Figure 20

Spectral changes. In this figure we compare the VIMS spectra of Hetpet Regio both before (blue) and after (dark red) the brightening in the wake of the 2010 September 27 cloudburst. To minimize the effects of differing observation geometry on atmospheric effects, we used an area near the change area from the same flyby, T76, for the ‘before’ baseline. The two areas had identical spectra on T61, before the change event. We compare those spectra to that of a cloud from T33 at top and to Xanadu from T12 and Tui Regio from T46 at bottom. For intercomparability the cloud, Xanadu, and Tui pixels were chosen to have identical incidence and emission angles as Hetpet Regio on T76 (Xanadu had a different phase, leading to some differences in atmospheric contribution). The changed area spectrum is inconsistent with that of a cloud (see arrows), and likewise does not represent a linear combination of pre-changed spectrum and either Xanadu or Tui either.