  We present a retrospective analysis of Earth-based mid-infrared observations
of Jupiter capturing the aftermath of the impacts by Comet D/Shoemaker-Levy 9
(henceforth SL9) in July 1994 and the Wesley impactor in July 2009. While the
atmospheric effects of both impacts have been reported previously, we were
motivated to re-examine both events using consistent methods to enable robust,
quantitative comparisons. We analyzed spectrophotometry and spectroscopy
capturing both impacts using two independent analyses: 1) a least-squares
search over a grid of candidate mineral species to determine the composition of
impact residue and 2) a radiative transfer analysis to derive atmospheric
information. We observe that the SL9 impact sites are enhanced in stratospheric
CH4 emissions at 7.9 um, due to shock heating and adiabatic compression from
plume re-entry, and from 8.5 - 11.5 um due to stratospheric NH3 emission and
non-gaseous cometary material. We derive NH3 concentrations of 5.7 ppmv at 30
mbar. In new findings, we find that the SL9 impact sites also exhibit a
non-gaseous emission feature at 18 - 19 um. The non-gaseous emission at 8.5 -
11.5 and 18 - 19 um emission is best reproduced by predominantly amorphous
olivine and obsidian at similar abundances. The Wesley impact site exhibits
enhanced emissions from 8.8 - 11.5 and 18 - 19 um. We found this could be
reproduced by predominantly amorphous olivine and stratospheric NH3 at
concentrations of 150 ppbv at 30 mbar. Stratospheric NH3 abundances are a
factor of 40 higher in the SL9 impacts compared to the Wesley impact, which
confirms the former reached deeper, NH3-richer altitudes of the atmosphere. The
absence of silicas in the Wesley impact would place an upper limit of 10 km/s
on the incident velocity and 9 degree on the entry angle of the impactor such
that temperatures were insufficient to convert silicates.
