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Abstract: Vertically-resolved spectral characteristics of the Titanian haze in the 2-μm wavelength range were derived from solar occultation spectra measured by Cassini/VIMS on January 15, 2006. At the various altitudes probed by the solar occultation measurements, we reproduced the observed spectra using a radiative transfer program including absorption by CH4 ro-vibrational bands, collision-induced absorption by N2–N2 pairs, and H2–N2 dimers, as well as absorption and scattering by the haze particles. The retrieved optical depth spectra (or τ-spectra) for the haze show marked variations in the 2.1–2.8μm range, with peaks near 2.30 and 2.35μm, and the relative amplitude of these peaks changing with altitude. The gross spectral shape of the τ-spectra is found similar to the typical 2-μm absorption spectra of the alkane group of hydrocarbon (C n H2n+2) ices. The τ-spectra retrieved at 2μm and those previously retrieved at 3μm by Kim et al. (2011) are simultaneously reproduced by combinations of 2- and 3-μm absorbance spectra of alkane ices such as CH4, C2H6, C5H12, C6H14, with the addition of a nitrile ice, CH3CN. These combinations are neither unique nor limited and need more fine-tuning to fit the detailed features of the τ-spectra. There is a need for additional laboratory measurements of absorbance and indices of refraction for a wider variety of hydrocarbon and nitrile ices in the temperature range relevant to Titan. [Copyright &y& Elsevier]

We have obtained Gemini/GNIRS 3.3–3.4 μm spectra of Jupiter at 65o North latitude over a range of longitudes roughly centered on the 8-μm CH 4 north polar hot spot (8CNPHS). The spectra were measured on four occasions during a four-month period in 2018, in order to search for variability of the 3-μm emissions of CH 4 and C 2 H 6. The observed locations of the brightest spots of the C 2 H 6 and CH 4 emissions at 65oN differed in longitude typically by 20o during this period. The peak emission intensities of these species showed large variations, with the highest intensities 3–4 times greater than the lowest intensities. In addition, the brightest 3-μm CH 4 emissions and hottest temperatures at the 8CNPHS were significantly less than those at the 3-μm CH 4 north polar hot spot (3CNPHS, Kim et al., 2015). Recently, Sinclair et al. (2019) reported a coincidence between solar wind dynamical pressure and the 8-μm brightening of the 8CNPHS. In contrast, we find lack of correlation in our data between the 3-μm hydrocarbon emission intensities at the 8CNPHS and the solar wind strength. We also find lack of correlation between H 3 + intensities and the solar wind strength during the period. However, due to the limited observational data, it is too early to conclude whether this lack of correlation indicates that the solar wind activity induced no significant changes in local temperatures (<40 K) and/or mixing ratios of these molecules. Our observing period was close to the historic grand solar minimum. The detailed influence of the solar activity on the 3 and 8 μm brightness at the 8CNPHS is not quantitatively understood at the present time. • Gemini/GNIRS 3.3–3.4 μm spectra of the 8-μm CH 4 north polar hot spot (8CNPHS) of Jupiter were obtained. • Four occasions during a five-month period in 2018 were observed. • The variability of the 3-μm emission intensities of CH 4 , C 2 H 6 , and H 3 + was studied. • The peak intensities of these species showed the highest 3–4 times greater than the lowest. • We find lack of correlation between the 3-μm hydrocarbon intensities at the 8CNPHS and the solar wind strength. [ABSTRACT FROM AUTHOR]

We have analyzed the 2-μm spectro-images of the polar haze of Jupiter, which were observed by the JIRAM/Juno between 2016 and 2021, to study the vertical and latitudinal distributions of the polar haze and its absorption and scattering properties. We construct 2-μm brightness maps of the polar haze by selecting specific spectral ranges where the haze spectral features are revealed. The constructed haze images show no distinctive structure above the 55oN/S latitudes showing fairly uniform and symmetrical distribution around the poles. We find no traces of the recently discovered stratospheric polar jets seen at radio wavelengths (Cavalié et al., 2021), of the circumpolar waves seen in the UV and around 8900 Å (e.g., Vincent et al., 2000; Barrado-Izagirre et al., 2008), nor of the mid-IR hot/bright spots on these images. These non-detections indicate that the major polar haze layers are lower than the jets and the mid-IR bright spots, but possibly higher than the circumpolar waves, and the thermal radiation from the mid-IR hot spots is negligible at 2 μm. We construct synthetic spectra between 2.0 and 2.5 μm, compare them with the JIRAM polar spectra, and find that the 2-μm polar haze is mostly located between 3 and 40 mbar pressure levels, approximately consistent with the previous results of Kim et al. (1991b), and also the literature values. We attempt to derive the anisotropic scattering properties of the haze particles for scattering angles between 60o and 120o, which is the only available range. The derived anisotropy tends to be moderate, but we are unable to determine a definite anisotropy within the statistical error bars of the observed data. We also derive the haze optical depths and single scattering albedos between 2.0 and 2.5 μm. The derived spectral structure of the opacity is roughly similar to those of hydrocarbon and nitrile ices of Titan retrieved by Sim et al. (2013) suggesting similar chemical compositions and possibly similar formation scenarios for Jupiter's haze particles but excluding nitrile ices. • We study the vertical and latitudinal distributions of the polar haze. • We construct 2-μm brightness maps of the polar haze. • We find that the 2-μm polar haze is mostly located between 3 and 40 mbar pressure levels. • Derived anisotropic scattering properties of the haze tend to be moderate. • Derived spectra of the haze are similar to those of Titan suggesting similar formation scenario. [ABSTRACT FROM AUTHOR]