Hot CH_4 in the polar regions of Jupiter

Abstract

We have obtained 3.3–3.4-μm spectro-images of Jupiter including CH_4 and H_3^+ emission lines from both polar regions at the Gemini North telescope. We find that the peak of the 3-μm CH_4 northern bright spot is located at ∼200° (SysIII) longitude, ∼20° west of the center of the 8-μm north-polar bright spot, and does not coincide with the 3-μm H_3^+ bright spot. We derive high temperatures (500–850 K) from CH_4 rotational lines on the bright spots of both polar regions, above the 1-μbar pressure level, while we find cooler temperatures (<350 K) over the 8-μm spot. The intensity ratios of the various 3-μm vibrational bands of CH4 are roughly constant, indicating that the upper states of these bands are mostly populated by non-thermal excitation mechanisms, such as auroral particle precipitation and/or Joule heating, in contrast with the 8-μm thermal emission.

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