Editing Terrestrial planet (section)

===Density trends===
The uncompressed density of a terrestrial planet is the average density its materials would have at zero [[pressure]]. A greater uncompressed density indicates a greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within planet cores increases their density; the average density depends on planet size, temperature distribution, and material stiffness as well as composition.

Calculations to estimate uncompressed density inherently require a model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and also moment of inertia data derived from the spacecraft's orbits. Where such data is not available, uncertainties are inevitably higher.<ref>{{cite web|url=http://web.gps.caltech.edu/~mbrown/classes/ge131/notes/djs08.pdf|title=Course materials on "mass-radius relationships" in planetary formation.|website=caltech.edu|access-date=2 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171222105139/http://web.gps.caltech.edu/~mbrown/classes/ge131/notes/djs08.pdf|archive-date=22 December 2017}}</ref>

The uncompressed densities of the rounded terrestrial bodies directly orbiting the Sun trend towards lower values as the distance from the [[Sun]] increases, consistent with the temperature gradient that would have existed within the primordial solar nebula. The Galilean satellites show a similar trend going outwards from Jupiter; however, no such trend is observable for the icy satellites of Saturn or Uranus.<ref>{{cite book |first=John S. |last=Lewis |date=2004 |title=Physics and Chemistry of the Solar System |page=265 |edition=2nd |publisher=Academic Press |isbn=978-0-12-446744-6}}</ref> The icy worlds typically have densities less than 2 g·cm<sup>−3</sup>. Eris is significantly denser ({{val|2.43|0.05|u=g·cm<sup>−3</sup>}}), and may be mostly rocky with some surface ice, like Europa.<ref name=planetarysociety/> It is unknown whether extrasolar terrestrial planets in general will follow such a trend.

The data in the tables below are mostly taken from a [[list of gravitationally rounded objects of the Solar System]] and [[planetary-mass moon]]. All distances from the Sun are averages.

{{col-begin}}
{{col-break}}
{| class="wikitable" style="text-align: center;"
|+ Densities of the terrestrial geophysical planets<br />(including borderline Pallas and Vesta)
|-
! scope="col" rowspan="2" | Object
! scope="col" colspan="2" | Density (g·cm<sup>−3</sup>)
! scope="col" rowspan="2" | Distance from Sun ([[Astronomical unit|AU]])
|-
! scope="col" | Mean
! scope="col" | Uncompressed
|-
| style="text-align: left;" | [[Mercury (planet)|Mercury]]
| 5.4
| 5.3
| 0.39
|-
| style="text-align: left;" | [[Venus]]
| 5.2
| 4.4
| 0.72
|-
| style="text-align: left;" | [[Earth]]
| 5.5
| 4.4
| rowspan=2| 1.0
|-
| style="text-align: left;" | [[Moon]]
| 3.3
| 3.3<ref>{{cite conference |title=Uncompressed density of the Moon, lunar mantle and core |last=Szurgot |first=Marian |conference=Workshop on Modern Analytical Methods Applied to Earth, Budapest, Hungary |year=2017 |url=https://www.hou.usra.edu/meetings/methods2017/pdf/6007.pdf}}</ref>
|-
| style="text-align: left;" | [[Mars]]
| 3.9
| 3.8
| 1.52
|-
| style="text-align: left;" | [[4 Vesta|Vesta]]
| 3.5
| 3.5
| 2.36
|-
| style="text-align: left;" | [[2 Pallas|Pallas]]
| 2.9
| 2.9
| 2.77
|-
| style="text-align: left;" | [[Io (moon)|Io]]
| 3.5
| 3.5
| rowspan=2| 5.20
|-
| style="text-align: left;" | [[Europa (moon)|Europa]]
| 3.0
| 3.0
|}
{{col-break}}
{| class="wikitable" style="text-align: center;"
|+ Densities of some icy geophysical planets<br />(other [[Kuiper Belt Objects|KBO]] densities are poorly known)
|-
! scope="col" | Object
! scope="col" | Density (g·cm<sup>−3</sup>)
! scope="col" | Distance from Sun (AU)
|-
| style="text-align: left;" | [[Ceres (dwarf planet)|Ceres]]
| 2.2
| 2.77
|-
| style="text-align: left;" | [[10 Hygiea|Hygiea]]
| 2.1
| 3.14
|-
| style="text-align: left;" | [[Ganymede (moon)|Ganymede]]
| 1.9
| rowspan=2|5.20
|-
| style="text-align: left;" | [[Callisto (moon)|Callisto]]
| 1.8
|-
| style="text-align: left;" | [[Mimas (moon)|Mimas]]
| 1.2
| rowspan=7|9.54
|-
| style="text-align: left;" | [[Enceladus]]
| 1.6
|-
| style="text-align: left;" | [[Tethys (moon)|Tethys]]
| 1.0
|-
| style="text-align: left;" | [[Dione (moon)|Dione]]
| 1.5
|-
| style="text-align: left;" | [[Rhea (moon)|Rhea]]
| 1.2
|-
| style="text-align: left;" | [[Titan (moon)|Titan]]
| 1.9
|-
| style="text-align: left;" | [[Iapetus (moon)|Iapetus]]
| 1.1
|-
| style="text-align: left;" | [[Miranda (moon)|Miranda]]
| 1.2
| rowspan=5|19.2
|-
| style="text-align: left;" | [[Ariel (moon)|Ariel]]
| 1.6
|-
| style="text-align: left;" | [[Umbriel]]
| 1.5
|-
| style="text-align: left;" | [[Titania (moon)|Titania]]
| 1.7
|-
| style="text-align: left;" | [[Oberon (moon)|Oberon]]
| 1.6
|-
| style="text-align: left;" | [[Triton (moon)|Triton]]
| 2.1
| 30.1
|-
| style="text-align: left;" | [[Pluto]]
| 1.9
| rowspan=2|39.5
|-
| style="text-align: left;" | [[Charon (moon)|Charon]]
| 1.7
|-
| style="text-align: left;" | [[50000 Quaoar|Quaoar]]
| 1.7
| 43.7
|-
| style="text-align: left;" | [[Eris (dwarf planet)|Eris]]
| 2.4
| 67.9
|}
{{col-end}}