Is this planet possible in real life?
In the Halo series there's a habitable planet called Harvest with a diameter of 4,012 kilometres, and gravity 99% of Earth's, though the planet only has 9% of Earth's mass. If such a planet is possible, what are some factors that might lead to its formation?
Some more information on the planet can be found here.
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1 answer
Doing a simple density calculation, I get $$\rho=\frac{0.09M_{\oplus}}{\frac{4}{3}\pi R^3}\approx15.97\text{ grams/cm}^3$$ For comparison, here's a list of the average densities, $\bar{\rho}$, of the planets in the Solar System: $$\begin{array}{|c|c|c|} \hline \text{Planet} & \bar{\rho}\text{ (g/cm)}^3\\ \hline \text{Mercury} & \text{5.4}\\ \hline \text{Venus} & \text{5.2}\\ \hline \text{Earth} & \text{5.5}\\ \hline \text{Mars} & \text{3.9}\\ \hline \text{Jupiter} & \text{1.3}\\ \hline \text{Saturn} & \text{0.7}\\ \hline \text{Uranus} & \text{1.3}\\ \hline \text{Neptune} & \text{1.6}\\ \hline \end{array}$$ This means that your planet would have a density much greater than any of the planets in the Solar System. I looked up some mass-radius curves from Seager et al. (2008). Your planet is fairly low-mass, and so it's possible that their models fail in that regime, but your world ($0.09M_{\oplus}$ $0.315R_{\oplus}$, still falls on the pure iron track.
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