Beta decay is exclusively the emission of electrons ... or its
oppositely charged relative, the positron ... from an atomic
nucleus.
Beta-minus is the emission of an electron, with a negative charge.
The change in the mass of the nucleus, if any, is minuscule.
The mass number of a nucleus is the sum of its protons and
neutrons, and the mass of an emitted electron is something
like 0.0005 the mass of one of those.
C.Earth is the largest and most dense of the terrestrial planets
