  Observations of the water inventory as well as other chemically important
species on Jupiter will be performed in the frame of the guaranteed time key
project of the Herschel Space Observatory entitled "Water and related chemistry
in the Solar system". Among other onboard instruments, PACS (Photodetector
Array Camera and Spectrometer) will provide new data of the spectral atlas in a
wide region covering the far-infrared and submillimetre domains, with an
improved spectral resolution and a higher sensitivity compared to previous
observations carried out by Cassini/CIRS (Composite InfraRed Spectrometer) and
by ISO (Infrared Space Observatory). In order to optimise the observational
plan and to prepare for the data analysis, we have simulated the expected
spectra of PACS Jupiter observations. Our simulation shows that PACS will
promisingly detect several H2O emission lines. As PACS is capable of spatially
resolving the Jovian disk, we will be able to discern the external oxygen
sources in the giant planets by exploring the horizontal distribution of water.
In addition to H2O lines, some absorption lines due to tropospheric CH4, HD,
PH3 and NH3 lines will be observed with PACS. Furthermore, owing to the high
sensitivity of the instrument, the current upper limit on the abundance of
hydrogen halides such as HCl will be also improved.
