Geological Processes
Jun. 13th, 2009 02:56 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
stickmakerSomeone recently asked me why, in one of my stories, I had an alien species which has the habit of sneaking onto inhabited worlds and stealing mineral resources. They wanted to know why they didn't just process asteroids.
The answer is in two words: differentiation and metamorphosis.
Only the largest asteroids - such as Ceres - are large enough for a significant amount of gravitational differentiation. That is, denser materials settling to the core.
Metamorphosis is the chemical alteration of minerals through geologic processes. Remember how excited scientists were over the discovery of olivine by one of the Mars rovers? Olivine requires water to form. Which means Mars at some time had significant amounts of water. You're not likely to have much water on an asteroid.
Differentiation also takes place on a smaller scale. Materials which don't combine with the rock around them tend to form nodules and veins. Hence gold and silver mines. Aliens with advanced sensor and excavation technology could find and efficiently remove such concentrated minerals.
So, yeah. It could happen, especially if the operation was planned as a short-term, high-return project, rather than a long mission.
The answer is in two words: differentiation and metamorphosis.
Only the largest asteroids - such as Ceres - are large enough for a significant amount of gravitational differentiation. That is, denser materials settling to the core.
Metamorphosis is the chemical alteration of minerals through geologic processes. Remember how excited scientists were over the discovery of olivine by one of the Mars rovers? Olivine requires water to form. Which means Mars at some time had significant amounts of water. You're not likely to have much water on an asteroid.
Differentiation also takes place on a smaller scale. Materials which don't combine with the rock around them tend to form nodules and veins. Hence gold and silver mines. Aliens with advanced sensor and excavation technology could find and efficiently remove such concentrated minerals.
So, yeah. It could happen, especially if the operation was planned as a short-term, high-return project, rather than a long mission.
no subject
Date: 2009-06-14 07:07 am (UTC)That's *why* we have nickel-iron and stony bodies. They originated from bodies that were molten all the way thru and did in fact settle some as they slowly cooled as the radioactive heating declined.
What's missing are geothermal processes which are how most ore bodies are formed.
no subject
Date: 2009-06-14 02:45 pm (UTC)Okay, yeah, I was thinking more of inner solar system bodies still present. I've actually read both articles and stories about large planetesimals still out in the Oort cloud which not only have differentiation but actual ecosystems. (Of course, those would count as small planets.)
Metallic asteroids are rare. As I understand it, they are from the cores of large bodies - where some differentiation took place, as you note - being burst apart in collisions. Differentiation is much more thorough on a true planet.
Of course, in addition to differentiation and geothermal processes (some large satellites of gas giants may actually have those, due to tidal heating) there's the tectonic plate conveyor. Materials are repeatedly subducted and extruded.
Hey, this gives me an idea for a new Joy of High Tech. "Why We Need to Mine Planets." I know a professional astronomer, who has done work with meteorites. I should talk to him about this.