetosphere, limiting the amount of harmful radiation
that future space colonists will experience.
Other orbits are useful too, including geostationary orbit, which is
about 36,000 kilometers above the surface of the Earth. Here
spacecraft orbit the Earth at exactly the same rate as the rotation
of Earth, which means that stations appear in fixed positions above
our planet, useful for communication.
Geostationary orbit is higher up in Earth's gravity well, which
means these stations will serve a low-velocity jumping off points to
reach other places in the Solar System.
They're also outside the Earth's
atmospheric drag, and don't require any orbital boosting to keep
them in place.
By perfecting orbital colonies around Earth, we'll develop
technologies for surviving in deep space, anywhere in the Solar
System. The same general technology will work anywhere, whether
we're in orbit around the Moon, or out past Pluto.
When the technology is advanced enough, we might learn to build
space elevators to carry material and up down from Earth's gravity
well. We could also build launch loops, electromagnetic rail-guns
that launch material into space.
These launch systems would also be able
to loft supplies into transfer trajectories from world to world
throughout the Solar System.
Earth orbit, close to the home-world gives us the perfect place to
develop and perfect the technologies we need to become a true
space-faring civilization. Not only that, but we've got the Moon.
collection on the surface of the Moon.
Apollo 16 astronaut
Charles M. Duke Jr.
is shown collecting
with the Lunar Roving
in the left
The Moon, of course, is the Earth's only natural satellite, which
orbits us at an average distance of about 400,000 kilometers. Almost
ten times further than geostationary orbit.
The Moon takes a surprising amount of velocity to reach from Low
Earth Orbit. It's close, but expensive to reach, thrust speaking.
But that fact that it's close makes the Moon an ideal place to
colonize. It's close to Earth, but it's not Earth. It's airless,
bathed in harmful radiation and has very low gravity. It's the place
that humanity will learn to survive in the harsh environment of
But it still does have some resources we can exploit. The lunar
regolith, the pulverized rocky surface of the Moon, can be used as
concrete to make structures. Spacecraft have identified large
water at the Moon's poles, in its permanently shadowed
As with Mercury, these would make ideal locations for
Here, a surface exploration crew begins its
of a typical,
small lava tunnel,
to determine if
it could serve as a natural shelter
habitation modules of a Lunar Base.
Johnson Space Center
Our spacecraft have also captured images of openings to underground
lava tubes on the surface of the Moon.
Some of these could be gigantic, even
kilometers high. You could fit massive cities inside some of these
lava tubes, with room to spare.
Helium-3 from the Sun rains down on the surface of the Moon,
deposited by the Sun's solar wind, which could be mined from the
surface and provide a source of fuel for lunar fusion reactors. This
abundance of helium could be exported to other places in the Solar
far side of the Moon is permanently shadowed from Earth-based
radio signals, and would make an ideal location for a giant radio
observatory. Telescopes of massive size could be built in the much
lower lunar gravity.
We talked briefly about an Earth-based space elevator, but an
elevator on the Moon makes even more sense. With the lower gravity,
you can lift material off the surface and into lunar orbit using
cables made of materials we can manufacture today, such as
One of the greatest threats on the Moon is the dusty
Without any kind of weathering on the
surface, these dust particles are razor sharp, and they get into
Lunar colonists will need very strict protocols to keep
the lunar dust out of their machinery, and especially out of their
lungs and eyes, otherwise it could cause permanent damage.
a Near-Earth Asteroid
passing by Earth.
Although the vast majority of asteroids in the Solar System are
located in the main asteroid belt, there are still many asteroids
orbiting closer to Earth.
These are known as the
Asteroids, and they've been the cause of many of Earth's great
extinction events. These asteroids are dangerous to our planet, but
they're also an incredible resource, located close to our
The amount of velocity it takes to get to some of these asteroids is
very low, which means travel to and from these asteroids takes
little energy. Their low gravity means that extracting resources
from their surface won't take a tremendous amount of energy.
And once the orbits of these asteroids are fully understood, future
colonists will be able to change the orbits using thrusters. In
fact, the same system they use to launch minerals off the surface
would also push the asteroids into safer orbits.
These asteroids could be hollowed out, and set rotating to provide
artificial gravity. Then they could be slowly moved into safe,
useful orbits, to act as space stations, resupply points, and
There are also gravitationally stable points at the Sun-Earth L4 and
These asteroid colonies could be parked
there, giving us more locations to live in the Solar System.
of the Valles Marineris hemisphere of Mars,
similar to what
one would see
distance of 2500 km.
The future of humanity will include the colonization
of Mars, the
fourth planet from the Sun.
On the surface, Mars has a lot going for
it. A day on Mars is only a little longer than a day on Earth. It
receives sunlight, unfiltered through the thin Martian atmosphere.
There are deposits of water ice at the poles, and under the surface
across the planet.
Martian ice will be precious, harvested from the planet and used for
breathable air, rocket fuel and water for the colonists to drink and
grow their food. The Martian regolith can be used to grow food. It
does have have toxic
perchlorates in it, but that can just be washed
The lower gravity on Mars makes it another ideal place for a space
elevator, ferrying goods up and down from the surface of the planet.
depicted is Noctis Labyrinthus
in the Valles
Marineris system of enormous canyons.
The scene is just
and on the canyon
floor four miles below,
early morning clouds
can be seen.
The frost on the
surface will melt very quickly
as the Sun climbs
higher in the Martian sky.
Unlike the Moon, Mars has a weathered surface.
Although the planet's red dust will get
everywhere, it won't be toxic and dangerous as it is on the Moon.
Like the Moon, Mars has lava tubes, and these could be used as
pre-dug colony sites, where human Martians can live underground,
protected from the hostile environment.
Mars has two big problems that must be overcome.
First, the gravity
on Mars is only a third that of Earth's, and we don't know the long
term impact of this on the human body. It might be that humans just
can't mature properly in the womb in low gravity.
Researchers have proposed that Mars colonists might need to spend
large parts of their day on rotating centrifuges, to simulate Earth
gravity. Or maybe humans will only be allowed to spend a few years
on the surface of Mars before they have to return to a high gravity
The second big challenge is the radiation from the Sun and
interstellar cosmic rays. Without a protective magnetosphere,
Martian colonists will be vulnerable to a much higher dose of
But then, this is the same challenge that colonists will
face anywhere in the entire Solar System.
That radiation will cause an increased risk of cancer, and could
cause mental health issues, with dementia-like symptoms. The best
solution for dealing with radiation is to block it with rock, soil
And Martian colonists, like all Solar
System colonists will need to spend much of their lives underground
or in tunnels carved out of rock.
The explorers have
descended to the surface
of Phobos in a small
"excursion" vehicle, and they are navigating
with the aid of a personal spacecraft, which
fires a line into the soil to anchor the unit.
The astronaut on the
right is examining a large boulder; if the
boulder weighed 1,000 pounds on Earth, it would
weigh a mere pound in the nearly absent gravity
field of Phobos.
explore the rugged surface of Phobos.
Mars, as it would
appear to the human eye from Phobos,
looms on the horizon.
The mother ship, powered by solar energy,
orbits Mars while two
crew members inside
rovers on the Martian surface.
In addition to
Mars itself, the Red Planet has two
small moons, Phobos and Deimos.
These will serve as ideal places for
small colonies. They'll have the same low gravity as asteroid
colonies, but they'll be just above the gravity well of Mars.
Ferries will travel to and from the Martian moons, delivering fresh
supplies and sending Martian goods out to the rest of the Solar
We're not certain yet, but there are good indicators these moons
might have ice inside them, if so that is an excellent source of
fuel and could make initial trips to Mars much easier by allowing us
to send a first expedition to those moons, who then begin producing
fuel to be used to land on Mars and to leave Mars and return home.
According to Elon Musk, if a Martian colony can reach a
million inhabitants, it'll be self-sufficient from Earth or any
At that point, we would have a true,
Solar System civilization.