Terraforming of Venus - AbsoluteAstronomy.com

The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus

Venus

Venus is the second planet from the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus, the Roman goddess of love and beauty. After the Moon, it is the brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to cast shadows...

in such a way as to make it suitable for human habitation. Terraforming Venus was first seriously proposed by the astronomer Carl Sagan

Carl Sagan

Carl Edward Sagan was an American astronomer, astrophysicist, cosmologist, author, science popularizer and science communicator in astronomy and natural sciences. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books...

in 1961. The minimum adjustments to the existing environment of Venus to support human life would require three major changes to the planet. These three changes are closely interrelated, since Venus's extreme temperature is due to the greenhouse effect

Greenhouse effect

The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...

caused by its dense carbon-dioxide atmosphere:

Reducing Venus's 450°C (850°F
Fahrenheit
Fahrenheit is the temperature scale proposed in 1724 by, and named after, the German physicist Daniel Gabriel Fahrenheit . Within this scale, the freezing of water into ice is defined at 32 degrees, while the boiling point of water is defined to be 212 degrees...

) surface temperature.
Eliminating most of the planet's dense 9 MPa
MPA
-Academic degrees:* Master of Professional Accountancy* Master of Public Administration* Master of Public Affairs* Master of Physician's Assistant-Chemicals:* Medroxyprogesterone acetate, also known by the brand name Depo-Provera* Morpholide of pelargonic acid...

(~90 atm
Atmosphere (unit)
The standard atmosphere is an international reference pressure defined as 101325 Pa and formerly used as unit of pressure. For practical purposes it has been replaced by the bar which is 105 Pa...

) carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

atmosphere
Atmosphere of Venus
The atmosphere of Venus is much denser and hotter than that of Earth. The temperature at the surface is 740 K , while the pressure is 93 bar. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible...

, via removal or conversion to some other form.
Addition of breathable oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

to the atmosphere.

Furthermore, the following two changes would also be highly desirable:

Establishing a day/night light cycle shorter than Venus's extant solar day (presently 116.75 Earth days).
Establishing a planetary magnetic field or substitute for protection against solar and cosmic radiation.

Solar shades

Venus receives about twice the sunlight that Earth does, which is thought to have contributed to its runaway greenhouse effect

Runaway greenhouse effect

A runaway greenhouse effect is not a clearly defined term, but is understood to mean an event analogous to that which is believed to have happened in the early history of Venus, where positive feedback increased the strength of its greenhouse effect until its oceans boiled away...

. Terraforming Venus would likely involve reducing the insolation at Venus's surface to prevent the planet from heating up again.

Space based

Solar shades could be used to reduce the total insolation

Insolation

Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

received by Venus, cooling the planet somewhat. A shade placed in the Sun–Venus Lagrangian point

Lagrangian point

The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...

also serves to block the solar wind

Solar wind

The solar wind is a stream of charged particles ejected from the upper atmosphere of the Sun. It mostly consists of electrons and protons with energies usually between 1.5 and 10 keV. The stream of particles varies in temperature and speed over time...

, removing the radiation exposure problem on Venus.

Construction of a suitably large solar shade is a daunting task. The size of the shade would be four times the diameter of Venus itself if at the point. This size would necessitate construction in space. There would also be the difficulty of balancing a thin-film shade perpendicular to the Sun's rays at the Sun–Venus Lagrangian point with the incoming radiation pressure

Radiation pressure

Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. If absorbed, the pressure is the power flux density divided by the speed of light...

, which would tend to turn the shade into a huge solar sail

Solar sail

Solar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....

. If the shade were left at the point, the pressure would add force to the sunward side and necessitate moving the shade even closer to the Sun than the point.

Modifications to the solar shade design have been suggested to solve the solar-sail problem. One suggested method is to use polar orbit

Polar orbit

A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...

ing, solar-synchronous mirrors that reflect light toward the back of the sunshade, from the non-sunward side of Venus. Photon pressure would push the support mirrors to an angle of 30 degrees away from the sunward side.

Paul Birch

Paul Birch (writer)

Paul Birch is a British author, engineer and scientist, who has worked in radioastronomy and satellite communications, and now writes full time.He is a former Fellow of the British Interplanetary Society....

proposed a slatted system of mirrors near the point between Venus and the Sun. The shade's panels would not be perpendicular to the sun's rays, but instead at an angle of 30 degrees, such that the reflected light would strike the next panel, negating the photon pressure. Each successive row of panels would be +/- 1 degree off the 30-degree deflection angle, causing the reflected light to be skewed 4 degrees from striking Venus.

Another possibility, suggested by Bradley C. Edwards

Bradley C. Edwards

In space engineering, Bradley C. Edwards is a researcher who is notable for having worked on Space elevators. He received funding from NIAC from 2001 to 2003 to write a paper proposing a way in which one could be built...

, is to put into orbit around Venus a belt of material, blocking a portion of sunlight. Multiple thinner belts may be used, and may be composed of a thin net of fibers spaced so that certain wavelengths could not get through while using less material.

Solar shades could also serve as solar power generators. Space-based solar shade techniques, and thin-film solar sails in general, are only in an early stage of development. The vast sizes require a quantity of material that is many orders of magnitude greater than any man-made object that has ever been brought into space or constructed in space.

Atmospheric or surface-based

Cooling could also be effected by placing reflectors in the atmosphere or on the surface. Reflective balloons floating in the upper atmosphere could create shade. The number and/or size of the balloons would necessarily be great. Geoffrey A. Landis

Geoffrey A. Landis

Geoffrey A. Landis is an American scientist, working for the National Aeronautics and Space Administration on planetary exploration, interstellar propulsion, solar power and photovoltaics...

has suggested that if enough floating cities were built, they could form a solar shield around the planet, and could simultaneously be used to process the atmosphere into a more desirable form, thus combining the solar shield theory and the atmospheric processing theory with a scalable technology that would immediately provide living space in the Venusian atmosphere. If made from carbon nanotube

Carbon nanotube

Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...

s (recently fabricated into sheet form) or graphene

Graphene

Graphene is an allotrope of carbon, whose structure is one-atom-thick planar sheets of sp2-bonded carbon atoms that are densely packed in a honeycomb crystal lattice. The term graphene was coined as a combination of graphite and the suffix -ene by Hanns-Peter Boehm, who described single-layer...

(a sheet-like carbon allotrope), then the major structural materials can be produced using carbon dioxide gathered in situ from the atmosphere. The recently synthesised amorphous carbonia

Amorphous carbonia

Amorphous carbonia, also called a-carbonia or a-CO2, is an exotic amorphous solid form of carbon dioxide that is analogous to amorphous silica glass. It was first made in the laboratory in 2006 by subjecting dry ice to high pressures , in a diamond anvil...

might prove a useful structural material if it can be quenched to STP conditions, perhaps in a mixture with regular silica glass. According to Birch's analysis such colonies and materials would provide an immediate economic return from colonizing Venus, funding further terraforming efforts.

Increasing the planet's albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

by deploying light color or reflective material on the surface could help keep the atmosphere cool. The amount would be large and would have to be put in place after the atmosphere had been modified already, since Venus's surface is currently completely shrouded by clouds.

An advantage of atmospheric and surface cooling solutions is that they take advantage of existing technology. A disadvantage is that Venus already has highly reflective clouds (giving it an albedo of 0.65), so any approach would have to significantly surpass this to make a difference.

Biological approaches

A method proposed in 1961 by Carl Sagan involves the use of genetically engineered bacteria to fix carbon into organic forms. Although this method is still commonly proposed in discussions of Venus terraforming, later discoveries showed it would not be successful. The production of organic molecules from carbon dioxide requires an input of hydrogen, which on Earth is taken from its abundant supply of water but which is nearly nonexistent on Venus. Since Venus lacks a magnetic field, the upper atmosphere is exposed to direct erosion by solar wind

Solar wind

and has lost most of its original hydrogen to space.

Furthermore, any carbon that was bound up in organic molecules would quickly be converted to carbon dioxide again by the hot surface environment. Venus would not begin to cool down until after most of the carbon dioxide has already been removed. Twenty-three years later, in Pale Blue Dot
Pale Blue Dot (book)
Pale Blue Dot: A Vision of the Human Future in Space is a non-fiction book by Carl Sagan. It is the sequel to Cosmos: A Personal Voyage and was inspired by the "Pale Blue Dot" photograph, for which Sagan provides a sobering description...

, Sagan conceded that his original proposal for terraforming would not work because the atmosphere of Venus is far denser than was known in 1961.

Floating colonies could gradually transform the Venerian atmosphere: for example, their reflectivity could alter the overall albedo of Venus. Colonies could also grow plant matter, if water or another source of hydrogen were imported, which would gradually sequester carbon dioxide in the air. However, it would take an enormous number of such colonies, and large quantities of introduced hydrogen, to have a significant atmospheric impact, as there is over 1.2 kg of carbon in Venus's atmosphere.

Introduction of hydrogen

Bombarding Venus with hydrogen, possibly from some outer-Solar-System source, and reacting with carbon dioxide, could produce elemental carbon (graphite) and water by the Bosch reaction

Bosch reaction

The Bosch reaction is a chemical reaction between carbon dioxide and hydrogen that produces elemental carbon , water and a 10% return of invested heat...

. It would take about 4×10¹⁹ kg of hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

to convert the whole Venerian atmosphere. (Loss of hydrogen due to the solar wind

Solar wind

is unlikely to be significant on the timescale of terraforming.) Due to the relatively flat surface, this water would cover about 80% of the surface compared to 70% for Earth, even though it would amount to only roughly 10% of the water found on Earth.

The remaining atmosphere, at around 3 bars (about three times that of Earth), will mainly be composed of nitrogen, some of which will dissolve into the new oceans of water, reducing atmospheric pressure further, in accordance with Henry's law

Henry's law

In physics, Henry's law is one of the gas laws formulated by William Henry in 1803. It states that:An equivalent way of stating the law is that the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid...

Capture in carbonates

Bombardment of Venus with refined magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

and calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

metal could sequester carbon dioxide

Carbon dioxide sink

A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. The process by which carbon sinks remove carbon dioxide from the atmosphere is known as carbon sequestration...

in the form of calcium

Calcium carbonate

Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...

and magnesium carbonate

Magnesium carbonate

Magnesium carbonate, MgCO3, is a white solid that occurs in nature as a mineral. Several hydrated and basic forms of magnesium carbonate also exist as minerals...

s. About 8 kg of calcium or 5 kg of magnesium would be required, which would entail a great deal of mining and mineral refining. 8 kg is a few times the mass of the asteroid 4 Vesta

4 Vesta

Vesta, formally designated 4 Vesta, is one of the largest asteroids, with a mean diameter of about . It was discovered by Heinrich Wilhelm Olbers on March 29, 1807, and is named after the Roman virgin goddess of home and hearth, Vesta....

(more than 300 miles in diameter).

Modelling by Mark Bullock of Venus' atmospheric evolution suggests that existing surface minerals, particularly calcium and magnesium oxides, could serve as a sink of carbon dioxide and sulphur dioxide. If these could be exposed to the atmosphere then the planet would cool and its atmospheric pressure decline somewhat. One of the possible end states modelled by Bullock was a 43 bar atmosphere and 400 K surface temperature.

Direct liquefaction and sequestration

Birch's proposal involves using a solar shade to cool Venus down sufficiently to permit liquefaction

Liquefaction of gases

Liquefaction of gases includes a number of phases used to convert a gas into a liquid state. The processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require...

, from a temperature less than 304.18 K and partial pressures of CO₂ down to 73.8 bar (carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

's critical point

Critical point (thermodynamics)

In physical chemistry, thermodynamics, chemistry and condensed matter physics, a critical point, also called a critical state, specifies the conditions at which a phase boundary ceases to exist...

) and then down to 5.185 bar and 216.85 K (carbon dioxide's triple point

Triple point

In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases of that substance coexist in thermodynamic equilibrium...

). Below that temperature, freezing of atmospheric carbon dioxide into dry ice

Dry ice

Dry ice, sometimes referred to as "Cardice" or as "card ice" , is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue...

will cause it to deposit onto the surface, after which the frozen CO₂ would be buried and maintained in that condition by pressure, or shipped off-world. After this process was complete, the shades could be removed or soletta

Soletta

Soletta may refer to:*The Swiss city of Solothurn*A hypothetical magnifying device constructed in space for the purpose of amplifying the solar radiation a planet receives, in order to generate power or aid in the process of Terraforming. Also see Solar mirror....

s added, allowing the planet to partially warm again to temperatures comfortable for Earth life. A source of hydrogen

Hydrogen

or water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

would still be needed, and some of the remaining 3.5 bar of atmospheric nitrogen

Nitrogen

Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...

would need to be fixed into the soil. Birch suggests disrupting an ice-moon of Saturn and bombarding Venus with its fragments to provide perhaps an average depth of 100 meters of water over the whole planet.

Removing atmosphere

The removal of Venus's atmosphere could be attempted by a variety of methods, possibly in combination. Directly lifting atmospheric gas from Venus into space would likely prove difficult. Venus has sufficiently high escape velocity to make blasting it away with asteroid impacts impractical. Pollack

James B. Pollack

James B. Pollack was an American astrophysicist who worked for NASA's Ames Research Center.Pollack was born on 9 July 1938, and was brought up in Woodmere, Long Island by a Jewish family that was in the women's garment business. He was a high school valedictorian and graduated from Princeton...

and Sagan

Carl Sagan

calculated in 1993 that an impactor of 700 km diameter striking Venus at greater than 20 km/s, would eject all the atmosphere above the horizon as seen from the point of impact, but since this is less than a thousandth of the total atmosphere and there would be diminishing returns as the atmosphere's density decreased a very great number of such giant impactors would be required. Smaller objects would not work either, requiring even more. The violence of the bombardment could well result in significant outgassing that replaces removed atmosphere. Most of the ejected atmosphere would go into solar orbit near Venus, and, without further intervention, could be captured by Venus' gravitational field and become part of the atmosphere once again.

Removal of atmospheric gas in a more controlled manner could also prove difficult. Venus's extremely slow rotation means that space elevator

Space elevator

A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...

s would be very difficult to construct as the planet's geostationary orbit

Geostationary orbit

A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...

lies an impractical distance above the surface; and the very thick atmosphere to be removed makes mass driver

Mass driver

A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential...

s useless for removing payloads from the planet's surface. Possible workarounds include placing mass driver

Mass driver

s on high-altitude balloons or balloon-supported towers extending above the bulk of the atmosphere, using space fountain

Space fountain

A space fountain is a proposed form of space elevator that does not require the structure to be in geostationary orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design , a space fountain is a tremendously tall tower extending up from the ground...

s, or rotovators.

Rotation

Venus rotates once every 243 days – by far the slowest rotation period of any of the major planets. A Venerian sidereal day thus lasts more than a Venerian year (243 versus 224.7 Earth days). However, the length of a solar day on Venus is significantly shorter than the sidereal day; to an observer on the surface of Venus the time from one sunrise to the next would be 116.75 days. Nevertheless, Venus's extremely slow rotation rate would result in extremely long days and nights, which could prove difficult for most known Earth species of plants and animals to adapt to. The slow rotation also likely accounts for the lack of a significant magnetic field.

One proposal is a system of orbiting solar mirrors which might be used to provide sunlight to the night side of Venus and possibly shade to the day side surface. In addition to his suggestion of slatted system of mirrors near the point between Venus and the Sun, Paul Birch

Paul Birch (writer)

has proposed a rotating soletta mirror in a polar orbit

Polar orbit

A polar orbit is an orbit in which a satellite passes above or nearly above both poles of the body being orbited on each revolution. It therefore has an inclination of 90 degrees to the equator...

, which would produce a 24-hour light cycle.

Increasing the speed of Venus's rotation would require many orders of magnitude greater amounts of energy than construction of orbiting solar mirrors, or even than the removal of Venus's atmosphere. Recent scientific research suggests that close fly-bys of asteroids or cometary bodies larger than 60 miles across could be used to move a planet in its orbit, or increase the speed of rotation. G. David Nordley

G. David Nordley

G. David Nordley is a science fiction writer and physicist whose fiction writing is most associated with Analog Science Fiction and Fact. His fiction is under the name G. David Nordley while his technical writing is written under the name Gerald D. Nordley...

has suggested, in fiction, that Venus might be spun-up to a day-length of 30 Earth-days by exporting the atmosphere of Venus into space via mass driver

Mass driver

s. This concept was also explored more rigorously by Birch.

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