  Magnetic field reconnection is often invoked to explain electromagnetic
energy conversion in planetary magnetospheres, stellar coronae, and other
astrophysical objects. Because of the huge dynamic range of magnetic fields in
these bodies, it is important to understand energy conversion as a function of
magnetic field strength and related parameters. It is conjectured theoretically
and shown experimentally that the energy conversion rate per unit area in
reconnection scales as the cube of an appropriately weighted magnetic field
strength divided by the square root of an appropriately weighted density. With
this functional dependence, the energy release in flares on the Sun, the large
and rapid variation of the magnetic flux in the tail of Mercury, and the
apparent absence of reconnection on Jupiter and Saturn, may be understood.
Electric fields at the perihelion of the Solar Probe Plus mission may be tens
of volts/meter.
