# Could 1I/'Oumuamua be an icy fractal aggregate?

## TL;DR

This paper explores whether 1I/'Oumuamua could be an extremely porous icy fractal aggregate, which might explain its acceleration via radiation pressure without requiring a planar sheet shape, offering insights into planet formation.

## Contribution

It proposes a mass fractal structure for 1I/'Oumuamua, suggesting it could be an icy, highly porous aggregate formed beyond the snowline, providing a new perspective on interstellar objects.

## Key findings

- Porous fractal aggregates with density ~10^{-5} g/cm^3 could explain the acceleration.
- Such aggregates can naturally form from icy dust collisions beyond the snowline.
- This hypothesis links 1I/'Oumuamua to planet-building blocks around other stars.

## Abstract

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}