Preface: With this post, our goal is to identify the top ten best places in the solar system for humanity to colonize in the near future. While these celestial bodies will be selected based off of our personal expectations for how the future may play out, we will do our best to support each choice with some facts. Also, keep in mind that we will be focusing on answering “where” and “why” with this list; we may explore the actual “how” more in the future, but that will not be discussed here for brevity’s sake. The main criteria for these selections are resources, location, gravity, and radiation level, although some other aspects of each site may also be considered. If you have some additional thoughts about why our choices may be faulted, if you think we have left something off the list which should have made the top ten, or if you personally would have switched up some of these rankings, leave a comment below. We’re interested to hear everyone’s rationales.

10) Eris ~ Eris is a dwarf planet in the far reaches of the known solar system. With a small size and mass, the gravity on the surface would be low, likely less than 10% of Earth’s. This could be partially resolved by creating a large, rotating habitat on the surface or simply ignoring habitation of the surface altogether and settling people in a rotating artificial habitat inserted into an Eris orbit instead. The planet would also be extremely cold and has no atmosphere to protect colonists from radiation, but this can be resolved by building thick walls and having good heating.

The main reason to settle Eris, strangely enough, is its location. With an eccentric orbit bringing it as near as 38 AU (astronomical units, with 1 being the average distance from Earth to the Sun) and as far as 98 AU, Eris seems like a decent place to set up an interstellar gas station of sorts. Most icy bodies have the materials available to manufacture rocket fuel, and there’s no reason to believe Eris is any different. Additionally, Eris is in a prime location to construct an observatory to explore the Oort Cloud and beyond since it has no atmosphere and is far away from the Sun’s light.

9) Triton ~ As the largest moon of Neptune, Triton is the prime place to make a base of operations around the furthest (known) planet. Thought to be a captured Kuiper Belt Object, Triton is the only sizable rocky object in the Neptunian system. As such, Triton is the only place with a colonizable surface in the system. Current understanding of the moon also indicates that there is ample water ice on the surface, and as humanity extends its reach out into the solar system and beyond, water will likely be a valuable resource. Triton would also be another nice stopping point for interstellar transit. In the distant future, it is feasible that raw goods (likely just precious metals) will be transported between star systems. If that becomes the case, most large, rocky bodies in the outer solar system may be turned into refueling stations or interstellar shipyards.

8) Europa ~ Europa is an interesting place to consider colonizing. As one of Jupiter’s Jovian moons, it is located relatively close to the Earth, and that would make colonizing it a bit more manageable than colonizing anything in the far outer solar system. However, it is also subjected to high levels of radiation emanating from Jupiter. The main point of interest which works in Europa’s favor is the presumed presence of a liquid ocean. The surface is composed mainly of water ice which may be more than enough to fuel humanity for a great number of years, but the liquid ocean underneath is the more intriguing feature since it could potentially be harboring life. NASA has taken great interest in Europa. It is currently developing the Europa Clipper mission which is set to launch sometime in the 2020s.

7) Pluto ~ Once a planet, a planet no more. Pluto is more-or-less tied with Eris as the largest known object residing primarily beyond Neptune, and this makes it another attractive place to set up an interstellar pit-stop. We previously published a post with a more in-depth discussion of Pluto’s habitability, and you may find that post here. Pluto could serve some of the same purposes as Eris in terms of colonization, but since it has already been visited by NASA’s New Horizons mission in July of 2015, it is feasible that the system will get a human presence sooner than other Kuiper Belt Objects.

6) Callisto ~ Callisto, like Europa, is another one of Jupiter’s four Galilean moons. The moon is geologically inert, so any settlers on Callisto would never have to worry about anything like cryovolcanism. The main unique purpose in colonizing Europa would be to use it as a base to explore the rest of the Jovian system. As the furthest Galilean moon from Jupiter, Callisto is the best site because it receives the least amount of radiation. This fact actually led NASA to choose Callisto as the prime site for a mock-up manned mission to the outer solar system, although the mission was never meant to be put into development.

5) Venus ~ Depending on how technology progresses, Venus might actually be the best place to colonize in the solar system. PBS Space Time had a nice little video about this, but the basic idea is that if you are able to substantially elevate a habitat into Venus’ atmosphere, you will be able to get a temperature that is much more bearable than the excruciating heat felt at Venus’ surface elevations. It’s also important to note that Venus is very similar in size to Earth, so we can be fairly confident that its surface gravity (90.4% of Earth’s) is strong enough to pose no significant human health concerns.

Venus also has the benefit of being in close proximity to Earth, so communications ought to be quite easy. Sadly, due to the harsh conditions on the surface, the floating or raised colonies on Venus would not have as much industrial potential as other colonies in the solar system. Robots could be used to mine materials from the surface, but the human population would almost certainly be confined to their cities.

4) Titan ~ Titan is Saturn’s largest moon and the second-largest moon in the solar system. It is also the only moon in the solar system boasting a dense atmosphere, and that dense atmosphere’s ability to block radiation is one of the main reasons it is this high on our list. Titan also has lakes made of liquid hydrocarbons. The unique geology of Titan makes it an interesting place to set up a science-minded colony to study how active processes can occur outside Earth. It would be a fantastic opportunity to prepare scientists for the exploration of other interstellar solar systems in the more distant future. However, Titan also suffers from the common problem on this list: low gravity. We still don’t know how low gravity affects humans in the long term, and Titan’s surface gravity is only 14% of Earth’s. It’s also in a somewhat-distant location, although by the time humanity is ready to colonize Titan, there will likely be well-established colonies on Mars which could provide a nearer source of communication and supplies.

For a more detailed musing into the colonization of Titan, I highly recommend checking out this Youtube video by Isaac Arthur.

3) Ceres/The Asteroid Belt ~ With the value of the asteroid belt being seemingly limitless (in the quintillions of dollars), it’s an almost assured bet that humanity will try to exploit it as a natural resource. With Ceres being the largest object in our solar system’s asteroid belt, it’s reasonable to believe that humanity will eventually set up some sort of asteroid mining colony there.

Asteroids are actually some of the best places to build a colony. Smaller asteroids, while not giving colonists much space to build, can be manually rotated through heating in a way that produces artificial gravity. These miner-colonists could then hollow out the asteroid and live comfortably within it while mining from the outside of nearby asteroids. The asteroid itself would be able to provide sufficient protection from radiation, so colonies inside asteroids would really only need to worry about heating, power, and water. The heat could be held inside by tightly sealing the internal manmade structures, and water could either be shipped into the colony and recycled or found in the form of ice somewhere nearby.

2) The Moon ~ Most people already know all they need to know about the Moon, and really it only has one glaring benefit that makes it a great site to colonize: it’s nearby. All of these other sites take months or even years to get to from Earth using current technology. Getting to the Moon takes mere days.

Although the gravity is low and any habitation structures would need to be under the surface to protect settlers from radiation, the Moon is close enough to the Earth that the colony could be built rapidly since materials may be shipped in from Earth with relative ease.

In the long term, the purpose of a lunar colony would likely be to act as a propellant factory. Spaceships in the future will likely be manufactured in-orbit around either the Earth or the Moon to reduce launch costs, but rocket propellant will almost certainly be manufactured on the moon since it could be transported to the spaceships in-orbit at a much lower cost since less fuel would be initially expended on launch due to the lower gravity and lack of an atmosphere on the Moon.

1) Mars ~ Without a doubt, Mars will be colonized by humanity in the near future, likely before the end of the 21st Century. Elon Musk and his team at SpaceX are hell-bent in striving towards this goal, and they have already made extensive plans for initially getting to Mars and starting a new colony there. Additionally, Boeing has risen up and issued a challenge to SpaceX as to which company will reach Mars first, and Lockheed Martin even has plans to construct a space station which will orbit around Mars.

Why is Mars such an attractive destination? Why does a Martian colony top our list of the “top ten best places to colonize” in the entire solar system? For starters, it’s the third-nearest spot on this list. It’s also well-explored at this point, so colonists will have to deal with less unforeseen circumstances than they may encounter in places like Europa or Titan. Mars’ axial tilt and day length are very similar to Earth’s, so any biological changes that have to do with day length or seasons will be minimal. Water ice is also present on Mars, so colonists will not have to import water from elsewhere and should be able to have a self-sustaining resource system once enough flora and fauna are brought in from Earth and adjusted to the Martian environment.

However, Mars is not perfect. With a force of only 38% of Earth’s surface gravity, it is not clear if Martian gravity is significant enough to offset the negative health effects of weightlessness on the human body. Also, Mars’ atmosphere is too thin to provide significant protection from radiation, so Martian habitats will need to be built underground or have very thick coverings if built on the surface.

Among all places on this list, I think it’s safe and exciting to say that most of us will see the founding of a Martian colony in our lifetimes. The first few attempts at colonization may not work out how we hope, but humanity is resilient, innovative, and persistent. We’ll figure it out eventually.