  One of the most intriguing, long-standing questions regarding Venus'
atmosphere is the origin and distribution of the unknown UV-absorber,
responsible for the absorption band detected at the near-UV and blue range of
Venus' spectrum. In this work, we use data collected by MASCS spectrograph on
board the MESSENGER mission during its second Venus flyby in June 2007 to
address this issue. Spectra range from 0.3 {\mu}m to 1.5 {\mu}m including some
gaseous H2O and CO2 bands, as well as part of the SO2 absorption band and the
core of the UV absorption. We used the NEMESIS radiative transfer code and
retrieval suite to investigate the vertical distribution of particles in the
Equatorial atmosphere and to retrieve the imaginary refractive indices of the
UV-absorber, assumed to be well mixed with Venus' small mode-1 particles. The
results show an homogeneous Equatorial atmosphere, with cloud tops (height for
unity optical depth) at 75+/-2 km above surface. The UV absorption is found to
be centered at 0.34+/-0.03 {\mu}m with a full width half maximum of 0.14+/-0.01
{\mu}m. Our values are compared with previous candidates for the UV aerosol
absorber, among which disulfur oxide (S2O) and dioxide disulfur (S2O2) provide
the best agreement with our results.
