According to a new study from Brown University, it appears Ceres has more organic molecules on its surface than previously thought
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According to a new study from Brown University, it appears Ceres has more organic molecules on its surface than previously thought
The post Ceres Has Even More Organic Molecules on it Than Previously Thought appeared first on Universe Today.
Two new studies produced by the Dawn mission team have shown that the protoplanet may have once had an ocean, the remnants of which are likely in its interior today.
The post Wow! Asteroid/Dwarf Planet Ceres Once had an Ocean? appeared first on Universe Today.
A new study by an international team of scientists has found a connection between debris disks and giant planets, which could aid in the hunt for exoplanets.
The post Debris Disks Around Stars Could Point the Way to Giant Exoplanets appeared first on Universe Today.
An international team of scientists recently used the Hubble space telescope to spot a unique binary asteroid that behaves like a comet in in the Main Asteroid Belt.
The post Hubble Spots Unique Object in the Main Asteroid Belt appeared first on Universe Today.
Fraser Cain and Isaac Arthur team up again to bring you another epic collaboration. This time, it’s construction tips from an engineer from a Type 2 Civilization.
The post Construction Tips from a Type 2 Engineer: Collaboration with Isaac Arthur appeared first on Universe Today.
Between the orbits of Mars and Jupiter lies the Solar System’s Main Asteroid Belt. Consisting of millions of objects that range in size from hundreds of kilometers in diameter (like Ceres and Vesta) to one kilometer or more, the Asteroid Belt has long been a source of fascination for astronomers. Initially, they wondered why the many objects that make it up did not come together to form a planet. But more recently, human beings have been eyeing the Asteroid Belt for other purposes.
Whereas most of our efforts are focused on research – in the hopes of shedding additional light on the history of the Solar System – others are looking to tap for its considerable wealth. With enough resources to last us indefinitely, there are many who want to begin mining it as soon as possible. Because of this, knowing exactly how long it would take for spaceships to get there and back is becoming a priority.
The distance between the Asteroid Belt and Earth varies considerably depending on where we measure to. Based on its average distance from the Sun, the distance between Earth and the edge of the Belt that is closest to it can be said to be between 1.2 to 2.2 AUs, or 179.5 and 329 million km (111.5 and 204.43 million mi).
However, at any given time, part of the Asteroid Belt will be on the opposite side of the Sun, relative to Earth. From this vantage point, the distance between Earth and the Asteroid Blt ranges from 3.2 and 4.2 AU – 478.7 to 628.3 million km (297.45 to 390.4 million mi). To put that in perspective, the distance between Earth and the Asteroid Belt ranges between being slightly more than the distance between the Earth and the Sun (1 AU), to being the same as the distance between Earth and Jupiter (4.2 AU) when they are at their closest.
But of course, for reasons of fuel economy and time, asteroid miners and exploration missions are not about to take the long way! As such, we can safely assume that the distance between Earth and the Asteroid Belt when they are at their closest is the only measurement worth considering.
The Asteroid Belt is so thinly populated that several unmanned spacecraft have been able to move through it on their way to the outer Solar System. In more recent years, missions to study larger Asteroid Belt objects have also used this to their advantage, navigating between the smaller objects to rendezvous with bodies like Ceres and Vesta. In fact, due to the low density of materials within the Belt, the odds of a probe running into an asteroid are now estimated at less than one in a billion.
The first spacecraft to make a journey through the asteroid belt was the Pioneer 10 spacecraft, which entered the region on July 16th, 1972 (a journey of 135 days). As part of its mission to Jupiter, the craft successfully navigated through the Belt and conducted a flyby of Jupiter (in December of 1973) before becoming the first spacecraft to achieve escape velocity from the Solar System.
At the time, there were concerns that the debris would pose a hazard to the Pioneer 10 space probe. But since that mission, 11 additional spacecraft have passed through the Asteroid Belt without incident. These included Pioneer 11, Voyager 1 and 2, Ulysses, Galileo, NEAR, Cassini, Stardust, New Horizons, the ESA’s Rosetta, and most recently, the Dawn spacecraft.
For the most part, these missions were part of missions to the outer Solar System, where opportunities to photograph and study asteroids were brief. Only the Dawn, NEAR and JAXA’s Hayabusa missions have studied asteroids for a protracted period in orbit and at the surface. Dawn explored Vesta from July 2011 to September 2012, and is currently orbiting Ceres (and sending back gravity data on the dwarf planet’s gravity) and is expected to remain there until 2017.
The fastest mission humanity has ever mounted was the New Horizons mission, which was launched from Earth on Jan. 19th, 2006. The mission began with a speedy launch aboard an Atlas V rocket, which accelerated it to a a speed of about 16.26 km per second (58,536 km/h; 36,373 mph). At this speed, the probe reached the Asteroid Belt by the following summer, and made a close approach to the tiny asteroid 132524 APL by June 13th, 2006 (145 days after launching).
However, even this pales in comparison to Voyager 1, which was launched on Sept. 5th, 1977 and reached the Asteroid Belt on Dec. 10th, 1977 – a total of 96 days. And then there was the Voyager 2 probe, which launched 15 days after Voyager 1 (on Sept. 20th), but still managed to arrive on the same date – which works out to a total travel time of 81 days.
Not bad as travel times go. At these speed, a spacecraft could make the trip to the Asteroid Belt, spend several weeks conducting research (or extracting ore), and then make it home in just over six months time. However, one has to take into account that in all these cases, the mission teams did not decelerate the probes to make a rendezvous with any asteroids.
Ergo, a mission to the Asteroid Belt would take longer as the craft would have to slow down to achieve orbital velocity. And they would also need some powerful engines of their own in order to make the trip home. This would drastically alter the size and weight of the spacecraft, which would inevitably mean it would be bigger, slower and a heck of a lot more expensive than anything we’ve sent so far.
Another possibility would be to use ionic propulsion (which is much more fuel efficient) and pick up a gravity assist by conducting a flyby of Mars – which is precisely what the Dawn mission did. However, even with a boost from Mars’ gravity, the Dawn mission still took over three years to reach the asteroid Vesta – launching on Sept. 27th, 2007, and arriving on July 16th, 2011, (a total of 3 years, 9 months, and 19 days). Not exactly good turnaround!
A number of possibilities exist that could drastically reduce both travel time and fuel consumption to the Asteroid Belt, many of which are currently being considered for a number of different mission proposals. One possibility is to use spacecraft equipped with nuclear engines, a concept which NASA has been exploring for decades.
In a Nuclear Thermal Propulsion (NTP) rocket, uranium or deuterium reactions are used to heat liquid hydrogen inside a reactor, turning it into ionized hydrogen gas (plasma), which is then channeled through a rocket nozzle to generate thrust. A Nuclear Electric Propulsion (NEP) rocket involves the same basic reactor converting its heat and energy into electrical energy, which would then power an electrical engine.
In both cases, the rocket would rely on nuclear fission or fusion to generates propulsion rather than chemical propellants, which has been the mainstay of NASA and all other space agencies to date. According to NASA estimates, the most sophisticated NTP concept would have a maximum specific impulse of 5000 seconds (50 kN·s/kg).
Using this engine, NASA scientists estimate that it would take a spaceship only 90 days to get to Mars when the planet was at “opposition” – i.e. as close as 55,000,000 km from Earth. Adjusted for a distance of 1.2 AUs, that means that a ship equipped with a NTP/NEC propulsion system could make the trip in about 293 days (about nine months and three weeks). A little slow, but not bad considering the technology exists.
Another proposed method of interstellar travel comes in the form of the Radio Frequency (RF) Resonant Cavity Thruster, also known as the EM Drive. Originally proposed in 2001 by Roger K. Shawyer, a UK scientist who started Satellite Propulsion Research Ltd (SPR) to bring it to fruition, this drive is built around the idea that electromagnetic microwave cavities can allow for the direct conversion of electrical energy to thrust.
According to calculations based on the NASA prototype (which yielded a power estimate of 0.4 N/kilowatt), a spacecraft equipped with the EM drive could make the trip to Mars in just ten days. Adjusted for a trip to the Asteroid Belt, so a spacecraft equipped with an EM drive would take an estimated 32.5 days to reach the Asteroid Belt.
Impressive, yes? But of course, that is based on a concept that has yet to be proven. So let’s turn to yet another radical proposal, which is to use ships equipped with an antimatter engine. Created in particle accelerators, antimatter is the most dense fuel you could possibly use. When atoms of matter meet atoms of antimatter, they annihilate each other, releasing an incredible amount of energy in the process.
According to the NASA Institute for Advanced Concepts (NIAC), which is researching the technology, it would take just 10 milligrams of antimatter to propel a human mission to Mars in 45 days. Based on this estimate, a craft equipped with an antimatter engine and roughly twice as much fuel could make the trip to the Asteroid Belt in roughly 147 days. But of course, the sheer cost of creating antimatter – combined with the fact that an engine based on these principles is still theoretical at this point – makes it a distant prospect.
Basically, getting to the Asteroid Belt takes quite a bit of time, at least when it comes to the concepts we currently have available. Using theoretical propulsion concepts, we are able to cut down on the travel time, but it will take some time (and lots of money) before those concepts are a reality. However, compared to many other proposed missions – such as to Europa and Enceladus – the travel time is shorter, and the dividends quite clear.
As already stated, there are enough resources – in the form of minerals and volatiles – in the Asteroid Belt to last us indefinitely. And, should we someday find a way to cost-effective way to send spacecraft there rapidly, we could tap that wealth and begin to usher in an age of post-scarcity! But as with so many other proposals and mission concepts, it looks like we’ll have to wait for the time being.
We have written many articles about the asteroid belt for Universe Today. Here’s Where Do Asteroids Come From?, Why the Asteroid Belt Doesn’t Threaten Spacecraft, and Why isn’t the Asteroid Belt a Planet?.
The post How Long Does it Take to get to the Asteroid Belt? appeared first on Universe Today.
We continue our “Definitive Guide to Terraforming” series with a look at another body in our Solar System – the dwarf planet Ceres. Like many moons in the outer Solar System, Ceres is a world of ice and rock, and is the largest body in the Asteroid Belt. Humans beings could one day call it home, but could its surface also be made “Earth-like”?
In the Solar System’s Main Asteroid Belt, there are literally millions of celestial bodies to be found. And while the majority of these range in size from tiny rocks to planetesimals, there are also a handful of bodies that contain a significant percentage of the mass of the entire Asteroid Belt. Of these, the dwarf planet Ceres is the largest, constituting of about a third of the mass of the belt and being the sixth-largest body in the inner Solar System by mass and volume.
In addition to its size, Ceres is the only body in the Asteroid Belt that has achieved hydrostatic equilibrium – a state where an object becomes rounded by the force of its own gravity. On top of all that, it is believed that this dwarf planet has an interior ocean, one which contains about one-tenth of all the water found in the Earth’s oceans. For this reason, the idea of colonizing Ceres someday has some appeal, as well as terraforming.
Ceres also has the distinction of being the only dwarf planet located within the orbit of Neptune. This is especially interesting considering the fact that in terms of size and composition, Ceres is quite similar to several Trans-Neptunian Objects (TNOs) – such as Pluto, Eris, Haumea, Makemake, and several other TNOs that are considered to be potential candidates for dwarf planets status.
Current estimates place Ceres’ mean radius at 473 km, and its mass at roughly 9.39 × 1020 kg (the equivalent of 0.00015 Earths or 0.0128 Moons). With this mass, Ceres comprises approximately a third of the estimated total mass of the Asteroid Belt (between 2.8 × 1021 and 3.2 × 1021 kg), which in turn is approximately 4% of the mass of the Moon.
The next largest objects are Vesta, Pallas and Hygiea, which have mean diameters of more than 400 km and masses of 2.6 x 1020 kg, 2.11 x 1020 kg, and 8.6 ×1019 kg respectively. The mass of Ceres is large enough to give it a nearly spherical shape, which makes it unique amongst objects and minor planets in the Asteroid Belt.
Ceres follows a slightly inclined and moderately eccentric orbit, ranging from 2.5577 AU (382.6 million km) from the Sun at perihelion and 2.9773 AU (445.4 million km) at aphelion. It has an orbital period of 1,680 Earth days (4.6 years) and takes 0.3781 Earth days (9 hours and 4 minutes) to complete a single rotation on its axis.
Based on its size and density (2.16 g/cm³), Ceres is believed to be differentiated between a rocky core and an icy mantle. Based on evidence provided by the Keck telescope in 2002, the mantle is estimated to be 100 km-thick, and contains up to 200 million cubic km of water, which is equivalent to about 10% of what is in Earth’s oceans, and more water than all the freshwater on Earth.
What’s more, infrared data on the surface also suggests that Ceres may have an ocean beneath its icy mantle. If true, it is possible that this ocean could harbor microbial extraterrestrial life, similar to what has been proposed about Mars, Titan, Europa and Enceladus. It has further been hypothesized that ejecta from Ceres could have sent microbes to Earth in the past.
Other possible surface constituents include iron-rich clay minerals (cronstedtite) and carbonate minerals (dolomite and siderite), which are common minerals in carbonaceous chondrite meteorites. The surface of Ceres is relatively warm, with the maximum temperature estimated to reach approximately 235 K (-38 °C, -36 °F) when the Sun is overhead.
Assuming the presence of sufficient antifreeze (such as ammonia), the water ice would become unstable at this temperature. Therefore, it is possible that Ceres may have a tenuous atmosphere caused by outgassing from water ice on the surface. The detection of significant amounts of hydroxide ions near Ceres’ north pole, which is a product of water vapor dissociation by ultraviolet solar radiation, is another indication of this.
However, it was not until early 2014 that several localized mid-latitude sources of water vapor were detected on Ceres. Possible mechanisms for the vapor release include sublimation from exposed surface ice (as with comets), cryovolcanic eruptions resulting from internal heat, and subsurface pressurization. The limited amount of data thus far suggests that the vaporization is more likely caused by sublimation from exposure to the Sun.
As with the moons of Jupiter and Saturn, terraforming Ceres would first require that the surface temperature be raised in order to sublimate its icy outer layer. This could be done by using orbital mirrors to focus sunlight onto the surface, by detonating thermonuclear devices on the surface, or colliding small asteroids harvested from the Main Belt onto the surface.
This would result in Ceres’ crust thawing and turning into a dense, water vapor-rich atmosphere. The orbital mirrors would once again come into play here, where they would be used to trigger photolysis and transform the water vapor into hydrogen and oxygen gas. While the hydrogen gas would be lost to space, the oxygen would remain closer to the surface.
Ammonia could also be harvested locally, since Ceres is believed to have plentiful deposits of ammonia-rich clay soils. With the introduction of 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. The end result would be an ocean world with seas that are 100 km in depth.
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 Ceres moons, this could involve building large “Shell Worlds” to encase it, keeping the newly-created atmospheres inside long enough to effect long-term changes. Within this shell, Ceres temperature could be increased, UV lights would convert water vapor to oxygen gas, ammonia could be converted to nitrogen, and other elements could be added as needed.
In the same vein, a dome could be built over one or more of Ceres’ craters – particularly the Occator, Kerwan and Yalode craters – where the surface temperature could slowly be raised, and silicates and organic molecules could be introduced to create a terrestrial-like environment. Using water harvested from the surface, this land could be irrigated, oxygen gas could be processed, and nitrogen could be pumped in to act as a buffer gas.
The benefits of colonizing and (para)terraforming Ceres are numerous. For instance, it would take comparatively less energy to sublimate the surface than with the moons of Jupiter or Saturn. Under normal conditions, Ceres’ surface is warm enough (and it is likely there is sufficient ammonia) that its ices are unstable.
Also, Ceres appears from all accounts to be rich in resources, which include water ices and ammonia, and has a surface that is equivalent in total land area to Argentina. Also, the surface receives an estimated 150 W/m2 of solar irradiance at aphelion, one ninth that of Earth. This level of energy is high enough that solar-power facilities could run on its surface.
And being the largest body in the asteroid belt, Ceres could become the main base and transport hub for future asteroid mining infrastructure, allowing mineral resources to be transported to Mars, the Moon, and Earth. Its small escape velocity, combined with large amounts of water ice, means that it also could process rocket fuel, water and oxygen gas on site for ships going through and beyond the Asteroid Belt.
Despite the benefits of a colonized or transformed Ceres, there are also numerous challenges that would need to be addressed first. As always, they can be broken down into the following categories – Distance, Resources and Infrastructure, Hazards and Sustainability. For starters, Ceres and Earth are (on average) approximately 264,411,977 km apart, which is 1.7675 times the distance between the Earth and the Sun (and twice that between Earth and Mars).
Hence, any crewed mission to Ceres – which would involve the transport of both colonists, construction materials, and robotic workers – would take a considerable amount of time and involve a large expenditure in fuel. To put it in perspective, missions to Mars have taken anywhere from 150 to over 300 days, depending on how much fuel was expended. Since Ceres is roughly twice that distance, we can safely say that it would take a minimum of a year for a spacecraft to get there.
However, since these spacecraft would likely be several orders of magnitude heavier than anything previously flown to Mars – i.e. large enough to carry crews, supplies and heavy equipment – they would either need tremendous amounts of thrust to make the journey in the same amount of time, would have to spend much longer in transit, or would need more advanced propulsion systems altogether.
And while NASA currently has plans on the table to build laser-sail spacecraft that could make it Mars in three days times, these plans are not practical as far as colonization or terraforming are concerned. More than likely, advanced drive systems such as Nuclear-Thermal Propulsion (NTP) or a Fusion-drive system would be needed. And while certainly feasible, no such drive systems exist at this time.
Second, the process of building colonies on Ceres’ surface and/or orbital mirrors in orbit would require a huge commitment in material and financial resources. These could be harvested from the Asteroid Belt, but the process would be time-consuming, expensive, and require a large fleet of haulers and robotic miners. There would also need to be a string of bases between Earth and the Asteroid Belt in order to refuel and resupply these missions – i.e. a Lunar base, a permanent base on Mars, and most likely bases in the Asteroid Belt as well.
In terms of hazards, Ceres is not known to have a magnetic field, and would therefore not be shielded from cosmic rays or other forms of radiation. This would necessitate that any colonies on the surface either have significant radiation shielding, or that an orbital shield be put in place to deflect a significant amount of the radiation the planet receives. This latter idea further illustrates the problem of resource expenditure.
The extensive system of craters on Ceres attests to the fact that impactors would be a problem, requiring that they be monitored and redirected away from the planet. The surface gravity on Ceres is also quite low, being roughly 2.8% that on Earth (0.27 m/s2 vs. 9.8 m/s2). This would raise the issue of the long-term effects of near-weightlessness on the human body, which (like exposure to zero-g environments) would most likely involve loss of muscle mass, bone density, and damage to vital organs.
In terms of sustainability, terraforming Ceres presents a major problem. If the dwarf planet’s surface ice were to be sublimated, the result would be an ocean planet with depths of around 100 km. With a mean radius of less than 500 km, this means that about 21% of the planet’s diameter would consist of water. It is unlikely that such a planet (especially one with gravity as low as Ceres’) would be able to retain its oceans for long, and a significant amount of the water would likely be lost to space.
Under the circumstances, it seems like it would make more sense to colonize or paraterraform Ceres than to subject it to full terraforming. However, any such venture would have to wait upon the creation of a Lunar base, a settlement on Mars, and the development of more advanced propulsion technology. It was also require the creation of a fleet of deep-space ships and an army of construction and mining robots.
However, if and when such a colony were created, the resources of the Asteroid Belt would be at our disposal. Humanity would effectively enter an age of post-scarcity, and would be in a position to mount missions deeper into the Solar System (which could include colonizing the Jovian and Cronian systems, and maybe even the Trans-Neptunian region).
So for the time being, it looks like we’ll just have to be satisfied with developing faster spacecraft, returning to the Moon, and mounting crewed missions to Mars. As they say, baby steps!
We have written many interesting articles on terraforming here at Universe Today. Here’s The Definitive Guide to Terraforming, How Do We Terraforming Mars?, How Do We Terraform Venus?, How Do We Terraform the Moon?, How Do We Terraform Mercury?, How Do We Terraform Jupiter’s Moons?, and How Do We Terraform Saturn’s Moons?
For learn more about Ceres here, here are some articles on the many bright spots captured by the Dawn probe, and what they likely are. And here are some articles on the Asteroid Belt and Why it Isn’t a Planet.
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).
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.
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.
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:
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?
Astronomy Cast also has good episodes on the subject, like Episode 61: Saturn’s Moons.
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