Jupiter’s 3.3-micron CH4 polar brightening: Retrieval of methane effective temperature in the jovian auroral regions using Juno/JIRAM data

<p>Despite the multiple evidence of the diffuse presence of methane in Jupiter&#8217;s auroral regions, the mechanisms leading to the CH₄ brightening observed both from ground- and space-based platforms are not yet fully understood. During the first NASA/Juno&#8217;s orbit, the on-board imager/spectrometer JIRAM (Jovian Infrared Auroral Mapper) detected the 3.3-&#181;m methane emission on both Jupiter&#8217;s poles. The signal was found to be mostly confined within the main auroral ovals, although the lack of spectral coverage over 80&#176;S prevented a deep investigation of the southern methane spot. The CH_4&#160;polar emissions at 3.3 &#181;m are likely originated by non-thermal excitation mechanisms occurring above the 1 &#181;bar level, such as auroral particle precipitation and/or Joule heating. However, aurorally driven upwelling of methane inside the main oval might also explain the enhanced concentrations of CH₄ observed at the jovian poles. To address this controversy, we derive the effective temperature of methane in Jupiter&#8217;s auroral regions, which is a key information to understand the origin of the detected fluorescence. The goal is achieved by exploring three Juno&#8217;s orbits and focusing on the spectra with the highest methane emissions and the smallest contribution from other auroral features due to H₃⁺. JIRAM measurements from the first perijove are used to investigate the northern methane brightening, while observations from perijoves 7 and 8 are examined for its southern counterpart. The analysis reveals similar temperatures in the north- and south-polar spots, mainly ranging between 400 K and 670 K.&#160;</p> <p>&#160;</p>