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Earth has the highest density out of all planets, planetoids and moons of our planetary system, and also has a higher density than the Sun. Do we know any exoplanets or moons denser than Earth?

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I feel it's a cheap answer but heavy Jupiters can get much denser than Earth because planets with Jupiter's mass stop adding size as they add more mass. A planet with Jupiter's size and 10-12 times Jupiter's mass would be over twice Earth's density.

As far as Earth-like planets, there's a cool property of terrestrial planets, more mass means more tightly packed in their cores. Basically a similar effect to the heavy Jupiters but not as pronounced. If you double the mass and keep the element ratio the same, the density should increase. For example, a planet like Mercury with a very high iron content, but much greater mass should easily surpass Earth's density.

Kepler 10b, appears to be a super-earth and its estimated density is greater than Earth's at 5.8 ± 0.8 g/cm3. It has a mass of about 3.7 Earths. The ± 0.8 g/cm3 offers some room for uncertainty, but some of the more massive terrestrial planets should be more dense than Earth.

I'd take this list with a grain of salt, but you can sort by density.

Kepler 131c which you mention appears to be a super Earth but its mass has a high margin for error. I would add that a mass 8 times that of Earth and a radius smaller than Earth is probably impossible, so I'm highly skeptical of some of those numbers.

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From the Wikipedia page on Chthonian planet:

Transit-timing variation measurements indicate for example that Kepler-52b, Kepler-52c and Kepler-57b have maximum-masses between 30 and 100 times the mass of Earth (although the actual masses could be much lower); with radii about 2 Earth radii, they might have densities larger than that of an iron planet of the same size. These exoplanets are orbiting very close to their stars and could be the remnant cores of evaporated gas giants or brown dwarfs. If cores are massive enough they could remain compressed for billions of years despite losing the atmospheric mass.

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From another question on the stack exchange I just found out about an exoplanet with a much higher density than Earth: Kepler-131c.

http://www.exoplanetkyoto.org/exohtml/Kepler-131_c.html

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  • $\begingroup$ What density are you seeing there? I see 0.026 $M_J$ and 0.075 $R_J$ and I assume $J$ stands for Jupiter. What density does that work out to? $\endgroup$
    – uhoh
    Feb 6, 2020 at 13:11
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    $\begingroup$ @uhoh See userLTK's answer. $\endgroup$
    – user30007
    Feb 6, 2020 at 16:04
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    $\begingroup$ NASA page on Kepler-131c: exoplanets.nasa.gov/exoplanet-catalog/5941/kepler-131-c . Those numbers correspond to a density of $76.4\text{g}/\text{cm}^3$, or 13.9 times the average density of the Earth. That makes no sense, as noted in Mass-radius relations and core-envelope decompositions of super-Earths and sub-Neptunes. There's something wrong with the reported mass, the reported size, or both. The linked article gives the uncertainty in the mass of Kepler-131c. It's very large. $\endgroup$
    – David Hammen
    Feb 6, 2020 at 16:05
  • $\begingroup$ @DavidHammen As userLTK said it has a high margin of error. $\endgroup$
    – user30007
    Feb 6, 2020 at 16:07

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