Helium Gas Giants? (NOT helium-rich gas giants)

[plansci]

While going through some ED statistics and such, I happened upon something strange. This chart shows the frequency of various planet types by their height above and below the galactic plane: https://edastro.com/mapcharts/heightgraph-planets.png

Showing a very interesting peak of ~11 objects existing between 100 and 150 light years above/below the galactic plane, and nowhere else. Something called 'helium gas giants'. This isn't a typo, as helium-rich gas giants are also included (and are interestingly the second rarest after these) and I double-checked in the codex to make sure these actually exist.

Indeed, a quick check found that 'helium gas giants' are included in the codex, with one in 52 Herculis in the orion spur.

So what exactly are these, and why do they exist when they're basically the same thing as helium-rich gas giants?

 

[Sapyx]

Back when 52 Herculis was the only system containing objects in the class, we assumed that "Helium giants" were a type of planet that ED were planning to introduce to the Stellar Forge, but never actually got around to doing it.

Then a few procedurally-generated ones actually turned up, so the code for creating them must actually be in the Forge - it's just that they're so darned rare. And nobody really knows why, except to say that the composition criteria must be nigh-on impossible for the Forge to create.

Semantically, and logically, a "helium giant" is a gas giant planet made almost entirely of helium, with little or no hydrogen or other gases present; a "helium-rich" giant simply has more helium than "normal". Just like a "water giant" is a planet made almost entirely of water vapour. In truth, this is not actually the case; the "hand-crafted" ones in 52 Herculis are indeed as one would expect (97% helium, 3% hydrogen). But the one found in Ooch Chrea US-U d2-21 is actually a "nitrogen giant" - 99% nitrogen, 0.15% helium. I suppose one could redefine a "helium giant" as "a gas giant with virtually no hydrogen or water in its atmosphere", but that seems a bit cumbersome.