What's the biggest reasonable natural planet or moon with Earth-like surface gravity?

Sister question to: What's the smallest reasonable natural planet or moon with Earth-like surface gravity? - I want us to have both upper and lower bounds for 1g planets available for authors.

We all know that equation for surface gravity is

$$ g = \frac{4\pi}{3} G \rho r $$

So if we want Earth-like surface gravity of $ g = 9.81 \frac {m}{s²}$, then the equation for radius is

$$ r = \frac{3 g}{4\pi G \rho } $$

where $\rho$ is mean density of a planet.

So what's the biggest radius, or lowest density we can reasonably find in space to give us Earth-like gravity and still have a solid surface? By reasonable, I mean that it does not have to be common or even normal. I mean that:

• It could, theoretically, occur naturally
• First reaction of scientists should be "what a coincidence!" and not "it's an alien construct!" or "we have a serious problem with our methodology, this can't be!"

Sadly, on the "above 400km" table here bodies are either smaller than Earth or gaseous in nature, and I don't know how could we get less dense, but bigger.

Note: I'm avare of other questions about big planets but here I don't care for life, tectonics, civilizations etc. I want baseline, canonical answer about biggest size for given gravity.

posted over 6 years ago

Mołot‭

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