Jupiter in the Ultraviolet: Acetylene and Ethane Abundances in the Stratosphere of Jupiter from Cassini Observations between 0.15 and 0.19μm

Abstract

At wavelengths between 0.15 and 0.19 μm, the far-ultraviolet spectrum of\nJupiter is dominated by the scattered solar spectrum, attenuated by molecular\nabsorptions primarily by acetylene and ethane, and to a lesser extent ammonia\nand phosphine. We describe the development of our radiative transfer code that\nenables the retrieval of abundances of these molecular species from ultraviolet\nreflectance spectra. As a proof-of-concept we present an analysis of Cassini\nUltraviolet Imaging Spectrograph (UVIS) observations of the disk of Jupiter\nduring the 2000/2001 flyby. The ultraviolet-retrieved acetylene abundances in\nthe upper stratosphere are lower than those predicted by models based solely on\ninfrared thermal emission from the mid-stratosphere observed by the Composite\nInfrared Spectrometer (CIRS), requiring an adjustment to the vertical profiles\nabove 1 mbar. We produce a vertical acetylene abundance profile that is\ncompatible with both CIRS and UVIS, with reduced abundances at pressures $<$1\nmbar: the 0.1 mbar abundances are $1.21 \\pm 0.07$ ppm for acetylene and $20.8\n\\pm 5.1$ ppm for ethane. Finally, we perform a sensitivity study for the JUICE\nUVS instrument, which has extended wavelength coverage out to 0.21μm,\nenabling the retrieval of ammonia and phosphine abundances, in addition to\nacetylene and ethane.

Topics & Concepts