Updated Galileo probe mass spectrometer measurements of carbon, oxygen, nitrogen, and sulfur on Jupiter

The in situ measurements of the Galileo Probe Mass Spectrometer (GPMS) were expected to constrain the abundances of the cloud-forming condensible volatile gases: H₂O, H₂S, and NH₃. However, since the probe entry site (PES) was an unusually dry meteorological system—a 5-μm hotspot—the measured condensible volatile abundances did not follow the canonical condensation-limited vertical profiles of equilibrium cloud condensation models (ECCMs) such as Weidenschilling and Lewis (1973, Icarus 20, 465-476). Instead, the mixing ratios of H₂S and NH₃ increased with depth, finally reaching well-mixed equilibration levels at pressures far greater than the lifting condensation levels, whereas the mixing ratio of H₂O in the deep well-mixed atmosphere could not be measured. The deep NH₃ mixing ratio (with respect to H₂) of (6.64±2.54)×10⁻⁴ from 8.9-11.7 bar GPMS data is consistent with the NH₃ profile from probe-to-orbiter signal attenuation (Folkner et al., 1998, J. Geophys. Res. 103, 22847-22856), which had an equilibration level of about 8 bar. The GPMS deep atmosphere H₂S mixing ratio of (8.9±2.1)×10⁻⁵ is the only measurement of Jupiter's sulfur abundance, with a PES equilibration level somewhere between 12 and 15.5 bar. The deepest water mixing ratio measurement is (4.9±1.6)×10⁻⁴ (corresponding to only about 30% of the solar abundance) at 17.6-20.9 bar, a value that is probably much smaller than Jupiter's bulk water abundance. The ¹⁵N/¹⁴N ratio in jovian NH₃ was measured at (2.3±0.3)×10⁻³ and may provide the best estimate of the protosolar nitrogen isotopic ratio. The GPMS methane mixing ratio is (2.37±0.57)×10⁻³; although methane does not condense on Jupiter, we include its updated analysis in this report because like the condensible volatiles, it was presumably brought to Jupiter in icy planetesimals. Our detailed discussion of calibration and error analysis supplements previously reported GPMS measurements of condensible volatile mixing ratios (Niemann et al., 1998, J. Geophys. Res. 103, 22831-22846; Atreya et al., 1999, Planet. Space Sci. 47, 1243-1262; Atreya et al., 2003, Planet. Space Sci. 51, 105-112) and the nitrogen isotopic ratio (Owen et al., 2001b, Astrophys. J. Lett. 553, L77-L79). The approximately three times solar abundance of NH₃ (along with CH₄ and H₂S) is consistent with enrichment of Jupiter's atmosphere by icy planetesimals formed at temperatures <40 K (Owen et al., 1999, Nature 402 (6759), 269-270), but would imply that H₂O should be at least 3×solar as well. An alternate model, using clathrate hydrates to deliver the nitrogen component to Jupiter, predicts O/H?9×solar (Gautier et al., 2001, Astrophys. J. 550 (2), L227-L230). Finally we show that the measured condensible volatile vertical profiles in the PES are consistent with column-stretching or entraining downdraft scenarios only if the basic state (the pre-stretched column or the entrainment source region) is described by condensible volatile vertical profiles that are drier than those in the equilibrium cloud condensation models. This dryness is supported by numerous remote sensing results but seems to disagree with observations of widespread clouds on Jupiter at pressure levels predicted by equilibrium cloud condensation models for ammonia and H₂S.