  `Oumuamua (1I/2017 U1) is the first object of interstellar origin observed in
the Solar System. Recently, \citet{Micheli2018} reported that `Oumuamua showed
deviations from a Keplerian orbit at a high statistical significance. The
observed trajectory is best explained by an excess radial acceleration $\Delta
a \propto r^{-2}$, where $r$ is the distance of `Oumuamua from the Sun. Such an
acceleration is naturally expected for comets, driven by the evaporating
material. However, recent observational and theoretical studies imply that
`Oumuamua is not an active comet. We explore the possibility that the excess
acceleration results from Solar radiation pressure. The required mass-to-area
ratio is $(m/A)\approx 0.1$ g cm$^{-2}$. For a thin sheet this requires a
thickness of $\approx 0.3-0.9$ mm. We find that although extremely thin, such
an object would survive an interstellar travel over Galactic distances of $\sim
5$ kpc, withstanding collisions with gas and dust-grains as well as stresses
from rotation and tidal forces. We discuss the possible origins of such an
object. Our general results apply to any light probes designed for interstellar
travel.
