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.
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.
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:
- Natural Hazards
- 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.
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