Colonization of the outer solar system
Encyclopedia
Some of the moons of the outer planets of the solar system
are large enough to be suitable places for colonization. Many of the larger moons contain water ice
, liquid water, and organic compound
s that might be useful for sustaining human life. Colonies in the outer Solar System could also serve as centers for long term investigation of the planet and the other moons. In particular, robotic devices
could be controlled by humans without the very long time delays needed to communicate with Earth
. There have also been proposals to place robotic aerostat
s in the upper atmospheres of the Solar System's gas giant
planets for exploration and possibly mining of helium-3
, which could have a very high value per unit mass as a thermonuclear fuel.
system in general poses particular disadvantages for colonizing because of its severe radiation environment and its particularly deep gravity well
. Its radiation would deliver about 3,600 rems per day to unshielded colonists at Io
and about 540 rems per day to unshielded colonists at Europa. Exposure of approximately 75 rems over a period of a few days is enough to cause radiation poisoning, and about 500 rems over a few days is fatal.
(such as through rotation of the structure) would need to be employed. These bases would also need to withstand radiation from all angles. This type of structure could also serve as a dock for ships visiting other parts of the Jovian system. Additionally, science fiction writers have sometimes proposed that Jupiter could be the site of airborne colonies such as floating cities
, assuming the radiation and gravity issues in traveling to and from the atmosphere are properly addressed. So far no serious proposals or studies have been made of such a colony within Jupiter's atmosphere. However, there does exist a depth within Jupiter's atmosphere at which the pressure is the same as Earth's at sea level, and where there is a blue sky, although it is colder than on Earth; further down, there is a location that has the same average temperature as the surface of the Earth, although the pressure is about five bars.
One significant challenge to overcome in colonizing Jupiter would be the intense radiation in the planet's magnetosphere
.
The Artemis Project
designed a plan to colonize Europa
. Scientists are to inhabit igloos and drill down into the Europan ice crust, exploring any sub-surface ocean. It also discusses use of air pockets for human inhabitation.
is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere
but it is overshadowed by Jupiter's magnetic field. Ganymede receives about 8 rem
of radiation per day.
performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the solar system. The target chosen was Callisto
. It could be possible to build a surface base that would produce fuel for further exploration of the solar system.
617 Patroclus
, and possibly large numbers of other Trojan objects in Jupiter's orbit, are likely composed of water ice, with a layer of dust, suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar system, perhaps via the proposed Interplanetary Transport Network
, may be feasible in the not-so-distant future. This could make colonization of the Moon
, Mercury
and main-belt asteroids
more practical.
identified Saturn
, Uranus
and Neptune
as "the Persian Gulf
of the solar system", as the largest sources of deuterium and helium-3 to drive the pending fusion
economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons.
Robert Zubrin identified Titan
as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization, and saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization." A widely published expert on terraforming
, Christopher McKay, is also a co-investigator on the Huygens probe
that landed on Titan in January 2005.
The surface of Titan is mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) it should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather, such as potential flash floods, are also factors to consider.
's Cassini space probe found possible evidence of liquid water on Enceladus
. According to that article, "pockets of liquid water may be no more than tens of meters below the surface." If these findings are confirmed, it would mean liquid water could be collected much more easily on Enceladus than on, for instance, Europa (see above). Discovery of water, especially liquid water, generally improves a celestial body's consideration for colonization dramatically. An alternative model of Enceladus' activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that should provide materials for base operations.
has the lowest escape velocity
of the four gas giants, it has been proposed as a mining site for helium-3
. If human supervision of the robotic activity proved necessary, one of Uranus' natural satellites
might serve as a base. An alternative is to place floating cities in its atmosphere, as its surface gravity is only 90% of Earth's. Saturn and Neptune could be suitable as well, but Jupiter
would likely not be, due to its high gravity, escape velocity, and radiation.
's surface shows signs of extensive geological activity implying a sub-surface ocean, perhaps of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion
power.
The noted physicist
Freeman Dyson
identified comet
s, rather than planet
s, as the major potential habitat of life in space.
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
are large enough to be suitable places for colonization. Many of the larger moons contain water ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, liquid water, and organic compound
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
s that might be useful for sustaining human life. Colonies in the outer Solar System could also serve as centers for long term investigation of the planet and the other moons. In particular, robotic devices
Robot
A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
could be controlled by humans without the very long time delays needed to communicate with Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. There have also been proposals to place robotic aerostat
Aerostat
An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...
s in the upper atmospheres of the Solar System's gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...
planets for exploration and possibly mining of helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...
, which could have a very high value per unit mass as a thermonuclear fuel.
The Jovian system
The JovianJupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
system in general poses particular disadvantages for colonizing because of its severe radiation environment and its particularly deep gravity well
Gravity well
A gravity well or gravitational well is a conceptual model of the gravitational field surrounding a body in space. The more massive the body the deeper and more extensive the gravity well associated with it. The Sun has a far-reaching and deep gravity well. Asteroids and small moons have much...
. Its radiation would deliver about 3,600 rems per day to unshielded colonists at Io
Io (moon)
Io ) is the innermost of the four Galilean moons of the planet Jupiter and, with a diameter of , the fourth-largest moon in the Solar System. It was named after the mythological character of Io, a priestess of Hera who became one of the lovers of Zeus....
and about 540 rems per day to unshielded colonists at Europa. Exposure of approximately 75 rems over a period of a few days is enough to cause radiation poisoning, and about 500 rems over a few days is fatal.
Jupiter
Orbiting colonies could exist around Jupiter, as around any body in the solar system, but artificial gravityArtificial gravity
Artificial gravity is the varying of apparent gravity via artificial means, particularly in space, but also on the Earth...
(such as through rotation of the structure) would need to be employed. These bases would also need to withstand radiation from all angles. This type of structure could also serve as a dock for ships visiting other parts of the Jovian system. Additionally, science fiction writers have sometimes proposed that Jupiter could be the site of airborne colonies such as floating cities
Floating city (science fiction)
In science fiction, floating cities are settlements that strictly use buoyancy to remain in the atmosphere of a planet. However the term generally refers to any city that is flying, hovering, or otherwise suspended in the air via any means technological or even magical.-Earth:In Jonathan Swift's...
, assuming the radiation and gravity issues in traveling to and from the atmosphere are properly addressed. So far no serious proposals or studies have been made of such a colony within Jupiter's atmosphere. However, there does exist a depth within Jupiter's atmosphere at which the pressure is the same as Earth's at sea level, and where there is a blue sky, although it is colder than on Earth; further down, there is a location that has the same average temperature as the surface of the Earth, although the pressure is about five bars.
One significant challenge to overcome in colonizing Jupiter would be the intense radiation in the planet's magnetosphere
Jupiter's magnetosphere
The magnetosphere of Jupiter is the cavity created in the solar wind by the planet's magnetic field. Extending up to seven million kilometers in the Sun's direction and almost to the orbit of Saturn in the opposite direction, Jupiter's magnetosphere is the largest and most powerful of any planetary...
.
Europa
Artemis Project
The Artemis Project was a private venture to establish a permanent, self-supporting base on the Moon by 2002. It was named after Artemis, the goddess of the Moon and twin sister of Apollo . The project's creators, The Lunar Resources Company, formed the Artemis Society as a non-profit NGO in 1994...
designed a plan to colonize Europa
Europa (moon)
Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
. Scientists are to inhabit igloos and drill down into the Europan ice crust, exploring any sub-surface ocean. It also discusses use of air pockets for human inhabitation.
Ganymede
GanymedeGanymede (moon)
Ganymede is a satellite of Jupiter and the largest moon in the Solar System. It is the seventh moon and third Galilean satellite outward from Jupiter. Completing an orbit in roughly seven days, Ganymede participates in a 1:2:4 orbital resonance with the moons Europa and Io, respectively...
is the largest moon in the Solar System. Ganymede is the only moon with a magnetosphere
Magnetosphere
A magnetosphere is formed when a stream of charged particles, such as the solar wind, interacts with and is deflected by the intrinsic magnetic field of a planet or similar body. Earth is surrounded by a magnetosphere, as are the other planets with intrinsic magnetic fields: Mercury, Jupiter,...
but it is overshadowed by Jupiter's magnetic field. Ganymede receives about 8 rem
Röntgen equivalent man
Named after Wilhelm Röntgen , the roentgen equivalent in man or rem is a unit of radiation dose equivalent...
of radiation per day.
Callisto
Due to its distance from Jupiter's powerful radiation belt, Callisto is subject to only 0.01 rem a day. NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
performed a study called HOPE (Revolutionary Concepts for Human Outer Planet Exploration) regarding the future exploration of the solar system. The target chosen was Callisto
Callisto (moon)
Callisto named after the Greek mythological figure of Callisto) is a moon of the planet Jupiter. It was discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. Callisto has about 99% the diameter of the...
. It could be possible to build a surface base that would produce fuel for further exploration of the solar system.
Trojan asteroids
The 2006 announcement by the Keck Observatory that the binary Trojan asteroidTrojan asteroid
The Jupiter Trojans, commonly called Trojans or Trojan asteroids, are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of the planet's two Lagrangian points of stability, and , that respectively lie 60° ahead...
617 Patroclus
617 Patroclus
617 Patroclus is a binary minor planet made up of two similarly-sized objects orbiting their common centre of gravity. It is a Trojan asteroid, sharing an orbit with Jupiter. It was discovered in 1906 by August Kopff, and was the second trojan to be discovered...
, and possibly large numbers of other Trojan objects in Jupiter's orbit, are likely composed of water ice, with a layer of dust, suggests that mining water and other volatiles in this region and transporting them elsewhere in the Solar system, perhaps via the proposed Interplanetary Transport Network
Interplanetary Transport Network
The Interplanetary Transport Network is a collection of gravitationally determined pathways through the solar system that require very little energy for an object to follow. The ITN makes particular use of Lagrange points as locations where trajectories through space are redirected using little...
, may be feasible in the not-so-distant future. This could make colonization of the Moon
Colonization of the Moon
The colonization of the Moon is the proposed establishment of permanent human communities on the Moon. Advocates of space exploration have seen settlement of the Moon as a logical step in the expansion of humanity beyond the Earth. Recent indication that water might be present in noteworthy...
, Mercury
Colonization of Mercury
Mercury has been suggested as one possible target for space colonization of the inner Solar System, along with Mars, Venus, the Moon and the asteroid belt. Permanent colonies would almost certainly be restricted to the polar regions due to the extreme daytime temperatures elsewhere on the planet...
and main-belt asteroids
Colonization of the asteroids
The asteroids have long been suggested as possible sites for human colonization. This idea is popular in science fiction. Asteroid mining, a proposed industrial process in which asteroids are mined for valuable materials, especially platinum group metals, may be automated or require a crew to...
more practical.
The Saturnian system
Robert ZubrinRobert Zubrin
Robert Zubrin is an American aerospace engineer and author, best known for his advocacy of the manned exploration of Mars. He was the driving force behind Mars Direct—a proposal intended to produce significant reductions in the cost and complexity of such a mission...
identified Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
, Uranus
Uranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
and Neptune
Neptune
Neptune is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
as "the Persian Gulf
Persian Gulf
The Persian Gulf, in Southwest Asia, is an extension of the Indian Ocean located between Iran and the Arabian Peninsula.The Persian Gulf was the focus of the 1980–1988 Iran-Iraq War, in which each side attacked the other's oil tankers...
of the solar system", as the largest sources of deuterium and helium-3 to drive the pending fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
economy, with Saturn the most important and most valuable of the three, because of its relative proximity, low radiation, and excellent system of moons.
Titan
Robert Zubrin identified Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
as possessing an abundance of all the elements necessary to support life, making Titan perhaps the most advantageous locale in the outer Solar System for colonization, and saying "In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonization." A widely published expert on terraforming
Terraforming
Terraforming of a planet, moon, or other body is the hypothetical process of deliberately modifying its atmosphere, temperature, surface topography or ecology to be similar to those of Earth, in order to make it habitable by terrestrial organisms.The term is sometimes used more generally as a...
, Christopher McKay, is also a co-investigator on the Huygens probe
Huygens probe
The Huygens probe was an atmospheric entry probe carried to Saturn's moon Titan as part of the Cassini–Huygens mission. The probe was supplied by the European Space Agency and named after the Dutch 17th century astronomer Christiaan Huygens....
that landed on Titan in January 2005.
The surface of Titan is mostly uncratered and thus inferred to be very young and active, and probably composed of mostly water ice, and lakes of liquid hydrocarbons (methane/ethane) in its polar regions. While the temperature is cryogenic (95 K) it should be able to support a base, but more information regarding Titan's surface and the activities on it is necessary. The thick atmosphere and the weather, such as potential flash floods, are also factors to consider.
Enceladus
On March 9, 2006, NASANASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
's Cassini space probe found possible evidence of liquid water on Enceladus
Enceladus (moon)
Enceladus is the sixth-largest of the moons of Saturn. It was discovered in 1789 by William Herschel. Until the two Voyager spacecraft passed near it in the early 1980s very little was known about this small moon besides the identification of water ice on its surface...
. According to that article, "pockets of liquid water may be no more than tens of meters below the surface." If these findings are confirmed, it would mean liquid water could be collected much more easily on Enceladus than on, for instance, Europa (see above). Discovery of water, especially liquid water, generally improves a celestial body's consideration for colonization dramatically. An alternative model of Enceladus' activity is the decomposition of methane/water clathrates – a process requiring lower temperatures than liquid water eruptions. The higher density of Enceladus indicates a larger than Saturnian average silicate core that should provide materials for base operations.
Uranus
Because UranusUranus
Uranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. It is named after the ancient Greek deity of the sky Uranus , the father of Cronus and grandfather of Zeus...
has the lowest escape velocity
Escape velocity
In physics, escape velocity is the speed at which the kinetic energy plus the gravitational potential energy of an object is zero gravitational potential energy is negative since gravity is an attractive force and the potential is defined to be zero at infinity...
of the four gas giants, it has been proposed as a mining site for helium-3
Helium-3
Helium-3 is a light, non-radioactive isotope of helium with two protons and one neutron. It is rare on Earth, and is sought for use in nuclear fusion research...
. If human supervision of the robotic activity proved necessary, one of Uranus' natural satellites
Uranus' natural satellites
Uranus, the seventh planet of the Solar System, has 27 known moons, all of which are named after characters from the works of William Shakespeare and Alexander Pope. William Herschel discovered the first two moons, Titania and Oberon, in 1787, and the other spherical moons were discovered in 1851...
might serve as a base. An alternative is to place floating cities in its atmosphere, as its surface gravity is only 90% of Earth's. Saturn and Neptune could be suitable as well, but Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
would likely not be, due to its high gravity, escape velocity, and radiation.
Neptune
It is hypothesized that one of Neptune's satellites could be used for colonization – TritonTriton (moon)
Triton is the largest moon of the planet Neptune, discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2,700 km in diameter, it is...
's surface shows signs of extensive geological activity implying a sub-surface ocean, perhaps of ammonia/water. If technology advanced to the point that tapping such geothermal energy was possible, it could make colonizing a cryogenic world like Triton feasible, supplemented by nuclear fusion
Nuclear fusion
Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy...
power.
Kuiper belt and Oort cloud
- See also Colonization of Trans-Neptunian ObjectsColonization of Trans-Neptunian ObjectsFreeman Dyson has proposed that Trans-Neptunian Objects, rather than planets, are the major potential habitat of life in space. Several hundred billion to trillion comet-like ice-rich bodies exist outside the orbit of Neptune, in the Kuiper Belt and Inner and Outer Oort Cloud...
The noted physicist
Physicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
Freeman Dyson
Freeman Dyson
Freeman John Dyson FRS is a British-born American theoretical physicist and mathematician, famous for his work in quantum field theory, solid-state physics, astronomy and nuclear engineering. Dyson is a member of the Board of Sponsors of the Bulletin of the Atomic Scientists...
identified comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s, rather than planet
Planet
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.The term planet is ancient, with ties to history, science,...
s, as the major potential habitat of life in space.
Challenges
There are various difficulties in colonizing the outer solar system. They include:- Distance from EarthEarthEarth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
: The outer planets are much further from Earth than inner planets, and would therefore be harder and more time-consuming to reach. - Planetary conditions: The outer planets have no surface to land on, so any habitation would have to use floating colonies, increasing complexity and decreasing reliability. The moons/comets do not have this problem, although some have specific problems (e.g., EuropaEuropa (moon)Europa Slightly smaller than Earth's Moon, Europa is primarily made of silicate rock and probably has an iron core. It has a tenuous atmosphere composed primarily of oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This surface is striated by cracks and...
is in JupiterJupiterJupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
's intense radiation bands). - Power: Solar powerSolar powerSolar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
is generally considered unsuitable because of the large distance from the SunSunThe Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Nuclear powerNuclear powerNuclear power is the use of sustained nuclear fission to generate heat and electricity. Nuclear power plants provide about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity...
is believed by some to be the only suitable power source for the colonies, although there have been proposals to use concentrated starlight/sunlight and the gravitational potential energy of planets or dwarf planets with moons.
See also
- Space colonizationSpace colonizationSpace colonization is the concept of permanent human habitation outside of Earth. Although hypothetical at the present time, there are many proposals and speculations about the first space colony...
- Floating cities
- Solar System in fictionSolar system in fictionThe Solar System and its various bodies were the earliest objects to be treated as fictional locations in works of science fiction. Among these, imaginary voyages to and explorations of Earth's Moon are found in seventeenth century literature...