Abundances of Jupiter's Trace Hydrocarbons From Voyager and Cassini

TL;DR

This study compares the vertical and latitudinal distributions of hydrocarbons on Jupiter from Voyager and Cassini data, revealing different seasonal variations in acetylene and ethane, which inform about atmospheric chemistry and dynamics.

Contribution

It provides the first detailed comparison of hydrocarbon distributions on Jupiter across two different epochs, highlighting seasonal changes in C2H2 and C2H6.

Findings

C2H6 shows increased and more symmetric abundance in 2000 compared to 1979.

C2H2 exhibits little variation in 1979 but decreases poleward in 2000.

Different seasonal behaviors of hydrocarbons suggest complex atmospheric processes.

Abstract

The flybys of Jupiter by the Voyager spacecraft in 1979, and over two decades later by Cassini in 2000, have provided us with unique datasets from two different epochs, allowing the investigation of seasonal change in the atmosphere. In this paper we model zonal averages of thermal infrared spectra from the two instruments, Voyager 1 IRIS and Cassini CIRS, to retrieve the vertical and meridional profiles of temperature, and the abundances of the two minor hydrocarbons, acetylene (C2H2) and ethane (C2H6). The spatial variation of these gases is controlled by both chemistry and dynamics, and therefore their observed distribution gives us an insight into both processes. We find that the two gases paint quite different pictures of seasonal change. Whilst the 2-D cross-section of C2H6 abundance is slightly increased and more symmetric in 2000 (northern summer solstice) compared to 1979 (northern fall equinox), the major trend of equator to pole increase remains. For C2H2 on the other hand, the Voyager epoch exhibits almost no latitudinal variation, whilst the Cassini era shows a marked decrease polewards in both hemispheres. At the present time, these experimental findings are in advance of interpretation, as there are no published models of 2-D Jovian seasonal chemical variation available for comparison.