  The dominant formation mechanism of brown dwarfs and planetary mass objects
in star-forming regions is presently uncertain. Do they form like stars, via
the collapse and fragmentation of cores in Giant Molecular clouds, or do they
form like planets in the discs around stars and are ejected via dynamical
interactions? In this paper, we quantify the spatial distribution of substellar
objects in NGC1333, in particular focusing on planetary-mass objects that have
been the target of recent deep imaging observations. We find that these objects
have a spatial distribution that is indistinguishable from the stars, and more
massive brown dwarfs. We also analyse N-body simulations and find that a
population of ejected planets would have a significantly different spatial and
kinematic distribution to stars, and brown dwarfs that also formed through
gravitational collapse and fragmentation. We therefore conclude that the
low-mass substellar objects in NGC1333 formed more like stars than planets,
although we predict that a population of hitherto undetected ejected planetary
mass objects may be lurking in this, and other star-forming regions.
