Crustal Fragments as Asteroids

Consider a solar system with a planet or dwarf planet somewhat smaller than Mars. If it is large enough, when it forms there will be a great amount of heat generated, meaning there will be separations of elements and compounds, and ore mixtures as well, in the core and crust of the planet. The largest glob will likely be an iron and nickel mixture, which would form the core of the planet. If it stays warm enough for long enough, compounds not very soluble in this metal will separate out, and assuming they are lighter in density, will rise to the crust. The crust will have all the interesting materials in it. The core will be fairly homogeneous, but the crust will have different ores separated out, provided the elements to make these up were there in the beginning.

Thus, small planets deep in the solar system, where dust would collect, would be treasure-troves of minerals, some of which might be very important to an alien civilization which had passed the point of being able to travel throughout their solar system.

As far as mining of inner, metallic planets goes, they do not need to be very small for mining to take place. Having no atmosphere may make it easier or harder to do mining, and that is not clear now. But smaller planets, with no atmosphere, would be vulnerable to the rain of smaller asteroids that happens in the early days of a solar system. Many of these would simply pulverize the surface. Those which came in on a grazing trajectory, if the size and speed were right, might chip off some piece of the crust and transfer enough momentum to it so that it escaped the gravitational pull of the small planet. This is a crustal fragment.

A larger planet could conceivably give rise to a crustal fragment asteroid as well, but via spallation rather than a grazing impact. If a large asteroid were to impact a larger inner planet, the shock wave from the impact would travel through the planet, arriving at the opposite point from the impact point. Perhaps it could have enough energy to blast some material past escape velocity, and possibly some of this material might still be intact, that is, some chunks of crust go flying into solar orbit.

Mining asteroids is thought to be a possibly profitable venture, in the sense that the retrieved material is worth more than the cost of retrieving it. For a crustal fragment asteroid, the materials might be much more valuable than an asteroid which simply has the average material of the solar system at some radius. There could be a hundred times more valuable ore on a crustal fragment asteroid than on a usual one. What would be important if finding which was which. This might require visits by some small robotic ship.

Suppose there was an asteroid, formed from one of the crustal fragmentation processes, which was of the order of a hundred kilometers in size. If it were explored, and there were sources of rich uranium ore in the asteroid, it might be able to form a self-sufficient colony of aliens there. Using the uranium as an energy source, the only energy source, could enough energy be generated to provide a habitable environment, where every other material had to be mined from somewhere on the asteroid and transformed into useful materials? If this is possible, a temporary colony could be established, either independent or part of some multiplanetary organization. How long could alien civilization last on the asteroid? Until the uranium ore was depleted so much that it could no longer supply the energy needed to power the entire asteroid and all its necessary activities, of mining, transporting, refining, manufacturing, and all the multiple activities needed to provide a habitable environment.

How likely is it that there would be one or more of these crustal fragment asteroids in an average solar system? We don't know what average is yet. We don't know what asteroids are in our own solar system, so the data is pretty sparse. At best, we can indicate it might be possible.

What might be the orbital characteristics of a crustal fragment asteroid? Ones which are formed from the grazing impact process would have something less than the orbital radius of the incoming asteroid, the one which hits the small planet. That could have been in orbit similar to the planet which was hit, meaning the resulting asteroid would also. However, in the early days of the formation of a solar system, some asteroids might be shot into orbits out of the planetary plane or even retrograde. This happens because of the interaction of the major planets with the small bodies co-inhabiting the solar system. It should be quite rare, but possible.

The spallation situation might serve to give the spallation fragments a higher speed that the incoming asteroid, if the shock wave was focussed sufficiently. Is it possible that it could be given solar escape velocity, and leave the solar system? Is it possible that later interactions with large planets could slingshot it out of the solar system? The later is certainly possible, and the former, maybe. Either way there is a process by which a crustal fragment asteroid could become an interstellar rogue. Since the crustal fragment asteroid is formed in such as way that its orbital parameters could be unusual, this is not too hard to imagine.

This means that for an alien solar system, there might be rogue crustal fragment asteroids passing through it, laden with massive amounts of uranium for energy and other crustal materials for manufacturing. Could an alien civilization, able to travel around its own solar system and very famiiar with mining asteroids, manage to get to such as asteroid before it passed through their system, and establish either a robotic colony or one comprised of some very brave colonist aliens? Only if they had prepared such spaceships in advance, so they could simply concentrate on getting their ship there and down on the surface in the months that the asteroid was present in their solar system.

They might be able to make small adjustments in its trajectory from solar system to solar system. If there were a sufficient number of this type of rogue asteroid passing through their solar system, it would mean that we should not be looking for some giant saucer-shaped ship for visiting aliens, but instead a large rock.