The spatial distribution of UV-absorbing regions on Triton

Abstract Using mosaic maps of Triton's surface made with images taken through the Voyager 2 UV and Clear filters, we have sought to: (1) distinguish between surface units containing UV-absorbing (UVA) materials and fresh volatile frosts; (2) place any such identified regions into a geological context; (3) suggest possible candidate materials for the UVAs; and (4) to interpret these regions in terms of seasonal volatile transport scenarios. In pursuit of these goals, we have identified both a region possibly containing involatile UVA materials and an adjoining region possibly covered by uncontaminated, fresh frosts. The UVA region correlates well with a distinct geological unit on Triton containing maculae and wind streaks. The location of these two regions suggests that they might be linked through the dynamical transport of volatiles between them. Hydrocarbon deposits may explain the UVA region. However, they cannot be ruled out in regions darker than average in the Clear filter. Also, we cannot rule out other UVA materials as a visible component of the UVA region, such as salts or sulfur-bearing compounds, but note that such material has not yet been detected and may be largely obscured by hydrocarbon deposits. Recent images of Triton taken by us with the post-COSTAR HST FOC in bandpasses centered near 4100 and 2780 A will be analyzed to provide further information on the possible UVA and adjoining fresh frost regions. With resolution elements of ⋍400–700 km (depending on wavelength) at Triton's distance, the FOC images will provide the first mapping of these regions in the mid-UV (2780 A). This wavelength corresponds to the extreme of the broad-band absorption feature seen in Triton's UV spectrum (Stern et al. , 1995), suggesting that the contrast between the UVA region and frost regions may be enhanced in the HST images.