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This question already has an answer here:

What is the maximum diameter and mass can a rock-based planet be before it collapsed to degenerate matter?

If "rocky" isn't defined enough, assume basalt.

"Degenerate" means the planet (or at least its core) has been gravitationally crushed to neutronium.

Assume no dense iron core, just rocky stuff.

I'm pretty sure maximum diameter will be at a mass less than the maximum.

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marked as duplicate by We are Monica., Cyn says make Monica whole, L.Dutch - Reinstate Monica Apr 22 at 3:01

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  • $\begingroup$ Hi Bohemian. Yes, you're building a world, but you might consider asking this on Astronomy or Physics. Do you realize that the gravity of such a planet would be so great that the denizens of Flatland would have trouble living there? $\endgroup$ – JBH Apr 22 at 2:26
  • $\begingroup$ You know it would become a star waaay before it would collapse into neutronium, right? Not sure what you're asking. $\endgroup$ – We are Monica. Apr 22 at 2:27
  • $\begingroup$ Just to clarify my comment, a given mass, sufficient to collapse into a neutron star (ie. a ball of neutronium) would first need to have sufficient mass to be a giant star (several times the mass of the sun). It would take a long time for the -> sworling matter -> star -> collapse into a neutron star to happen, much longer than for our sun - the general rule is the bigger, the slower. What you ask seems to have glossed over the gas giant stage of planets that have a rocky core and gone for something several orders of magnitude larger. I suggest you do some research in this area. $\endgroup$ – We are Monica. Apr 22 at 2:52
  • $\begingroup$ Are you looking for the maximum size of a naturally-occurring silicate (rocky) planet, or the maximum size that some sufficiently advanced alien could build one to without running into physical problems? $\endgroup$ – Cadence Apr 22 at 2:57
  • $\begingroup$ @Cadence I was thinking naturally occurring. Actually, I was wondering what the maximum diameter and its surface g would be for a naturally occurring non-gas planet. $\endgroup$ – Bohemian Apr 22 at 2:59

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