  The kilonova associated with GW170817 displayed early blue emission which has
been interpreted as a signature of either radioactive decay in low-opacity
ejecta, relativistic boosting of radioactive decay in high-velocity ejecta, the
cooling of material heated by a wind or by a "cocoon" surrounding a jet, or a
combination thereof. Distinguishing between these mechanisms is important for
constraining the ejecta components and their parameters, which tie directly
into the physics we can learn from these events. I compile published
ultraviolet, optical, and infrared light curves of the GW170817 kilonova and
examine whether the combined data set can be used to distinguish between
early-emission models. The combined optical data show an early rise consistent
with radioactive decay of low opacity ejecta as the main emission source, but
the subsequent decline is fit well by all models. A lack of constraints on the
ultraviolet flux during the first few hours after discovery allows for both
radioactive decay and other cooling mechanisms to explain the early bolometric
light curve. This analysis demonstrates that early (few hours after merger)
high-cadence optical and ultraviolet observations will be critical for
determining the source of blue emission in future kilonovae.
