  The supercritical state is currently viewed as uniform and homogeneous on the
pressure-temperature phase diagram in terms of physical properties. Here, we
study structural properties of the supercritical carbon dioxide, and discover
the existence of persistent medium-range order correlations which make
supercritical carbon dioxide non-uniform and heterogeneous on an intermediate
length scale, a result not hitherto anticipated. We report on the carbon
dioxide heterogeneity shell structure where, in the first shell, both carbon
and oxygen atoms experience gas-like type inter- actions with short range order
correlations, while within the second shell oxygen atoms essentially exhibit
liquid-like type of interactions with medium range order correlations due to
localisation of transverse-like phonon packets. We show that the local order
heterogeneity remains in the three phase-like equilibrium within very wide
temperature range. Importantly, we highlight a catalytic role of atoms inside
the nearest neighbor heterogeneity shell in providing a mechanism for diffusion
in the supercritical carbon dioxide on an intermediate length scale. Finally,
we discuss important implications for answering the intriguing question whether
Venus may have had carbon dioxide oceans and urge for an experimental detection
of this persistent local order heterogeneity.

Statistical Mechanics;Disordered Systems and Neural Networks;Materials Science;Soft Condensed Matter;Chemical Physics