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Asteroids and smaller celestial objects tend to be odd-shaped, whereas planets are always spherical (or slightly oblate due to their spin). The reason obviously is that for sufficiently large masses/sizes the gravitational force overwhelms any resistance of even rocky materials to maintain a shape other than a sphere (which minimises the gravitational energy).

The characteristic scale at which this transition occurs depends on the material and is different for ice and rock as mentioned in this answer (to a related question) which also links this useful Wikipedia article. I wonder whether this limit can be estimated from simple physics (involving material constants for ice/rock).

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  • $\begingroup$ @RoryAlsop Good catch (I didn't find that post). However, neither the question nor the answers ask/suggest any estimate for the limit. $\endgroup$ – Walter May 6 at 13:20
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    $\begingroup$ I think the read across from the answers there is that there is no specific limit. It depends on mass, density, rotation and makeup. $\endgroup$ – Rory Alsop May 6 at 13:22
  • $\begingroup$ The OP's question I wonder whether this limit can be estimated from simple physics (involving material constants for ice/rock) has an excellent answer here: How did early estimates of a “potato radius” set 1 eV ~ GMμ/R and get 200 to 300 km? I've voted to re-open in order to close as duplicate of this instead. $\endgroup$ – uhoh May 6 at 14:55