In more research on the Ryugu/Bennu set of C types, now delivered to Earth: Japan have marked their sample as CI if heated ~575 K in a "reducing" environment. Wiki still thinks Ryugu is Cb although, maybe now we can define Cb itself as "CI when heated with oxygen-poor volatiles". (We can't even unscrew the Bennu samples yet.)
This is, of course, from the asteroidal surface. It looks to me like it got baked with hot Sun - partly by protons, but I expect at first more by its own ices. Like by carbon-monoxide and/or ammonia.
Our own Moon's surface-regolith temperature runs up "only" to 400 K. So, assuming Ryugu shares albedo with the darker patches of our Moon - round down, 1.43 insolation. Reciprocal square-root, so, not so long to calculate: perihelion 0.836 AU.
That interests me given that the Ryugu perihelion was 0.9633 AU when the Hayabusa went there. As to the baked-CI, a Phaëthonesque perihelion assuming more-or-less constant semimajor suggests, in the past, a higher aphelion. Clearly Ryugu and Bennu both came in from Beyond.
Wiki is telling me different things as to where the two rubblepiles come from. Some say 495 Eulalia or 142 Polana. Some say comet. Mind: 495 Eulalia and/or 142 Polana could have drifted in from out where Ceres came from. They sail now in unstable resonances, 1:2 Mars and 3:1 Jupiter respectively. I don't even think the 67P "comet" was a true comet.
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