Major unsolved problems in space plasma physics

There are many space plasma physics problems that are both major and unsolv ed, there are other problems for which the categorization of solved or unso lved depends on one's point of view, and there are still other problems tha t are well understood but unsolved in the sense that quantitative predictio ns cannot be made although the basic physics is known. The following discus sion will, of necessity, be limited and selective. The nature of the Alfven ic turbulence in the solar wind remains a major unsolved mystery: Why is th e power spectrum of this anisotropic, compressible, magnetofluid often Kolm ogoroff-like, with a power spectral index close to the -5/3 value character istic of normal fluids? What is the three-dimensional symmetry of the turbu lence? Are the magnetic fields quasi-two-dimensional and stochastic, or hav e they been highly refracted by small velocity shears? What is the origin o f the -1 slope of the energy containing scales? What is the relationship be tween the turbulent fields and the diffusion coefficients for energetic par ticle transport parallel and perpendicular to the ambient magnetic field? A general problem in turbulence research is the relationship between the flu id approximation and the kinetic physics that describes the dissipation and damping of fluctuations. There is still much to learn about solar flares, coronal mass ejections and magnetospheric substorms. Another major puzzle i s how to quantitatively describe the interaction of the solar wind with the interstellar medium; a problem probably not amenable to solution using flu id equations.