What's the minimum possible size of a spherical shaped rocky planet or satellite? Is it possible to occur a spherical shaped planet without having a molten core?
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2$\begingroup$ Related: physics.stackexchange.com/q/555769/2451 , earthscience.stackexchange.com/q/9745 and links therein. $\endgroup$– Qmechanic ♦Commented Jun 15, 2021 at 12:56
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2$\begingroup$ The official international definition of ‘planet’, or do you just want a round something in orbit around something else? $\endgroup$– Jon CusterCommented Jun 15, 2021 at 13:21
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2 Answers
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The minimum radius of a celestial body that allows gravity to transform the body into a globe is informally called the potato radius. Empirical evidence suggests it is about 200-300 km, depending on the composition of the body - the higher the proportion of rock to ice, the larger the potato radius.
answered Jun 20, 2021 at 13:43
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This may depend on the source of heat: the kinetic energy of in-falling material or radioactivity. It has to get hot enough to flow under the action of gravity.
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$\begingroup$ For that matter, molten ejecta could conceivably go near-spherical before cooling to a solid object in a zero-g environment. $\endgroup$ Commented Jun 15, 2021 at 15:27