How can we find the size of a planet's metal
core? We can't dig down to the core to find out. We must infer the
size of the core. Density is a clue: metal is denser than
rock. A body with higher density must contain a larger fraction of
metal.
Measured Density of a planetary body is
determined from the body's observed mass and radius. By calculating
the pressure on the deep interior of a planetary body, the
uncompressed density of the body can be worked out. This
density can be compared with uncompressed densities of rock and metal
measured in a lab.
Calculated Density of a planetary body
is calculated from a chosen mixture of rock and metal. In the real world,
rock and metal have a range of densities depending on pressure,
chemical composition, and other factors.
For this simplified simulation, metal has a density
of 8000 kg per cubic meter (or 8 grams per cubic centimeter) while rock
has a density of 3000 kg per cubic meter (or 3 grams per cubic centimeter).
To begin your exploration, choose one of the 5 terrestrial
bodies. Earth is the default choice.
Move the slider up or down to change the relative amount of rock
and metal filling the interior of the body.
Adjust the fractions to match the Calculated Density to the
Measured Density.
A match between these densities reveals the approximate size of the
body's metallic core.