A Detection of Water Ice on Jupiter with Voyager IRIS

Possible water ice spectral signatures have been detected on Jupiter using Voyager Infrared Interferometer Spectrometer and Radiometer (IRIS) spectra taken near closest approach of the Voyager 1 and 2 missions. Comparison with simultaneous imaging data shows that these IRIS footprints approximately correspond to locations on the planet where deep convection is suspected. Of the sample of 7500+ spectra, approximately 1% show a water ice absorption feature near 44 μm. The infrared optical depths of the absorption features, between 0.18 and 0.44, indicate that large amounts of ice particles need not be present to produce the observed spectral signature. The water ice clouds would have visible optical depths on the order of unity and would not be distinguishable above a thick ammonia cloud deck, which can have much larger visible optical depths. These thin clouds yield about 1 precipitable micrometer of water, comparable to Martian Tharsis Ridge clouds.