Vertical Distribution of Aerosols and Hazes Over Jupiter's Great Red Spot and Its Surroundings in 2016 From HST/WFC3 Imaging

In this work, we have analyzed images provided by the Hubble Space Telescope's Wide Field Camera 3 (HST/WFC3) in December 2016, with a spectral coverage from the ultraviolet to the near infrared. We have obtained the spectral reflectivity of the GRS and its surroundings, with particular emphasis on selected, dynamically interesting regions. A spectral characterization of the GRS area is performed following two different procedures: (a) in terms of Altitude/Opacity and Color Indices (AOI and CI); (b) by means of automatic spectral classification. We used the NEMESIS radiative transfer suite to retrieve the main atmospheric parameters (e.g., particle vertical and size distributions, refractive indices) that are able to explain the observed spectral reflectivity. The optimal a priori model atmosphere used for the retrievals is obtained from a grid of about 12,000 different atmospheric models, and choosing the one that best fits South Tropical Zone (STrZ) spectra and its observed limb-darkening. We conclude that the spectral reflectivity of the GRS area is well reproduced with the following layout: (a) a stratospheric haze with its base near the 100 mbar level, with optical depths at 900 nm of the order of unity and particles with a size of 0.3 mu m; (b) a more vertically extended tropospheric haze, with tau (900 nm) similar to 10 down to 500 mbar and micron sized particles. Both haze layers show a stronger short wavelength absorption, and thus both act as chromophores. The altitude difference between clouds tops in the GRS and surrounding areas is similar to 10 km. Plain Language Summary One of the main questions concerning the Great Red Spot (GRS) of Jupiter is the origin of its reddish color. It is commonly understood that the cause of this feature are one or more unknown species of aerosols located in the upper atmosphere. Even in the whitest areas of Jupiter, stronger blue light absorption has been measured, suggesting the global presence of one or more species of blue absorbing aerosols. We use Hubble Space Telescope (HST) observations to retrieve atmospheric models describing the vertical structure and some of the main atmospheric properties of the hazes in the GRS and its surrounding area. Our results suggest that two different blue absorbing aerosols are able to account for the color of the GRS and its vicinity.