I found this similar idea done in a lab: https://cen.acs.org/articles/83/i3/Filling-Fullerene.html

They use H2 instead of He. Is that good enough?

Two side remarks:

* It's probably too hot there (2000K in the cold part) for fullerene. The atmosphere there is mostly C2, C3 and CO. (CO is mentioned in the paper as a very good guess, but not mentioned in the press release.)

* If you fill a fullerene with H2 or He, it will float less instead of more.

I'm no chemist, but I was under the impression that high pressure might allow for the creations of fullerenes even at these kinds of temperatures.

I didn't think they would float (but I can see how "hanging out" could be read that way).

I have a chemistry specification in high school, anyway the conditions are weird. It's like inside a burning coal, but much hotter, 2000K instead of 700K. The density is 2g/ml so it's more like a liquid than a gas. It's far away from the usual conditions in a lab, so my knowledge/intuition are not very useful.

Anyway, at so high pressure and density, I expect molecules with big voids to be crushed.

Indeed, unimaginable what is possible! There will also be traces of H, N, O, S etc due to comets crashing in, so room for carbon chemistry once temperature permits.