What generates a planet's magnetic field?

Convective motion of electrically conducting fluid (molten iron in Earth's outer core) produces a self-sustaining dynamo.

Which planet has the strongest magnetic field?

Jupiter, with a dipole moment about 20 000 times Earth's, giving a surface field of about 4 Gauss.

It deflects the solar wind and cosmic rays, protecting the atmosphere from erosion and the surface from harmful radiation.

Estimate a planet's dipole magnetic field strength at the surface using the dipole approximation B = (mu0 / 4pi) * M_dipole / R^3.

Magnetic Dipole Moment

A m2

Planet Radius

Surface Magnetic Field (equator)

0.00003070 T

Field (Gauss)0.3070 G

Polar Field0.00006141 T

Surface Magnetic Field (equator) vs Magnetic Dipole Moment

A planet's magnetic field can be approximated as a dipole near the surface.

B_eq = (mu0 / 4pi) * M / R cubed

where mu0/(4pi) = 1e-7 T m/A.

B_pole = 2 * B_eq

Earth's dipole moment is about 7.94 x 10^22 A m2, giving an equatorial field of roughly 3 x 10^-5 T (0.3 Gauss).

Earth: dipole moment = 7.94e22 A m2, radius = 6.371e6 m.

Compute bulk planet density.

Escape speed from a planet.

Effective surface temperature.