IRIS will obtain UV spectra and images with high resolution in
space (0.33-0.4 arcsec) and time (1-2s) focused on the
chromosphere and transition region of the Sun, a complex interface
region between the photosphere and corona. In this region, all but
a few percent of the non-radiative energy leaving the Sun is
converted into heat and radiation. Here, magnetic field and plasma
exert comparable forces, resulting in a dynamic region whose
understanding remains a challenge.
IRIS fills a crucial gap in our ability to advance Sun-Earth connection studies by tracing the flow of energy and plasma through this foundation of the corona and heliosphere.