Ceres colony
Dec. 23rd, 2011 10:30 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
steorran_woruldeKiel came over today and we ended up coming up with an interesting imaginary scenario for a colony on Ceres.
First, some basic info about Ceres, taken mostly from this page on the Planetary Society website and the Wikipedia article on Ceres.
Orbital properties:
Semimajor axis (roughly, radius of orbit): 2.8 AU (Mars: 1.5 AU; Jupiter: 5.2 AU)
Orbital period: 4.60 years / 1680 days (Mars: 1.88 years / 687 days; Jupiter: 11.86 years / 4333 days)
Eccentricity: 0.079 (Earth: 0.017; Mars: 0.093)
Inclination to invariable plane : 9.2° (Earth: 1.6°; Mars: 1.7°)
Rotational properties:
Rotational period: 0.38 days / 9.1 hours
Axial tilt: about 3° (Earth: 23°; Mars: 25°; Mercury: 2'; Jupiter: 3°)
Basic physical properties
Diameter: about 950 km (about 1/13 or 7.5% of Earth)
Mass: 9.43 x 10^20 kg (0.016% of Earth)
Density: 2.10 grams per cubic centimetre
Equatorial surface gravity: 0.028 g (Earth: 1 g; Mars: 0.38 g; Moon: 0.17 g). (Something that weighed 100 units on earth would way only almost 3 units on Ceres.)
Maximum surface temperature: 235 K (about -40° C)
Ideas for an imaginary colony
Okay, with those basic physical properties in mind, how could a colony on Ceres work? Here's what Kiel and I worked out.
Terraforming Ceres as a whole would never be plausible; it's not massive enough to maintain an atmosphere. So you'd want something to hold the atmosphere in - say, a dome of some sort over the region you were colonizing.
Even this raises an interesting problem. The density of Ceres (2.1 grams per cubic centimetre) is lower than that of rock (about 3.4) and higher than that of water ice (about 0.94). This is one of several indications that Ceres contains a significant amount of water ice along with rock; based on density, about 17% to 27% of Ceres' mass could be water ice. Ceres probably has a differentiated structure, with a rocky core, and a water ice mantle 70-120 km thick. We don't see a lot of evidence of water ice on the surface of Ceres, though, so it's probably covered in a fairly thin layer of rocky materials. (Unfortunately I haven't been able to find any suggestions about how thick this layer is, but I'm under the impression that it's more likely to be measured in metres than in kilometres). Ice close to the surface is both a resource and a challenge: resource in that it provides an abundant supply of liquid water, and challenge in that you need to make sure it doesn't melt under you. If you just put up an atmosphere-holding dome, fill it with atmosphere, and heat it to a good temperature for growing the plants you need to support you, you're probably going to melt some of the under-ice with those high temperatures, and that will be problematic.
So Kiel and I came up with a possible solution (although it might depend somewhat on what impurities the ice has in it, and so what temperature it would melt at). We thought about arctic climates and permafrost. Maybe you could set things up so that inside your dome you basically have an arctic: thick ground, with the lower part permafrost; artificial climate set up to maintain permafrost, with part time 'winter', below freezing, allowing the ground to freeze, and part time 'summer', above freezing, allowing arctic plants to grow. The permafrost layer would keep the Ceres ice from melting. There could be greenhouses and other smaller-scale warm spots that would not melt through the permafrost and would allow things to grow that need warm temperatures.
Ceres is very unlikely to have a significant magnetic field. That means people there will need to be protected from radiation by some kind of shielding. Kiel said that for astronauts going from Earth to Mars, 1 metre thickness of water is thought to be capable of shielding humans even from a major solar radiation event. That must be the thickness required at Earth orbit; presumably, out at Ceres, the thickness of shielding would be less. We came up with the idea that you could have a dome over the colony with water sandwiched between two transparent layers. Additionally, you could have things grow in that overhead sea! Seaweed, fish, etc. (Although you would probably want to make sure that the living stuff was confined to the inner part of the water, where it would be at least partly shielded from radiation effects that you wouldn't be protected from in the outer part.) Imagine having a mini-sea over your head!
Mineral resources might be a problem, but a look at what's thought to be on the surface of Ceres suggests that there would probably be a reasonable variety of minerals around, so it might be okay.
I know there were a few other things we talked about, but those are the main ones that come to mind, and I need to go to bed, so I'll stop here.
First, some basic info about Ceres, taken mostly from this page on the Planetary Society website and the Wikipedia article on Ceres.
Orbital properties:
Semimajor axis (roughly, radius of orbit): 2.8 AU (Mars: 1.5 AU; Jupiter: 5.2 AU)
Orbital period: 4.60 years / 1680 days (Mars: 1.88 years / 687 days; Jupiter: 11.86 years / 4333 days)
Eccentricity: 0.079 (Earth: 0.017; Mars: 0.093)
Inclination to invariable plane : 9.2° (Earth: 1.6°; Mars: 1.7°)
Rotational properties:
Rotational period: 0.38 days / 9.1 hours
Axial tilt: about 3° (Earth: 23°; Mars: 25°; Mercury: 2'; Jupiter: 3°)
Basic physical properties
Diameter: about 950 km (about 1/13 or 7.5% of Earth)
Mass: 9.43 x 10^20 kg (0.016% of Earth)
Density: 2.10 grams per cubic centimetre
Equatorial surface gravity: 0.028 g (Earth: 1 g; Mars: 0.38 g; Moon: 0.17 g). (Something that weighed 100 units on earth would way only almost 3 units on Ceres.)
Maximum surface temperature: 235 K (about -40° C)
Ideas for an imaginary colony
Okay, with those basic physical properties in mind, how could a colony on Ceres work? Here's what Kiel and I worked out.
Terraforming Ceres as a whole would never be plausible; it's not massive enough to maintain an atmosphere. So you'd want something to hold the atmosphere in - say, a dome of some sort over the region you were colonizing.
Even this raises an interesting problem. The density of Ceres (2.1 grams per cubic centimetre) is lower than that of rock (about 3.4) and higher than that of water ice (about 0.94). This is one of several indications that Ceres contains a significant amount of water ice along with rock; based on density, about 17% to 27% of Ceres' mass could be water ice. Ceres probably has a differentiated structure, with a rocky core, and a water ice mantle 70-120 km thick. We don't see a lot of evidence of water ice on the surface of Ceres, though, so it's probably covered in a fairly thin layer of rocky materials. (Unfortunately I haven't been able to find any suggestions about how thick this layer is, but I'm under the impression that it's more likely to be measured in metres than in kilometres). Ice close to the surface is both a resource and a challenge: resource in that it provides an abundant supply of liquid water, and challenge in that you need to make sure it doesn't melt under you. If you just put up an atmosphere-holding dome, fill it with atmosphere, and heat it to a good temperature for growing the plants you need to support you, you're probably going to melt some of the under-ice with those high temperatures, and that will be problematic.
So Kiel and I came up with a possible solution (although it might depend somewhat on what impurities the ice has in it, and so what temperature it would melt at). We thought about arctic climates and permafrost. Maybe you could set things up so that inside your dome you basically have an arctic: thick ground, with the lower part permafrost; artificial climate set up to maintain permafrost, with part time 'winter', below freezing, allowing the ground to freeze, and part time 'summer', above freezing, allowing arctic plants to grow. The permafrost layer would keep the Ceres ice from melting. There could be greenhouses and other smaller-scale warm spots that would not melt through the permafrost and would allow things to grow that need warm temperatures.
Ceres is very unlikely to have a significant magnetic field. That means people there will need to be protected from radiation by some kind of shielding. Kiel said that for astronauts going from Earth to Mars, 1 metre thickness of water is thought to be capable of shielding humans even from a major solar radiation event. That must be the thickness required at Earth orbit; presumably, out at Ceres, the thickness of shielding would be less. We came up with the idea that you could have a dome over the colony with water sandwiched between two transparent layers. Additionally, you could have things grow in that overhead sea! Seaweed, fish, etc. (Although you would probably want to make sure that the living stuff was confined to the inner part of the water, where it would be at least partly shielded from radiation effects that you wouldn't be protected from in the outer part.) Imagine having a mini-sea over your head!
Mineral resources might be a problem, but a look at what's thought to be on the surface of Ceres suggests that there would probably be a reasonable variety of minerals around, so it might be okay.
I know there were a few other things we talked about, but those are the main ones that come to mind, and I need to go to bed, so I'll stop here.