Temporally varying ethylene emission on Jupiter

Ethylene (C2H4) 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. C2H4 is an important product of methane chemistry in the outer planets. Knowledge of its abundance can help discriminate among the various proposed sets of CH4 photolysis branching ratios at Ly-α, and determine the relative importance of the reaction pathways that produce C2H2 and C2H6. In the equatorial region the C2H4 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 C2H4 of 4.5 × 10 −7 – 1.7 × 10 −6 near 2.2 × 10 −3 mbar , with a total column of 5.7 × 10 14 – 2.2 × 10 15 molecules cm−2 above 10 mbar depending upon choice of thermal profile. We observed enhanced C2H4 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 C2H4 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 C2H4 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 C2H4 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.