  Magnetic fields provide an important probe of the thermal, material, and
structural history of planetary and sub-planetary bodies. Core dynamos are a
potential source of magnetic fields for differentiated bodies, but evidence of
magnetization in undifferentiated bodies requires a different mechanism. Here
we study the amplified field provided by the stellar wind to an initially
unmagnetized body using analytic theory and numerical simulations, employing
the resistive MHD AstroBEAR adaptive mesh refinement (AMR) multiphysics code.
We obtain a broadly applicable scaling relation for the peak magnetization
achieved once a wind advects, piles-up, and drapes a body with magnetic field,
reaching a quasi-steady state. We find that the dayside magnetic field for a
sufficiently conductive body saturates when it balances the sum of incoming
solar wind ram, magnetic, and thermal pressures. Stronger amplification results
from pileup by denser and faster winds. Careful quantification of numerical
diffusivity is required for accurately interpreting the peak magnetic field
strength from simulations, and corroborating with theory. As specifically
applied to the Solar System, we find that early solar wind-induced field
amplification is a viable source of magnetization for observed paleointensities
in meteorites from some undifferentiated bodies. This mechanism may also be
applicable to other Solar System bodies, including metal-rich bodies to be
visited in future space missions such as the asteroid (16) Psyche.
