Why the target size in the header is 8 bytes?

[z1617]

-spec integer_to_scientific(integer()) -> sci_int().
integer_to_scientific(I) ->
    %% Find exponent and significand
    {Exp, Significand} = integer_to_scientific(I, 3),
    case Exp >= 0 of
        true ->
            %% 1st byte: exponent, next 3 bytes: significand
            (Exp bsl 24) + Significand;
        false ->
            %% flip sign bit in significand
            ((-Exp) bsl 24) + 16#800000 + Significand
    end.

Since sci_int is 4 bytes as with BTC.

[hanssv]

That looks like a copy-paste artifact, 4 bytes should be enough...

This is tracked here https://www.pivotaltracker.com/story/show/161211831