DETECTION OF H2O IN THE SPLASH PHASE OF G-IMPACT AND R-IMPACT 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 explosi on. Two strong emissions are detected, at 3-4 mu m and at 2.7 mu m. Th e 3-4 mu m emission. due to the CH4 nu(3) band, is attributed to an in crease of the stratospheric temperature (T=1000K 9 min after the impac t). The 2.7 mu m emission is attributed to H2O. Estimates of the total H2O mass are 0.6-2.9 x 10(12)g and 0.7-13 x 10(11)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 CO was detected, which implies an upper limit of 2 x 10(-4) for the CO2/CO ratio in the G impact, consistent with a tempera ture lower than 2500K. (C) 1997 Elsevier Science Ltd. All rights reser ved.