Detection of H2O in the splash phase of G- and R-impacts from NIMS-Galileo

Near-infrared spectra of Jupiter have been recorded from Galileo with the NIMS instrument at the time of the G- and R-impacts. The beginning of the splash phase is observed between 6 and 10 min after the explosion. Two strong emissions are detected, at 3–4 μm and at 2.7 μm. The 3–4 μm emission, due to the CH4 ν3 band, is attributed to an increase of the stratospheric temperature (T = 1000 K 9 min after the impact). The 2.7 μm emission is attributed to H2O. Estimates of the total H2O mass are 0.6–2.9 × 1012 g and 0.7–13 × 1011 g for the impacts G and R, respectively, 9 min after the explosion. The main uncertainty in the H2O mass estimate comes from the uncertainty in the temperature of the emitting area. The data show that the H2O formation started in the splash phase, about 7 and 9 min after the explosion for G and R, respectively. No CO2 was detected, which implies an upper limit of 2 × 10−4 for the CO2CO ratio in the G impact, consistent with a temperature lower than 2500K.