  Magnetic field line reconnection is a universal plasma process responsible
for the magnetic field topology change and magnetic field energy dissipation
into charged particle heating and acceleration. In many systems, the conditions
leading to the magnetic reconnection are determined by the pre-reconnection
configuration of a thin layer with intense currents -- otherwise known as the
thin current sheet. In this study we investigate two such systems: Earth's
magnetotail and helmet streamers in the solar corona. The pre-reconnection
current sheet evolution has been intensely studied in the magnetotail, where
in-situ spacecraft observations are available; but helmet streamer current
sheets studies are fewer, due to lack of in-situ observations -- they are
mostly investigated with numerical simulations and information that can be
surmised from remote sensing instrumentation. Both systems exhibit
qualitatively the same behavior, despite their largely different Mach numbers,
much higher at the solar corona than at the magnetotail. Comparison of
spacecraft data (from the magnetotail) with numerical simulations (for helmet
streamers) shows that the pre-reconnection current sheet thinning, for both
cases, is primarily controlled by plasma pressure gradients. Scaling laws of
the current density, magnetic field, and pressure gradients are the same for
both systems. We discuss how magnetotail observations and kinetic simulations
can be utilized to improve our understanding and modeling of the helmet
streamer current sheets.
