This article is about the theoretical planetary engineering process.
An artist's conception shows a terraformed
Mars in four stages of development.
Terraforming (literally, "Earth-shaping") of a
planet,
moon, or other body is the
theoretical process of deliberately modifying its
atmosphere,
temperature, surface
topography or
ecology to be similar to the
biosphere of
Earth to make it
habitable by Earth-like life.
The term "terraforming" is sometimes used more generally as a synonym for
planetary engineering, although some consider this more general usage an error.
[citation needed] The concept of terraforming developed from both
science fiction and actual
science. The term was coined by
Jack Williamson in a science-fiction story ("Collision Orbit") published during 1942 in
Astounding Science Fiction,
[1] but the concept may
pre-date this work.
Based on experiences with Earth, the environment of a planet can be
altered deliberately; however, the feasibility of creating an
unconstrained planetary biosphere that mimics Earth on another planet
has yet to be verified.
Mars
is usually considered to be the most likely candidate for terraforming.
Much study has been done concerning the possibility of heating the
planet and altering its atmosphere, and
NASA has even hosted debates on the subject. Several potential methods of
altering the climate of Mars
may fall within humanity's technological capabilities, but at present
the economic resources required to do so are far beyond that which any
government or society is willing to allocate to it. The long timescales
and practicality of terraforming are the subject of debate. Other
unanswered questions relate to the
ethics,
logistics,
economics,
politics, and
methodology of altering the environment of an extraterrestrial world.
History of scholarly study
Carl Sagan, an astronomer, proposed the planetary engineering of Venus in an article published in the journal
Science in 1961.
[2] Sagan imagined seeding the atmosphere of
Venus with
algae, which would convert water, nitrogen and carbon dioxide into
organic compounds. As this process removed
carbon dioxide from the atmosphere, the
greenhouse effect
would be reduced until surface temperatures dropped to "comfortable"
levels. The resulting carbon, Sagan supposed, would be incinerated by
the high surface temperatures of Venus, and thus be
sequestered in the form of "graphite or some involatile form of carbon" on the planet's surface.
[3] However, later discoveries about the conditions on
Venus made this particular approach impossible. One problem is that the clouds of Venus are composed of a highly concentrated
sulfuric acid
solution. Even if atmospheric algae could thrive in the hostile
environment of Venus' upper atmosphere, an even more insurmountable
problem is that its atmosphere is simply far too thick—the high
atmospheric pressure would result in an "atmosphere of nearly pure
molecular oxygen" and cause the planet's surface to be thickly covered
in fine graphite powder.
[3]
This volatile combination could not be sustained through time. Any
carbon that was fixed in organic form would be liberated as carbon
dioxide again through combustion, "short-circuiting" the terraforming
process.
[3]
Sagan also visualized making
Mars habitable for human life in "Planetary Engineering on Mars" (1973), an article published in the journal
Icarus.
[4]
Three years later, NASA addressed the issue of planetary engineering
officially in a study, but used the term "planetary ecosynthesis"
instead.
[5] The study concluded that it was possible for Mars to support life and be made into a
habitable planet. The first conference session on terraforming, then referred to as "Planetary Modeling", was organized that same year.
In March 1979, NASA engineer and author
James Oberg
organized the First Terraforming Colloquium, a special session at the
Lunar and Planetary Science Conference in Houston. Oberg popularized the
terraforming concepts discussed at the colloquium to the general public
in his book
New Earths (1981).
[6] Not until 1982 was the word
terraforming used in the title of a published journal article. Planetologist Christopher McKay wrote "Terraforming Mars", a paper for the
Journal of the British Interplanetary Society.
[7]
The paper discussed the prospects of a self-regulating Martian
biosphere, and McKay's use of the word has since become the preferred
term. In 1984,
James Lovelock and Michael Allaby published
The Greening of Mars.
[8] Lovelock's book was one of the first to describe a novel method of warming Mars, where
chlorofluorocarbons (CFCs) are added to the atmosphere.
Motivated by Lovelock's book, biophysicist
Robert Haynes worked behind the scenes to promote terraforming, and contributed the
neologism Ecopoiesis. The word was formed from the Greek,
οικος,
house, and
ποιησις,
production. Ecopoiesis refers to the
origin of an ecosystem.
In the context of space exploration, Haynes describes ecopoiesis as the
"fabrication of a sustainable ecosystem on a currently lifeless,
sterile planet". Ecopoiesis is a type of
planetary engineering and is one of the first stages of
terraformation. This primary stage of ecosystem creation is usually restricted to the initial seeding of microbial life.
[9]
As conditions approach that of Earth, plant life could be brought in,
and this will accelerate the production of oxygen, theoretically making
the planet eventually able to support animal life.
Aspects and definitions
Beginning in 1985,
Martyn J. Fogg began publishing several articles on terraforming. He also served as editor for a full issue on terraforming for the
Journal of the British Interplanetary Society in 1991. In his book
Terraforming: Engineering Planetary Environments (1995), Fogg proposed the following definitions for different aspects related to terraforming:
[10]
- Planetary engineering: the application of technology for the purpose of influencing the global properties of a planet.
- Geoengineering:
planetary engineering applied specifically to the Earth. It includes
only those macroengineering concepts that deal with the alteration of
some global parameter, such as the greenhouse effect, atmospheric
composition, insolation or impact flux.
- Terraforming: a process of planetary engineering, specifically
directed at enhancing the capacity of an extraterrestrial planetary
environment to support life as we know it. The ultimate achievement in
terraforming would be to create an open planetary biosphere emulating
all the functions of the biosphere of the Earth, one that would be fully
habitable for human beings.
- Astrophysical engineering:
taken to represent proposed activities, relating to future habitation,
that are envisaged to occur on a scale greater than that of
"conventional" planetary engineering.
Fogg also devised definitions for candidate planets of varying degrees of human compatibility:
[11]
- Habitable Planet (HP): A world with an environment sufficiently
similar to the Earth as to allow comfortable and free human habitation.
- Biocompatible Planet (BP): A planet possessing the necessary
physical parameters for life to flourish on its surface. If initially
lifeless, then such a world could host a biosphere of considerable
complexity without the need for terraforming.
- Easily Terraformable Planet (ETP): A planet that might be rendered
biocompatible, or possibly habitable, and maintained so by modest
planetary engineering techniques and with the limited resources of a
starship or robot precursor mission.
Fogg suggests that
Mars
was a biologically compatible planet in its youth, but is not now in
any of these three categories, since it could only be terraformed with
greater difficulty.
[citation needed] Mars Society founder
Robert Zubrin produced a plan for a Mars return mission called
Mars Direct that would set up a permanent human presence on Mars and steer efforts towards eventual terraformation.
[12]
Requirements for sustaining terrestrial life
An absolute requirement for life is an energy source, but the notion
of planetary habitability implies that many other geophysical,
geochemical, and astrophysical criteria must be met before the surface
of an astronomical body is able to support life. Of particular interest
is the set of factors that has sustained complex, multicellular animals
in addition to simpler organisms on this planet. Research and theory in
this regard is a component of
planetary science and the emerging discipline of
astrobiology.
In its astrobiology roadmap,
NASA has defined the principal habitability criteria as "extended regions of liquid
water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism."
[13]
Preliminary stages
Once conditions become more suitable for
life of the
introduced species, the importation of
microbial life could begin.
[10] As conditions approach that of Earth,
plant life
could also be brought in. This would accelerate the production of
oxygen, which theoretically would make the planet eventually able to
support
animal life.
Prospective planets
Artist's conception of a terraformed Mars
Mars
In many respects,
Mars is the most earthlike of all the other planets in our Solar system.
[14]
Indeed, it is thought that Mars once did have a more Earth-like
environment early in its history, with a thicker atmosphere and abundant
water that was lost over the course of hundreds of millions of years.
[15]
The exact mechanism of this loss is still unclear, though three
mechanisms in particular seem likely: First, whenever surface water is
present, carbon dioxide reacts with rocks to form
carbonates, thus drawing atmosphere off and binding it to the planetary surface. On Earth, this process is counteracted when
plate tectonics
works to cause volcanic eruptions that vent carbon dioxide back to the
atmosphere. On Mars, the lack of such tectonic activity worked to
prevent the recycling of gases locked up in sediments.
[16]
Second, the lack of a
magnetosphere surrounding the entire surface of Mars may have allowed the
solar wind to gradually erode the atmosphere.
[17] Convection within the core of Mars, which is made mostly of
iron,
[18] originally generated a
magnetic field. However the
dynamo ceased to function long ago,
[19]
and the magnetic field of Mars has largely disappeared, probably due to
"... loss of core heat, solidification of most of the core, and/or
changes in the mantle convection regime."
[20] Mars does still retain a limited
magnetosphere
that covers approximately 40% of its surface. Rather than uniformly
covering and protecting the atmosphere from solar wind, however, the
magnetic field takes the form of a collection of smaller,
umbrella-shaped fields, mainly clustered together around the planet's
southern hemisphere.
[21] It is within these regions that chunks of atmosphere are violently "blown away", as astronomer David Brain explains:
The joined fields wrapped themselves around a packet of gas at the
top of the Martian atmosphere, forming a magnetic capsule a thousand
kilometres wide with ionised air trapped inside... Solar wind pressure
caused the capsule to 'pinch off' and it blew away, taking its cargo of
air with it.[21]
Finally, between approximately 4.1 and 3.8 billion years ago,
asteroid impacts during the
Late Heavy Bombardment caused significant changes to the surface environment of objects in our Solar system. The low
gravity of Mars suggests that these impacts could have ejected much of the Martian atmosphere into deep space.
[22]
Terraforming Mars would entail two major interlaced changes: building the atmosphere and heating it.
[23] A thicker atmosphere of greenhouse gases such as
carbon dioxide would trap incoming
solar radiation. Because the raised temperature would add greenhouse gases to the atmosphere, the two processes would augment each other.
[24]
Artist's conception of a terraformed
Venus
Venus
Terraforming
Venus requires two major changes; removing most of the planet's dense 9
MPa carbon dioxide atmosphere and reducing the planet's 450 °C (723.15
K) surface temperature. These goals are closely interrelated, since Venus' extreme temperature is thought to be due to the
greenhouse effect caused by its dense atmosphere. Sequestering the atmospheric carbon would likely solve the temperature problem as well.
Europa (moon)
Europa, a moon of
Jupiter, is a potential candidate for terraforming.
[citation needed] One advantage to Europa is the presence of liquid
water which could be extremely helpful for the introduction of any form of life.
[25][not in citation given] The difficulties are numerous; Europa is near a huge radiation belt around Jupiter.
[26]
This would require the building of radiation deflectors, which is
currently impractical. Additionally, this satellite is covered in ice
and would have to be heated, and there would need to be a supply of
oxygen,
[27][dead link] though this could, at sufficient energy cost, be manufactured locally by
electrolysis of the copious water available.
Artist's conception of what the
Moon might look like terraformed
Other bodies in the Solar System
Other possible candidates for terraforming (possibly only partial or paraterraforming) include
Titan,
Callisto,
Ganymede, the
Moon, and even
Mercury, Saturn's moon
Enceladus and the dwarf planet
Ceres. Most, however, have too little mass and
gravity
to hold an atmosphere indefinitely (although it may be possible, but it
is not quite certain, that an atmosphere could remain for tens of
thousands of years or be replenished as needed). In addition, aside from
the Moon and Mercury, most of these worlds are so far from the
Sun that adding sufficient heat would be much more difficult than it would be for
Mars.
Terraforming Mercury would present different challenges, but in certain
aspects would be easier than terraforming Venus. Though not widely
discussed, the possibility of terraforming Mercury's poles has been
presented. Saturn's moon Titan offers several unique advantages, such as
an atmospheric pressure similar to Earth and an abundance of nitrogen
and frozen water. Jupiter's moons Europa, Ganymede, and Callisto also
have an abundance of water ice.
Paraterraforming
Also known as the "
worldhouse" concept, or
domes
in smaller versions, paraterraforming involves the construction of a
habitable enclosure on a planet which eventually grows to encompass most
of the planet's usable area.
[28]
The enclosure would consist of a transparent roof held one or more
kilometers above the surface, pressurized with a breathable atmosphere,
and anchored with tension towers and cables at regular intervals.
Proponents claim worldhouses can be constructed with technology known
since the 1960s. The
Biosphere 2
project built a dome on Earth that contained a habitable environment.
The project encountered difficulties in operation, including unexpected
population explosions of some plants and animals,
[29][30] and a lower than anticipated production of oxygen by plants, requiring extra oxygen to be pumped in.
[31]
Paraterraforming has several advantages over the traditional approach
to terraforming. For example, it provides an immediate payback to
investors (assuming a capitalistic financing model). Although it starts
out in a small area (a
domed city
for example), it quickly provides habitable space. The paraterraforming
approach also allows for a modular approach that can be tailored to the
needs of the planet's population, growing only as fast and only in
those areas where it is required. Finally, paraterraforming greatly
reduces the amount of atmosphere that one would need to add to planets
like Mars to provide Earth-like atmospheric pressures. By using a solid
envelope in this manner, even bodies which would otherwise be unable to
retain an atmosphere at all (such as
asteroids)
could be given a habitable environment. The environment under an
artificial worldhouse roof would also likely be more amenable to
artificial manipulation.
[citation needed]
Paraterraforming is also less likely to cause harm to any native
lifeforms that may hypothetically inhabit the planet, as the parts of
the planet outside the enclosure will not normally be affected unlike
terraforming which affects the entire planet.
[citation needed]
It has the disadvantage of requiring massive amounts of construction
and maintenance activity. It also would not likely have a completely
independent water cycle, because although rainfall may be able to
develop with a high enough roof, but probably not efficiently enough for
agriculture or a water cycle.
[citation needed] The extra cost might be off-set somewhat by automated manufacturing and repair mechanisms.
[citation needed]
A worldhouse might also be more susceptible to catastrophic failure if a
major breach occurred, though this risk might be reduced by
compartmentalization and other active safety precautions.
[citation needed] Meteor strikes are a particular concern because without any external atmosphere they would reach the surface before burning up.
[citation needed]
Ethical issues
There is a philosophical debate within
biology and
ecology as to whether terraforming other worlds is an
ethical endeavor. From the point of view of a
cosmocentric ethic,
this involves balancing the need for the preservation of human life
against the intrinsic value of existing planetary ecologies.
[32]
On the pro-terraforming side of the argument, there are those like
Robert Zubrin,
Martyn J. Fogg,
Richard L. S. Taylor and the late
Carl Sagan who believe that it is humanity's moral obligation to make other worlds suitable for
life, as a continuation of the history of life transforming the environments around it on Earth.
[33][34]
They also point out that Earth would eventually be destroyed if nature
takes its course, so that humanity faces a very long-term choice between
terraforming other worlds or allowing all terrestrial life to become
extinct. Terraforming totally
barren planets, it is asserted, is not morally wrong as it does not affect any other life.
The opposing argument posits that terraforming would be an unethical interference in
nature,
and that given humanity's past treatment of the Earth, other planets
may be better off without human interference. Still others strike a
middle ground, such as
Christopher McKay,
who argues that terraforming is ethically sound only once we have
completely assured that an alien planet does not harbor life of its own;
but that if it does, while we should not try to reshape the planet to
our own use, we should engineer the planet's environment to artificially
nurture the
alien life and help it thrive and co-evolve, or even co-exist with humans.
[35]
Even this would be seen as a type of terraforming to the strictest of
ecocentrists, who would say that all life has the right, in its home
biosphere, to evolve
without outside interference.
Economic issues
The initial cost of such projects as planetary terraforming would be
gargantuan, and the infrastructure of such an enterprise would have to
be built from scratch. Such
technology
is not yet developed, let alone financially feasible at the moment.
John Hickman has pointed out that almost none of the current schemes for
terraforming incorporate
economic strategies, and most of their models and expectations seem highly optimistic.
[36]
Access to the vast resources of space may make such projects more
economically feasible, though the initial investment required to enable
easy access to space will likely be tremendous (see
Asteroid mining,
solar power satellites,
In-Situ Resource Utilization,
bootstrapping,
space elevator).
Political issues
There are potential political issues arising from terraforming a planet.
[original research?] National pride, rivalries between nations, and the politics of
public relations have been a primary motivation for shaping space projects.
[37][38]
In popular culture
Terraforming is a common concept in
science fiction, ranging from
television,
movies and
novels to
video games.
The concept of changing a planet for habitation precedes the use of the word 'terraforming', with
H. G. Wells describing a reverse-terraforming, where aliens in his story
The War of the Worlds change Earth for their own benefit.
Olaf Stapledon's
Last and First Men
(1930) provides the first example in fiction in which Venus is
modified, after a long and destructive war with the original
inhabitants, who naturally object to the process. The word itself was
coined in fiction by
Jack Williamson, but features in many other stories of the 1950s & 60s, such
Poul Anderson's
The Big Rain, and
James Blish's "Pantropy" stories. Recent works involving terraforming of Mars include the
Mars trilogy by
Kim Stanley Robinson and The Platform by James Garvey. In
Isaac Asimov's
Robot Series,
fifty planets have been colonized and terraformed by the powerful race
of humans called Spacers, and when Earth is allowed to attempt
colonization once more, the Settlers begin the process of terraforming
their new worlds immediately. After twenty thousand years in the future,
all the habitable planets in the galaxy have been terraformed and form
the basis of the Galactic Empire in Asimov's
Foundation Series. In the
Star Wars
series, the planet Manaan uses a paraterraforming-like infrastructure,
with all buildings being built above the water as the habitable land of
the planet. There is no natural land on the planet. In the Star Wars
Expanded Universe, the planet Taris is restored to its former state
after a Sith bombardment through aggressive terraforming.
Terraforming has also been explored on television and in feature
films, including the "Genesis device", developed to quickly terraform
barren planets, in the
Star Trek movie
The Wrath of Khan. A similar device exists in the animated feature film
Titan A.E. which depicts the eponymous ship
Titan, capable of creating a
planet. The word 'terraforming' was used in James Cameron's
Aliens
to describe the act of processing a planet's atmosphere through nuclear
reactors over several decades in order to make it habitable. The 2000
movie
Red Planet
also uses the motif: after humanity faces heavy overpopulation and
pollution on Earth, uncrewed space probes loaded with algae are sent to
Mars with the aim of terraforming and creating a breathable atmosphere.
The television series
Firefly and its cinematic sequel
Serenity are set in a solar system with about seventy terraformed planets and moons. In the 2008 video game
Spore,
the player is able to terraform any planet by using either terraforming
rays or a "Staff of Life" that completely terraforms the planet and
fills it with creatures.
Doctor Who episode "
The Doctor's Daughter"
also references terraforming, where a glass orb is broken to release
gases which terraform the planet the characters are on at the time. One
crew member in Ridley Scott's 2012
Prometheus bets another that the purpose of their visit is Terraforming.
In the video game
Halo
(2001), the main setting is an ancient ring-shaped structure whose
radius is nearly that of Earth; the structure is terraformed to support
an Earthlike ecosystem. The rings are created using
Forerunner technology, and terraformed during their construction by an extra-galactic construct known as
The Ark or Installation 00. Various works of fiction based on
Halo also mention the terraforming of planets.
[39]
John Christopher's "Tripods" trilogy has a twist on terraforming.
Aliens have conquered the earth. They live in three domed cities located
in Germany, China, and Panama where they breathe an atmosphere
poisonous to earth life (probably containing chlorine). As the plot
unfolds, the protagonist determines the aliens are awaiting the arrival
of another ship from their home star containing the equipment for them
to terraform (or alienscape) the earth. If this occurs, all earth life
will be wiped out by the poisoned atmosphere. In M. Night Shyamalan's
After Earth,
the planet Nova Prime has been terraformed to be adaptable for human
life as the Earth has lost all properties of being adjustable for
humanity (e.g. violent thermal shifts)
In Zack Snyder's
Man of Steel, General Zod attempts to use terraforming to revive the environment of planet
Krypton on Earth.
See also
