A science-alert is saying that Bennu looks like what Enceladus is spraying out. Which cannot be so different from what's under Mimas.
So... did Bennu show up here from Saturn's part of the system? I mean, Ceres drifted in from outside, so...
What spawned Bennu, which is now mostly sooty rubble, would have been half Enceladus' size (a quarter Ceres') so: 250 km across. I would not call this midget an "ocean" world, out where it started. I'd call it a frozen iceball, like Mimas for most of its existence (honestly Enceladus' ocean is probably pretty young too).
Also they seem to think that, unlike Mimas, Bennu hasn't changed much since it got shot out, 4.5 Gya.
Future rock hoppers will appreciate the calcium and magnesium-rich phosphate
in the crust. Perfect farm fodder.
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