5
Patterns in Composition
•Terrestrial Planets
–Relatively small
–Made primarily of rocky material:
•Si, O, Fe, Mg  perhaps with Fe cores
(Note – for earth H2O is only a very small fraction of the total)
–
•Jovian Planets
–Relatively large
–Atmospheres made of H2, He, with traces of CH4, NH3, H2O, ...
–Surrounded by satellites covered with frozen H2O
–
•Within terrestrial planets inner ones tend to have higher densities
(when corrected for compression due to gravity)
       Planet Density Uncompressed Density
 (gm/cm3)        (gm/cm3)
– Mercury     5.44          5.30
– Venus     5.24          3.96
– Earth     5.50          4.07
– Mars     3.94          3.73
– (Moon)     3.36          3.40
•