Okay, so this article is Colonizing the Outer Solar System, and is actually part 2 of our team up with Fraser Cain of Universe Today, who looked at colonizing the inner solar system. You might want jump over there now and watch that part first, if you are coming in from having seen part 1, welcome, it is great having you here.
Without further ado let us get started. There is no official demarcation between the inner and outer solar system but for today we will be beginning the outer solar system at the Asteroid Belt.
Artist concept of the asteroid belt. Credit: NASA
The Asteroid Belt is always of interest to us for colonization. We have talked about mining them before if you want the details on that but for today I’ll just remind everyone that there are very rich in metals, including precious metals like gold and platinum, and that provides all the motivation we need to colonize them. We have a lot of places to cover so we won’t repeat the details on that today.
You cannot terraform asteroids the way you could Venus or Mars so that you could walk around on them like Earth, but in every respect they have a lot going for them as a candidate. They’ve got plenty for rock and metal for construction, they have lots of the basic organic elements, and they even have some water. They also get a decent amount of sunlight, less than Mars let alone Earth, but still enough for use as a power source and to grow plants.
But they don’t have much gravity, which – pardon the pun – has its ups and downs. There just isn’t much mass in the Belt. The entire thing has only a small fraction of the mass of our moon, and over half of that is in the four biggest asteroids, essentially dwarf planets in their own right. The remainder is scattered over millions of asteroids. Even the biggest, Ceres, is only about 1% of 1% of Earth’s mass, has a surface gravity of 3% Earth-normal, and an escape velocity low enough most model rockets could get into orbit. And again, it is the biggest, most you could get away from by jumping hard and if you dropped an object on one it might take a few minutes to land.
Don’t blink… an artist’s conception of an asteroid blocking out a distant star. Image credit: NASA.
You can still terraform one though, by definition too. The gentleman who coined the term, science fiction author Jack Williamson, who also coined the term genetic engineering, used it for a smaller asteroid just a few kilometers across, so any definition of terraforming has to include tiny asteroids too.
Of course in that story it’s like a small planet because they had artificial gravity, we don’t, if we want to fake gravity without having mass we need to spin stuff around. So if we want to terraform an asteroid we need to hollow it out and fill it with air and spin it around.
Of course you do not actually hollow out the asteroid and spin it, asteroids are loose balls of gravel and most would fly apart given any noticeable spin. Instead you would hollow it out and set a cylinder spinning inside it. Sort of like how a good thermos has an outside container and inside one with a layer of vacuum in between, we would spin the inner cylinder.
You wouldn’t have to work hard to hollow out an asteroid either, most aren’t big enough to have sufficient gravity and pressure to crush an empty beer can even at their center. So you can pull matter out from them very easily and shore up the sides with very thin metal walls or even ice. Or just have your cylinder set inside a second non-spinning outer skin or superstructure, like your washer or dryer.
You can then conduct your mining from the inside, shielded from space. You could ever pressurize that hollowed out area if your spinning living area was inside its own superstructure. No gravity, but warmth and air, and you could get away with just a little spin without tearing it apart, maybe enough for plants to grow to normally.
It should be noted that you can potentially colonize even the gas giants themselves, even though our focus today is mostly on their moons. That requires a lot more effort and technology then the sorts of colonies we are discussing today, Fraser and I decided to keep things near-future and fairly low tech, though he actually did an article on colonizing Jupiter itself last year that was my main source material back before got to talking and decided to do a video together.
Jupiter with Io and Ganymede taken by amateur astronomer Damian Peach. Credit: NASA / Damian Peach
Hydrogen is plentiful on Jupiter itself and floating refineries or ships that fly down to scoop it up might be quite useful, but again today we are more interested in its moons. The biggest problem with colonizing the moons of Jupiter is all the radiation the planet gives off.
Europa is best known as a place where the surface is covered with ice but beneath it is thought to be a vast subsurface ocean. It is the sixth largest moon coming right behind our own at number five and is one of the original four moons Galileo discovered back in 1610, almost two centuries before we even discovered Uranus, so it has always been a source of interest. However as we have discovered more planets and moons we have come to believe quite a few of them might also have subsurface oceans too.
Now what is neat about them is that water, liquid water, always leaves the door open to the possibility of life already existing there. We still know so little about how life originally evolved and what conditions permit that to occur that we cannot rule out places like Europa already having their own plants and animals swimming around under that ice.
They probably do not and obviously we wouldn’t want to colonize them, beyond research bases, if they did, but if they do not they become excellent places to colonize. You could have submarine cities in such places floating around in the sea or those buried in the surface ice layer, well shielded from radiation and debris. The water also geysers up to the surface in some places so you can start off near those, you don’t have to drill down through kilometers of ice on day one.
Water, and hydrogen, are also quite uncommon in the inner solar system so having access to a place like Europa where the escape velocity is only about a fifth of our own is quite handy for export. Now as we move on to talk about moons a lot it is important to note that when I say something has a fifth of the escape velocity of Earth that doesn’t mean it is fives time easier to get off of. Energy rises with the square of velocity so if you need to go five times faster you need to spend 5-squared or 25 times more energy, and even more if that place has tons of air creating friction and drag, atmospheres are hard to claw your way up through though they make landing easier too. But even ignoring air friction you can move 25 liters of water off of Europa for every liter you could export from Earth and even it is a very high in gravity compared to most moons and comets. Plus we probably don’t want to export lots of water, or anything else, off of Earth anyway.
Artist’s concept of Trojan asteroids, small bodies that dominate our solar system. Credit: NASA
We should start by noting two things. First, the Asteroid Belt is not the only place you find asteroids, Jupiter’s Trojan Asteroids are nearly as numerous, and every planet, including Earth, has an equivalent to Jupiter’s Trojan Asteroids at its own Lagrange Points with the Sun. Though just as Jupiter dwarfs all the other planets so to does its collection of Lagrangian objects. They can quite big too, the largest 624 Hektor, is 400 km across, and has a size and shape similar to Pennsylvania.
And as these asteroids are at stable Lagrange Points, they orbit with Jupiter but always ahead and behind it, making transit to and from Jupiter much easier and making good waypoints.
Before we go out any further in the solar system we should probably address how you get the energy to stay alive. Mars is already quite cold compared to Earth, and the Asteroids and Jupiter even more so, but with thick insulation and some mirrors to bounce light in you can do fairly decently. Indeed, sunlight out by Jupiter is already down to just 4% of what Earth gets, meaning at Jovian distances it is about 50 W/m²
That might not sound like much but it is actually almost a third of what average illumination is on Earth, when you factor in atmospheric reflection, cloudy days, nighttime, and higher, colder latitudes. It is also a good deal brighter than the inside of most well-lit buildings, and is enough for decently robust photosynthesis to grow food. Especially with supplemental light from mirrors or LED growth lamps.
But once you get out to Saturn and further that becomes increasingly impractical and a serious issue, because while food growth does not show up on your electric bill it is what we use virtually all our energy for. Closer in to the sun we can use solar panels for power and we do not need any power to grow food. As we get further out we cannot use solar and we need to heat or cold habitats and supply lighting for food, so we need a lot more power even as our main source dries up.
So what are our options? Well the first is simple, build bigger mirrors. A mirror can be quite large and paper thin after all. Alternatively we can build those mirrors far away, closer to the sun, and and either focus them on the place we want illuminated or send an energy beam, microwaves perhaps or lasers, out to the destination to supply energy.
We also have the option of using fission, if we can find enough Uranium or Thorium. There is not a lot of either in the solar system, in the area of about one part per billion, but that does amount to hundreds of trillions of tons, and it should only take a few thousand tons a year to supply Earth’s entire electric grid. So we would be looking at millions of years worth of energy supply.
Of course fusion is even better, particularly since hydrogen becomes much more abundant as you get further from the Sun. We do not have fusion yet, but it is a technology we can plan around probably having inside our lifetimes, and while uranium and thorium might be counted in parts per billion, hydrogen is more plentiful than every other element combines, especially once you get far from the Sun and Inner Solar System.
So it is much better power source, an effectively unlimited one except on time scales of billions and trillion of years. Still, if we do not have it, we still have other options. Bigger mirrors, beaming energy outwards from closer to the Sun, and classic fission of Uranium and Thorium. Access to fusion is not absolutely necessary but if you have it you can unlock the outer solar system because you have your energy supply, a cheap and abundant fuel supply, and much faster and cheaper spaceships.
Of course hydrogen, plain old vanilla hydrogen with one proton, like the sun uses for fusion, is harder to fuse than deuterium and may be a lot longer developing, we also have fusion using Helium-3 which has some advantages over hydrogen, so that is worth keeping in mind as well as we proceed outward.
Since NASA’s Cassini spacecraft arrived at Saturn, the planet’s appearance has changed greatly. This view shows Saturn’s northern hemisphere in 2016, as that part of the planet nears its northern hemisphere summer solstice in May 2017. Image credit: NASA/JPL-Caltech/Space Science Institute.
Okay, let’s move on to Saturn, and again our focus is on its moons more than the planet itself. The biggest of those an the most interesting for colonization is Titan.
Titan is aptly named, this titanic moon contains more mass than than all of Saturn’s sixty or so other moons and by an entire order of magnitude at that. It is massive enough to hold an atmosphere, and one where the surface pressure is 45% higher than here on Earth. Even though Titan is much smaller than Earth, its atmosphere is about 20% more massive than our own. It’s almost all nitrogen too, even more than our own atmosphere, so while you would need a breather mask to supply oxygen and it is also super-cold, so you’d need a thick insulated suit, it doesn’t have to be a pressure suit like it would on Mars or almost anyplace else.
There’s no oxygen in the atmosphere, what little isn’t nitrogen is mostly methane and hydrogen, but there is plenty of oxygen in the ice on Titan which is quite abundant. So it has everything we need for life except energy and gravity. At 14% of earth normal it is probably too low for people to comfortably and safely adapt to, but we’ve already discussed ways of dealing with that. It is low enough that you could probably flap your arms and fly, if you had wing attached.
On the left is TALISE (Titan Lake In-situ Sampling Propelled Explorer), the ESA proposal. This would have it’s own propulsion, in the form of paddlewheels. Credit: bisbos.com
It needs some source of energy though, and we discussed that. Obviously if you’ve got fusion you have all the hydrogen you need, but Titan is one of those places we would probably want to colonize early on if we could, it is something you need a lot of to terraform other places, and is also rich in a lot of the others things we want. So we often think of it as a low-tech colony since it is one we would want early on.
In an scenario like that it is very easy to imagine a lot of local transit between Titan and its smaller neighboring moons, which are more rocky and might be easier to dig fissile materials like Uranium and Thorium out of. You might have a dozen or so small outposts on neighboring moons mining fissile materials and other metals and a big central hub on Titan they delivered that too which also exported Nitrogen to other colonies in the solar system.
Moving back and forth between moons is pretty easy, especially since things landing on Titan can aerobrake quite easily, whereas Titan itself has a pretty strong gravity well and thick atmosphere to climb out of but is a good candidate for a space elevator, since it requires nothing more sophisticated than a Lunar Elevator on our own moon and has an abundant supply of the materials needed to make Zylon for instance, a material strong enough to make an elevator there and which we can mass manufacture right now.
Titan might be the largest and most useful of Saturn’s moons, but again it isn’t the only one and not all of the other are just rocks for mining. At last count it has over sixty and many of them quite large. One of those, Enceladus, Saturn’s sixth largest moon, is a lot like Jupiter’s Moon Europa, in that we believe it has a large and thick subsurface ocean. So just like Europa it is an interesting candidate for Colonization. So Titan might be the hub for Saturn but it wouldn’t be the only significant place to colonize.
While Saturn is best known for its amazing rings, they tend to be overlooked in colonization. Now those rings are almost all ice and in total mass about a quarter as much as Enceladus, which again is Saturn’s Sixth largest moon, which is itself not even a thousandth of the Mass of Titan.
In spite of that the rings are not a bad place to set up shop. Being mostly water, they are abundant in hydrogen for fusion fuel and have little mass individually makes them as easy to approach or leave as an asteroid. Just big icebergs in space really, and there are many moonlets in the rings that can be as large as half a kilometer across. So you can burrow down inside one for protection from radiation and impacts and possibly mine smaller ones for their ice to be brought to places where water is not abundant.
In total those rings, which are all frozen water, only mass about 2% of Earth’s oceans, and about as much as the entire Antarctic sheet. So it is a lot of fresh water that is very easy to access and move elsewhere, and ice mines in the rings of Saturn might be quite useful and make good homes. Living inside an iceball might not sound appealing but it is better than it sounds like and we will discuss that more when we reach the Kupier Belt.
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
But first we still have two more planets to look at, Uranus and Neptune.
Uranus, and Neptune, are sometimes known as Ice Giants instead of Gas Giants because it has a lot more water. It also has more ammonia and methane and all three get called ices in this context because they make up most of the solid matter when you get this far out in the solar system.
While Jupiter is over a thousand times the mass of Earth, Uranus weighs in at about 15 times the Earth and has only about double the escape velocity of Earth itself, the least of any of the gas giants, and it’s strange rotation, and its strange tilt contributes to it having much less wind than other giants. Additionally the gravity is just a little less than Earth’s in the atmosphere so we have the option for floating habitats again, though it would be a lot more like a submarine than a hot air balloon.
Like Venus, Uranus has very long days, at least in terms of places receiving continual sunlight, the poles get 42 years of perpetual sunlight then 42 of darkness. Sunlight being a relative term, the light is quite minimal especially inside the atmosphere. The low wind in many places makes it a good spot for gas extraction, such as Helium-3, and it’s a good planet to try to scoop gas from or even have permanent installations.
Now Uranus has a large collection of moons as well, useful and colonizable like the other moons we have looked at, but otherwise unremarkable beyond being named for characters from Shakespeare, rather than the more common mythological names. None have atmospheres though there is a possibility Oberon or Titania might have subsurface oceans.
Neptune makes for a brief entry, it is very similar to Uranus except it has the characteristically high winds of gas giants that Uranus’s skewed poles mitigate, meaning it has no advantages over Uranus and the disadvantages of high wind speeds everywhere and being even further from the Sun. It too has moons and one of them, Triton, is thought to have subsurface oceans as well. Triton also presumably has a good amount of nitrogen inside it since it often erupts geysers of nitrogen from its surface.
Neptune’s largest moon Triton photographed on August 25, 1989 by Voyager 2. Credit: NASA
Triton is one of the largest moons in the solar system, coming in seventh just after our Moon, number 5, and Europa at number 6. Meaning that were it not a moon it would probably qualify as a Dwarf Planet and it is often thought Pluto might be an escaped moon Neptune. So Triton might be one that didn’t escape, or didn’t avoid getting captured. In fact there are an awful lot of bodies in this general size range and composition wandering about in the outer regions of our solar system as we get out into the Kuiper Belt.
Pluto and its cohorts in the icy-asteroid-rich Kuiper Belt beyond the orbit of Neptune. Credit: NASA
The Kuiper Belt is one of those things that has a claim on the somewhat arbitrary and hazy boundary marking the edge of the Solar System. It extends from out past Neptune to beyond Pluto and contains a good deal more mass than the asteroid Belt. It is where a lot of our comets come from and while there is plenty of rocks out there they tend to be covered in ice. In other words it is like our asteroid belt only there’s more of it and the one thing the belt is not very abundant in, water and hydrogen in general, is quite abundant out there. So if you have a power source life fusion they can be easily terraformed and are just as attractive as a source of minerals as the various asteroids and moons closer in.
Discovered in 2005, Makemake, a Kuiper Belt Object (KBO) has . Credit: NASA
We mentioned the idea of living inside hollowed out asteroids earlier and you can use the same trick for comets. Indeed you could shape them to be much bigger if you like, since they would be hollow and ice isn’t hard to move and shape especially in zero gravity. Same trick as before, you place a spinning cylinder inside it. Not all the objects entirely ice and indeed your average comet is more a frozen ball of mud then ice with rocky cores. We think a lot of near Earth Asteroids are just leftover comets. So they are probably pretty good homes if you have fusion, lots of fuel and raw materials for both life and construction.
This is probably your cheapest interstellar spacecraft too, in terms of effort anyway. People often talk about re-directing comets to Mars to bring it air and water, but you can just as easily re-direct it out of the solar system entirely. Comets tend to have highly eccentric orbits, so if you capture one when it is near the Sun you can accelerate it then, actually benefiting from the Oberth Effect, and drive it out of the solar system into deep space. If you have a fusion power source to live inside one then you also have an interstellar spaceship drive, so you just carve yourself a small colony inside the comet and head out into deep space.
You’ve got supplies that will last you many centuries at least, even if it were home to tens of thousand of people, and while we think of smaller asteroids and comets as tiny, that’s just in comparison to planets. These things tend to be the size of mountain so there is plenty of living space and a kilometer of dirty ice between you and space makes a great shield against even the kinds of radiation and collisions you can experience at relativistic speeds.
Artists’ impression of the Kuiper belt and Oort cloud. Credit: NASA/JPL
Now the Oort Cloud is much like the Kupier Belt but begins even further out and extends out probably an entire light year or more. We don’t have a firm idea of its exact dimensions or mass, but the current notion is that it has at least several Earth’s worth of mass, mostly in various icy bodies. These will be quite numerous, estimates usually assumes at least trillion icy bodies a kilometer across or bigger, and even more smaller ones. However the volume of space is so large that those kilometer wide bodies might each be a around a billion kilometers distant from neighbors, or about a light hour. So it is spread out quite thinly, and even the inner edge is about 10 light days away.
That means that from a practical standpoint there is no source of power out there, the sun is simply too diffuse for even massive collections of mirrors and solar panels to be of use. It also means light-speed messages home or to neighbors are quite delayed. So in terms of communication it is a lot more like pre-modern times in sparsely settled lands where talking with your nearest neighbors might require an hour long walk over to their farm, and any news from the big cities might take months to percolate out to you.
There’s probably uranium and thorium out there to be found, maybe a decent amount of it, so fission as a power source is not ruled out. If you have fusion instead though each of these kilometer wide icy bodies is like a giant tank of gasoline, and as with the Kupier Belt, ice makes a nice shield against impacts and radiation.
And while there might be trillions of kilometer wide chunks of ice out there, and many more smaller bodies, you would have quite a few larger ones too. There are almost certainly tons of planets in the Pluto size-range out these, and maybe even larger ones. Even after the Oort cloud you would still have a lot of these deep space rogue planets which could bridge the gap to another solar system’s Oort Cloud. So if you have fusion you have no shortage of energy, and could colonize trillions of these bodies. There probably is a decent amount of rock and metal out there too, but that could be your major import/export option shipping home ice and shipping out metals.
That’s the edge of the Solar System so that’s the end of this article. If you haven’t already read the other half, colonizing the inner Solar System, head on over now.
Image taken by a crew member of Expedition 13 from the ISS, showing the eruption of Cleveland Volcano, Aleutian Islands, Alaska. Credit: NASA
A volcano is an impressive sight. When they are dormant, they loom large over everything on the landscape. When they are active, they are a destructive force of nature that is without equal, raining fire and ash down on everything in site. And during the long periods when they are not erupting, they can also be rather beneficial to the surrounding environment.
But just what causes volcanoes? When it comes to our planet, they are the result of active geological forces that have shaped the surface of the Earth over the course of billions of years. And interestingly enough, there are plenty of examples of volcanoes on other bodies within our Solar System as well, some of which put those on Earth to shame!
Definition:
By definition, a volcano is a rupture in the Earth’s (or another celestial body’s) crust that allows hot lava, volcanic ash, and gases to escape from a magma chamber located beneath the surface. The term is derived from Vulcano, a volcanically-active island located of the coast of Italy who’s name in turn comes from the Roman god of fire (Vulcan).
Artist’s illustration of the Earth’s Tectonic Plates. Credit: msnucleus.org
On Earth, volcanoes are the result of the action between the major tectonic plates. These sections of the Earth’s crust are rigid, but sit atop the relatively viscous upper mantle. The hot molten rock, known as magma, is forced up to the surface – where it becomes lava. In short, volcanoes are found where tectonic plates are diverging or converging – such as the Mid-Atlantic Ridge or the Pacific Ring of Fire – which causes magma to be forced to the surface.
Volcanoes can also form where there is stretching and thinning of the crust’s interior plates, such as in the the East African Rift and the Rio Grande Rift in North America. Volcanism can also occur away from plate boundaries, where upwelling magma is forced up into brittle sections of the crust, forming volcanic islands – such as the Hawaiian islands.
Erupting volcanoes pose many hazards, and not just to the surrounding countryside. In their immediate vicinity, hot, flowing lava can cause extensive damage to the environment, property, and endanger lives. However, volcanic ash can cause far-reaching damage, raining sulfuric acid, disrupting air travel, and even causing “volcanic winters” by obscuring the Sun (thus triggering local crop failures and famines).
Types of Volcanoes:
There are four major types of volcanoes – cinder cone, composite and shield volcanoes, and lava domes. Cinder cones are the simplest kind of volcano, which occur when magma is ejected from a volcanic vent. The ejected lava rains down around the fissure, forming an oval-shaped cone with a bowl-shaped crater on top. They are typically small, with few ever growing larger than about 300 meters (1,000 feet) above their surroundings.
Paricutin, an example of a cinder cone volcano. Credit: USGS
Composite volcanoes (aka. stratovolcanoes) are formed when a volcano conduit connects a subsurface magma reservoir to the Earth’s surface. These volcanoes typically have several vents that cause magma to break through the walls and spew from fissures on the sides of the mountain as well as the summit.
These volcanoes are known for causing violent eruptions. And thanks to all this ejected material, these volcanoes can grow up to thousands of meters tall. Examples include Mount Rainier (4,392 m; 14,411 ft), Mount Fuji (3,776 m; 12,389 ft), Mount Cotopaxi (5,897 m; 19,347 ft) and Mount Saint Helens (2,549 mm; 8,363 ft).
Shield volcanoes are so-named because of their large, broad surfaces. With these types of volcanoes, the lava that pours forth is thin, allowing it to travel great distances down the shallow slopes. This lava cools and builds up slowly over time, with hundreds of eruptions creating many layers. They are therefore not likely to be catastrophic. Some of the best known examples are those that make up the Hawaiian Islands, especially Mauna Loa and Mauna Kea.
Volcanic or lava domes are created by small masses of lava which are too viscous to flow very far. Unlike shield volcanoes, which have low-viscosity lava, the slow-moving lava simply piles up over the vent. The dome grows by expansion over time, and the mountain forms from material spilling off the sides of the growing dome. Lava domes can explode violently, releasing a huge amount of hot rock and ash.
Artist’s impression of a what lies beneath the Yellowstone volcano. Credit: Hernán Cañellas/National Geographic
Volcanoes can also be found on the ocean floor, known as submarine volcanoes. These are often revealed through the presence of blasting steam and rocky debris above the ocean’s surface, though the pressure of the ocean’s water can often prevent an explosive release.
In these cases, lava cools quickly on contact with ocean water, and forms pillow-shaped masses on the ocean floor (called pillow lava). Hydrothermal vents are also common around submarine volcano, which can support active and peculiar ecosystems because of the energy, gases and minerals they release. Over time, the formations created by submarine volcanoes may become so large that they become islands.
Volcanoes can also developed under icecaps, which are known as subglacial volcanoes. In these cases, flat lava flows on top of pillow lava, which results from lava quickly cooling upon contact with ice. When the icecap melts, the lava on top collapses, leaving a flat-topped mountain. Very good examples of this type of volcano can be seen in Iceland and British Columbia, Canada.
Examples on Other Planets:
Volcanoes can be found on many bodies within the Solar System. Examples include Jupiter’s moon Io, which periodically experiences volcanic eruptions that reach up to 500 km (300 mi) into space. This volcanic activity is caused by friction or tidal dissipation produced in Io’s interior, which is responsible for melting a significant amount of Io’s mantle and core.
Model of the possible interior composition of Io with various features labelled. Credit: Wikipedia Commons/Kelvinsong
It’s colorful surface (orange, yellow, green, white/grey, etc.) shows the presence of sulfuric and silicate compounds, which were clearly deposited by volcanic eruptions. The lack of impact craters on its surface, which is uncommon on a Jovian moon, is also indicative of surface renewal.
Mars has also experienced intense volcanic activity in its past, as evidenced by Olympus Mons – the largest volcano in the Solar System. While most of its volcanic mountains are extinct and collapsed, the Mars Express spacecraft observed evidence of more recent volcanic activity, suggesting that Mars may still be geologically active.
Much of Venus’ surface has been shaped by volcanic activity as well. While Venus has several times the number of Earth’s volcanoes, they were believed to all be extinct. However, there is a multitude of evidence that suggests that there may still be active volcanoes on Venus which contribute to its dense atmosphere and runaway Greenhouse Effect.
For instance, during the 1970s, multiple Soviet Venera missions conducted surveys of Venus. These missions obtained evidence of thunder and lightning within the atmosphere, which may have been the result of volcanic ash interacting with the atmosphere. Similar evidence was gathered by the ESA’s Venus Express probe in 2007.
3-D perspective of the Venusian volcano, Maat Mons generated from radar data from NASA’s Magellan mission. Credit: NASA/JPL
This same mission observed transient localized infrared hot spots on the surface of Venus in 2008 and 2009, specifically in the rift zone Ganis Chasma – near the shield volcano Maat Mons. The Magellan probe also noted evidence of volcanic activity from this mountain during its mission in the early 1990s, using radar-sounding to detect ash flows near the summit.
Cryovolcanism:
In addition to “hot volcanoes” that spew molten rock, there are also cryovolcanoes (aka. “cold volcanoes”). These types of volcanoes involve volatile compounds – i.e. water, methane and ammonia – instead of lava breaking through the surface. They have been observed on icy bodies in the Solar System where liquid erupts from ocean’s hidden in the moon’s interior.
For instance, Jupiter’s moon Europa, which is known to have an interior ocean, is believed to experiences cryovolcanism. The earliest evidence for this had to do with its smooth and young surface, which points towards endogenic resurfacing and renewal. Much like hot magma, water and volatiles erupt onto the surface where they then freeze to cover up impact craters and other features.
In addition, plumes of water were observed in 2012 and again in 2016 using the Hubble Space Telescope. These intermittent plumes were observed on both occasions to be coming in the southern region of Europa, and were estimated to be reach up to 200 km (125 miles) before depositing water ice and material back onto the surface.
In 2005, the Cassini-Huygens mission detected evidence of cryovolcanism on Saturn’s moons Titan and Enceladus. In the former case, the probe used infrared imaging to penetrate Titan’s dense clouds and detect signs of a 30 km (18.64 mi) formation, which was believed to be caused by the upwelling of hydrocarbon ices beneath the surface.
On Enceladus, cryovolcanic activity has been confirmed by observing plumes of water and organic molecules being ejected from the moon’s south pole. These plumes are are thought to have originated from the moon’s interior ocean, and are composed mostly of water vapor, molecular nitrogen, and volatiles (such as methane, carbon dioxide and other hydrocarbons).
In 1989, the Voyager 2 spacecraft observed cryovolcanoes ejecting plumes of water ammonia and nitrogen gas on Neptune’s moon Triton. These nitrogen geysers were observed sending plumes of liquid nitrogen 8 km (5 mi) above the surface of the moon. The surface is also quite young, which was seen as indication of endogenic resurfacing. It is also theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.
Here on Earth, volcanism takes the form of hot magma being pushed up through the Earth’s silicate crust due to convention in the interior. However, this kind of activity is present on all planet that formed from silicate material and minerals, and where geological activity or tidal stresses are known to exist. But on other bodies, it consists of cold water and materials from the interior ocean being forced through to the icy surface.
Color Mosaic of Olympus Mons on Mars. Credit: NASA/JPL
Today, our knowledge of volcanism (and the different forms it can take) is the result of improvements in both the field of geology, as well as space exploration. The more we learn of about other planets, the more we are able to see startling similarities and contrasts with our own (and vice versa).
Uranus and Neptune, the Solar System’s ice giant planets. Credit: Wikipedia Commons
“Hitler’s acid” is a colloquial name used to refer to Orthocarbonic acid – a name which was inspired from the fact that the molecule’s appearance resembles a swastika. As chemical compounds go, it is quite exotic, and chemists are still not sure how to create it under laboratory conditions.
But it just so happens that this acid could exist in the interiors of planets like Uranus and Neptune. According to a recent study from a team of Russian chemists, the conditions inside Uranus and Neptune could be ideal for creating exotic molecular and polymeric compounds, and keeping them under stable conditions.
The study was produced by researchers from the Moscow Institute of Physics and Technology (MIPT) and the Skolkovo Institute of Science and Technology (Skoltech). Titled “Novel Stable Compounds in the C-H-O Ternary System at High Pressure”, the paper describes how the high pressure environments inside planets could create compounds that exist nowhere else in the Solar System.
Orthocarbonic acid (also known as Hitler’s acid). Credit: Moscow Institute of Physics and Technology
Professor Artem Oganov – a professor at Skoltech and the head of MIPT’s Computational Materials Discovery Lab – is the study’s lead author. Years back, he and a team of researchers developed the worlds most powerful algorithm for predicting the formation of crystal structures and chemical compounds under extreme conditions.
Known as the Universal Structure Predictor: Evolutionary Xtallography (UPSEX), scientists have since used this algorithm to predict the existence of substances that are considered impossible in classical chemistry, but which could exist where pressures and temperatures are high enough – i.e. the interior of a planet.
With the help of Gabriele Saleh, a postdoc member of MIPT and the co-author of the paper, the two decided to use the algorithm to study how the carbon-hydrogen-oxygen system would behave under high pressure. These elements are plentiful in our Solar System, and are the basis of organic chemistry.
Until now, it has not been clear how these elements behave when subjected to extremes of temperature and pressure. What they found was that under these types of extreme conditions, which are the norm inside gas giants, these elements form some truly exotic compounds.
Diagram of the interior structure of Uranus. Credit: Moscow Institute of Physics and Technology
“The smaller gas giants – Uranus and Neptune – consist largely of carbon, hydrogen and oxygen. We have found that at a pressure of several million atmospheres unexpected compounds should form in their interiors. The cores of these planets may largely consist of these exotic materials.”
Under normal pressure – i.e. what we experience here on Earth (100 kPa) – any carbon, hydrogen or oxygen compounds (with the exception of methane, water and CO²) are unstable. But at pressures in the range 1 to 400 GPa (10,000 to 4 million times Earth normal), they become stable enough to form several new substances.
These include carbonic acid, orthocarbonic acid (Hitler’s acid) and other rare compounds. This was a very unusual find, considering that these chemicals are unstable under normal pressure conditions. In carbonic acid’s case, it can only remain stable when kept at very low temperatures in a vacuum.
Diagram of the interior structure of Neptune. Credit: Moscow Institute of Physics and Technology
At pressures of 314 GPa, they determined that carbonic acid (H²CO³) would react with water to form orthocarbonic acid (H4CO4). This acid is also extremely unstable, and so far, scientists have not yet been able to produce it in a laboratory environment.
This research is of considerable importance when it comes to modelling the interior of planets like Uranus and Neptune. Like all gas giants, the structure and composition of their interiors have remained the subject of speculation due to their inaccessible nature. But it could also have implications in the search for life beyond Earth.
According to Oganov and Saleh, the interiors of many moons that orbit gas giants (like Europa, Ganymede and Enceladus) also experience these types of pressure conditions. Knowing that these kinds of exotic compounds could exist in their interiors is likely to change what scientist’s think is going on under their icy surfaces.
“It was previously thought that the oceans in these satellites are in direct contact with the rocky core and a chemical reaction took place between them,” said Oganov. “Our study shows that the core should be ‘wrapped’ in a layer of crystallized carbonic acid, which means that a reaction between the core and the ocean would be impossible.”
Europa’s cracked, icy surface imaged by NASA’s Galileo spacecraft in 1998. Credit: NASA/JPL-Caltech/SETI
For some time, scientists have understood that at high temperatures and pressures, the properties of matter change pretty drastically. And while here on Earth, atmospheric pressure and temperatures are quite stable (just the way we like them!), the situation in the outer Solar System is much different.
By modelling what can occur under these conditions, and knowing what chemical buildings blocks are involved, we could be able to determine with a fair degree of confidence what the interior’s of inaccessible bodies are like. This will give us something to work with when the day comes (hopefully soon) that we can investigate them directly.
Who knows? In the coming years, a mission to Europa may find that the core-mantle boundary is not a habitable environment after all. Rather than a watery environment kept warm by hydrothermal activity, it might instead by a thick layer of chemical soup.
Then again, we may find that the interaction of these chemicals with geothermal energy could produce organic life that is even more exotic!
Artist's impression of a red giant star. If the star is in a binary pair, what happens to its sibling? Credit:NASA/ Walt Feimer
It is an well-known fact that all stars have a lifespan. This begins with their formation, then continues through their Main Sequence phase (which constitutes the majority of their life) before ending in death. In most cases, stars will swell up to several hundred times their normal size as they exit the Main Sequence phase of their life, during which time they will likely consume any planets that orbit closely to them.
However, for planets that orbit the star at greater distances (beyond the system’s “Frost Line“, essentially), conditions might actually become warm enough for them to support life. And according to new research which comes from the Carl Sagan Institute at Cornell University, this situation could last for some star systems into the billions of years, giving rise to entirely new forms of extra-terrestrial life!
In approximately 5.4 billion years from now, our Sun will exit its Main Sequence phase. Having exhausted the hydrogen fuel in its core, the inert helium ash that has built up there will become unstable and collapse under its own weight. This will cause the core to heat up and get denser, which in turn will cause the Sun to grow in size and enter what is known as the Red Giant-Branch (RGB) phase of its evolution.
The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser
This period will begin with our Sun becoming a subgiant, in which it will slowly double in size over the course of about half a billion years. It will then spend the next half a billion years expanding more rapidly, until it is 200 times its current size and several thousands times more luminous. It will then officially be a red giant star, eventually expanding to the point where it reaches beyond Mars’ orbit.
As we explored in a previous article, planet Earth will not survive our Sun becoming a Red Giant – nor will Mercury, Venus or Mars. But beyond the “Frost Line”, where it is cold enough that volatile compounds – such as water, ammonia, methane, carbon dioxide and carbon monoxide – remain in a frozen state, the remain gas giants, ice giants, and dwarf planets will survive. Not only that, but a massive thaw will set in.
In short, when the star expands, its “habitable zone” will likely do the same, encompassing the orbits of Jupiter and Saturn. When this happens, formerly uninhabitable places – like the Jovian and Cronian moons – could suddenly become inhabitable. The same holds true for many other stars in the Universe, all of which are fated to become Red Giants as they near the end of their lifespans.
However, when our Sun reaches its Red Giant Branch phase, it is only expected to have 120 million years of active life left. This is not quite enough time for new lifeforms to emerge, evolve and become truly complex (i.e. like humans and other species of mammals). But according to a recent research study that appeared in The Astrophysical Journal – titled “Habitable Zone of Post-Main Sequence Stars” – some planets may be able to remain habitable around other red giant stars in our Universe for much longer – up to 9 billion years or more in some cases!
Ramses Ramirez (left) and Lisa Kaltenegger are on the hunt for other places in the universe where life can thrive. Credit: Chris Kitchen/University Photo
To put that in perspective, nine billion years is close to twice the current age of Earth. So assuming that the worlds in question also have the right mix of elements, they will have ample time to give rise to new and complex forms of life. The study’s co-author, Professor Lisa Kaltennegeris, is also the director of the Carl Sagan Institute. As such, she is no stranger to searching for life in other parts of the Universe. As she explained to Universe Today via email:
“We found that planets – depending on how big their Sun is (the smaller the star, the longer the planet can stay habitable) – can stay nice and warm for up to 9 Billion years. That makes an old star an interesting place to look for life. It could have started sub-surface (e.g. in a frozen ocean) and then when the ice melts, the gases that life breaths in and out can escape into the atmosphere – what allows astronomers to pick them up as signatures of life. Or for the smallest stars, the time a formerly frozen planet can be nice and warm is up to 9 billion years. Thus life could potentially even get started in that time.”
Using existing models of stars and their evolution – i.e. one-dimensional radiative-convective climate and stellar evolutionary models – for their study, Kaltenegger and Ramirez were able to calculate the distances of the habitable zones (HZ) around a series of post-Main Sequence (post-MS) stars. Ramses M. Ramirez – a research associate at the Carl Sagan Institute and the lead author of the paper – explained the research process to Universe Today via email:
“We used stellar evolutionary models that tell us how stellar quantities, mainly the brightness, radius, and temperature all change with time as the star ages through the red giant phase. We also used a climate model to then compute how much energy each star is outputting at the boundaries of the habitable zone. Knowing this and the stellar brightness mentioned above, we can compute the distances to these habitable zone boundaries.”
After several billions years, yellow suns (like ours) become Red Giants, expanding to several hundred times their normal size. Credit: Wendy Kenigsburg
At the same time, they considered how this kind of stellar evolution could effect the atmosphere of the star’s planets. As a star expands, it loses mass and ejects it outward in the form of solar wind. For planets that orbit close to a star, or those that have low surface gravity, they may find some or all of their atmospheres blasted away. On the other hand, planets with sufficient mass (or positioned at a safe distance) could maintain most of their atmospheres.
“The stellar winds from this mass loss erodes planetary atmospheres, which we also compute as a function of time,” said Ramirez. “As the star loses mass, the solar system conserves angular momentum by moving outwards. So, we also take into account how the orbits move out with time.” By using models that incorporated the rate of stellar and atmospheric loss during the Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) phases of star, they were able to determine how this would play out for planets that ranged in size from super-Moons to super-Earths.
What they found was that a planet can stay in a post-HS HZ for eons or more, depending on how hot the star is, and figuring for metallicities that are similar to our Sun’s. As Ramirez explained:
“The main result is that the maximum time that a planet can remain in this red giant habitable zone of hot stars is 200 million years. For our coolest star (M1), the maximum time a planet can stay within this red giant habitable zone is 9 billion years. Those results assume metallicity levels similar to those of our Sun. A star with a higher percentage of metals takes longer to fuse the non-metals (H, He..etc) and so these maximum times can increase some more, up to about a factor of two.”
Could Europa’s cracked, icy surface thaw and give rise to a new habitable world when our Sun becomes a Red Giant in a few billion years? Credit: NASA/JPL-Caltech/SETI Institute
Within the context of our Solar System, this could mean that in a few billion years, worlds like Europa and Enceladus (which are already suspected of having life beneath their icy surfaces) might get a shot at becoming full-fledged habitable worlds. As Ramirez summarized beautifully:
“This means that the post-main-sequence is another potentially interesting phase of stellar evolution from a habitability standpoint. Long after the inner system of planets have been turned into sizzling wastelands by the expanding, growing red giant star, there could be potentially habitable abodes farther away from the chaos. If they are frozen worlds, like Europa, the ice would melt, potentially unveiling any preexisting life. Such pre-existing life may be detectable by future missions/telescopes looking for atmospheric biosignatures.”
But perhaps the most exciting take-away from their research study was their conclusion that planets orbiting within their star’s post-MS habitable zones would be doing so at distances that would make them detectable using direct imaging techniques. So not only are the odds of finding life around older stars better than previously thought, we should have no trouble in spotting them using current exoplanet-hunting techniques!
It is also worth noting that Kaltenegger and Dr. Ramirez have submitted a second paper for publication, in which they provide a list of 23 red giant stars within 100 light-years of Earth. Knowing that these stars, all of which are in our stellar neighborhood, could have life-sustaining worlds within their habitable zones should provide additional opportunities for planet hunters in the coming years.
And be sure to check out this video from Cornellcast, where Prof. Kaltenegger shares what inspires her scientific curiosity and how Cornell’s scientists are working to find proof of extra-terrestrial life.
Icy water vapor geysers erupting from fissures on Enceladus. Credit: NASA/JPL
A crowning achievement of the Cassini mission to Saturn is the discovery of water vapor jets spraying out from Enceladus‘ southern pole. First witnessed by the spacecraft in 2005, these icy geysers propelled the little 515-kilometer-wide moon into the scientific spotlight and literally rewrote the mission’s objectives. After 22 flybys of Enceladus during its nearly twelve years in orbit around Saturn, Cassini has gathered enough data to determine that there is a global subsurface ocean of salty liquid water beneath Enceladus’ frozen crust—an ocean that gets sprayed into space from long “tiger stripe” fissures running across the moon’s southern pole. Now, new research has shown that at least some of the vapor jets get a boost in activity when Enceladus is farther from Saturn.
The gravitational pull of Saturn changes the amount of particles spraying from Enceladus at different points in its orbit. When it’s farther from Saturn (left) the plume contains more icy particles and thus appears brighter. Credit: NASA/JPL-Caltech/University of Arizona/Cornell/SSI.
By measuring the changes in brightness of a distant background star as Enceladus’ plumes passed in front of it in March 2016, Cassini observed a significant increase in the amount of icy particles being ejected by one particular jet source.
“Baghdad Sulcus,” one of Enceladus’ plume sources, imaged by Cassini during a close pass in Nov. 2011. (NASA/JPL/SSI)
Named “Baghdad 1,” the jet went from contributing 2% of the total vapor content of the entire plume area to 8% when Enceladus was at the farthest point in its slightly-eccentric orbit around Saturn. This small yet significant discovery indicates that, although Enceladus’ plumes are reacting to morphological changes to the moon’s crust due to tidal flexing, it’s select small-scale jets that are exhibiting the most variation in output (rather than a simple, general increase in outgassing across the full plumes.)
“How do the tiger stripe fissures respond to the push and pull of tidal forces as Enceladus goes around its orbit to explain this difference? We now have new clues!” said Candice Hansen, senior scientist at the Planetary Science Institute and lead planner of the study. “It may be that the individual jet sources along the tiger stripes have a particular shape or width that responds most strongly to the tidal forcing each orbit to boost more ice grains at this orbital longitude.”
The confirmation that Enceladus shows an increase in overall plume output at farther points from Saturn was first made in 2013.
Whether this new finding means that the internal structure of the fissures is different than what scientists have suspected or some other process is at work either within Enceladus or in its orbit around Saturn still remains to be determined.
“Since we can only see what’s going on above the surface, at the end of the day, it’s up to the modelers to take this data and figure out what’s going on underground,” said Hansen.
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).
Artist's concept of some of the Phase I winners of the 2016 NIAC program. Credit: NASA
Every year, the NASA Innovative Advanced Concepts (NIAC) program puts out the call to the general public, hoping to find better or entirely new aerospace architectures, systems, or mission ideas. As part of the Space Technology Mission Directorate, this program has been in operation since 1998, serving as a high-level entry point to entrepreneurs, innovators and researchers who want to contribute to human space exploration.
This year, thirteen concepts were chosen for Phase I of the NIAC program, ranging from reprogrammed microorganisms for Mars, a two-dimensional spacecraft that could de-orbit space debris, an analog rover for extreme environments, a robot that turn asteroids into spacecraft, and a next-generation exoplanet hunter. These proposals were awarded $100,000 each for a nine month period to assess the feasibility of their concept.
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 uttered 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.
In recent years, we’ve heard luminaries like Elon Musk and Stephen Hawking claiming that humanity needs a “backup location” to ensure our survival, private ventures like Mars One enlisting thousands of volunteers to colonize the Red Planet, and space agencies like NASA, the ESA, and China discussing the prospect of long-term habitability on Mars or the Moon. From all indications, it looks like terraforming is yet another science-fiction concept that is migrating into the realm of 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 succeeding? Answering any or all of these questions requires 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 to make it suitable for human life. This could involve modifying the temperature, atmosphere, surface topography, ecology, or all of the above to make a planet or moon more “Earth-like.”
Venus is considered by many to be a prime candidate for terraforming. Credit: NASA/JPL/io9.com
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,” published in the 1942 edition of the magazineAstounding Science Fiction. This is the first known mention of the concept, though there are examples of it appearing in fiction beforehand.
Terraforming in Fiction:
Science fiction is filled with examples of altering planetary environments to be more suitable to human life, many of which predate 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 chapters are dedicated to describing how humanity’s descendants terraform Venus after Earth becomes uninhabitable. In the process, they commit genocide against the native aquatic life. By the 1950s and 60s, due to the beginning of the Space Age, terraforming appeared in works of science fiction with increasing frequency.
One such example is Farmer in the Sky (1950) by Robert A. Heinlein. In this novel, Heinlein offers a vision of Jupiter’s moon Ganymede that is being transformed into an agricultural settlement. This was a very significant work, in that it was the first where the concept of terraforming is presented as a serious and scientific matter, rather than the subject of mere fantasy.
Scene from 2010: The Year We Make Contact, the movie adaptation of Clarke’s novel. Credit: Metro-Goldwyn-Mayer
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 Mars’ moon Phobos into a second sun and growing plants that break down the Martian sands in order to release oxygen. In his seminal book 2001: A Space Odyssey – and its sequel,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 synonymous 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 are 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.
Kim Stanley Robinson’s Red Mars Trilogy. Credit: variety.com
In the 1990s, Kim Stanley Robinson released his famous trilogy that deals with the terraforming of Mars. Known as the Mars Trilogy – Red 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 – referred to as “Planetary Modeling” at the time- was organized that same year.
Artist concept of a ‘Living’ Mars. Credit: Kevin Gill
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 the 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.
An engineer suggests building a roof over a small planet so that Earth-like conditions could be maintained. Credit: Karl Tate/space.com
There is also the concept where a usable part of a planet is enclosed in a dome in order to transform its environment, which is known as “paraterraforming”. This concept, originally coined by British mathematician Richard L.S. Talyor in his 1992 publication Paraterraforming – The worldhouse concept, could be used to terraform sections of several planets that are otherwise inhospitable, or cannot be altered in whole.
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.
Artist’s conception of a terraformed Mars. Credit: Ittiz/Wikimedia Commons
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) skirt the inner and outer edge of the Sun’s habitable zone.
Mercury: 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.
Images of Mercury’s northern polar region, provided by MESSENGER. Credit: NASA/JPL
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 northern 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.
Venus: 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 will 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 carbonates. An 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 that 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.
Artist’s conception of a terraformed Venus, showing a surface largely covered in oceans. Credit: Wikipedia Commons/Ittiz
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.
Solar shades placed in orbit of Venus are a possible means of terraforming the planet. Credit: IEEE Spectrum/John MacNeill
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 is 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 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 comets 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.
Mars: 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 to 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 the stripping of Mars’ atmosphere by solar wind. This in turn is what led Mars to become the cold, desiccated place it is today.
Scientists were able to gauge the rate of water loss on Mars by measuring the ratio of water and HDO from today and 4.3 billion years ago. Credit: Kevin Gill
Ultimately, this means that in order for the planet to become habitable by human standards, its 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 a nitrogen-oxygen balance of about 70/30. And above all, the atmosphere would need to be replenished every so often to compensate for the loss.
Luckily, the first three requirements are largely complementary, 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 the 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).
The moons of the Solar System, shown to scale. Credit: planetary.org
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 1and 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 an 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 than 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.
Artist’s cut-away representation of the internal structure of Ganymede. Credit: Wikipedia Commons/kelvinsong
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, necessitating 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 the 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).
Diagram of the internal structure of Titan according to the fully differentiated dense-ocean model. Credit: Wikipedia Commons/Kelvinsong
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.
Artist’s rendering of possible hydrothermal activity that may be taking place on and under the seafloor of Enceladus. Credit: NASA/JPL
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.
Exoplanets: 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 planets 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.
The latest list of potentially habitable exoplanets, courtesy of The Planetary Habitability Laboratory. Credit: phl.upr.edu
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 are 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 a 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 Pliocene Era – when global temperatures and sea levels 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.
NASA predicts that, based on current emissions rates, temperatures could increase by up to 4.5 degrees Celsius by 2100. Credit: svs.gsfc.nasa.gov
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 on 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 planets 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.
Artist’s concept for a SpaceX Mars Colonization Transport (MCT). (Credit: Reddit user P3rkoz)
Last, but not least, there is the 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:
They are not possible with existing technology
They require a massive commitment of resources
They solve one problem, only to create another
They do not offer a significant return on the investment
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.
All asteroids and comets visited by spacecraft as of November 2010. Credits: Emily Lakdawalla/NASA/JPL/Ted Stryk/ESA/OSIRIS team/JHUAPL/ISAS/JAXA/RAS/UMD
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 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 moons of Saturn, from left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top) and Hyperion (bottom). Credit: NASA/JPL/Space Science Institute
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 harvested 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.
Mars-manned-mission vehicle (NASA Human Exploration of Mars Design Reference Architecture 5.0) Feb. 2009. Credit: NASA
There are 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.
Artist’s concept of a Martian astronaut standing outside the Mars One habitat. Credit: Bryan Versteeg/Mars One
Conclusion:
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 been good enough in the past, and it will likely be sufficient again in the not-too-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!
The crescent of Saturn's moon Enceladus hangs above the planet's rings in this image from the Cassini spacecraft. Water jets that spew from the moon’s south pole region are also visible. Credit: NASA/JPL-Caltech/Space Science Institute
I don’t think I’ll ever tire of seeing pictures of Saturn’s moon Enceladus, with those captivating water jets and plumes at its South Pole. And this new images from the Cassini mission is just stunning – and intriguing. Carolyn Porco, the Cassini imaging team lead described the image on Twitter: “Be moved by crescent Enceladus with its ghostly geysers floating above Saturn’s glowing rings.”
There are over 100 geyser jets of varying sizes near Enceladus’s south pole spraying water vapor, icy particles, and organic compounds out into space. Enticingly, this distant and small moon (313 miles or 504 kilometers across) has a global subsurface ocean of liquid water, as tidal forces from Enceladus’ orbital relationship to Saturn and another moon, Dione heats the interior.
Liquid water and the observation of organic chemicals in the plumes of Enceladus make this moon of high astrobiological interest to scientists. In a 2014 paper by Porco and astrobiologist Chris McKay, the due wrote that Enceladus’ “steady plume derives from a subsurface liquid water reservoir that contains organic carbon, biologically available nitrogen, redox energy sources, and inorganic salts. … No other world has such well-studied indications of habitable conditions.”
While the rings of Saturn are also beautiful, they are they are frozen and geologically dead. “The small ring particles are too tiny to retain internal heat and have no way to get warm,” the Cassini imaging team explained on the CICLOPS website.
This image was taken in July of 2015, and was not part of two close flybys of Enceladus in October of this year. Project scientist Linda Spilker hinted there might be some new discoveries from those flybys (see images here and here), as she said, “Cassini’s stunning images are providing us a quick look at Enceladus from this ultra-close flyby, but some of the most exciting science is yet to come.”
This beautiful view of Enceladus and Saturn’s rings looks toward the unilluminated side of the rings from about 0.3 degrees below the ring plane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 29, 2015.
The view was acquired at a distance of approximately 630,000 miles (1.0 million kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase angle of 155 degrees. Image scale is 4 miles (6 kilometers) per pixel.
Europa is probably the best place in the Solar System to go searching for life. But before they’re launched, any spacecraft we send will need to be squeaky clean so don’t contaminate the place with our filthy Earth bacteria. Continue reading “Will We Contaminate Europa?”
