•Iron and nickel are very common metals in
planetary cores, since they are produced abundantly as
end products in supernovae and in the final stages of silicon burning in
•Iron-56 is more common than nickel
isotopes; Production of nickel-56 (which
within a few weeks decays to iron 56) is the
last nuclear fusion reaction that is exothermic. (http://wapedia.mobi/en/Binding_energy?t=3 ).
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