The longest standing challenge in astronomical spectroscopy is identifying the carriers of the diffuse interstellar bands (DIBs); absorption features seen in optical and near-IR spectra towards stars with significant foreground material. The band carriers are thought to be carbonaceous molecules such as PAHs, carbon chains and fullerenes. Hence, the DIB carriers represent a large fraction of the cosmic carbon quota, and once identified, will make them a unique tool to probe the interstellar medium.

We present the results from a high resolution UV Hubble Space Telescope investigation of small scale structure (SSS) towards a selection of ρ Oph stars. Previous ρ Oph observations show DIB strength variations of up to 9% over distances as small as ~350 AU, and larger still for those further apart. We examine the factors that control DIB strength in this relatively small system, and examine the properties of the gas responsible for SSS.