Are there any planets or moons denser than Earth?

Question

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?

different but related: How small can a planet be and still have Earth-like gravity? as well as Is Earth's 1g solid surface gravity unusually high for exoplanets? and also Are there any known asteroids with average density similar to that of Earth's? This one may be hard to answer because there aren't likely to be very good ways to determine the masses of exoplanets directly. At least that's my guess. — uhoh, Feb 06 '20 at 12:47
you say earth has a higher density than that of the sun.... but given that the core is 150g/cm3 (vs earths 5g/cm3) when you say "density" do you mean "average density"? — UKMonkey, Feb 07 '20 at 21:40
@UKMonkey I mean total density, not just the core or other layers. The Earth's core also has a higher density (12.9 g/cm3) than the entire Earth. — user30007, Feb 08 '20 at 06:08
@qqjkztd No, because there are no humans on other planets in this world unless one goes there from Earth. :-) — user30007, Feb 11 '20 at 14:46
Actually, Mercury has a much higher density (13.6 gm/cm3 as opposed to Earth's 5.5 gm/cm3). The planet may even be a remnant core of a much larger planet. Many similar exoplanets are out there, but I'd have to go through the NASA Exoplanet Archive https://exoplanetarchive.ipac.caltech.edu/cgi-bin/TblView/nph-tblView?app=ExoTbls&config=planets to find them. Check out the website, it's awesome with easy to use interactive capabilities. — Jack R. Woods, Feb 23 '20 at 22:05
@JackR.Woods No, Mercury's density is 5.43 g/cm3 and Venus' is 5.24 g/cm3. While both are close to the Earth's they're not as high or higher. Your value is propably for Mercury's core only. — user30007, Feb 25 '20 at 07:27
@user30007 My mistake, I googled "density of Mercury". I would still say that Mercury has a very high density "for its size" indicating it being a possible "core remnant". Density does have a correlation with size given similar composition, so there must be many super-earths out there with a higher density. — Jack R. Woods, Mar 09 '20 at 01:04

score 23 · Answer 1 · edited Feb 07 '20 at 16:39

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.

score 9 · Accepted Answer · edited May 28 '21 at 07:07

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.

score 2 · Answer 3 · edited May 28 '21 at 07:06

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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

edited May 28 '21 at 07:06

Nilay Ghosh

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answered Feb 06 '20 at 13:08

user30007

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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? – uhoh Feb 06 '20 at 13:11
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@uhoh See userLTK's answer. – user30007 Feb 06 '20 at 16:04
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NASA page on Kepler-131c: https://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. – David Hammen Feb 06 '20 at 16:05
@DavidHammen As userLTK said it has a high margin of error. – user30007 Feb 06 '20 at 16:07

Are there any planets or moons denser than Earth?

3 Answers3