How Do We Terraform Saturn’s Moons?

The  moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and irregularly shaped Hyperion (bottom). Some small moons are also shown. All to scale. Credit: NASA/JPL/Space Science Institute

Continuing with our “Definitive Guide to Terraforming“, Universe Today is happy to present our guide to terraforming Saturn’s Moons. Beyond the inner Solar System and the Jovian Moons, Saturn has numerous satellites that could be transformed. But should they be?

Around the distant gas giant Saturn lies a system of rings and moons that is unrivaled in terms of beauty. Within this system, there is also enough resources that if humanity were to harness them – i.e. if the issues of transport and infrastructure could be addressed – we would be living in an age a post-scarcity. But on top of that, many of these moons might even be suited to terraforming, where they would be transformed to accommodate human settlers.

As with the case for terraforming Jupiter’s moons, or the terrestrial planets of Mars and Venus, doing so presents many advantages and challenges. At the same time, it presents many moral and ethical dilemmas. And between all of that, terraforming Saturn’s moons would require a massive commitment in time, energy and resources, not to mention reliance on some advanced technologies (some of which haven’t been invented yet).

The Cronian Moons:

All told, Saturn system is second only to Jupiter in terms of its number of satellites, with 62 confirmed moons. Of these, the largest moons are divided into two groups: the inner large moons (those that orbit close to Saturn within its tenuous E-Ring) and the outer large moons (those beyond the E-Ring). They are, in order of distance from Saturn, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, and Iapetus.

These moons are all composed primarily of water ice and rock, and are believed to be differentiated between a rocky core and an icy mantle and crust. Among them, Titan is appropriately named, being the largest and most massive of all the inner or outer moons (to the point that it is larger and more massive than all the others combined).

In terms of their suitability for human habitation, each one present its own share of pros and cons. These include their respective sizes and compositions, the presence (or absence) of an atmosphere, gravity, and the availability of water (in ice form and subsurface oceans), And in the end, it is the presence of these moons around Saturn that makes the system an attractive option for exploration and colonization.

As aerospace engineer and author Robert Zubrin stated in his book Entering Space: Creating a Spacefaring Civilization, Saturn, Uranus and Neptune could one day become “the Persian Gulf of the Solar System”, due to their abundance of hydrogen and other resources. Of these systems, Saturn would be the most important, thanks to its relative proximity to Earth, low radiation, and excellent system of moons.

Possible Methods:

Terraforming one or more of Jupiter’s moons would be a relatively straightforward process. In all cases, this would involve heating the surfaces through various means – like thermonuclear devices, impacting the surface with asteroids or comets, or focusing sunlight with orbital mirrors – to the point that surface ice would sublimate, releasing water vapor and volatiles (such as ammonia and methane) to form an atmosphere.

However, due to the comparatively low amounts of radiation coming from Saturn (compared to Jupiter), these atmospheres would have to be converted to a nitrogen-oxygen rich environment through means other than radiolysis. This could be done by using the same orbital mirrors to focus sunlight onto the surfaces, triggering the creation of oxygen and hydrogen gas from water ice through photolysis. While the oxygen would remain closer to the surface, the hydrogen would escape into space.

The presence of ammonia in many of the moon’s ices would also mean that a ready supply of nitrogen could be created to act as a buffer gas. By introducing specific strains of bacteria into the newly created atmospheres – such as the Nitrosomonas, Pseudomonas and Clostridium species – the sublimated ammonia could be converted into nitrites (NO²-) and then nitrogen gas.

Another option would be to employ a process known as “paraterraforming” – where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment. In the case of the Cronian moons, this would involve building large “Shell Worlds” to encase them, keeping the newly-created atmospheres inside long enough to effect long-term changes.

Within this shell, a Cronian moon could have its temperatures slowly raised, the water-vapor atmospheres could be exposed to ultra-violet radiation from internal UV lights, bacteria could then be introduced, and other elements added as needed. Such a shell would ensure that the process of creating of an atmosphere could be carefully controlled and none would be lost before the process was complete.


With a diameter of 396 km and a mass of 0.4×1020 kg, Mimas is the smallest and least massive of these moons. It is ovoid in shape and orbits Saturn at a distance of 185,539 km with an orbital period of 0.9 days. The low density of Mimas, which is estimated to be 1.15 g/cm³ (just slightly higher than that of water), indicates that it is composed mostly of water ice with only a small amount of rock.

As a result of this, Mimas is not a good candidate for terraforming. Any atmosphere that could be created by melting its ice would likely be lost to space. In addition, its low density would mean that the vast majority of the planet would be ocean, with only a small core of rock. This, in turn,  makes any plans to settle on the surface impractical.


Enceladus, meanwhile, has a diameter of 504 km, a mass of 1.1×1020 km and is spherical in shape. It orbits Saturn at a distance of 237,948 km and takes 1.4 days to complete a single orbit. Though it is one of the smaller spherical moons, it is the only Cronian moon that is geologically active – and one of the smallest known bodies in the Solar System where this is the case. This results in features like the famous “tiger stripes” – a series of continuous, ridged, slightly curved and roughly parallel faults within the moon’s southern polar latitudes.

Large geysers have also been observed in the southern polar region that periodically release plumes of water ice, gas and dust which replenish Saturn’s E-ring. These jets are one of several indications that Enceladus has liquid water beneath it’s icy crust, where geothermal processes release enough heat to maintain a warm water ocean closer to its core.

The presence of a warm-water liquid ocean makes Enceladus an appealing candidate for terraforming. The composition of the plumes also indicate that the subsurface ocean is salty, and contains organic molecules and volatiles. These include ammonia and simple hydrocarbons like methane, propane, acetylene, and formaldehyde.

Ergo, once the icy surface was sublimated, these compounds would be released, triggering a natural greenhouse effect. Combined with photolysis, radiolysis, and bacteria, the water vapor and ammonia could also be converted to a nitrogen-oxygen atmosphere. The higher density of Enceladus (~1.61 g/cm3) indicates that it has a larger than average silicate and iron core (for a Cronian moon). This could provide materials for any operations on the surface, and also means that if the surface ice were to be sublimated, Enceladus would not consist mainly of incredibly deep oceans.

However, the presence of this liquid salt-water ocean, organic molecules and volatiles also indicates that the interior of Enceladus experiences hydrothermal activity. This energy source, combined with organic molecules, nutrients, and the prebiotic conditions for life, means that is possible that Enceladus is home to extraterrestrial life.

Much like Europa and Ganymede, these would probably take the form of extremophiles living in environments similar to Earth’s deep-ocean hydrothermal vents. As a result, terraforming Enceladus could result in the destruction of the natural life cycle on the moon, or release life forms that could prove harmful to any future colonists.


At 1066 km in diameter, Tethys is the second-largest of Saturn’s inner moons and the 16th-largest moon in the Solar System. The majority of its surface is made up of heavily cratered and hilly terrain and a smaller and smoother plains region. Its most prominent features are the large impact crater of Odysseus, which measures 400 km in diameter, and a vast canyon system named Ithaca Chasma – which is concentric with Odysseus and measures 100 km wide, 3 to 5 km deep and 2,000 km long.

With a mean density of 0.984 ± 0.003 grams per cubic centimeter, Tethys is believed to be comprised almost entirely of water ice. It is not currently known whether Tethys is differentiated into a rocky core and ice mantle. However, given the fact that rock accounts for less 6% of its mass, a differentiated Tethys would have a core that did not exceed 145 km in radius. On the other hand, Tethys’ shape – which resembles that of a triaxial ellipsoid – is consistent with it having a homogeneous interior (i.e. a mix of ice and rock).

Because of this, Tethys is also off the terraforming list. If in fact it has a tiny rocky interior, treating the surface to heating would mean that the vast majority of the moon would melt and be lost to space. Alternately, if the interior is a homogeneous mix of rock and ice, then all that would remain after melting occurred would be a cloud of debris.


With a diameter and mass of 1,123 km and 11×1020 kg, Dione is the fourth largest moon of Saturn. The majority of Dione’s surface is heavily cratered old terrain, with craters that measure up to 250 km in diameter. With an orbital distance of 377,396 km from Saturn, the moon takes 2.7 days to complete a single rotation.

Dione’s mean density of about 1.478 g/cm³ indicates that it is composed mainly of water ice, with a small remainder likely consisting of a silicate rock core. Dione also has a very thin atmosphere of oxygen ions (O+²), which was first detected by the Cassini space probe in 2010. While the source of this atmosphere is currently unknown, it is believed that it is the product of radiolysis, where charged particles from Saturn’s radiation belt interact with water ice on the surface to create hydrogen and oxygen (similar to what happens on Europa).

Because of this tenuous atmosphere, it is already known that sublimating Dione’s ice could produce an oxygen atmosphere. However, it is not currently known if Dione possesses the right combination of volatilizes to ensure that nitrogen gas can be created, or that a greenhouse effect will be triggered. Combined with Dione’s low density, this makes it an unattractive target for terraforming.


Measuring 1,527 km in diameter and 23×1020 kg in mass, Rhea is the second largest of Saturn’s moons and the ninth largest moon of the Solar System. With an orbital radius of 527,108 km, it is the fifth-most distant of the larger moons, and takes 4.5 days to complete an orbit. Like other Cronian satellites, Rhea has a rather heavily cratered surface, and a few large fractures on its trailing hemisphere.

With a mean density of about 1.236 g/cm³, Rhea is estimated to be composed of 75% water ice (with a density of roughly 0.93 g/cm³) and 25% of silicate rock (with a density of around 3.25 g/cm³). This low density means that although Rhea is the ninth-largest moon in the Solar System, it is also the tenth-most massive.

In terms of its interior, Rhea was originally suspected of being differentiated between a rocky core and an icy mantle. However, more recent measurements would seem to indicate that Rhea is either only partly differentiated, or has a homogeneous interior – likely consisting of both silicate rock and ice together (similar to Jupiter’s moon Callisto).

Models of Rhea’s interior also suggest that it may have an internal liquid-water ocean, similar to Enceladus and Titan. This liquid-water ocean, should it exist, would likely be located at the core-mantle boundary, and would be sustained by the heating caused from the decay of radioactive elements in its core. Interior ocean or not, the fact that the vast majority of the moon is composed of ice water makes it an unattractive option for terraforming.


As already noted, Titan is the largest of the Cronian moons. In fact, at 5,150 km in diameter, and 1,350×1020 kg in mass, Titan is Saturn’s largest moon and comprises more than 96% of the mass in orbit around the planet. Based on its bulk density of 1.88 g/cm3, Titan’s composition is half water ice and half rocky material – most likely differentiated into several layers with a 3,400 km rocky center surrounded by several layers of icy material.

It is also the only large moon to have its own atmosphere, which is cold, dense, and is the only nitrogen-rich dense atmosphere in the Solar System aside from Earth’s (with small amounts of methane). Scientists have also noted the presence of polycyclic aromatic hydrocarbons in the upper atmosphere, as well as methane ice crystals. Another thing Titan has in common with Earth, unlike every other moon and planet in the Solar System, is atmospheric pressure. On the surface of Titan, the air pressure is estimated to be around 1.469 bars (1.45 times that of Earth).

The surface of Titan, which is difficult to observe due to persistent atmospheric haze, shows only a few impact craters, evidence of cryovolcanoes, and longitudinal dune fields that were apparently shaped by tidal winds. Titan is also the only body in the Solar System beside Earth with bodies of liquid on its surface, in the form of methane–ethane lakes in Titan’s north and south polar regions.

With an orbital distance of 1,221,870 km, it is the second-farthest large moon from Saturn, and completes a single orbit every 16 days. Like Europa and Ganymede, it is believed that Titan has a subsurface ocean made of water mixed with ammonia, which can erupt to the surface of the moon and lead to cryovolcanism. The presence of this ocean, plus the prebiotic environment on Titan, has led some to suggest that life may exist there as well.

Such life could take the form of microbes and extremophiles in the interior ocean (similar to what is thought to exist on Enceladus and Europa), or could take the even more extreme form of methanogenic life forms. As has been suggested, life could exist in Titan’s lakes of liquid methane just as organisms on Earth live in water. Such organisms would inhale dihydrogen (H²) in place of oxygen gas (O²), metabolize it with acetylene instead of glucose, and then exhale methane instead of carbon dioxide.

However, NASA has gone on record as stating that these theories remain entirely hypothetical. So while the prebiotic conditions that are associated with organic chemistry exist on Titan, life itself may not. However, the existence of these conditions remains a subject of fascination among scientists. And since its atmosphere is thought to be analogous to Earth’s in the distant past, proponents of terraforming emphasize that Titan’s atmosphere could be converted in much the same way.

Beyond that, there are several reasons why Titan is a good candidate. For starters, it possess an abundance of all the elements necessary to support life (atmospheric nitrogen and methane), liquid methane, and liquid water and ammonia. Additionally, Titan has an atmospheric pressure one and a half times that of Earth, which means that the interior air pressure of landing craft and habitats could be set equal or close to the exterior pressure.

This would significantly reduce the difficulty and complexity of structural engineering for landing craft and habitats compared with low or zero pressure environments such as on the Moon, Mars, or the Asteroid Belt. The thick atmosphere also makes radiation a non-issue, unlike with other planets or Jupiter’s moons.

And while Titan’s atmosphere does contain flammable compounds, these only present a danger if they are mixed with sufficient enough oxygen – otherwise, combustion cannot be achieved or sustained. Finally, the very high ratio of atmospheric density to surface gravity also greatly reduces the wingspan needed for aircraft to maintain lift.

With all these things going for it, turning Titan into a livable world would be feasible given the right conditions. For starters, orbital mirrors could be used to direct more sunlight onto the surface. Combined with the moon’s already dense and greenhouse gas-rich atmosphere, this would lead to a considerable greenhouse effect that would melt the ice and release water vapor into the air.

Once again, this could be converted into a nitrogen/oxygen-rich mix, and more easily than with other Cronian moons since the atmosphere is already very rich in nitrogen. The presence of nitrogen, methane and ammonia could also be used to produce chemical fertilizers to grow food. However, the orbital mirrors would need to remain in place in order to ensure the environment did not become extremely cold again and revert to an icy state.


At 1,470 km in diameter and 18×1020 kg in mass, Iapetus is the third-largest of Saturn’s large moons. And at a distance of 3,560,820 km from Saturn, it is the most distant of the large moons, and takes 79 days to complete a single orbit. Due to its unusual color and composition – its leading hemisphere is dark and black whereas its trailing hemisphere is much brighter – it is often called the “yin and yang” of Saturn’s moons.

With an average distance (semi major axis) of 3,560,820 km, Iapetus takes 79.32 days to complete an single orbit of Saturn. Despite being Saturn’s third-largest moon, Iapetus orbits much farther from Saturn than its next closest major satellite (Titan). Like many of Saturn’s moons – particularly Tethys, Mimas and Rhea – Iapetus has a low density (1.088 ± 0.013 g/cm³) which indicates that it is composed primary of water ice and only about 20% rock.

But unlike most of Saturn’s larger moons, its overall shape is neither spherical or ellipsoid, instead consisting of flattened poles and a bulging waistline. Its large and unusually high equatorial ridge also contributes to its disproportionate shape. Because of this, Iapetus is the largest known moon to not have achieved hydrostatic equilibrium. Though rounded in appearance, its bulging appearance disqualifies it from being classified as spherical.

Because of this, Iapetus is not a likely contender for terraforming. If in fact its surface were melted, it too would be an ocean world with unrealistically deep seas, and this water would likely be lost to space.

Potential Challenges:

To break it down, only Enceladus and Titan appear to be viable candidates for terraforming. However, in both cases, the process of turning them into habitable worlds where human beings could exist without the need for pressurized structures or protective suits would be a long and costly one. And much like terraforming the Jovian moons, the challenges can be broken down categorically:

  1. Distance
  2. Resources and Infrastructure
  3. Hazards
  4. Sustainability
  5. Ethical Considerations

In short, while Saturn may be abundant in resources and closer to Earth than either Uranus or Neptune, its really very far. On average, Saturn is approximately 1,429,240,400,000 kms away from Earth (or ~8.5 AU the equivalent of eight and a half times the average distance between the Earth and the Sun). To put that in perspective, it took the Voyager 1 probe roughly thirty-eight months to reach the Saturn system from Earth. For crewed spacecraft, carrying colonists and all the equipment needed to terraform the surface, it would take considerably longer to get there.

These ships, in order to avoid being overly large and expensive, would need to rely on cryogenics or hibernation-related technology in order to be smaller, faster and more cost-effective. While this sort of technology is being investigated for crewed missions to Mars, it is still very much in the research and development phase. What’s more, a large fleet of robotic spaceships and support craft would also be needed to build the orbital mirrors, capture asteroids or debris to use as impactors, and provide logistical support to crewed spaceships.

Unlike the crewed vessels, which could keep crews in stasis until their arrival, these ships would need to have advanced propulsion systems to ensure that they were able to make the trips to and from the Cronian moons in a realistic amount of time. All of this, in turn, raises the crucial issue of infrastructure. Basically, any fleet operating between Earth and Saturn would require a network of bases between here and there to keep them supplied and fueled.

So really, any plans to terraform Saturn’s moons would have to wait upon the creation of permanent bases on the Moon, Mars, the Asteroid Belt, and the Jovian moons. In addition, building orbital mirrors would require considerable amounts of minerals and other resources, many of which could be harvested from the Asteroid Belt or from Jupiter’s Trojans.

This process would be punitively expensive by current standards and (again) would require a fleet of ships with advanced drive systems. And paraterraforming using Shell Worlds would be no different, requiring multiple trips to and from the Asteroid Belt, hundreds (if not thousands) of construction and support craft, and all the necessary bases in between.

And while radiation is not a major threat in the Cronian system (unlike around Jupiter), the moons have been subject to a great deal of impacts over the course of their history. As a result, any settlements built on the surface would likely need additional protection in orbit, like a string of defensive satellites that could redirect comets and asteroids before they reached orbit.

Fourth, terraforming Saturn’s moons presents the same challenges as Jupiter’s. Namely, every moon that was terraformed would be an ocean planet And whereas most of Saturn’s moons are untenable due to their high concentrations of water ice, Titan and Enceladus are not that much better off. In fact, if all of Titan’s ice were melted, including the layer that is believed to sit beneath its interior ocean, its sea level would be up to 1700 km in depth!

Not only that, but this sea would surround a hydrous core, which would likely make the planet unstable. Enceladus would not fair any better, as gravity measurements by Cassini have shown that the density of the core is low, indicating that the core contains water in addition to silicates. So in addition to a deep ocean on its surface, its core might also be unstable.

And last, there are the ethical considerations. If both Enceladus and Titan are home to extra-terrestrial life, than any efforts to alter their environments could result in their destruction. Barring that, melting the surface ice could cause any indigenous life forms to proliferate and mutate, and exposure to them could prove to be a health hazard for human settlers.


Once again, when faced with all of these considerations, one is forced to ask, “why bother?” Why bother altering the natural environment of the Cronian moons when we could settle on them as is, and use their natural resources to usher in an age of post-scarcity? Quite literally, there is enough water ice, volatiles, hydrocarbons, organic molecules, and minerals in the Saturn system to keep humanity supplied indefinitely.

What’s more, without the effects of terraforming, settlements on Titan and Enceladus would probably be a lot more tenable. We could also fathom building settlements on the moons of Tethys, Dione, Rhea, and Iapetus as well, which would prove much more beneficial in terms of being able to harness the system’s resources.

And, as with Jupiter’s moons of Europa, Ganymede, and Callisto, foregoing the act of terraforming would mean there would be an abundant supply of resources that could be used to terraform other places – namely, Venus and Mars. As has been argued many times over, the abundance of methane, ammonia, and water ices in the Cronian system would be very useful in helping to turn “Earths twins” into “Earth-like” planets.

Once again, it would seem that the answer to the question “can/should we?” is a disappointing no.

We have written many interesting articles about terraforming here at Universe Today. Here’s The Definitive Guide To Terraforming, How Do We Terraform Mars?, How Do We Terraform Venus?, How Do We Terraform the Moon?, and How Do We Terraforming Jupiter’s Moons?

We’ve also got articles that explore the more radical side of terraforming, like Could We Terraform Jupiter?, Could We Terraform The Sun?, and Could We Terraform A Black Hole?

Astronomy Cast also has good episodes on the subject, like Episode 61: Saturn’s Moons.

For more information, check out NASA’s Solar System Exploration page on Saturn’s Moons and the Cassini mission page.

And if you like the video, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!

The post How Do We Terraform Saturn’s Moons? appeared first on Universe Today.

How Do We Terraform Jupiter’s Moons?

Surface features of the four members at different levels of zoom in each row

Fans of Arthur C. Clarke may recall how in his novel, 2010: Odyssey Two (or the movie adaptation called 2010: The Year We Make Contact), an alien species turned Jupiter into a new star. In so doing, Jupiter’s moon Europa was permanently terraformed, as its icy surface melted, an atmosphere formed, and all the life living in the moon’s oceans began to emerge and thrive on the surface.

As we explained in a previous video (“Could Jupiter Become a Star“) turning Jupiter into a star is not exactly doable (not yet, anyway). However, there are several proposals on how we could go about transforming some of Jupiter’s moons in order to make them habitable by human beings. In short, it is possible that humans could terraform one of more of the Jovians to make it suitable for full-scale human settlement someday.

The Jovian Moons:

Within the Jupiter system, there are 67 confirmed moons of varying size, shape and composition. In honor of Jupiter’s namesake, they are sometimes collectively referred to as the Jovians. Of these, the four largest – Io, Europa, Ganymede and Callisto – are known as the Galileans (in honor of their founder, Galileo Galilei). These four moons are among the largest in the Solar System, with Ganymede being the largest of them all, and even larger than the planet Mercury.

In addition, three of these moons – Europa, Ganymede and Callisto – are all believed or known to have interior oceans at or near their core-mantle boundary. The presence of warm water oceans is not only considered an indication of potential life on these moons, but is also cited as a reason for possible human habitation.

Of the Galilean Moons, Io, Europa and Ganymede are all in orbital resonance with each other. Io has a 2:1 mean-motion orbital resonance with Europa and a 4:1 resonance with Ganymede, which means that it completes two orbits of Jupiter for every one orbit of Europa, and four orbits for every orbit Ganymede. This resonance helps maintain these moons’ orbital eccentricities, which in turn triggers tidal flexing their interiors.

Naturally, each moon presents its own share of advantages and disadvantages when it comes to exploration, settlement, and terraforming. Ultimately, these come down to the particular moon’s structure and composition, its proximity to Jupiter, the availability of water, and whether or not the moon in question is dominated by Jupiter’s powerful magnetic field.

Possible Methods:

The process of converting Jupiter’s Galilean moons is really quite simple. Basically, its all about leveraging the indigenous resources and the moons’ own interactions with Jupiter’s magnetic field to create a breathable atmosphere. The process would begin by heating the surface in order to sublimate the ice, a process which could involve orbital mirrors to focus sunlight onto the surface, nuclear detonators, or crashing comets/meteors into the surface.

Once the surface ice begins to melt, it would form dense clouds of water vapor and gaseous volatiles (such as carbon dioxide, methane and ammonia). These would in turn create a greenhouse effect, warming the surface even more, and triggering a process known as radiolysis (the dissociation of molecules through exposure to nuclear radiation).

Basically, the exposure of water vapor to Jupiter’s radiation would result in the creation of hydrogen and oxygen gas, the former of which would escape into space while the latter remained closer to the surface. This process already takes place around Europa, Ganymede and Callisto, and is responsible for their tenuous atmospheres (which contain oxygen gas).

And since ammonia is predominantly composed of nitrogen, it could be converted into nitrogen gas (N²) through the introduction of certain strains of bacteria. These would include members of the Nitrosomonas, Pseudomonas and Clostridium species, which would convert ammonia gas into nitrites (NO²-), and then nitrites into nitrogen gas. With nitrogen acting as a buffer gas, a nitrogen-oxygen atmosphere with sufficient air pressure to sustain humans could be created.

Another option falls under the heading of “paraterraforming” – a process where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment. In the case of the Jovians, this would involve building large “Shell Worlds” to encase them, keeping the atmospheres inside long enough to effect long-term changes.

Within this shell, Europa, Ganymede and Callisto could have their temperatures slowly raised, the water-vapor atmospheres could be exposed to ultra-violet radiation from internal UV lights, bacteria could then be introduced, and other elements added as needed. Such a shell would ensure that the process of creating of an atmosphere could be carefully controlled and none would be lost before the process was complete.


With a mean radius of 1821.6 ± 0.5 km, and an average distance (semi-major axis) of 421,700 km from Jupiter, Io is the innermost of the Galileans. Because of this, Io is completely enveloped by Jupiter’s powerful magnetic field, which also the surface is exposed to significant amounts of harmful radiation. In fact, Io receives an estimated 3,600 rem (36 Sv) of ionizing radiation per day, whereas living organisms here on Earth experience an average of 24 rem per year!

The moon has the shortest orbital period of any of the Galileans, taking roughly 42.5 hours to complete a single orbit around the gas giant. The moon’s 2:1 and 4:1 orbital resonance with Europa and Ganymede (see below) also contributes to its orbital eccentricity of 0.0041, which is the primary reason for Io’s geologic activity.

With a mean density of 3.528 ± 0.006 g/cm3, Io has the highest density of any moon in the Solar System, and is significantly denser than the other Galilean Moons. Composed primarily of silicate rock and iron, it is closer in bulk composition to the terrestrial planets than to other satellites in the outer Solar System, which are mostly composed of a mix of water ice and silicates.

Unlike its Jovian cousins, Io has no warm-water ocean beneath its surface. In fact, based on magnetic measurements and heat-flow observations, a magma ocean is believed to exist some 50 km below the surface, which itself is about 50 km thick and makes up 10% of the mantle.  It is estimated that the temperature in the magma ocean reaches 1473 K (1200 °C/2192 °F).

The main source of internal heat that allows for this comes from tidal flexing, which is the result of Io’s orbital resonance with Europa and Ganymede. The friction or dissipation produced in Io’s interior due to this varying tidal pull creates significant tidal heating within Io’s interior, melting a significant amount of Io’s mantle and core.

This heat is also responsible for Io’s volcanic activity and its observed heat flow, and periodically causes lava to erupt up to 500 km (300 mi) into space. Consistently, the surface of is covered in smooth plains dotted with tall mountains, pits of various shapes and sizes, and volcanic lava flows. It’s colorful appearance (a combination of orange, yellow, green, white/grey, etc.) is also indicative of volcanic activity which has covered the surface in sulfuric and silicate compounds and leads to surface renewal.

Io contains little to no water, though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons. In fact, Io has the least amount of water of any known body in the Solar System, which is likely due to Jupiter being hot enough early in the evolution of the Solar System to drive volatile materials like water off its surface.

Taken together, all of this adds up to Io being a total non-starter when it comes to terraforming or settlement. The planet is far too hostile, far too dry, and far too volcanically active to ever be turned into something habitable!


Europa, by contrast, has a lot of appeal for proponents of terraforming. If Io could be characterized as hellish, lava-spewing place (and it certainly can!), then Europa would be calm, icy and watery by comparison. With a mean radius of about 1560 km and a mass of 4.7998 ×1022 kg, Europa is also slightly smaller than Earth’s Moon, which makes it the sixth-largest moon and fifteenth largest object in the Solar System.

It’s orbit is nearly circular, with a eccentricity of 0.09, and lies at an average distance of 670 900 km from Jupiter. The moon takes 3.55 Earth days to complete a single orbit around Jupiter, and is tidally locked with the planet (though some theories say that this may not be absolute). At this distance from Jupiter, Europa still experiences quite a bit of radiation, averaging about 540 rem per day.

Europa is significantly more dense than the other Galilean Moons (except for Io), which indicates that its interior is differentiated between a rock interior composed of silicate rock and a possible iron core. Above this rocky interior is layer of water ice that is estimated to be around 100 km (62 mi) thick, likely differentiated between a frozen upper crust and  a liquid water ocean beneath.

If present, this ocean is likely a warm-water, salty ocean that contains organic molecules, is oxygenated, and heated by Europa’s geologically-active core. Given the combination of these factors, it is considered a strong possibility that organic life also exists in this ocean, possibly in microbial or even multi-celled form, most likely in environments similar to Earth’s deep-ocean hydrothermal vents.

Because of its abundant water, which comes in both liquid and solid form, Europa is a popular candidate for proponents of colonization and terraforming. Using nuclear devices, cometary impacts, or some other means to increase the surface temperature, Europa’s surface ice could be sublimated and form a massive atmosphere of water vapor.

This vapor would then undergo radiolysis due to exposure to Jupiter’s magnetic field, converting it into oxygen gas (which would stay close to the planet) and hydrogen that would escape into space. The resulting planet would be an ocean world, where floating settlements could be built that floated across the surface (due to oceans depths of ~100 km, they could not be anchored). Because Europa is tidally-locked, these colonies could move from the day-side to the night-side in order to create the illusion of a diurnal cycle.


Ganymede’s is the third most distant moon from Jupiter, and orbits at an average distance (semi-major axis) of 1,070,400 km – varying from 1,069,200 km at periapsis to at 1,071,600 km apoapsis. At this distance, it takes seven days and three hours to completes a single revolution. Like most known moons, Ganymede is tidally locked, with one side always facing toward the planet.

With a mean radius of 2634.1 ± 0.3 kilometers (the equivalent of 0.413 Earths), Ganymede is the largest moon in the Solar System, even larger than the planet Mercury. However, with a mass of 1.4819 x 10²³ kg (the equivalent of 0.025 Earths), it is only half as massive, which is due to its composition, which consists of water ice and silicate rock.

Ganymede is considered another possible candidate for human settlement – and even terraforming – for several reasons. For one, as Jupiter’s largest moon, Ganymede has a gravitational force of 1.428 m/s2 (the equivalent of 0.146 g) which is comparable to Earth’s Moon. Sufficient enough to limit the effects of muscle and bone degeneration, this lower gravity also means that the moon has a lower escape velocity – which means it would take considerably less fuel for rockets to take off from the surface.

What’s more, the presence of a magnetosphere means that colonists would be better shielded from cosmic radiation than on other bodies, and more shielded from Jupiter’s radiation than Europa or Io. All told, Ganymede receives about 8 rem of radiation per day – a significant reduction from Europa and Io, but still well above human tolerances.

The prevalence of water ice means that colonists could also produce breathable oxygen, their own drinking water, and would be able to synthesize rocket fuel. Like Europa, this could be done by heating up the surface through various means, sublimating the water ice, and allowing radiolysis to convert it into oxygen. Again, the result would be an ocean world, but one with significantly deeper oceans (~800 km).

And then there is the distinct possibility that Ganymede, like Europa, has an interior ocean due to the heat created by tidal flexing in its mantle. This heat could be transferred into the water via hydrothermal vents, which could provide the necessary heat and energy to sustain life. Combined with oxygenated water, life forms could exist at the core-mantle boundary in the form of extremophiles, much like on Europa.


Callisto is the outermost of the Galileans, orbiting Jupiter at an average distance (semi-major axis) of 1,882,700 km. With a mean radius of 2410.3 ± 1.5 km (0.378 Earths) and a mass of 1.0759 × 1023 kg (0.018 Earths), Callisto is the second largest of  Jupiter’s moons (after Ganymede) and the third largest satellite in the solar system. It is similarly comparable in size to Mercury – being 99% as large – but due to its mixed composition, it has less than one-third of Mercury mass.

Compared to the other Galileans, Callisto presents numerous advantages as far as colonization is concerned. Much like the others, the moon has an abundant supply of water in the form of surface ice (but also possibly liquid water beneath the surface). But unlike the others, Callisto’s distance from Jupiter means that colonists would have far less to worry about in terms of radiation. In fact, with a surface exposure of about  0.01 rem a day, Callisto is well within human tolerances.

Much like Europa and Ganymede, and Saturn’s moons of Enceladus, Mimas, Dione, Titan, the possible existence of a subsurface ocean on Callisto has led many scientists to speculate about the possibility of life. This is particularly likely if the interior ocean is made up of salt-water, since halophiles (which thrive in high salt concentrations) could live there.

However, the environmental conditions necessary for life to appear (which include the presence of sufficient heat due to tidal flexing) are more likely on Europa and Ganymede. The main difference is the lack of contact between the rocky material and the interior ocean, as well as the lower heat flux in Callisto’s interior. In essence, while Callisto possesses the necessary pre-biotic chemistry to host life, it lacks the necessary energy.

Like Europa and Ganymede, the process of terraforming Callisto would involve heating up the surface in order to sublimate the surface ice and create an atmosphere, one which produces oxygen through radiolysis. The resulting world would be an ocean planet, but with oceans that reached to depths of between 130 and 350 km.

Potential Challenges:

Okay, we’ve covered the potential methods and targets, which means its time for the bad news. To break it down, converting one or more of the Galileans into something habitable to humans presents many difficulties, some of which may prove to be insurmountable. These include, but are are not limited to:

  1. Distance
  2. Resources/Infrastructure
  3. Natural Hazards
  4. Sustainability
  5. Ethical Considerations

Basically, the Jovian system is pretty far from Earth. On average, the distance between Jupiter and Earth is 628,411,977 million km (4.2 AU), roughly four times the distance between the Earth and the Sun. To put that into perspective, it took the Voyager probes between 18 months and two years to reach Jupiter from Earth. Ships designed to haul human passengers (with enough supplies and equipment to sustain them) would be much larger and heavier, which would make the travel time even longer.

In addition, depending on the method used, transforming the surfaces of Europa, Ganymede, and/or Callisto could require harvesting comets and iceteroids from the edge of the Solar System, which is significantly farther. To put that in perspective, it took the New Horizons mission over eight years to reach Pluto and the Kuiper Belt. And since any mission to this region of space would need to haul back several tons of icy cargo, the wait time involved would be on the order of decades.

Ergo, any vessels transporting human crews to the Jovian system would likely have to rely on cryogenics or hibernation-related technology in order to be smaller, faster and more cost-effective. While this sort of technology is being investigated for crewed missions to Mars, it is still very much in the research and development phase.

As for transport missions to and from the Kuiper Belt, these ships could be automated, but would have to come equipped with advanced propulsion systems in order to make the trips in a decent amount of time. This could take the form of Nuclear-Thermal Propulsion (NTP), Fusion-drive systems, or some other advanced concept. So far, no such drive systems exist, with some being decades or more away from feasibility.

An alternative to this last item could be to harvest asteroids from near Earth, the Asteroid Belt, or Jupiter’s Trojans. However, this brings up the second aspect of this challenge, which is the problem of infrastructure. In order to mount multiple crewed missions to the Jovian system, as well as asteroid/iceteroid retrieval missions, a considerable amount of infrastructure would be needed that either does not exist or is severely lacking.

This includes having lots of spaceships, which would also need advanced propulsion systems. Just as important is the need for refueling and supply stations between Earth and the Jovian System – like an outpost on the Moon, a permanent base on Mars, and bases on Ceres and in the Asteroid Belt. Harvesting resources from the Kuiper Belt would require more outposts between Jupiter and most likely Pluto.

Where “Shell Worlds” are concerned, the challenge remains the same. Building an enveloping structure big enough for an entire moon – which range from 3121.6 km to 5262.4 km in diameter – would require massive amounts of material. While these could be harvested from the nearby Asteroid Belt, it would require thousands of ships and robot workers to mine, haul, and assemble the minerals into large enough shells.

Third, radiation would be a significant issue for humans living on Europa or Ganymede. As noted already, Earth organisms are exposed to an average of 24 rem per year, which works out to 0.0657 rem per day. An exposure of approximately 75 rems over a period of a few days is enough to cause radiation poisoning, while about 500 rems over a few days would be fatal. Of all the Galileans, only Callisto falls beneath this terminal limit.

As a result, any settlements established on Europa or Ganymede would require radiation shielding, even after the creation of viable atmospheres. This in turn would require large shields to be built in orbit of the moons (requiring another massive investment in resources), or would dictate that all settlements built on the surfaces include heavy radiation shielding.

On top of that, as the surfaces of Europa, Ganymede and Callisto (especially Callisto!) will attest, the Jovian system is frequented by space rocks. In fact, most of Jupiter’s satellites are asteroids it picked up as they sailed through the system. These satellites are lost on a regular basis, and new ones are added all the time. So colonists would naturally have to worry about space rocks slamming into their ocean world, causing massive waves and blotting out the sky with thick clouds of water vapor.

Fourth, the issue of sustainability, has to do with the fact that all of the Jovian moons either do not have a magnetosphere or, in the case of Ganymede, are not powerful enough to block the effects of Jupiter’s magnetic field. Because of this, any atmosphere created would be slowly stripped away, much as Mars’ atmosphere was slowly stripped away after it lost its magnetosphere about 4.3 billion years ago. In order to maintain the effects of terraforming, colonists would need to replenish the atmosphere over time.

Another aspect of sustainability, one which is often overlooked, has to do with the kinds of planets that would result from terraforming. While estimates vary, transforming Europa, Ganymede and Callisto would result in oceans that varied in depth – from 100 km (in the cae of Europa) to extreme depths of up to 800 km (in the case of Ganymede). In contrast, the greatest depth ever measured here on Earth was only about 10 km (6 miles) deep, in the Pacific’s Mariana Trench.

With oceans this deep, all settlements would have to take the form of floating cities that could not be anchored to solid ground. And in the case of Ganymede, the oceans would account for a considerable portion of the planet. What the physicals effects of this would be are hard to imagine. But it is a safe bet that they would result in tremendously high tides (at best) to water being lost to space.

And finally, there is the issue of the ethics of terraforming. If, as scientists currently suspect, there is in fact indigenous life on one or more of the Jovian moons, then the effects of terraforming could have severe consequences or them. For instance, if bacterial life forms exist on the underside of Europa’s icy surface, then melting it would mean death for these organisms, since it would remove their only source of protection from radiation.

Life forms that exist close to the core-mantle boundary, most likely around hydrothermal vents, would be less effected by the presence of humans on the surface. However, any changes to the ec0logical balance could lead to a chain reaction that would destroy the natural life cycle. And the presence of organisms introduced by humans (i.e. germs), could have a similarly devastating effect.

So basically, if we choose to alter the natural environment of one or more of the Jovian moons, we will effectively be risking the annihilation of any indigenous life forms. Such an act would be tantamount to genocide (or xenocide, as the case may be), and exposure to alien organisms would surely pose health risks for human colonists as well.


All in all, it appears that terraforming the outer Solar System might be a bit of a non-starter. While the prospect of doing it is certainly exciting, and presents many interesting opportunities, the challenges involved do seem to add up. For starters, it doesn’t seem likely or practical for us to contemplate doing this until we’ve established a presence on the Moon, Mars, and in the Asteroid Belt.

Second, terraforming any of Jupiter’s moons would involve a considerable amount of time, energy and resources. And given that a lot of these moon’s resources could be harvested for terraforming other worlds (such as Mars and Venus), would it not make sense to terraform these worlds first and circle back to the outer Solar System later?

Third, a terraformed Europa, Ganymede and Callisto would all be water worlds with extremely deep oceans. Would it even be possible to build floating cities on such a world? Or would they be swallowed up by massive tidal waves; or worse, swept off into space by waves so high, they slipped the bonds of the planet’s gravity? And how often would the atmosphere need to be replenished in order to ensure it didn’t get stripped away?

And last, but not least, any act of terraforming these moons would invariably threaten any life that already exists there. And the threat caused by exposure wouldn’t exactly be one-way. Under all of these circumstances, would it not be better to simply establish outposts on the surface, or perhaps within or directly underneath the ice?

All valid questions, and ones which we will no doubt begin to explore once we start mounting research missions to Europa and the other Jovian moons in the future. And depending on what we find there, we might just choose to put down some roots. And in time, we might even begin thinking about renovating the places so more of our kin can drop by. Before we do any of that, we had better make sure we know what we’re doing, and be sure we aren’t doing any harm in the process!

We have written many interesting articles about Jupiter’s Moons here at Universe Today. Here’s What Are Jupiter’s Moons?, Io, Jupiter’s Volcanic Moon, Jupiter’s Moon Europa, Jupiter’s Moon Ganymede, and Jupiter’s Moon Callisto.

To learn more about terraforming, check out The Definitive Guide To Terraforming, How Do We Terraform Mars?, How Do We Terraform Venus?, and How Do We Terraform the Moon? and Could We Terraform Jupiter?

For more information, check out NASA’s Solar System Exploration page on Jupiter’s Moons.

The post How Do We Terraform Jupiter’s Moons? appeared first on Universe Today.

Ten Interesting Facts About Jupiter

Jupiter's Red Spot, seen by Voyager 1. Image credit: NASA/JPL

Jupiter was appropriately named after the king of the gods. It’s massive, has a powerful magnetic field, and more moons that any planet in the Solar System. Though it has been known to astronomers since ancient times, the invention of the telescope and the advent of modern astronomy has taught us so much about this gas giant.

In short, there are countless interesting facts about this gas giant that many people just don’t know about. And we here at Universe Today have taken the liberty of compiling a list of ten particularly interesting ones that we think will fascinate and surprise you. Think you know everything about Jupiter? Think again!

1. Jupiter Is Massive:

It’s no secret that Jupiter is the largest planet in the Solar System. But this description really doesn’t do it justice. For one, the mass of Jupiter is 318 times as massive as the Earth. In fact, Jupiter is 2.5 times more massive than all of the other planets in the Solar System combined. But here’s the really interesting thing…

If Jupiter got any more massive, it would actually get smaller. Additional mass would actually make the planet more dense, which would cause it to start pulling it in on itself. Astronomers estimate that Jupiter could end up with 4 times its current mass, and still remain about the same size.

2. Jupiter Cannot Become A Star:

Astronomers call Jupiter a failed star, but that’s not really an appropriate description. While it is true that, like a star, Jupiter is rich in hydrogen and helium, Jupiter does not have nearly enough mass to trigger a fusion reaction in its core. This is how stars generate energy, by fusing hydrogen atoms together under extreme heat and pressure to create helium, releasing light and heat in the process.

This is made possible by their enormous gravity. For Jupiter to ignite a nuclear fusion process and become a star, it would need more than 70 times its current mass. If you could crash dozens of Jupiters together, you might have a chance to make a new star. But in the meantime, Jupiter shall remain a large gas giant with no hopes of becoming a star. Sorry, Jupiter!

3. Jupiter Is The Fastest Spinning Planet In The Solar System:

For all its size and mass, Jupiter sure moves quickly. In fact, with an rotational velocity of 12.6 km/s (~7.45 m/s) or 45,300 km/h (28,148 mph), the planet only takes about 10 hours to complete a full rotation on its axis. And because it’s spinning so rapidly, the planet has flattened out at the poles a little and is bulging at its equator.

In fact, points on Jupiter’s equator are more than 4,600 km further from the center than the poles. Or to put it another way, the planet’s polar radius measures to 66,854 ± 10 km (or 10.517 that of Earth’s), while its diameter at the equator is 71,492 ± 4 km (or 11.209 that of Earth’s). This rapid rotation also helps generate Jupiter’s powerful magnetic fields, and contribute to the dangerous radiation surrounding it.

4. The Clouds On Jupiter Are Only 50 km Thick:

That’s right, all those beautiful whirling clouds and storms you see on Jupiter are only about 50 km thick. They’re made of ammonia crystals broken up into two different cloud decks. The darker material is thought to be compounds brought up from deeper inside Jupiter, and then change color when they reacted with sunlight. But below those clouds, it’s just hydrogen and helium, all the way down.

5. The Great Red Spot has been around for a long time

The Great Red Spot on Jupiter is one of its most familiar features. This persistent anticyclonic storm, which is located south of its equator, measures between 24,000 km in diameter and 12–14,000 km in height. As such, it is large enough to contain two or three planets the size of Earth’s diameter. And the spot has been around for at least 350 years, since it was spotted as far back as the 17th century.

The Great Red Spot was first identified in 1665 by Italian astronomer Giovanni Cassini. By the 20th century, astronomers began to theorize that it was a storm, one which was created by Jupiter’s turbulent and fast-moving atmosphere. These theories were confirmed by the Voyager 1 mission, which observed the Giant Red Spot up close in March of 1979 during its flyby of the planet.

However, it appears to have been shrinking since that time. Based on Cassini’s observations, the size was estimated to be 40,000 km in the 17th century, which was almost twice as large as it is now. Astronomers do not know if or when it will ever disappear entirely, but they are relatively sure that another one will emerge somewhere else on the planet.

6. Jupiter Has Rings:

When people think of ring systems, Saturn naturally comes to mind. But in truth, both Uranus and Jupiter have ring systems of their own. Jupiter’s were the third set to be discovered (after the other two), due to the fact that they are particularly faint. Jupiter’s rings consist of three main segments – an inner torus of particles known as the halo, a relatively bright main ring, and an outer gossamer ring.

These rings are widely believed to have come from material ejected by its moons when they’re struck by meteorite impacts. In particular, the main ring is thought to be composed of material from the moons of Adrastea and Metis, while the moons of Thebe and Amalthea are believed to produce the two distinct components of the dusty gossamer ring.

This material fell into orbit around Jupiter (instead of falling back to their respective moons) because if Jupiter’s strong gravitational influence. The ring is also depleted and replenished regularly as some material veers towards Jupiter while new material is added by additional impacts.

7. Jupiter’s Magnetic Field Is 14 Times Stronger Than Earth’s:

Compasses would really work on Jupiter. That’s because it has the strongest magnetic field in the Solar System. Astronomers think the magnetic field is generated by the eddy currents – i.e. swirling movements of conducting materials – within the liquid metallic hydrogen core. This magnetic field traps particles of sulfur dioxide from Io’s volcanic eruptions, which producing sulfur and oxygen ions. Together with hydrogen ions originating from the atmosphere of Jupiter, these form a plasma sheet in Jupiter’s equatorial plane.

Farther out, the interaction of the magnetosphere with the solar wind generates a bow shock, a dangerous belt of radiation that can cause damage tos spacecraft. Jupiter’s four largest moons all orbit within the magnetosphere, which protects them from the solar wind, but also make the likelihood of establishing outposts on their surface problematic. The magnetosphere of Jupiter is also responsible for intense episodes of radio emission from the planet’s polar regions.

8. Jupiter Has 63 Moons:

As of the penning of this article, Jupiter has a 67 confirmed and named satellites. However, it is estimated that the planet has over 200 natural satellites orbiting it. Almost all of them are less than 10 kilometers in diameter, and were only discovered after 1975, when the first spacecraft (Pioneer 10) arrived at Jupiter.

However, it also has four major moons, which are collectively known as the Galilean Moons (after their discovered Galileo Galilei). These are, in order of distance from Jupiter, Io, Europa, Ganymede, and Callisto. These moons are some of the largest in the Solar System, with Ganymede being the largest, measuring 5262 km in diameter.

9. Jupiter Has Been Visited 7 Times By Spacecraft:

Jupiter was first visited by NASA’s Pioneer 10 spacecraft in December 1973, and then Pioneer 11 in December 1974. Then came the Voyager 1 and 2 flybys, both of which happened in 1979. This was followed by a long break until Ulysses arrived in February 1992. Then Cassini made a flyby in 2000, on its way to Saturn. And finally, NASA’s New Horizons spacecraft made its flyby in 2007. This was the last mission to fly past Jupiter, but it surely won’t be the last.

10. You Can See Jupiter With Your Own Eyes:

Jupiter is the third brightest object in the Solar System, after Venus and the Moon. Chances are, you saw Jupiter in the sky, and had no idea that’s what you were seeing. And here at Universe Today, we are in the habit of letting readers know when the best opportunities for spotting Jupiter in the night sky are.

Chances are, if you see a really bright star high in the sky, then you’re looking at Jupiter. Get your hands on a pair of binoculars, and if you know someone with a telescope, that’s even better. Using even modest magnification, you might even spot small specks of light orbiting it, which are its Galilean Moons. Just think, you’ll be seeing precisely what Galileo did when he gazed at the planet in 1610.

We have written many interesting articles about Jupiter here at Universe Today. Here’s The Gas Giant Jupiter, How Strong Is Jupiter’s Gravity?, Does Jupiter Have A Solid Core?, and Jupiter Compared To Earth.

And here are 10 Interesting Facts About Planet Earth, and 1o Interesting Facts About Mars.

For more information, check out the Hubblesite’s News Releases about Jupiter, and NASA’s Solar System Exploration.

We’ve also recorded an entire show just on Jupiter for Astronomy Cast. Listen to it here, Episode 56: Jupiter, and Episode 57: Jupiter’s Moons.

The post Ten Interesting Facts About Jupiter appeared first on Universe Today.

The Definitive Guide To Terraforming

Artist's impression of the terraforming of Mars, from its current state to a livable world. Credit: Daein Ballard

Terraforming. Chances are you’ve heard that word thrown around before, most likely in the context of some science fiction story. However, in recent years, thanks to renewed interest in space exploration, this word is being used in an increasingly serious manner. And rather than being talked about like a far-off prospect, the issue of terraforming other worlds is being addressed as a near-future possibility.

Whether it’s Elon Musk claiming that humanity needs a “backup location” in order to survive, private ventures like MarsOne looking to send humans on a one-way mission to colonize the Red Planet, or space agencies like NASA and the ESA discussing the prospect of long-term habitability on Mars or the Moon, terraforming is yet another science fiction concept that appears to be moving towards science fact.

But just what does terraforming entail? Where exactly could we go about using this process? What kind of technology would we need? Does such technology already exist, or do we have to wait? How much in the way of resources would it take? And above all, what are the odds of it actually succeeding? Answering any or all of these questions requires that we do a bit of digging. Not only is terraforming a time-honored concept, but as it turns out, humanity already has quite a bit of experience in this area!

Origin Of The Term:

To break it down, terraforming is the process whereby a hostile environment (i.e. a planet that is too cold, too hot, and/or has an unbreathable atmosphere) is altered in order to be suitable for human life. This could involve modifying the temperature, atmosphere, surface topography, ecology – or all of the above – in order to make a planet or moon more “Earth-like”.

The term was coined by Jack Williamson, an American science fiction writer who has also been called “the Dean of science fiction” (after the death of Robert Heinlein in 1988). The term appeared as part of a science-fiction story titled “Collision Orbit”, which was published in the 1942 editions of the magazine Astounding Science Fiction. This is the first known mention of the concept, though there are examples of it appearing in fiction beforehand (see below).

Terraforming in Fiction:

Science fiction is filled with examples of altering planetary environments to be more suitable to human life, many of which predate the scientific studies by many decades. For example, in H.G. Wells’ War of the Worlds, he mentions at one point how the Martian invaders begin transforming Earth’s ecology for the sake of long-term habitation.

In Olaf Stapleton’s Last And First Men (1930), two chapter are dedicated to describing how humanity’s descendants terraform Venus after Earth becomes uninhabitable; and in the process, commit genocide against the native aquatic life in the process. By the 1950s and 60s, owing to the beginning of the Space Age, terraforming began to appear in many works of science fiction.

For example, in Farmer in the Sky (1950), Robert A. Heinlein offers a vision of how Ganymede is being transformed into an agricultural settlement. This was a very significant novel, in that it was the first novel where the concept of terraforming is presented as a serious and scientific matter, rather than the subject of mere fantasy.

In 1951, Arthur C. Clarke wrote the first novel in which the terraforming of Mars was presented in fiction. Titled The Sands of Mars, the story involves Martian settlers heating up the planet by converting Phobos into a second sun, and growing plants that break down the Martians sands in order to release oxygen. In his seminal book 2001: A Space Odyssey, and 2010: Odyssey Two, Clarke presents a race of ancient beings (“Firstborn”) turning Jupiter into a second sun so that Europa will become a life-bearing planet.

Poul Anderson also wrote extensively about terraforming in the 1950s. In his 1954 novel, The Big Rain, Venus is altered through planetary engineering techniques over a very long period of time. The book was so influential that the term term “Big Rain” has since come to be snyonimous with the terraforming of Venus.  This was followed in 1958 by the Snows of Ganymede, where the Jovian moon’s ecology is made habitable through a similar process.

In Issac Asimov’s Robot series, colonization and terraforming is performed by a powerful race of humans known as “Spacers”, who conduct this process on fifty planets in the known universe.  In his Foundation series, humanity has effectively colonized every habitable planet in the galaxy and terraformed them to become part of the Galactic Empire.

In 1984, James Lovelock and Michael Allaby wrote what is considered by many to be one of the most influential books on terraforming. Titled The Greening of Mars, the novel explores the formation and evolution of planets, the origin of life, and Earth’s biosphere. The terraforming models presented in the book actually foreshadowed future debates regarding the goals of terraforming.

In the 1990s, Kim Stanley Robinson released his famous trilogy that deals with the terraforming Mars. Known as the Mars TrilogyRed Mars, Green Mars, Blue Mars – this series centers on the transformation of Mars over the course of many generations into a thriving human civilization. This was followed up in 2012 with the release of 2312, which deals with the colonization of the Solar System – including the terraforming of Venus and other planets.

Countless other examples can be found in popular culture, ranging from television and print to films and video games.

Study Of Terraforming:

In an article published by the journal Science in 1961, famed astronomer Carl Sagan proposed using planetary engineering techniques to transform Venus. This involved seeding the atmosphere of Venus with algae, which would convert the atmosphere’s ample supplies of water, nitrogen and carbon dioxide into organic compounds and reduce Venus’ runaway greenhouse effect.

In 1973, he published an article in the journal Icarus titled “Planetary Engineering on Mars“, where he proposed two scenarios for transforming Mars. These included transporting low albedo material and/or planting dark plants on the polar ice caps to ensure it absorbed more heat, melted, and converted the planet to more “Earth-like conditions”.

In 1976, NASA addressed the issue of planetary engineering officially in a study titled “On the Habitability of Mars: An Approach to Planetary Ecosynthesis“. The study concluded that photosynthetic organisms, the melting of the polar ice caps, and the introduction of greenhouse gases could all be used to create a warmer, oxygen and ozone-rich atmosphere. The first conference session on terraforming, then referred to as “Planetary Modeling”, was organized that same year.

And then in March of 1979, NASA engineer and author James Oberg organized the First Terraforming Colloquium – a special session at the Tenth Lunar and Planetary Science Conference, which is held annually in Houston, Texas. In 1981, Oberg popularized the concepts that were discussed at the colloquium in his book New Earths: Restructuring Earth and Other Planets.

In 1982, Planetologist Christopher McKay wrote “Terraforming Mars”, a paper for the Journal of the British Interplanetary Society. In it, McKay discussed the prospects of a self-regulating Martian biosphere, which included both the required methods for doing so and ethics of it. This was the first time that the word terraforming was used in the title of a published article, and would henceforth become the preferred term.

This was followed by James Lovelock and Michael Allaby’s The Greening of Mars in 1984. This book was one of the first to describe a novel method of warming Mars, where chlorofluorocarbons (CFCs) are added to the atmosphere in order to trigger global warming. This book motivated biophysicist Robert Haynes to begin promoting terraforming as part of a larger concept known as Ecopoiesis.

Derived from the Greek words oikos (“house”) and poiesis (“production”), this word refers to the origin of an ecosystem. In the context of space exploration, it involves a form of planetary engineering where a sustainable ecosystem is fabricated from an otherwise sterile planet. As described by Haynes, this begins with the seeding of a planet with microbial life, which leads to conditions approaching that of a primordial Earth. This is then followed by the importation of plant life, which accelerates the production of oxygen, and culminates in the introduction of animal life.

In 2009, Kenneth Roy – an engineer with the US Department of Energy – presented his concept for a “Shell World” in a paper published with the Journal of British Interplanetary Sciences. Titled “Shell Worlds – An Approach To Terraforming Moons, Small Planets and Plutoids“, his paper explored the possibility of using a large “shell” to encase an alien world, keeping its atmosphere contained long enough for long-term changes to take root.

These and other concepts where a world is enclosed (in whole or in part) in an artificial shell in order to transform its environment is also known as “paraterraforming”.

Potential Sites:

Within the Solar System, several possible locations exist that could be well-suited to terraforming. Consider the fact that besides Earth, Venus and Mars also lie within the Sun’s Habitable Zone (aka. “Goldilocks Zone”). However, owing to Venus’ runaway greenhouse effect, and Mars’ lack of a magnetosphere, their atmospheres are either too thick and hot, or too thin and cold, to sustain life as we know it. However, this could theoretically be altered through the right kind of ecological engineering.

Other potential sites in the Solar System include some of the moons that orbit the gas giants. Several Jovian (i.e. in orbit of Jupiter) and Cronian (in orbit of Saturn) moons have an abundance of water ice, and scientists have speculated that if the surface temperatures were increased, viable atmospheres could be created through electrolysis and the introduction of buffer gases.

There is even speculation that Mercury and the Moon (or at least parts thereof) could be terraformed in order to be suitable for human settlement. In these cases, terraforming would require not only altering the surface, but perhaps also adjusting their rotation. In the end, each case presents its own share of advantages, challenges, and likelihoods for success. Let’s consider them in order of distance from the Sun.

Inner Solar System:

The terrestrial planets of our Solar System present the best possibilities for terraforming. Not only are they located closer to our Sun, and thus in a better position to absorb its energy, but they are also rich in silicates and minerals – which any future colonies will need to grow food and build settlements. And as already mentioned, two of these planets (Venus and Mars) are located within Earth’s habitable zone.

The vast majority of Mercury’s surface is hostile to life, where temperatures gravitate between extremely hot and cold – i.e. 700 K (427 °C; 800 °F) 100 K (-173 °C; -280 °F). This is due to its proximity to the Sun, the almost total lack of an atmosphere, and its very slow rotation. However, at the poles, temperatures are consistently low -93 °C (-135 °F) due to it being permanently shadowed.

The presence of water ice and organic molecules in the northern polar region has also been confirmed thanks to data obtained by the MESSENGER mission. Colonies could therefore be constructed in the regions, and limited terraforming (aka. paraterraforming) could take place. For example, if domes (or a single dome) of sufficient size could be built over the Kandinsky, Prokofiev, Tolkien and Tryggvadottir craters, the norther region could be altered for human habitation.

Theoretically, this could be done by using mirrors to redirect sunlight into the domes which would gradually raise the temperature. The water ice would then melt, and when combined with organic molecules and finely ground sand, soil could be made. Plants could then be grown to produce oxygen, which combined with nitrogen gas, would produce a breathable atmosphere.

As “Earth’s Twin“, there are many possibilities and advantages to terraforming Venus. The first to propose this was Sagan with his 1961 article in Science. However, subsequent discoveries – such as the high concentrations of sulfuric acid in Venus’ clouds – made this idea unfeasible. Even if algae could survive in such an atmosphere, converting the extremely dense clouds of CO² into oxygen would result in an over-dense oxygen environment.

In addition, graphite would become a by-product of the chemical reactions, which would likely form into a thick powder on the surface. This would become CO² again through combustion, thus restarting the entire greenhouse effect. However, more recent proposals have been made that advocate using carbon sequestration techniques, which are arguably much more practical.

In these scenarios, chemical reactions would be relied on to convert Venus’ atmosphere to something breathable while also reducing its density. In one scenario, hydrogen and iron aerosol would be introduced to convert the CO² in the atmosphere into graphite and water. This water would then fall to the surface, where it cover roughly 80% of the planet – due to Venus having little variation in elevation.

Another scenario calls for the introduction of vast amounts of calcium and magnesium into the atmosphere. This would sequester carbon in the form of calcium and magnesium carbonites. And advantage to this plan is that Venus already has deposits of both minerals in its mantle, which could then be exposed to the atmosphere through drilling. However, most of the minerals would have to come from off-world in order to reduce the temperature and pressure to sustainable levels.

Yet another proposal is to freeze the atmospheric carbon dioxide down to the point of liquefaction – where it forms dry ice – and letting it accumulate on the surface. Once there, it could be buried and would remain in a solid state due to pressure, and even mined for local and off-world use. And then there is the possibility of bombarding the surface with icy comets (which could be mined from one of Jupiter’s or Saturn’s moons) to create a liquid ocean on the surface, which would sequester carbon and aid in any other of the above processes.

Last, there is the scenario in which Venus’ dense atmosphere could be removed. This could be characterized as the most direct approach to thinning an atmosphere which is far too dense for human occupation. By colliding large comets or asteroids into the surface, some of the dense CO² clouds could be blasted into space, thus leaving less atmosphere to be converted.

A slower method could be achieved using mass drivers (aka. electromagnetic catapults) or space elevators, which would gradually scoop up the atmosphere and either lift it into space, or fire it away from the surface. And beyond altering or removing the atmosphere, there are also concepts that call for reducing the heat and pressure by either limiting sunlight (i.e. with solar shades) or altering the planet’s rotational velocity.

The concept of solar shades involves using either a series of small spacecraft or a single large lens to divert sunlight from a planet’s surface, thus reducing global temperatures. For Venus, which absorbs twice as much sunlight as Earth, solar radiation is believed to have played a major role in the runaway greenhouse effect that has made it what it is today.

Such a shade could be space-based, located in the Sun–Venus L1 Lagrangian Point, where it would not only prevent some sunlight from reaching Venus, but also serve to reduce the amount of radiation Venus is exposed to. Alternately, solar shades or reflectors could be placed in the atmosphere or on the surface. This could consist of large reflective balloons, sheets of carbon nanotubes or graphene, or low-albedo material.

Placing shades or reflectors in the atmosphere offers two advantages: for one, atmospheric reflectors could be built in-situ, using locally-sourced carbon. Second, Venus’ atmosphere is dense enough that such structures could easily float atop the clouds. However, the amount of material would have to be large and would have to remain in place long after the atmosphere had been modified. Also, since Venus already has highly reflective clouds, any approach would have to significantly surpass its current albedo (0.65) to make a difference.

Also, the idea of speeding up Venus’ rotation has been floating around as a possible means of terraforming. If Venus could be spun-up to the point where its diurnal (day-night) cycle were similar to Earth’s, the planet might just begin to generate a stronger magnetic field. This would have the effect of reducing the amount of solar wind (and hence radiation) from reaching the surface, thus making it safer for terrestrial organisms.

The Moon:
As Earth’s closest celestial body, colonizing the Moon would be comparatively easy compared to other bodies. But when it comes to terraforming the Moon, the possibilities and challenges closely resemble those of Mercury. For starters, the Moon has an atmosphere that is so thin that it can only be referred to as an exosphere. What’s more, the volatile elements that are necessary for life are in short supply (i.e. hydrogen, nitrogen, and carbon).

These problems could be addressed by capturing comets that contain water ices and volatiles and crashing them into the surface. The comets would sublimate, dispersing these gases and water vapor to create an the atmosphere. These impacts would also liberate water that is contained in the lunar regolith, which could eventually accumulate on the surface to form natural bodies of water.

The transfer of momentum from these comet would also get the Moon rotating more rapidly, speeding up its rotation so that it would no longer be tidally-locked. A Moon that was sped up to rotate once on its axis every 24 hours would have a steady diurnal cycle, which would make colonization and adapting to life on the Moon easier.

There is also the possibility of paraterraforming parts of the Moon in a way that would be similar to terraforming Mercury’s polar region. In the Moon’s case, this would take place in the Shackleton Crater, where scientists have already found evidence of water ice. Using solar mirrors and a dome, this crater could be turned into a micro-climate where plants could be grown and a breathable atmosphere created.

When it comes to terraforming, Mars is the most popular destination. There are several reasons for this, ranging from its proximity to Earth, its similarities to Earth, and the fact that it once had an environment that was very similar to Earth’s – which included a thicker atmosphere and the presence of warm, flowing water on the surface. Lastly, it is currently believed that Mars may have additional sources of water beneath its surface.

In brief, Mars has a diurnal and seasonal cycle that are very close what we experience here on Earth. In the former case, a single day on Mars lasts 24 hours and 40 minutes. In the latter case, and owing to Mars similarly tilted axis (25.19° compared to Earth’s 23°), Mars experiences seasonal changes that are very similar to Earth’s. Though a single season on Mars lasts roughly twice as long, the temperature variation that results is very similar – ±178 °C (320°F) compared to Earth’s ±160 °C (278°F).

Beyond these, Mars would need to undergo vast transformations in order for human beings to live on its surface. The atmosphere would need to be thickened drastically, and its composition would need to be changed. Currently, Mars’ atmosphere is composed of 96% carbon dioxide, 1.93% argon and 1.89% nitrogen, and the air pressure is equivalent to only 1% of Earth’s at sea level.

Above all, Mars lacks a magnetosphere, which means that its surface receives significantly more radiation than we are used to here on Earth. In addition, it is believed that Mars once had a magnetosphere, and that the disappearance of this magnetic field led to solar wind to stripping away Mars’ atmosphere. This in turn is what led Mars to become the cold, desiccated place it is today.

Ultimately, this means that in order for the planet to become habitable by human standards, it’s atmosphere would need to be significantly thickened and the planet significantly warmed. The composition of the atmosphere would need to change as well, from the current CO²-heavy mix to an nitrogen-oxygen balance of about 70/30. And above all, the atmosphere would need to be replenished every so often to compensate for loss.

Luckily, the first three requirements are largely complimentary, and present a wide range of possible solutions. For starters, Mars’ atmosphere could be thickened and the planet warmed by bombarding its polar regions with meteors. These would cause the poles to melt, releasing their deposits of frozen carbon dioxide and water into the atmosphere and triggering a greenhouse effect.

The introduction of volatile elements, such as ammonia and methane, would also help to thicken the atmosphere and trigger warming. Both could be mined from the icy moons of the outer Solar System, particularly from the moons of Ganymede, Callisto, and Titan. These could also be delivered to the surface via meteoric impacts.

After impacting on the surface, the ammonia ice would sublimate and break down into hydrogen and nitrogen – the hydrogen interacting with he CO² to form water and graphite, while the nitrogen acts as a buffer gas. The methane, meanwhile, would act as a greenhouse gas that would further enhance global warming. In addition, the impacts would throw tons of dust into the air, further fueling the warming trend.

In time, Mars’ ample supplies of water ice – which can be found not only in the poles but in vast subsurface deposits of permafrost – would all sublimate to form warm, flowing water. And with significantly increased air pressure and a warmer atmosphere, humans might be able to venture out onto the surface without the need for pressure suits.

However, the atmosphere will still need to be converted into something breathable. This will be far more time-consuming, as the process of converting the atmospheric CO² into oxygen gas will likely take centuries. In any case, several possibilities have been suggested, which include converting the atmosphere through photosynthesis – either with cyanobacteria or Earth plants and lichens.

Other suggestions include building orbital mirrors, which would be placed near the poles and direct sunlight onto the surface to trigger a cycle of warming by causing the polar ice caps to melt and release their CO² gas. Using dark dust from Phobos and Deimos to reduce the surface’s albedo, thus allowing it to absorb more sunlight, has also been suggested.

In short, there are plenty of options for terraforming Mars. And many of them, if not being readily available, are at least on the table…

Outer Solar System:

Beyond the Inner Solar System, there are several sites that would make for good terraforming targets as well. Particularly around Jupiter and Saturn, there are several sizable moons – some of which are larger than Mercury – that have an abundance of water in the form of ice (and in some cases, maybe even interior oceans).

At the same time, many of these same moons contain other necessary ingredients for functioning ecosystems, such as frozen volatiles  – like ammonia and methane. Because of this, and as part of our ongoing desire to explore farther out into our Solar System, many proposals have been made to seed these moons with bases and research stations. Some plans even include possible terraforming to make them suitable for long-term habitation.

The Jovian Moons:
Jupiter’s largest moons, Io, Europa, Ganymede and Callisto – known as the Galileans, after their founder (Galileo Galilei) – have long been the subject of scientific interest. For decades, scientists have speculated about the possible existence of a subsurface ocean on Europa, based on theories about the planet’s tidal heating (a consequence of its eccentric orbit and orbital resonance with the other moons).

Analysis of images provided by the Voyager 1 and Galileo probes added weight to this theory, showing regions where it appeared that the subsurface ocean had melted through. What’s more, the presence of this warm water ocean has also led to speculation about the existence of life beneath Europa’s icy crust – possibly around hydrothermal vents at the core-mantle boundary.

Because of this potential for habitability, Europa has also been suggested as a possible site for terraforming. As the argument goes, if the surface temperature could be increased, and the surface ice melted, the entire planet could become a ocean world. Sublimation of the ice, which would release water vapor and gaseous volatiles, would then be subject to electrolysis (which already produces a thin oxygen atmosphere).

However, Europa has no magnetosphere of its own, and lies within Jupiter’s powerful magnetic field. As a result, its surface is exposed to significant amounts of radiation – 540 rem of radiation per day compared to about 0.0030 rem per year here on Earth – and any atmosphere we create would begin to be stripped away by Jupiter. Ergo, radiation shielding would need to be put in place that could deflect the majority of this radiation.

And then there is Ganymede, the third most-distant of Jupiter’s Galilean moons. Much like Europa, it is a potential site of terraforming, and presents numerous advantages. For one, it is the largest moon in our Solar System, larger than our own moon and even larger that the planet Mercury. In addition, it also has ample supplies of water ice, is believed to have an interior ocean, and even has its own magnetosphere.

Hence, if the surface temperature were increased and the ice sublimated, Ganymede’s atmosphere could be thickened. Like Europa, it would also become an ocean planet, and its own magnetosphere would allow for it to hold on to more of its atmosphere. However, Jupiter’s magnetic field still exerts a powerful influence over the planet, which means radiation shields would still be needed.

Lastly, there is Callisto, the fourth-most distant of the Galileans. Here too, abundant supplies of water ice, volatiles, and the possibility of an interior ocean all point towards the potential for habitability. But in Callisto’s case, there is the added bonus of it being beyond Jupiter’s magnetic field, which reduces the threat of radiation and atmospheric loss.

The process would begin with surface heating, which would sublimate the water ice and Callisto’s supplies of frozen ammonia. From these oceans, electrolysis would lead to the formation of an oxygen-rich atmosphere, and the ammonia could be converted into nitrogen to act as a buffer gas. However, since the majority of Callisto is ice, it would mean that the planet would lose considerable mass and have no continents. Again, an ocean planet would result, necessitated floating cities or massive colony ships.

The Cronians Moons:
Much like the Jovian Moons, Saturn’s Moons (also known as the Cronian) present opportunities for terraforming. Again, this is due to the presence of water ice, interior oceans, and volatile elements. Titan, Saturn’s largest moon, also has an abundance of methane that comes in liquid form (the methane lakes around its northern polar region) and in gaseous form in its atmosphere. Large caches of ammonia are also believed to exist beneath he surface ice.

Titan is also the only natural satellite to have a dense atmosphere (one and half times the pressure of Earth’s) and the only planet outside of Earth where the atmosphere is nitrogen-rich. Such a thick atmosphere would mean that it would be far easier to equalize pressure for habitats on the planet. What’s more, scientists believe this atmosphere is a prebiotic environment rich in organic chemistry – i.e. similar to Earth’s early atmosphere (only much colder).

As such, converting it to something Earth-like would be feasible. First, the surface temperature would need to be increased. Since Titan is very distant from the Sun, and already has an abundance of greenhouse gases, this could only be accomplished through orbital mirrors. This would sublimate the surface ice, releasing ammonia beneath, which would lead to more heating.

The next step would involve converting the atmosphere to something breathable. As already noted, Titan’s atmosphere is nitrogen-rich, which would remove the need for introducing a buffer gas. And with the availability of water, oxygen could be introduced by generating it through electrolysis. At the same time, the methane and other hydrocarbons would have to be sequestered, in order to prevent an explosive mixture with the oxygen.

But given the thickness and multi-layered nature of Titan’s ice, which is estimated to account for half of its mass, the moon would be very much an ocean planet- i.e. with no continents or landmasses to build on. So once again, any habitats would have to take the form of either floating platforms or large ships.

Enceladus is another possibility, thanks to the recent discovery of a subsurface ocean. Analysis by the Cassini space probe of the water plumes erupting from its southern polar region also indicated the presence of organic molecules. As such, terraforming it would be similar to terraforming Jupiter’s moon of Europa, and would yield a similar ocean moon.

Again, this would likely have to involve orbital mirrors, given Enceladus’ distance from our Sun. Once the ice began to sublimate, electrolysis would generate oxygen gas. The presence of ammonia in the subsurface ocean would also be released, helping to raise the temperature and serving as a source of nitrogen gas, with which to buffer the atmosphere.

In addition to the Solar System, extra-solar planets (aka. exoplanets) are also potential sites for terraforming. Of the 1,941 confirmed exoplanets discovered so far, these planets are those that have been designated “Earth-like. In other words, they are terrestrial planets that have atmospheres and, like Earth, occupy the region around a star where the average surface temperature allows for liquid water (aka. habitable zone).

The first planet confirmed by Kepler to have an average orbital distance that placed it within its star’s habitable zone was Kepler-22b. This planet is located about 600 light years from Earth in the constellation of Cygnus, was first observed on May 12th, 2009 and then confirmed on Dec 5th, 2011. Based on all the data obtained, scientists believe that this world is roughly 2.4 times the radius of Earth, and is likely covered in oceans or has a liquid or gaseous outer shell.

In addition, there are star systems with multiple “Earth-like” planets occupying their habitable zones. Gliese 581 is a good example, a red dwarf star that is located 20.22 light years away from Earth in the Libra constellation. Here, three confirmed and two possible planets exist, two of which are believed to orbit within the star’s habitable zone. These include the confirmed planet Gliese 581 d and the hypothetical Gliese 581 g.

Tau Ceti is another example. This G-class star, which is located roughly 12 light years from Earth in the constellation Cetus, has five possible planets orbiting it. Two of these are Super-Earths that are believed to orbit the star’s habitable zone – Tau Ceti e and Tau Ceti f. However, Tau Ceti e is believed to be too close for anything other than Venus-like conditions to exist on its surface.

In all cases, terraforming the atmospheres of these planet’s would most likely involve the same techniques used to terraform Venus and Mars, though to varying degrees. For those located on the outer edge of their habitable zones, terraforming could be accomplished by introducing greenhouse gases or covering the surface with low albedo material to trigger global warming. On the other end, solar shades and carbon sequestering techniques could reduce temperatures to the point where the planet is considered hospitable.

Potential Benefits:

When addressing the issue of terraforming, there is the inevitable question – “why should we?” Given the expenditure in resources, the time involved, and other challenges that naturally arise (see below), what reasons are there to engage in terraforming? As already mentioned, there is the reasons cited by Musk, about the need to have a “backup location” to prevent any particular cataclysm from claiming all of humanity.

Putting aside for the moment the prospect of nuclear holocaust, there is also the likelihood that life will become untenable on certain parts of our planet in the coming century. As the NOAA reported in March of 2015, carbon dioxide levels in the atmosphere have now surpassed 400 ppm, a level not seen since the the Pliocene Era – when global temperatures and sea level were significantly higher.

And as a series of scenarios computed by NASA show, this trend is likely to continue until 2100, and with serious consequences. In one scenario, carbon dioxide emissions will level off at about 550 ppm toward the end of the century, resulting in an average temperature increase of 2.5 °C (4.5 °F). In the second scenario, carbon dioxide emissions rise to about 800 ppm, resulting in an average increase of about 4.5 °C (8 °F). Whereas the increases predicted in the first scenario are sustainable, in the latter scenario, life will become untenable on many parts of the planet.

As a result of this, creating a long-term home for humanity on Mars, the Moon, Venus, or elsewhere in the Solar System may be necessary. In addition to offering us other locations from which to extract resources, cultivate food, and as a possible outlet for population pressures, having colonies on other worlds could mean the difference between long-term survival and extinction.

There is also the argument that humanity is already well-versed in altering planetary environments. For centuries, humanity’s reliance on industrial machinery, coal and fossil fuels has had a measurable effect Earth’s environment. And whereas the Greenhouse Effect that we have triggered here was not deliberate, our experience and knowledge in creating it here on Earth could be put to good use on planet’s where surface temperatures need to be raised artificially.

In addition, it has also been argued that working with environments where there is a runaway Greenhouse Effect – i.e. Venus – could yield valuable knowledge that could in turn be used here on Earth. Whether it is the use of extreme bacteria, introducing new gases, or mineral elements to sequester carbon, testing these methods out on Venus could help us to combat Climate Change here at home.

It has also been argued that Mars’ similarities to Earth are a good reason to terraform it. Essentially, Mars once resembled Earth, until its atmosphere was stripped away, causing it to lose virtually all the liquid water on its surface. Ergo, terraforming it would be tantamount to returning it to its once-warm and watery glory. The same argument could be made of Venus, where efforts to alter it would restore it to what it was before a runaway Greenhouse Effect turned it into the harsh, extremely hot world it is today.

Last, but not least, there is argument that colonizing the Solar System could usher in an age of “post-scarcity”. If humanity were to build outposts and based on other worlds, mine the asteroid belt and harvest the resources of the Outer Solar System, we would effectively have enough minerals, gases, energy, and water resources to last us indefinitely. It could also help trigger a massive acceleration in human development, defined by leaps and bounds in technological and social progress.

Potential Challenges:

When it comes right down to it, all of the scenarios listed above suffer from one or more of the following problems:

  1. They are not possible with existing technology
  2. They require a massive commitment of resources
  3. They solve one problem, only to create another
  4. They do not offer a significant return on the investment
  5. They would take a really, REALLY long time

Case in point, all of the potential ideas for terraforming Venus and Mars involve infrastructure that does not yet exist and would be very expensive to create. For instance, the orbital shade concept that would cool Venus calls for a structure that would need to be four times the diameter of Venus itself (if it were positioned at L1). It would therefore require megatons of material, all of which would have to be assembled on site.

In contrast, increasing the speed of Venus’s rotation would require energy many orders of magnitude greater than the construction of orbiting solar mirrors. As with removing Venus’ atmosphere, the process would also require a significant number of impactors that would have to be harnessed from the outer solar System – mainly from the Kuiper Belt.

In order to do this, a large fleet of spaceships would be needed to haul them, and they would need to be equipped with advanced drive systems that could make the trip in a reasonable amount of time. Currently, no such drive systems exist, and conventional methods – ranging from ion engines to chemical propellants – are neither fast or economical enough.

To illustrate, NASA’s New Horizons mission took more than 11 years to get make its historic rendezvous with Pluto in the Kuiper Belt, using conventional rockets and the gravity-assist method. Meanwhile, the Dawn mission, which relied relied on ionic propulsion, took almost four years to reach Vesta in the Asteroid Belt. Neither method is practical for making repeated trips to the Kuiper Belt and hauling back icy comets and asteroids, and humanity has nowhere near the number of ships we would need to do this.

The Moon’s proximity makes it an attractive option for terraforming. But again, the resources needed – which would likely include several hundred comets – would again need to be imported from the outer Solar System. And while Mercury’s resources could be harvested in-situ or brought from Earth to paraterraform its northern polar region, the concept still calls for a large fleet of ships and robot builders which do not yet exist.

The outer Solar System presents a similar problem. In order to begin terraforming these moons, we would need infrastructure between here and there, which would mean bases on the Moon, Mars, and within the Asteroid Belt. Here, ships could refuel as they transport materials to the Jovian sand Cronian systems, and resources could be harvested from all three of these locations as well as within the systems themselves.

But of course, it would take many, many generations (or even centuries) to build all of that, and at considerable cost. Ergo, any attempts at  terraforming the outer Solar System would have to wait until humanity had effectively colonized the inner Solar System. And terraforming the Inner Solar System will not be possible until humanity has plenty of space hauler on hand, not to mention fast ones!

The necessity for radiation shields also presents a problem. The size and cost of manufacturing shields that could deflect Jupiter’s magnetic field would be astronomical. And while the resources could be harvest from the nearby Asteroid Belt, transporting and assembling them in space around the Jovian Moons would again require many ships and robotic workers. And again, there would have to be extensive infrastructure between Earth and the Jovian system before any of this could proceed.

As for item three, there are plenty of problems that could result from terraforming. For instance, transforming Jupiter’s and Saturn’s moons into ocean worlds could be pointless, as the volume of liquid water would constitute a major portion of the moon’s overall radius. Combined with their low surface gravities, high orbital velocities and the tidal effects of their parent planets, this could lead to severely high waves on their surfaces. In fact, these moons could become totally unstable as a result of being altered.

There is also several questions about the ethics of terraforming. Basically, altering other planets in order to make them more suitable to human needs raises the natural question of what would happen to any lifeforms already living there. If in fact Mars and other Solar System bodies have indigenous microbial (or more complex) life, which many scientists suspect, then altering their ecology could impact or even wipe out these lifeforms. In short, future colonists and terrestrial engineers would effectively be committing genocide.

Another argument that is often made against terraforming is that any effort to alter the ecology of another planet does not present any immediate benefits. Given the cost involved, what possible incentive is there to commit so much time, resources and energy to such a project? While the idea of utilizing the resources of the Solar System makes sense in the long-run, the short-term gains are far less tangible.

Basically, harvested resources from other worlds is not economically viable when you can extract them here at home for much less. And real-estate is only the basis of an economic model if the real-estate itself is desirable. While MarsOne has certainly shown us that there are plenty of human beings who are willing to make a one-way trip to Mars, turning the Red Planet, Venus or elsewhere into a “new frontier” where people can buy up land will first require some serious advances in technology, some serious terraforming, or both.

As it stands, the environments of Mars, Venus, the Moon, and the outer Solar System are all hostile to life as we know it. Even with the requisite commitment of resources and people willing to be the “first wave”, life would be very difficult for those living out there. And this situation would not change for centuries or even millennia. Like it not, transforming a planet’s ecology is very slow, laborious work.


So… after considering all of the places where humanity could colonize and terraform, what it would take to make that happen, and the difficulties in doing so, we are once again left with one important question. Why should we? Assuming that our very survival is not at stake, what possible incentives are there for humanity to become an interplanetary (or interstellar) species?

Perhaps there is no good reason. Much like sending astronauts to the Moon, taking to the skies, and climbing the highest mountain on Earth, colonizing other planets may be nothing more than something we feel we need to do. Why? Because we can! Such a reason has good enough in the past, and it will likely be sufficient again in the not-to-distant future.

This should is no way deter us from considering the ethical implications, the sheer cost involved, or the cost-to-benefit ratio. But in time, we might find that we have no choice but to get out there, simply because Earth is just becoming too stuffy and crowded for us!

We have written many interesting articles about terraforming here at Universe Today. Here’s Could We Terraform the Moon?, Should We Terraform Mars?, How Do We Terraform Mars?, How Do We Terraform Venus?, and Student Team Wants to Terraform Mars Using Cyanobacteria.

We’ve also got articles that explore the more radical side of terraforming, like Could We Terraform Jupiter?, Could We Terraform The Sun?, and Could We Terraform A Black Hole?

Astronomy Cast also has good episodes on the subject, like Episode 96: Humans to Mar, Part 3 – Terraforming Mars

For more information, check out Terraforming Mars  at NASA Quest! and NASA’s Journey to Mars.

The post The Definitive Guide To Terraforming appeared first on Universe Today.

By Jove: Jupiter Reaches Opposition on February 6th

Did you see the brilliant Full Snow Moon rising last night? Then you might’ve also noticed a bright nearby ‘star’. Alas, that was no star, but the largest planet in our solar system, Jupiter. And it was no coincidence that the king of the gas giants is near the Full Moon this February, as Jupiter […]

NASA’s “Remastered” View of Europa is the Best Yet

Europa, Jupiter’s sixth-closest moon, has long been a source of fascination and wonder for astronomers. Not only is it unique amongst its Jovian peers for having a smooth, ice-covered surface, but it is believed that warm, ocean waters exist beneath that crust – which also makes it a strong candidate for extra-terrestrial life. And now, […]

Observing Challenge: Catch a Series of Mutual Eclipses by Jupiter’s Moons

Missing the planets this month? With Mars receding slowly to the west behind the Sun at dusk, the early evening sky is nearly devoid of planetary action in the month of November 2014. Stay up until about midnight local, however, and brilliant Jupiter can be seen rising to the east.  Well placed for northern hemisphere […]