Ammonia in Jupiter's Troposphere From High-Resolution 5 μm Spectroscopy

Abstract

Jupiter's tropospheric ammonia (NH3) abundance is studied using spatially resolved 5 μm observations from the cryogenic high-resolution infrared spectrograph (CRIRES) at the European Southern Observatory's Very Large Telescope. The high-resolving power (R = 96,000) allows the line shapes of three NH3 absorption features to be resolved. We find that within the 1–4 bar pressure range, the NH3 abundance decreases with altitude. The instrument slit was aligned north-south along Jupiter's central meridian, allowing us to search for latitudinal variability. There is considerable uncertainty in the large-scale latitudinal variability, as the increase in cloud opacity in zones compared to belts can mask absorption features. However, we do find evidence for a strong NH3 enhancement at 4–6°N, consistent with a localized “ammonia plume” on the southern edge of Jupiter's North Equatorial Belt.