Can a planet have 10x Earth mass, 4x Earth gravity and support intelligent life?
In the Mass Effect series there's a terrestrial planet called Dekuuna with 10 times the mass of Earth, a surface gravity of 4G and a native intelligent race. I was just wondering if it was possible for a planet like that to exist in reality, and if yes, what are some factors that might lead to its formation assuming it formed around a Sun like star?
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I'm going to work off of celtschk's excellent answer, which correctly comes up with a radius of $\sim1.6 R_{\oplus}$ and a density of $\sim2.5\rho_{\oplus}$, where $_{\oplus}$ denotes Earth. If we look at the mass-radius curves of Mocquet et al. (2014), we see that the planet lies very close to the line for pure iron planets:
Some fun facts about iron planets:
- They're essentially just cores of terrestrial planets.
- They likely cannot hold water.
- They have no tectonic activity or magnetic field.
- They may be close to their parent star, meaning surface temperatures will be extremely high.
This doesn't seem like a very pleasant place for life.
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If $R$ is the planet's radius and $\rho$ is the planet's average density, then its surface gravity is $\propto \rho R$ and its mass is $\propto \rho R^3$.
Let's measure in units where the Earth's radius and average density are both 1. Then for Dekuuna we have $\rho R=4$ and $\rho R^3=10$. Therefore we get \begin{align} R &= \sqrt{\frac{\rho R^3}{\rho R}} = \sqrt{\frac{10}{4}} \approx 1.6\\ \rho &= \sqrt{\frac{(\rho R)^3}{\rho R^3}} = \sqrt{\frac{64}{10}} \approx 2.5 \end{align} So that planet would have a radius of about 1.6 times the Earth's radius and an average density of about 2.5 times the Earth's average density. The radius is definitely possible, and I think the density should be, too. To begin with, the higher radius and mass would already cause an increased density, although that alone will not get a factor 2.5. But then, the planet could have a relatively bigger core, and it might have more heavy elements in its core.
I also think 4 times earth gravity should not preclude the evolution of intelligent life.
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