This is a follow-up to my original question about my planets, but this one is mostly for a different planet.

Basically, I have a small terrestrial planet close to the Sun, about the size of Mercury. I've noticed a trend in the planets close to the sun having heavier elements, but specifically, what are the elements? And in what percentages will I usually find them?

Also, if anyone also can talk about the elements found in the other four planets, that would be great, but not required ^^

How should I position my planets? <<< prev question, have decided to use different orbital paths for them all


1 Answer 1


The issue is that the element content of planets is highly affected by collisions. And the collisions have a huge amount of happenstance involved. In particular, the type of collision is important. A glancing collision tends to blast away all the lighter stuff and leave most of the heavier elements. A direct collsion can produce a number of different effects from the two joining up, to both getting pulverized, to them exhanging material and going on, depending on the relative speeds and the exact angle.

So Mercury seems to have been the result of a glancing collision. The debris wound up getting absorbed into the sun. The Earth-Moon system seems to have been more direct, but with the two objects exchanging material and the smaller becoming our Moon.

So you can pretty much dial-up how much metal and heavier elements you want in a planet. Within the range of what Mercurt has to what Mars has. You just choose which collisions happened. You can also dial up whether they are larger or smaller within the range, by having the extra mass blalsted off into space or absorbed by the two colliding objects.

There will be limits, of course. But those limits will be exceedingly difficult to pull out for any specific stellar system candidate. It would require a huge amount of computer calculations to determine if a particular set of planet sizes and metal contents could have resulted from a plausible series of collisions. As long as things don't look too drastically different from our own solar system, your audience will have a difficult time knowing if it is impossible. Probably you don't want a Jupiter-sized planet in the place of Mercury, for example.

Otherwise, you can just dial up what your story needs.

  • $\begingroup$ There are solar sysems with Jupiter sized planets at the distance of Mercury or even closer. Giant planets close to their stars are called "hot Jupiters" and are among the easiest exoplanets to detect. Presumabley they would have form farther from their stars migrated inwards which owuld hav edsiputed he orbits of any planets in their way, so they shouldn't be found in systems with planets in the habitable zone. $\endgroup$ Commented Dec 16, 2022 at 18:21

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