Sharrukin's Palace

Sometimes a bit of research comes across my desk that leads to big changes in one of my creative projects. Today we have a case in point.

At the beginning of December, Ken Burnside was kind enough to bring this article from phys.org to my attention: The solar system follows the galactic standard – but it is a rare breed.

The article was from the Niels Bohr Institute, summarizing some research done there by Nanna Bach-Møller and Uffe G. Jørgensen. The upshot is that, based on our extensive sample of detected exoplanets, we can conclude that there’s a fairly strong correlation between the number of planets in a planetary system and the average eccentricity of the orbits of those planets. “Just a few planets” seems to correlate to highly elliptical orbits, while “more planets” means closer-to-circular orbits.

It makes sense. We know a lot more about the process of planetary formation than we did even twenty years ago. That process appears to be pretty chaotic. Planets sometimes interact a lot while they’re forming, with unpredictable results. Sometimes that interaction leads to some of the young planets getting “pumped” into highly eccentric orbits, but that also leads to more of them being “ejected” from the planetary system entirely. So it makes sense that planetary systems that end up with fewer planets might also see those planets line up into more eccentric orbits.

The article claims that our own planetary system is unusual in that we ended up with more planets than the average. As a corollary, it shouldn’t be a surprise that the planets we still see have settled into a well-behaved stack of nearly circular orbits.

Okay. The article was interesting enough. The problem was that the actual research paper behind it was sitting behind a paywall. I put off reading that until after I had finished the rough draft of the Architect of Worlds design sequence. Maybe then I would track down a copy, and it might suggest a way to improve the step in which I assign orbital eccentricities. Not a big deal.

Well, I finished the rough draft just before Christmas, and yesterday I found a way to get a copy of the paper for a reasonable fee. I sat down to read it, and . . .

Whoa. This is a lot bigger than I thought.

Here’s a link to the abstract for the paper in question: Orbital eccentricity–multiplicity correlation for planetary systems and comparison to the Solar system. From there you can get to the whole paper, assuming that you have an Oxford Academic account or can work through DeepDyve.

Bach-Møller and Jørgensen have done something a little more remarkable than I expected. They haven’t just derived a strong correlation between planetary multiplicity and eccentricity of orbits. They’ve demonstrated that we can derive a clear power law for how many total planets a given system has, including the ones we can’t detect yet, just based on the observed eccentricity of the ones we can detect.

Applying this result to my models in Architect of Worlds, I find that I can do a lot more than just superficial improvement to one step of the system design process. I can actually rework several of the steps in the sequence, making them simpler and easier to use, and also making them line up a lot better with the current state of exoplanetary science.

The executive summary is that instead of laying down planets until you run into any of several limiting conditions, you randomly generate the total number of planets first, and then place that many. Much simpler, and it fixes the problem that the current version seems to generate too many planets.

This isn’t a small improvement. We’re talking about eliminating several of the most cumbersome computations and procedures, while also forcing the outcome to match observed results much more closely. I can’t really let that sit in the idle stack, especially since I have a couple of other projects that are dependent on having a complete draft here.

One complication is that one of those other projects was something I was planning to put together for my patrons, as a charged release, before the end of December. Although I think I see how to make all the necessary changes to the Architect of Worlds draft, that’s going to take a day or two of work, and I have a pile of other things to get finished over the next few weeks as well.

So here’s a revision to my creative plan for the next couple of weeks:

• The top priority right now is to revise the partial Architect of Worlds draft to fit these new results. This should be complete no later than 28 December. At that point, I will release a revised version of all of the completed sections of the draft, for my patrons only (with one or two exceptions for non-patrons who have been helping out with extensive comments on the draft). That will constitute my charged release on Patreon for December 2020.
• The PDFs that are already on the Architect of Worlds page will remain there. Those won’t constitute the most up-to-date version, but they are certainly “playable” for anyone who wants to experiment with them. I won’t be updating those PDFs for at least three months. During that time, I’ll continue to polish and tweak the system with input from my patrons, and possibly work on some additional material. I’ll reassess the situation in early April. By then I may be within striking distance of starting to prepare a publication-ready draft of the entire book. If not, then I’ll create and post new PDFs at that point.
• By the end of December, I need to write a new book review, and also finish and release another piece of short fiction. Those will be posted here and released to my patrons for free. I also need to get started on a new piece of short fiction (more about that later).
• Once all of the above is finished – probably over the New Year’s holiday – I’ll take stock. That’s a traditional time for such things anyway.