Temporally varying ethylene emission on Jupiter

Ethylene (C 2H 4) emission has been measured in the poles and equator of Jupiter. The 949 cm -1 spectra were recorded with a high resolution spectrometer at the McMath-Pierce telescope at Kitt Peak in October-November 1998 and at the Infrared Telescope Facility at Mauna Kea in June 2000. C 2H 4 is an important product of methane chemistry in the outer planets. Knowledge of its abundance can help discriminate among the various proposed sets of CH 4 photolysis branching ratios at Ly- α, and determine the relative importance of the reaction pathways that produce C 2H 2 and C 2H 6. In the equatorial region the C 2H 4 emission is weak, and we were only able to detect it at high air-mass, near the limb. We derive a peak equatorial molar abundance of C 2H 4 of 4.5×10-1.7×10 near 2.2×10 mbar, with a total column of 5.7×10-2.2×10 molecules cm -2 above 10 mbar depending upon choice of thermal profile. We observed enhanced C 2H 4 emission from the poles in the regions where auroras are seen in X-ray, UV, and near infrared images. In 2000 we measured a short-term change in the distribution of polar C 2H 4 emission; the emission in the north IR auroral "hot spot" decreased by a factor of three over a two-day interval. This transient behavior and the sensitivity of C 2H 4 emission to temperature changes near its contribution peak at 5-10 microbar suggests that the polar enhancement is primarily a thermal effect coupled with vertical transport. Comparing our observations from Kitt Peak and Mauna Kea shows that the C 2H 4 emission of the northern non-"hot spot" auroral regions did not change over the three-year period while that in the southern polar regions decreased.