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10 Hygeia a dwarf planet
post Oct 31 2019, 10:22 PM
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Did people notice this?

SPHERE is a powerful instrument, I'm waiting for it to have a go at the more recondite 704 Internamnia and 324 Bamberga.

ESOCast 211


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post Nov 2 2019, 09:03 PM
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Just because it's spherical now on account of an accident of formation doesn't mean that it meets the definition of a dwarf planet ("has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape")

I think ESO is reaching on this one.

Without attempting to debate the definition of a planet... given some reasonable assumptions about composition, and what is known of Hygia's density and mass, surely this can be quickly settled by calculation, at least to a reasonable approximation?

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post Nov 2 2019, 09:26 PM
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Wikipedia gives presumably accurate (with noted error bars) physical dimensions for the larger asteroids.

However, whatever is known about mass and size, the internal physical structure is an unknown in every case.

The exemplars on either side of the hydrostatic equilibrium boundary are all significantly larger than Hygeia, so it seems more likely to be an accident than actual hydrostatic equilibrium, but it's always possible that it's got a composition that flows more easily than other comparably-sized worlds. Or, that it underwent state changes in the past, and that was once true.
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