  1I/'Oumuamua is the first interstellar interloper to be detected, and it
shows a non-gravitational acceleration that cannot be accounted for by
outgassing, given the strict upper limits of outgassing evident from {\it
Spitzer} observations, unless the relative abundances of the common volatiles
are very different to those in comets. As an alternative, it has been suggested
that its peculiar acceleration is due to radiation pressure, requiring a
planar-sheet geometry of an unknown natural or artificial origin. Here we
assess whether or not the internal structure of 1I/'Oumuamua, rather than its
geometry, could support a radiation-pressure-driven scenario. We adopt a mass
fractal structure and find that the type of aggregate that could yield the
required area-to-mass ratio would have to be extraordinarily porous, with a
density $\sim$ 10$^{-5}$ g cm$^{-3}$. Such porous aggregates can naturally
arise from the collisional grow of icy dust particles beyond the snowline of a
protoplanetary disk, and we propose that 1I/'Oumuamua might be a member of this
population. This is a hypothesis worth investigating because, if this were the
case, 1I/'Oumuamua would have opened a new observation window on to the study
of the building blocks of planets around other stars. This could set
unprecedented constraints on planet formation models.\end{abstract}
