New Models for Planetary Formation
The science of planetary formation has been advancing in leaps and bounds for the last decade or two, driven by the discovery of thousands of exoplanets and fine-detail imaging of other planetary systems. This has been giving us a lot of insight into not only the history of our own Solar System, but also the general case of planetary formation elsewhere.
With my Architect of Worlds project, I’ve been trying to keep abreast of the current science while designing a world-building system for use in game design and literary work. The current state of the system is pretty good, I think, but it’s a bit complicated. I’ve built a model that tracks the formation of a system’s primary gas giant (if any), follows that planet as it migrates inward (and possibly outward), and uses the results of that evolution to determine the mass and placement of the rest of the planets. Lots of moving parts there, and a few of the steps are kind of unwieldy.
Now there’s some recent research suggesting that I might be able to simplify the model and still get good results. The pertinent paper is “Planetesimal rings as the cause of the Solar System’s planetary architecture,” by Andre Izidoro et al., released in December 2021. Here’s a layman’s article from Rice University: “Earth isn’t ‘super’ because the sun had rings before planets,” published on 4 January.
The idea is that it wasn’t specifically the migrations of Jupiter that brought about the architecture we see of the inner Solar System. Instead, the protoplanetary disk probably had several “pressure bumps,” places where infalling particles released gases due to the increasing temperature close to the embryonic Sun. These pressure bumps tended to accumulate dust particles, and created an environment where planetesimals could form and coalesce, without continuing to spiral into the Sun. The authors of the paper predict the presence of three such “pressure bumps,” which ended up giving rise to the rocky inner planets, the gas giants, and the Kuiper Belt objects respectively.
The idea makes a lot of sense, especially since we’ve started to get fine-detail images of young stars and their protoplanetary disks, and we sometimes see exactly the system of “rings” that the model would predict. Take the image that leads the Rice University article, which I’ve included above.
Scientifically, speaking, the neat thing about this new model is that it explains several things that previous models (which assumed a more uniform disk and relied on Jupiter-migrations to make things work out) had trouble with – especially the specific isotopic composition of inner-system as opposed to outer-system material. The new model also doesn’t have any trouble producing a small Mercury or Mars, or a planetoid belt (with mixed composition) between Mars and Jupiter.
From my perspective, it may mean that I can simplify the model on which Architect of Worlds is built, making the whole thing much easier for people to use. I’m going to be reading the literature on this, and thinking about the implications.
