Jupiter's Equatorial Plumes and Hot Spots: Spectral Mapping from Gemini/TEXES and Juno/MWR
journal contributionposted on 24.04.2020, 14:44 by LN Fletcher, GS Orton, TK Greathouse, JH Rogers, Z Zhang, FA Oyafuso, G Eichstädt, H Melin, C Li, SM Levin, S Bolton, M Janssen, H-J Mettig, D Grassi, A Mura, A Adriani
We present multi-wavelength measurements of the thermal, chemical, and cloud contrasts associated with the visibly dark formations (also known as 5-μm hot spots)and intervening bright plumes on the boundary between Jupiter’s Equatorial Zone (EZ)and North Equatorial Belt (NEB). Observations made by the TEXES 5-20μm spectrometer at the Gemini North Telescope in March 2017 reveal the upper-tropospheric properties of 12 hot spots, which are directly compared to measurements by Juno using the Microwave Radiometer (MWR), JIRAM at 5μm, and Juno Cam visible images. MWR and thermal-infrared spectroscopic results are consistent near 0.7 bar. Mid-infrared-derived aerosol opacity is consistent with that inferred from visible-albedo and 5-μm opacity maps. Aerosol contrasts, the defining characteristics of the cloudy plumes and aerosol-depleted hot spots, are not a good proxy for microwave brightness. The hot spots are neither uniformly warmer nor ammonia-depleted compared to their surroundings at p <1 bar. At 0.7 bar, the microwave brightness at the edges of hot spots is comparable to other features within the NEB. Conversely, hot spots are brighter at 1.5 bar, signifying either warm temperatures and/or depleted NH3 at depth. Temperatures and ammonia are spatially variable within the hot spots, so the precise location of the observations matters to their interpretation. Reflective plumes sometimes have enhanced NH3, cold temperatures, and elevated aerosol opacity, but each plume appears different. Neither plumes nor hot spots had microwave signatures in channels sensing p >10 bars, suggesting that the hot-spot/plume wave is a relatively shallow feature.
Plain Language Summary
To date, our only direct measurement of Jupiter’s gaseous composition came from the descent of the Galileo probe in 1995. However, the results from Galileo appeared to be biased due to the unusual meteorological conditions of its entry location: a dark,cloud-free region just north of the equator, known as a hot spot. One of the aims of NASA’s Juno mission was to place the findings of the Galileo probe into broader con-text, which requires a detailed characterisation of these equatorial hot spots and their neighbouring plumes. We combine (a) data from Juno (microwave observations sounding conditions below the clouds, and visible/infrared observations revealing variations in cloud opacity) with (b) observations from amateur observers (to track the hot spots over time) and (c) observations from the TEXES infrared spectrometer mounted on the Gemini-North telescope. The latter provides the highest-resolution thermal maps of Jupiter’s tropics ever obtained, and reveals contrasts within and between the individual hot spots and plumes. We find that the hot spots are distinguishable from their surroundings for relatively shallow pressures, but that the deep measurements from Juno and Galileo are probably more representative of Jupiter’s North Equatorial Belt than previously thought.