Observing Coronal Microscales and Their Connection With Mesoscales

Why the Sun has a tenuous upper atmosphere some 1000 times hotter than the photosphere is a fundamental open problem in space plasma physics despite decades of study. A leading hypothesis, supported by indirect evidence, is that in most of the corona heating is confined to narrow current sheets in which energy is dissipated despite the low large-scale resistivity of the coronal plasma. Although the kinetic scales of reconnection or wave heating are beyond remote observation, thermal structure on scales ≲100 km are expected to be produced by the primary heating mechanisms operating within a filamentary magnetic field. This white paper considers what could be learned from direct observations of coronal plasma on those scales and outlines a mission concept that is more fully described in a Heliophysics Mission Concept Study for the Coronal Microscale Observatory.