  Large numbers of small opaque dust clouds - termed 'globulettes' by Gahm et
al - have been observed in the H II regions surrounding young stellar clusters.
With masses typically in the planetary (or low mass brown dwarf) regime, these
objects are so numerous in some regions (e.g. the Rosette) that, if only a
small fraction of them could ultimately collapse, then they would be a very
significant source of free floating planets. Here we review the properties of
globulettes and present a theoretical framework for their structure and
evolution. We demonstrate that their interior structure is well described by a
pressure confined isothermal Bonnor-Ebert sphere and that the observed
mass-radius relation (mass approximately proportional to the radius squared) is
a systematic consequence of a column density threshold below which components
of the globulette are not identified. We also find that globulettes with this
interior structure are very stable against collapse within H II regions. We
follow Gahm et al in assuming that globulettes are detached from the tips of
pillars protruding in from the swept up shell that borders the expanding H II
region and produce a model for their dynamics, finding that globulettes will
eventually impact the shell. We derive an expression for the time it takes to
do so and show that dissipation of energy via dust cooling allows all
globulettes to survive this encounter and escape into the wider ISM. Once there
the ambient pressure drops and they disperse on timescales around 30-300 kyr
and should be observable using ALMA out to distances of order a parsec. Since
we find that globulettes are stable, the only route via which they might still
form brown dwarfs or planets is during their collision with the shell or some
other violent perturbative event.
