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I have a world which has a high iron content in its core, like a more extreme version of Mercury, geologically speaking. The system only has this world and a tidally locked hot Jovian (of which the main world in question is a moon), which also has another couple small moons. I might have other planets join them, but they aren't going to be for anything but fluff, so it's a low priority. The idea is that the Jovian happened to capture the iron world (unlikely, but the sun has a low mass, so a close flyby might have gotten lucky, and it's unimportant anyway).

For this world, I did some cursory reading and it seems like what would be more common here are siderophilic elements, which would be platinum group metals, cobalt, iridium, etc. That sounds fun, and provides a nice economic niche for the planet--cobalt for lithium ion batteries, the naturally occurring superconductor covellite, etc. But, and here's my issue, I'm not sure if that's accurate. Would such a world with a high iron-content core have more availability of these more rare elements?

Endstate: I would like for this planet to have an economic reason to have been taken over, since in this setting "planet cracking" is a thing one nation is described to do (well, we can split hairs about ecological stewardship extending to the stability of star systems, but that bit wasn't up to me lol). In the face of that it's questionable why anyone would bother doing conventional mining unless there's a good wrinkle, and I think what I have would be a good one, if it makes sense.

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  • $\begingroup$ Tidally locked jovian planet? Does that have any meaning for a gas giant? I would think there would be too much moving fluid to meaningfully lock it. More expected would be the moon tidally locked to the jovian planet. $\endgroup$ May 18 at 0:02
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    $\begingroup$ for a large iron cored moon orbiting a gas giant see Io a planet that is the most geologically active body in the solar system. Io is so volcanically active we have never seen it without a dozen volcanoes erupting on it. you world is an even more extreme version becasue the iron core is bigger. $\endgroup$
    – John
    May 18 at 0:13

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Depends on history of formation.

In the proto-planetary disk, everything is kinda uniform. But once they go above certain size there is a lot of energy added via collisions, combine that with heating via gravity the cores of planets start melting. Once large scale melting occurs, the elements start separating out with denser material sinking. This is how iron cores form. The overall mass and temperature will dictate how fast this occurs.

For a moon of a gas giant. It could be supposed that a large moon formed early and large enough to have melt and start forming a core. Then a collision caused an orbit change where perihelion was close enough to the parent to strip the outer layers off. Due to its soft molten core, the core portion would resist being stripped. Then with time and more collisions would return the moon to more circular orbit.

How much non iron heavy metals present would depend on how long and how hot did the core get, how much of the outer layers were stripped off. Including how much of the iron core was stripped off.

With the molten metallic core exposed it would cool down faster freezing in a more homogeneous mix of mostly heavier metals. But still mostly diluted. With no flowing solvents there are few means to create concentraions of minerals. Mining such a world would mean having lots of iron as tailings to process enough material to get more interesting metals.

That is, yes a metallic world would have more heavy metals comparatively per typical cubic meter. However they are unlikely to be host concentrated deposits.

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I've not read very thoroughly on this, but my interpretation of planetary formation implies that if such elements are abundant during the formation of planets a metal rich planet would have a variety of rare metals, including platinum group metals.

The amount available has details like the nature of the supernova that formed the initial gas and dust involved in planetary formation. I believe denser cores of metal can be formed by planetary collision if the planet in question moves orbits after the collision and doesn't reabsorb the lighter materials (this can be caused by another planet transiting its orbit, some models suggested this happened pretty often in our early solar system because Saturn and Jupiter were essentially throwing planets out of orbit before their orbits stabilized).

Most cores in the inner solar system will have a similar composition but if the planet is very small, it cools more quickly (even with intense solar radiation on one side). So the core is more likely to be solid (and thus can be harvested with advanced interplanetary level mining technology).

If the planet is the result of planetary collision, the statistical occurrence of the metals will be relatively high compared to other planets. So the metallic core should be larger, and the additional material actually on the planet would be smaller. It's really a matter of the density of the material and its ability to be absorbed into the greater mass of metallic elements (like some elements just don't mix in molten form, and if lower density will rise to the top leaving a dense core of intermixed metals).

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