  The first interstellar object to be observed in our solar system 1I/2017 U1
'Oumuamua combines the lack of observable cometary activity with an
extra-gravitational acceleration. This has given rise to several mutually
exclusive explanations based on different assumptions in the material
composition of 'Oumuamua. We show how a combination of observations in the
infrared and optical spectra may serve to distinguish between these
explanations once another object with 'Omuamua-like properties comes close
enough to earth. This possibility is linked to the widely different thermal
properties of the different material models that have been proposed. Developing
a model for the thermal conduction and infrared signal from a fractal model we
compare predictions of the infrared signal with that from standard thermal
models that assume 'Oumuamua to be either a solid piece of rock/ice or a thin
sheet.
