Abundances of trace constituents in Jupiter's atmosphere inferred from Herschel/PACS observations

Context. On October 31, 2009, the Photodetector Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory observed far-infrared spectra of Jupiter between 50 and 220μm as part of the program "Water and Related Chemistry in the Solar System". Aims. We investigate the disk-averaged chemical composition of Jupiter's atmosphere as a function of height using these observations. Methods. We used the Planetary Spectrum Generator (PSG) and the least-squares fitting technique to infer the abundances of trace constituents. Results. The PACS data include numerous spectral lines attributable to ammonia (NH_3), methane (CH_4), phosphine (PH_3), water (H_2O), and deuterated hydrogen (HD) in the Jovian atmosphere. We infer an ammonia abundance profile that decreases from a mole fraction of (1.7± 0.8)× 10^-4 at p∼ 900mbar to (1.7± 0.9)× 10^-8 at p∼ 275mbar, following a fractional scale height of about 0.114. For phosphine, we find a mole fraction of (7.2± 1.2)× 10^-7 at pressures higher than (550± 100)mbar and a decrease of its abundance at lower pressures following a fractional scale height of (0.09± 0.02). Our analysis delivers a methane mole fraction of (1.49± 0.09)× 10^-3. Analyzing the HD R(0) line at 112.1 μm yields a new measurement of Jupiter's D/H ratio, D/H=(1.5± 0.6)× 10^-5. Finally, the PACS data allow us to put the most stringent 3σ upper limits yet on the mole fractions of hydrogen halides in the Jovian troposphere. These new upper limits are <1.1× 10^-11 for hydrogen fluoride (HF), <6.0× 10^-11 for hydrogen chloride (HCl), <2.3× 10^-10 for hydrogen bromide (HBr) and <1.2× 10^-9 for hydrogen iodide (HI) and support the proposed condensation of hydrogen halides into ammonium halide salts in the Jovian troposphere.