There’s no two-ways about it, the Universe is an extremely big place! And thanks to the limitations placed upon us by Special Relativity, traveling to even the closest star systems could take millennia. As we addressed in a previous article, the estimated travel time to the nearest star system (Alpha Centauri) could take anywhere from 19,000 to 81,000 years using conventional methods.
For this reason, many theorists have recommended that humanity rely on generation ships to spread the seed of humanity among the stars. Naturally, such a project presents many challenges, not the least of which is how large a spacecraft would need to be to sustain a multi-generational crew. In a new study, of international scientists addressed this very question and determined that a lot of interior space would be needed!
It’s always wise to be prepared for a disaster, but space sperm is taking it a little too far. Having things like food, water, and medicines on hand constitutes a reasonable level of preparation. But now one company wants to freeze your eggs and sperm in space.
For some time, scientists have known that the Moon and Mars have some fascinating similarities to Earth. In addition to being similar in composition, there is ample evidence that both bodies had active geological pasts. This includes stable lava tubes which are very similar to those that exist here on Earth. And in the future, these tubes could be an ideal location for outposts and colonies.
However, before we can begin choosing where to settle, these locations need to be mapped out to determining which would be suitable for human habitation. Luckily, a team of speleologists (cave specialists), geologists and ESA astronauts recently created the largest 3D image of a lava tube ever created. As part of the ESA’s PANGAEA program, this technology could one day help scientists map out cave systems on the Moon and Mars.
The lava tube in question was the La Cueva de Los Verdes, a famous tourist destination in Lanzarote, Spain. In addition to ESA astronaut Matthias Mauer, the team consisted of Tommaso Santagata (a speleologist from the University of Padova and the co-founder of the Virtual Geographic Agency), Umberto Del Vecchio and Marta Lazzaroni – a geologists and a masters student from the University of Padova, respectively.
For five days in November 2017, this campaign mobilized 50 people, four space agencies and 18 organizations in five different locations. The La Cueva de los Verdes lava tube was of particular importance since it is one of the world’s largest volcanic cave complexes, measuring roughly 8 km in length. Some of these caves are even large enough to accommodate residential streets and houses.
During the campaign, Mauer, Santagata, Vecchio and Lazzaroni relied on two instruments to map the lava tube in detail. These included the Pegasus Backpack, a wearable mapping solution that collects geometric data without a satellite ad synchronizes images collected by five cameras and two 3D imaging laser profilers, and the Leica BLK360 – the smallest and lightest imaging scanner on the market.
In less than three hours, the team managed to map all the contours of the lava tube. And while the results of the campaign continue to be analyzed, the team chose to use the data they obtained to produce a 3D visual of all the twists and turns of the lava tube. The scan that resulted covers a 1.3 km section of the cave system with an unprecedented resolution of a few centimeters.
Santagata and the Virtual Geography Agency also turned their 3D visual into a lovely video titled “Lave tube fly-through”, which beautifully illustrates the winding and organic nature of the lava tube system. This video was posted to the ESA’s twitter feed on Tuesday, March 13th (shown above). This video, like the scans that preceded it, represent a breakthrough in geological mapping and astronaut training.
While lava tubes have been mapped since the 1970s, a clear view of this subterranean passage has remained elusive until now. Beyond being the first, the scans the team conducted could also help scientists to study the origins of the cave system, its peculiar formations, and assist local institutions in protecting the subterranean environment. As intended, the scans could also assist future space exploration and colonization efforts.
For instance, the 8 km lava tube has both dry and water-filled sections. In the six-kilometer dry section, the lava tube has natural openings (jameos), that are aligned along the top of the cave pathway. These formations are very similar to “skylights” that have been observed on the Moon and Mars, which are holes in the surface that open into stable lava tubes.
Such structures are considered to be a good place for building outposts and colonies since they are naturally shielded from radiation and micrometeorites. Lava tubes also have a constant temperature, therefore offering protection against environmental extremes, and could provide access to underground sources of water ice. Some sections could also be sealed off and pressurized to create a colony.
As such, exploring such environments here on Earth is a good way to train astronauts to explore them on other bodies. As all astronauts know, mapping an environment is the first step in exploration, especially when you are looking for a place to establish a base camp. And in time, this information can be used to establish more permanent settlements, giving rise to eventual colonization.
Elon Musk has never been one to keep his long-term plans to himself. Beyond the development of reusable rockets, electric cars, and revolutionizing solar power, he has also been quite vocal about establishing a colony on Mars within his lifetime. The goal here is nothing less than ensuring the survival of the human race by creating a “backup location”, and calls for some serious planning and architecture.
The paper was produced by Scott Hubbard, a consulting professor at Stanford University and the Editor-in-Chief of NewSpace, and includes all the material and slides from Musk’s original presentation. Contained within are Musk’s thoughts on how the colonization of Mars could be accomplished in this century and what issues would need to be addressed.
These include the costs of sending people and payloads to Mars, the technical details of the rocket and vehicle that would be making the trip, and possible cost breakdowns and timelines. But of course, he also addresses the key philosophical questions – “Why go?” and “Why Mars?”
Addressing this first question is one of the most important aspects of space exploration. Remember John F. Kennedy’s iconic “We Choose to go to the Moon” speech? Far from just being a declaration of intent, this speech was a justification by the Kennedy administration for all the time, energy, and money it was committing to the Apollo program. As such, Kennedy’s speech stressed above all else why the goal was a noble undertaking.
In looking to Mars, Musk struck a similar tone, emphasizing survival and humanity’s need to expand into space. As he stated:
“I think there are really two fundamental paths. History is going to bifurcate along two directions. One path is we stay on Earth forever, and then there will be some eventual extinction event. I do not have an immediate doomsday prophecy, but eventually, history suggests, there will be some doomsday event. The alternative is to become a space-bearing civilization and a multi-planetary species, which I hope you would agree is the right way to go.”
As for what makes Mars the natural choice, that was a bit more of a tough sell. Granted, Mars has a lot of similarities with Earth – hence why it is often called “Earth’s Twin” – which makes it a tantalizing target for scientific research. But it also has some rather stark differences that make long-term stays on the surface seem less than appealing. So why would it be the natural choice?
As Musk explains, proximity has a lot to do with it. Sure, Venus is closer to Earth, getting as close as 41 million km (25,476,219 mi), compared to 56 million km (3,4796,787 mi) with Mars. But Venus’ hostile environment is well-documented, and include a super-dense atmosphere, temperatures hot enough to melt lead and sulfuric acid rain! Mercury is too hot and airless, and the Jovian moons are very far.
This leaves us with just two options for the near-future, as far as Musk is concerned. One is the Moon, which is likely to have a permanent settlement on it in the coming years. In fact, between the ESA, NASA, Roscosmos, and the Chines National Space Administration, there is no shortage of plans to build a lunar outpost, which will serve as a successor to the ISS.
But compared to Mars, it is less resource rich, has no atmosphere, and represents a major transition as far as gravity (0.165 g compared to 0.376 g) and length of day (28 days vs. 24.5 hours) are concerned. Herein lies the greatest reason to go to Mars, which is the fact that our options are limited and Mars is the most Earth-like of all the bodies that are currently accessible to us.
What’s more, Musk makes allowances for the fact that colonists could start kick-starting the terraforming process, to make it even more Earth-like over time. As he states (bold added for emphasis):
“In fact, we now believe that early Mars was a lot like Earth. In effect, if we could warm Mars up, we would once again have a thick atmosphere and liquid oceans. Mars is about half as far again from the Sun as Earth is, so it still has decent sunlight. It is a little cold, but we can warm it up. It has a very helpful atmosphere, which, being primarily CO2 with some nitrogen and argon and a few other trace elements, means that we can grow plants on Mars just by compressing the atmosphere.
“It would be quite fun to be on Mars because you would have gravity that is about 37% of that of Earth, so you would be able to lift heavy things and bound around. Furthermore, the day is remarkably close to that of Earth. We just need to change the populations because currently we have seven billion people on Earth and none on Mars.”
Naturally, no mission can be expected to happen without the all-important vehicle. To this end, Musk used the annual IAC meeting to unveil his company’s plans for the Interplanetary Transport System. An updated version of the Mars Colonial Transporter (which Musk began talking about in 2012), the ITS will consist of two main components – a reusable rocket booster and the Interplanetary Spaceship.
The process for getting to Mars with these components involves a few steps. First, the rocket booster and spaceship take off together and the spaceship is delivered into orbit. Next, while the spaceship assumes a parking orbit, the booster returns to Earth to be reloaded with the tanker craft. This vehicle is the same design as the spaceship, but contains propellant tanks instead of cargo areas.
The tanker is then launched into orbit with the booster, where it will rendezvous with the spaceship and refuel it for the journey to Mars. Overall, the propellant tanker will go up anywhere from three to five times to fill the tanks of the spacecraft while it is in orbit. Musk estimates that the turnaround time between the spacecraft launch and the booster retrieval could eventually be as low as 20 minutes.
This process (if Musk gets its way) would expand to include multiple spaceships making the journey to and from Mars every 26 months (when Mars and Earth are closest together):
“You would ultimately have upwards of 1,000 or more spaceships waiting in orbit. Hence, the Mars Colonial fleet would depart en masse. It makes sense to load the spaceships into orbit because you have got 2 years to do so, and then you can make frequent use of the booster and the tanker to get really heavy reuse out of those. With the spaceship, you get less reuse because you have to consider how long it is going to last—maybe 30 years, which might be perhaps 12–15 flights of the spaceship at most.”
In terms of the rocket’s structure, it would consist of an advanced carbon fiber exterior surrounding fuel tanks, which would rely on an autogenous pressurization system. This involves the fuel and oxygen being gasified through heat exchanges in the engine, which would then be used to pressurize the tanks. This is a much simpler system than what is currently being used for the Falcon 9 rocket.
The booster would use 42 Raptor engines arranged in concentric rings to generate thrust. With 21 engines in the outer ring, 14 in the inner ring, and seven in a center cluster, the booster would have an estimated lift-off thrust of 11,793 metric tons (13,000 tons) – 128 MegaNewtons – and a vacuum thrust of 12,714 metric tons (14,015 tons), or 138 MN. This would make it the first spacecraft where the rocket performance bar exceeds the physical size of the rocket.
As for the spacecraft, the designs calls for a pressurized section at the top with an unpressurized section beneath. The pressurized section would hold up to 100 passengers (thought Musk hopes to eventually increase that capacity to 200 people per trip), while all the luggage and cargo necessary for building the Martian colony would be kept in the unpressurized section below.
As for the crew compartments themselves, Musk was sure to illustrate how time in them would not be boring, since the transit time is a long. “Therefore, the crew compartment or the occupant compartment is set up so that you can do zero-gravity games – you can float around,” he said. “There will be movies, lecture halls, cabins, and a restaurant. It will be really fun to go. You are going to have a great time!”
Below both these sections, the liquid oxygen tank, fuel tank and spacecraft engines are located. The engines, which would be directly attached to the thrust cone at the base, would consists of an outer ring of three sea-level engines – which would generate 361 seconds of specific impulse (Isp) – and an inner cluster of six vacuum engines that would generate 382s Isp.
The exterior of the spacecraft will also be fitted with a heatshield, which will be composed of the same material that SpaceX uses on its Dragon spacecraft. This is known as a phenolic-impregnated carbon ablator (PICA), which SpaceX is on their third version of. In total, Musk estimates that the Interplanetary Spaceship will be able to transport 450 tons of cargo to Mars, depending upon how many times the tanker can refill the craft.
And, depending on the Earth-Mars rendezvous, the transit time could be as little as 80 days one-way (figuring for a speed of 6km/s). But with time, Musk hopes to cut that down to just 30 days, which would make it possible to establish a sizable population on Mars in a relatively short amount of time. As Musk indicated, the magic number here in 1 million, meaning the number of people it would take to establish a self-sustaining colony on Mars.
He admitted that this would be a major challenge, and could as long as a century to complete:
“If you can only go every 2 years and if you have 100 people per ship, that is 10,000 trips. Therefore, at least 100 people per trip is the right order of magnitude, and we may end up expanding the crew section and ultimately taking more like 200 or more people per flight in order to reduce the cost per person. However, 10,000 flights is a lot of flights, so ultimately you would really want in the order of 1,000 ships. It would take a while to build up to 1,000 ships. How long it would take to reach that million-person threshold, from the point at which the first ship goes to Mars would probably be somewhere between 20 and 50 total Mars rendezvous—so it would take 40–100 years to achieve a fully self-sustaining civilization on Mars.”
When the ITS is ready to launch, it will do so from Launch Pad 39A at the Kennedy Space Center in Florida, which SpaceX currently uses to conduct Falcon 9 launches from. But of course, the most daunting aspect of any colonization effort is cost. At present, and using current methods, sending upwards of 1 million people to Mars is simply not affordable.
Using Apollo-era methods as a touchstone, Musk indicated that the cost to go to Mars would be around $10 billion per person – which is derived from the fact that the program itself cost between $100 and $200 billion (adjust for inflation) and resulted in 12 astronauts setting foot on the Moon. Naturally, this is far too high for the sake of creating a self-sustaining colony with a population of 1 million.
As a result, Musk claimed that the cost of transporting people to Mars would have to be cut by a whopping 5 million percent! Musk’s desire to lower the costs associated with space launches is well-known, and is the very reason he founded SpaceX and began developing reusable technology. However, costs would need to be lowered to the point where a ticket to Mars would cost about the same as a median house – i.e. $200,000 – before any trips to Mars could happen.
As to how this could be done, several strategies are outlined, many of which Musk and space agencies like NASA are already actively pursuing. They include full Reusability, where all stages of a rocket and its cargo module (not just the first stage) would have to be retrievable and reusable. Refueling in Orbit is a second means, which would mean the spacecraft would not have to carry all the fuel they need with them from Earth.
On top of that, there would have to be the option for propellant Production on Mars, where the spaceship will be able to refuel at Mars to make the return trip. This concept has been explored in the past for lunar and Martian missions. And in Mars’ case, the presence of atmospheric and frozen CO², and water in both the soil and the polar ice caps, would mean that methane, oxygen and hydrogen fuel could all be manufactured.
Lastly, there is the question of which propellant would be best. As it stands, there are there basic choices when it comes – kerosene (rocket fuel), hydrogen, and methane. All of these present certain advantages and can be manufactured in-situ on Mars. But based on a cost-benefit breakdown, Musk claims that methane would be the most cost-effective propellant.
As always, Musk also raised the issue of timelines and next steps. This consisted of a rundown of SpaceX’s accomplishments over the past decade and a half, followed by an outline of what he hopes to see his company do in the coming years and decades.
These include the development of the first Interplanetary Spaceship in about four years time, which will be followed by suborbital test flights. He even hinted how the spacecraft could have commercial applications, being used for the rapid transportation of cargo around the world. As for the development of the booster, he indicated that this would be a relatively straightforward process since it simply involves scaling up the existing Falcon 9 booster.
Beyond that, he estimated that (assuming all goes well) a ten-year time frame would suffice for putting all the components together so that it would work for bringing people to Mars. Last, but not least, he offered some glimpses of what could be accomplished with ITS beyond Mars. As the name suggests, Musk is hoping to conduct missions to other destination in the Solar System someday.
Given the opportunities for in-situ fuel production (thanks to the abundance of water ice), the moons of both Jupiter and Saturn were mentioned as possible destination. But beyond moons like Europa, Enceladus, and Titan (all of which were mentioned), even destinations in the trans-Neptunian region of the Solar System were indicated as a possibility.
Given that Pluto also has an abundance of water ice on its surface, Musk claimed that a refueling depot could be built here to service missions to the Kuiper Belt and Oort Cloud. “I would not recommend this for interstellar journeys,” he admitted, “but this basic system—provided we have filling stations along the way—means full access to the entire greater solar system.”
The publication of this paper, many months after Musk presented the details of his plan to the annual IAC meeting, has naturally generated both approval and skepticism. While there are those who would question Musk’s timelines and his ability to deliver on the proposals contained within, others see it as a crucial step in the fulfillment of Musk’s long-held desire to see the colonization of Mars happen in this century.
To Scott Hubbard, it serves as a valuable contribution to the history of space exploration, something that future generations will be able to access so they can chart the history of Mars exploration – much in the same way NASA archival materials are used to study the history of the Moon landing. As he remarked:
“In my view, publishing this paper provides not only an opportunity for the spacefaring community to read the SpaceX vision in print with all the charts in context, but also serves as a valuable archival reference for future studies and planning. My goal is to make New Space the forum for publication of novel exploration concepts-particularly those that suggest an entrepreneurial path for humans traveling to deep space.”
Elon Musk is no stranger to thinking big and dreaming big. And while many of his proposals in the past did not come about in the time frame he originally specified, no one can doubt that he’s delivered so far. It will be very exciting to see if he can take the company he founded 15 years ago for the sake of fostering the exploration of Mars, and use it instead to lead a colonization effort!
Update: Musk tweeted his thanks to Hubbard for the publication and has indicated that there are some “major changes to the plan coming soon.”
And be sure to check out this video of Musk’s full speech at the 67th annual meeting of the IAC, courtesy of SpaceX:
Welcome back to our series on Colonizing the Solar System! Today, we take a look at the largest of the Jovian Moons – Io, Europa, Ganymede and Callisto!
In 1610, Galileo Galilei became the first astronomer to discover the large moons of Jupiter, using a telescope of his own design. As time passed, these moons – Io, Europa, Ganymede and Callisto – would collectively come to be referred to as the Galilean Moons, in honor of their discoverer. And with the birth of space exploration, what we’ve come to know about these satellites has fascinated and inspired us.
For example, ever since the Pioneer and Voyager probes passed through the system decades ago, scientists have suspected that moons like Europa might be our best bet for finding life in our Solar System beyond Earth. And because of the presence of water ice, interior oceans, minerals, and organic molecules, it has been speculated that humanity might establish colonies on one or more of these worlds someday.
Examples in Fiction:
The concept of a colonized Jovian system is featured in many science fiction publications. For instance, Robert A. Heinlein’s novel Farmer in the Sky (1953) centers on a teenage boy and his family moving to Ganymede. The moon is in the process of being terraformed in the story, and farmers are being recruited to help turn it into an agricultural colony.
In the course of the story, it is mentioned that there are also efforts to introduce an atmosphere on Callisto. Many of his Heinlein’s other novels include passing mentions of a colony on Ganymede, including The Rolling Stones (1952), Double Star (1956), I Will Fear No Evil (1970), and the posthumously-written Variable Star (2006).
In 1954, Poul Anderson published a novella titled The Snows of Ganymede(1954). In this story, a party of terraformers visit a settlement on Ganymede called X, which was established two centuries earlier by a group of American religious fanatics.
In Arthur C. Clarke’s Space Odyssey series, the moon of Europa plays a central role. In 2010: Odyssey Two(1982) an ancient race of advanced aliens are turning the moon into a habitable body by converting Jupiter into a second sun. The warmth of this dwarf star (Lucifer) causes the surface ice on Europa to melt, and the life forms that are evolving underneath are able to emerge.
In 2061: Odyssey Three, Clarke also mentions how Lucifer’s warmth has caused Ganymede’s surface to partially sublimate, creating a large equatorial lake. Isaac Asimov also used the moons of Jupiter in his stories. In the short stories “Not Final!” (1941) and “Victory ‘Unintentional'” (1942), a conflict arises between humans living on Ganymede and the inhabitants of Jupiter.
In Philip K. Dick’s short-story The Mold of Yancy (1955), Callisto is home to a colony where the people conform to the dicates of Yancy, a public commentator who speaks to them via public broadcasts. In Bruce Sterling’s Schismatrix (1985), Europa is inhabited by a faction of genetically-engineered posthumans which are vying for control of the Solar System.
Alastair Reynolds’s short story “A Spy in Europa” depicts colonies built on the underside of Europa’s icy surface. Meanwhile, a race of genetically-altered humans (called the “Denizens”) are created to live in the subsurface ocean, close to the core-mantle boundary where hydrothermal vents keep the water warm and the native life forms live.
Kim Stanley Robinson’s novels Galileo’s Dream (2009) and 2312 (2012) feature colonies on Io, where settlements are adapted to deal with the volcanically active, hostile surface. The former novel is partly set on Callisto, where a massive city called Valhalla is built around the concentric rings of the moon’s giant crater (also mentioned in 2312).
In Robinson’s The Memory of Whiteness (1985), the protagonists visit Europa, which hosts large human colonies who live around pools of melted ice. And in his novel Blue Mars (1996), Robinson makes a passing description of a flourishing colony on Callisto.
Since the Voyager probes passed through the Jovian system, several proposals have been made for crewed missions to Jupiter’s moons and even the creation of settlements. For instance, in 1994, the private spaceflight venture known as the Artemis Project was established with the intent of colonizing the Moon in the 21st century.
However, in 1997, they also drafted plans to colonize Europa, which called for igloos to be established on the surface. These would serve as based for scientists who then drill down into the Europan ice crust and explore the sub-surface ocean. This plan also discussed the possible use of “air pockets” in the ice sheet for long-term human habitation.
In 2003, NASA produced a study called Revolutionary Concepts for Human Outer Planet Exploration (HOPE) which addressed future exploration of the Solar System. Because of its distance from Jupiter, and therefore low exposure to radiation, the target destination in this study was the moon Callisto.
The plan called for operations to begin in 2045. These would begin with the creation of a base on Callisto, where science teams would be able to teleoperate a robotic submarine that would be used to explore Europa’s internal ocean. These science teams would also excavate surface samples near their landing site on Callisto.
Last, but not least, the expedition to Callisto would establish a reusable surface habitat where water ice could be harvested and converted into rocket fuel. This base could therefore serve as a resupply base for all future exploitation missions in the Jovian system.
Also in 2003, NASA reported that a manned mission to Callisto might be possible in the 2040s. According to a joint-study released by the Glenn Research Center and the Ohio Aerospace Institute, this mission would rely on a ship equipped with Nuclear-Electric Propulsion (NEP) and artificial gravity, which would transport a crew on a 5-year mission to Callisto to establish a base.
In his book Entering Space: Creating a Spacefaring Civilization (1999), Robert Zubrin advocated mining the atmospheres of the outer planets – including Jupiter – to obtain Helium-3 fuel. A base on one or more of the Galilean moons would be necessary for this. NASA has also speculated on this, citing how it could yield limitless supplies of fuel for fusion reactors here on Earth and anywhere else in the Solar System where colonies exist.
In October of 2012, Elon Musk unveiled his concept for an Mars Colonial Transporter (MCT), which was central to his long-term goal of colonizing Mars. At the time, Musk stated that the first unmanned flight of the Mars transport spacecraft would take place in 2022, followed by the first manned MCT mission departing in 2024.
In September 2016, during the 2016 International Astronautical Congress, Musk revealed further details of his plan, which included the design for an Interplanetary Transport System (ITS) and estimated costs. This system, which was originally intended to transport settlers to Mars, had evolved in its role to transport human beings to more distant locations in the Solar System – including Europa and other Jovian moons.
Establishing colonies on the Galilean moons has many potential benefits for humanity. For one, the Jovian system is incredibly rich in terms of volatiles – which include water, carbon dioxide, and ammonia ices – as well as organic molecules. In addition, it is believed that Jupiter’s moons also contain massive amounts of liquid water.
For example, volume estimates placed on Europa’s interior ocean suggest that it may contain as much as 3 × 1018 m3 – three quadrillion cubic kilometers, or 719.7 trillion cubic miles – of water. This is slightly more than twice the combined volume of all of Earth’s oceans. In addition, colonies on the moons of Jupiter could enable missions to Jupiter itself, where hydrogen and helium-3 could be harvested as nuclear fuel.
Colonies established on Europa and Ganymede would also allow for multiple exploration missions to be mounted to the interior oceans that these moons are believed to have. Given that these oceans are also thought to be some of the most likely locations for extra-terrestrial life in our Solar System, the ability to examine them up close would be a boon for scientific research.
Colonies on the moons of Io, Europa, Ganymede and Callisto would also facilitate missions farther out into the Solar System. These colonies could serve as stopover points and resupply bases for missions heading to and from the Cronian system (Saturn’s system of moons) where additional resources could be harvested.
In short, colonies in the Jovian system would provide humanity with access to abundant resources and immense research opportunities. The chance to grow as a species, and become a post-scarcity one at that, are there; assuming that all the challenges can be overcome.
And of course, these challenges are great in size and many in number. They include, but are not limited to, radiation, the long-term effects of lower gravity, transportation issues, lack of infrastructure, and of course, the sheer cost involved. Considering the hazard radiation poses to exploration, it is appropriate to deal with this aspect first.
Io and Europa, being the closest Galileans to Jupiter, receive the most radiation of any of these moons. This is made worse by the fact that neither have a protective magnetic field and very tenuous atmospheres. As such, Io’s surface receives an average of about 3,600 rems per day, while Europa receives about 540 per day.
For comparison, people here on Earth are exposed to less than 1 rem a day (0.62 for those living in developed nations). Exposure to 500 rems a day is likely to be fatal, and exposure to roughly 75 in a period of a few days is enough to cause severe health problems and radiation poisoning.
Ganymede is the only Galilean moon (and only non-gas giant body other than Earth) to have a magnetosphere. However, it is still overpowered by Jupiter’s powerful magnetic field. On average, the moon receives about 8 rads of radiation per day, which is the equivalent of what the surface of Mars is exposed to in an average year.
Only Callisto is far enough from Jupiter that it is not dominated by its magnetic environment. Here, radiation levels only reach about 0.01 rems per day, just a fraction of what we are exposed to here on Earth. However, its distance from Jupiter means that it experiences its fair share of problems as well (not the least of which is a lack of tidal heating in its interior).
Another major issue is the long-term effects the lower gravity on these moons would have on human health. On the Galilean moons, the surface gravity ranges from 0.126 g (for Callisto ) to 0.183 g (for Io). This is comparable to the Moon (0.1654 g), but substantially less than Mars (0.376 g). And while the effects of low-g are not well-understood, it is known that the long-term effect of microgravity include loss of bone density and muscle degeneration.
Compared to other potential locations for colonization, the Jovian system is also very far from Earth. As such, transporting crews and all the heavy equipment necessary to build a colony would be very time-consuming, as would missions where resources were being transported to and from the Jovian moons.
To give you a sense of how long it would take, let’s consider some actual missions to Jupiter. The first spacecraft to travel from Earth to Jupiter was NASA’s Pioneer 10 probe, which launched on March 3rd, 1972, and reached the Jupiter system on December 3, 1973 – 640 days (1.75 or years) of flight time.
Pioneer 11 made the trip in 606 days, but like its predecessor, it was simply passing through the system on its way to the Outer planets. Similarly, the Voyager 1 and 2 probes, which were also passing through the system, took 546 days and 688 days, respectively. For direct missions, like the Galileo probe and the recent Juno mission, the travel time was even longer.
In the case of Galileo, the probe left Earth on October 18th, 1989, and arrived at Jupiter on December 7th, 1995. In other words, it took 6 years, 1 month, and 19 days to make it to Jupiter from Earth without flying by. Juno, on the other hand, launched from Earth on Aug. 5th, 2011, and achieved orbit around Jupiter on July 5th, 2016 – 1796 days, or just under 5 years.
And, it should be noted, these were uncrewed missions, which involved only a robotic probe and not a vessel large enough to accommodate large crews, supplies and heavy equipment. As a result, colony ships would have to be much larger an heavier, and would require advanced propulsion systems – like nuclear-thermal/nuclear-electr ic engines – to ensure they made the trip in a reasonable amount of time.
Missions to and from the Jovian moons would also require bases between Earth and Jupiter in order to provide refueling and resupplying, and cut down on the costs of individual missions. This would mean that permanent outposts would need to be established on the Moon, Mars, and most likely in the Asteroid Belt before any missions to Jupiter’s moons were considered feasible or cost-effective.
These last two challenges raise the issue of cost. Between building ships that have the ability to make the trip to Jupiter in a fair amount of time, established the bases needed to support them, and the cost of establishing the colonies themselves, the colonization of the Jovian moons would be incredibly expensive! Combined with the hazards of doing so, one has to wonder if its even worth it.
On the other hand, in the context of space exploration and colonization, the idea of establishing permanent human outposts on Jupiter’s moons makes sense. All of the challenges can be addressed, provided the proper precautions are taken and the right kind of resources are committed. And while it will have to wait until after similar colonies/bases are established on the Moon and Mars, it is not a bad idea as far as “next steps” go.
With colonies on any of the Galilean moons, humanity will have a foothold in the outer Solar System, a stopover point for future missions to Saturn and beyond, and access to abundant resources. Again, it all comes down to how much we are willing to spend.