Recently I've been working on adding the outer solar system to High Frontier. That, along with this recent news story, has got me thinking about a population of minor planets in the outer solar system known as centaurs.
Centaurs are small bodies that orbit somewhere out between Jupiter and Neptune. But they're not that small; the largest known, Chariklo, has a diameter of about 250 km. Many centaurs (including Chariklo) have a system of rings, as shown in this artist's concept.
![[Image: asteroid_ring-580x379.jpg]](http://www.universetoday.com/wp-content/uploads/2014/03/asteroid_ring-580x379.jpg)
What really struck me this week is how many centaurs there are. Check out this map of the outer solar system. Only known objects are plotted on the map, but the estimated total number of objects is shown in in the key below.
![[Image: KP6cIZC.png]](http://imgur.com/KP6cIZC.png)
That's right -- there are an estimated 44 thousand centaurs at least 1 km in diameter. They're a very interesting and diverse bunch of objects too, with characteristics of both comets and asteroids, and a variety of colors that suggest complex composition. In short, they look like great places to build space colonies and make a home.
So how many people could do that? Let's run some numbers.
First, since most of the centaurs are still unknown, let's estimate how many there are of various sizes. Like most things in nature, they probably follow a power law, with many more small objects than large ones. Here's a possible distribution that totals about 44,000 objects. (Note that quantity is a log scale.)
![[Image: NJkvyXe.png]](http://i.imgur.com/NJkvyXe.png)
Now, doing some simple geometry, approximating each object as a sphere and assuming a typical density of 2 gm/cm^3, here's a table showing volume and mass.
![[Image: LDh2ABx.png]](http://i.imgur.com/LDh2ABx.png)
6.6x10^22 sounds like a lot of mass, and it is. It's about the same mass as our Moon. But unlike the Moon, this mass is distributed in convenient, bite-sized pieces, most of them only a few kilometers in diameter. Also unlike the Moon, this mass is rich in volatiles like water, as well as heavier stuff (carbon, iron, titanium, etc.) for building with. For an experienced spacefaring civilization (say, us a thousand or so years from now), these centaurs would be very accessible sources of material for turning into deep-space colonies.
While those colonies will no doubt come in an amazing variety of shapes and sizes, for the sake of argument, let's suppose they look like this.
![[Image: muae0CI.png]](http://i.imgur.com/muae0CI.png)
This is a cylinder 1 km in radius and 1 km long, with inverted endcaps for stability. It rotates at a little under 1 RPM, producing Earth-like gravity for 6.3 km^2 of living area inside. At a population density of 1500 people per km -- comparable to a typical American small town -- each habitat would house about 10,000 people. Power is provided by a nuclear (fission or fusion) plant on the other end, not visible in this view. The mass of this habitat works out to 150 Mt (1.5x10^11 kg).
So, assuming only half the mass of each centaur is useful for building, and plugging that back into our table, what do we get?
![[Image: shaofzn.png]](http://i.imgur.com/shaofzn.png)
Yep, that's right. We're looking at over 200 million habitats, housing 2 quadrillion people, all living comfortably in small towns of 10,000 people each. The total area of these habitats is nearly 3000 times the surface area of Earth, including the oceans. If you compare to just the land area of Earth, it's nearly 10,000 times greater.
And this is just the centaurs. There are other many collections of useful stuff in the solar system, including the main asteroid belt, the trojan asteroids co-orbiting with each of the gas giants, the Kuiper belt, and eventually the Oort cloud.
The solar system is friggin' huge.
Centaurs are small bodies that orbit somewhere out between Jupiter and Neptune. But they're not that small; the largest known, Chariklo, has a diameter of about 250 km. Many centaurs (including Chariklo) have a system of rings, as shown in this artist's concept.
What really struck me this week is how many centaurs there are. Check out this map of the outer solar system. Only known objects are plotted on the map, but the estimated total number of objects is shown in in the key below.
That's right -- there are an estimated 44 thousand centaurs at least 1 km in diameter. They're a very interesting and diverse bunch of objects too, with characteristics of both comets and asteroids, and a variety of colors that suggest complex composition. In short, they look like great places to build space colonies and make a home.
So how many people could do that? Let's run some numbers.
First, since most of the centaurs are still unknown, let's estimate how many there are of various sizes. Like most things in nature, they probably follow a power law, with many more small objects than large ones. Here's a possible distribution that totals about 44,000 objects. (Note that quantity is a log scale.)
Now, doing some simple geometry, approximating each object as a sphere and assuming a typical density of 2 gm/cm^3, here's a table showing volume and mass.
While those colonies will no doubt come in an amazing variety of shapes and sizes, for the sake of argument, let's suppose they look like this.
This is a cylinder 1 km in radius and 1 km long, with inverted endcaps for stability. It rotates at a little under 1 RPM, producing Earth-like gravity for 6.3 km^2 of living area inside. At a population density of 1500 people per km -- comparable to a typical American small town -- each habitat would house about 10,000 people. Power is provided by a nuclear (fission or fusion) plant on the other end, not visible in this view. The mass of this habitat works out to 150 Mt (1.5x10^11 kg).
So, assuming only half the mass of each centaur is useful for building, and plugging that back into our table, what do we get?
Yep, that's right. We're looking at over 200 million habitats, housing 2 quadrillion people, all living comfortably in small towns of 10,000 people each. The total area of these habitats is nearly 3000 times the surface area of Earth, including the oceans. If you compare to just the land area of Earth, it's nearly 10,000 times greater.
And this is just the centaurs. There are other many collections of useful stuff in the solar system, including the main asteroid belt, the trojan asteroids co-orbiting with each of the gas giants, the Kuiper belt, and eventually the Oort cloud.
The solar system is friggin' huge.
Joe Strout
Lead Developer, High Frontier
