# Mass of Earth's Magnetic Field

*Most recent answer: 05/28/2013*

- Aaqib shah (age 19)

India

Classical electromagnetism gives a magnetic energy density of B^{2}/8π in Gaussian CGS units. That would give a mass density of B^{2}/8πc^{2} . (You don't really need the "virtual photon" picture for this calculation.) So if the earth's field is around 0.5 Gauss, that gives a mass density of around 10^{-23} gram/cm^{3}. For comparison, the mass density of water is 1.0 gram/cm^{3}. I don't know the shape of the earth's field well enough to figure out exactly what total mass that adds up to, but very roughly the volume we need to multiply that density by to get a general idea of the total magnetic mass is around the volume of the earth, roughly 10^{27} cm^{3}. So I get something in the range of 10 kg total, not much compared to the earth's total mass.

Mike W.

*(published on 05/28/2013)*