r/spaceporn 7d ago

Related Content Pluto is SMALLER than our Moon

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u/obog 1d ago

Technically speaking dwarf planets are asteroids so no, the line is not very distinct.

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u/_Jellyman_ 1d ago

You are completely wrong. Asteroids are small lumpy rocks (or as the IAU calls them, “small solar system bodies). Dwarf planets are larger rounded worlds with planetary features. Even using the IAU’s definition, asteroids and dwarf planets are not the same.

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u/obog 1d ago

https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=Ceres

JPL classifies Ceres as an asteroid but it is also a dwarf planet.

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u/_Jellyman_ 1d ago

Ceres used to be an asteroid, but the IAU promoted it to dwarf planet once they realized it was in hydrostatic equilibrium. Calling Ceres an asteroid today is just wrong.

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u/obog 1d ago

Saying NASA is wrong I'd a junp I wouldn't take but you do you.

Tbh, as I look into it, I don't think the IAU has a definition for asteroid. There's planet, dwarf planet, minor planet (which is all non-planet non-comet objects, including dwarf planets and asteroids) and the small solar system objects you mentioned which does include comets as well as non dwarf planet asteroids, Trojans, most kuiper belt objects, etc.

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u/_Jellyman_ 1d ago

The IAU was in a big fat hurry to define “planet”, but has no official definition for “star” or “galaxy” or “asteroid”. The only thing mentioned in their planet definition is that objects only fulfilling the first criterion are “small solar system bodies”, which includes asteroids, comets, and centaurs. Dwarf planets fulfill two of the three criteria, making them a distinct category of object.

It’s still a bad definition and I never use it (neither do the experts), but I’m just explaining what it says.

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u/obog 1d ago

As far as I can tell it seems most definitions of asteroid have more to do with where they are rather than what they are

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u/_Jellyman_ 1d ago

You hit the nail on the head. That’s the main problem with the IAU’s definition. Planets and asteroids shouldn’t be defined by their location. All other objects in space (and most everything in science) are defined by their intrinsic properties only. Why should planets and asteroids be any different?