Jupiter's hydrocarbon polar brightening: Discovery of 3-micron line emission from south polar CH4, C2H2, and C2H6

Jupiter exhibits bright H+3 auroral arcs at 3–4 microns that cool the hot (>1000 K) ionosphere above the ∼10−7 bar∼10−7 bar level through the infrared bands of this trace constituent. Below the 10−7 bar10−7 bar level significant cooling proceeds through infrared active bands of CH4, C2H2, and C2H6. We report the discovery of 3-micron line emission from these hydrocarbon species in spectra of the jovian south polar region obtained on April 18 and 20, 2006 (UT) with CGS4 on the United Kingdom Infrared Telescope. Estimated cooling rates through these molecules are 7.5×10−37.5×10−3, 1.4×10−31.4×10−3, and 0.72×10−3 Wm−2, respectively, for a total nearly half that of H+3. We derive a temperature of 450 ± 50 K in the 10−7–10−510−7–10−5 bar region from the C2H2 lines.