  I consider phenomenological changes in the standard solar model with the goal
of testing recent claims that the solar neutrino puzzle requires new particle
physics. The assumption of a steady-state sun producing the correct luminosity
and governed by standard microphysics appears to leave only one nonstandard
solar model possibility open, slow mixing of the solar core on timescales
characteristic of 3He equilibration. The conjecture of such mixing raises
striking physics issues connected with the standard model 3He instability and
the possibility that the 3He abundance gradient might allow the sun's early
convective core to persist. While helioseismology might eventually rule out
such a "model," contrary to one recent claim I will argue that the
helioseismology of a mixed two-fluid sun is as yet far from clear. Finally, I
conclude by stressing that 3He-driven slow mixing is not being proposed as a
solution of the solar neutrino problem, but as an example of a possibility that
has not been quantitatively modeled and yet could produce neutrino fluxes far
closer to experiment than the standard solar model. Thus, despite the
attractiveness of neutrino oscillation solutions, astrophysical explanations of
the solar neutrino problem are not yet, in my view, ruled out definitively.
