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Science Astronomy Planets (2) Planets Dwarf Planets Satellites (Moons)

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Astronomy: Planets (2)

This page lists further characteristics of the planets and other major bodies of the Solar System.  For more basic details (size, orbit etc.), see Planets (1).  For anything else, see Solar System.


... in order of the radius of their orbits around the Sun – in other words, their distances from the Sun.

Name AtmosphereSurface Structure
MercuryMinute traces of argon & heliumSilicate rock (lava flows)Iron core, diameter approx. 75% of the whole (2,250 miles)
VenusCO2 (pressure 90 times Earth’s)Silicate rockSimilar to Earth (core / mantle / crust)
Earth78% nitrogen, 21% oxygenSilicate rockIron/nickel core, diameter 1,600 miles (approx. 25% of the whole)
Mars95% CO2 (pressure <1% Earth’s)Eroded lava plain, polar ice capsSimilar to Earth. Metallic core 50% of total diameter; crust 22 miles thick
JupiterAmmonia crystalsHydrogen and heliumRocky core larger than Earth
SaturnFrozen ammoniaLiquid hydrogenSmall core of rock and iron
UranusHydrogen and helium83% hydrogen, 15% helium, 2% methaneRock, ice, 15% hydrogen and some helium – evenly distributed throughout
NeptuneMethane (CH4)Hydrogen, helium, methaneSimilar to Uranus; possibly a rocky core

Dwarf Planets

... in order of discovery.

Name AtmosphereSurface Structure
CeresWater vapour?Water iceRocky core; mantle of water ice (60 to 120km – 12 to 25% of the whole)
PlutoSmall amount of methaneRock and ice (frozen methane)Probably about 70% rock and 30% water ice
ErisUnknown (probably none)Methane iceMethane ice?
SednaNoneUnknownRock and ice (possibly)
MakemakeMethane, possibly nitrogenSolid methane, ethane, possibly nitrogen Unknown
HaumeaProbably none Water iceUnknown

Satellites (Moons)

This section lists the ten most significant satellites or moons in the Solar System.  (That is, the ones you're most likely to get asked about in a quiz.) For which satellite belongs to which planet, see the Planets table above.  But for the record: Titan belongs to Saturn, and the other four biggest ones (other than The Moon) belong to Jupiter; Triton belongs to Neptune, Charon belongs to Pluto, and Phobos and Deimos both belong to Mars.

NameSurface Structure
GanymedeTectonic – similar to EarthSmall iron core; silicate rock and water ice; ice crust
TitanUnknownProbably about 50% rock and 50% ice – more rocky in the centre

Titan is the only satellite that has an atmosphere. It's about 95% nitrogen and has a pressure of about 1.5 bar – in other words, half as much again as Earth's atmosphere.

CallistaIcy crust with many cratersProbably about 50% rock and 50% ice – more rocky in the centre
IoThe most volcanically active body in the SSIron core approx 50% of the total diameter. Silicate rock
The MoonThe crust is composed of several primary elementsSolid rock, low metal content, crust about 42 miles thick
EuropaFrozen ice crustSilicate rock, outer layer of water. Possible a small iron core
TritonWater ice30% rock, 70% ice (probably)
CharonRock and iceCarbon–rich rock, and ice
PhobosRock and iceCarbon–rich rock, and ice
DeimosSouthern hemisphere is frozen nitrogen and methane Probably about 75% rock, 25% ice

© Haydn Thompson 2017