Ground-based observations of Jupiter (and Saturn) in support of the NASA Juno mission

The clouds of the Solar System's Gas Giants (Jupiter and Saturn) are amongst the most beautiful and complex phenomena displayed by the planets. Their spatial distribution reveals the forces and energy exchange mechanisms (e.g., moist convection) shaping the banded appearance of the planetary weather layers; their vertical structure tells us about the composition and cloud microphysics; and their colour reveals the chemical alteration of aerosols in a giant planet atmosphere. While most clouds are white, the clouds of Jupiter and Saturn are coloured with various hues of yellow and red, but the nature of these colours, or 'chromophores,' has yet to be determined, and remains an enduring mystery.The NASA Juno mission arrived at Jupiter in July 2016 and entered into a series of elliptical polar orbits designed to probe Jupiter's interior structure through measurement of its gravity and magnetic fields and remote sensing of its deep atmosphere. Juno's highly elliptical orbit minimises the damaging effects of Jupiter's extremely harsh radiation belts, but means that its UV, visible and near-IR observations are mostly of Jupiter's poles, while microwave observations using the MWR instrument are mostly confined to narrow north-south swaths during perijove (closest approach) passes that lack the global spatial context necessary to interpret them properly. Hence, a global campaign is under way to provide Earth-based observational support for Juno, in which our group closely involved making observations with the MUSE instrument at ESO's Very Large Telescope (VLT) in Chile. The MUSE (Multi Unit Spectroscopic Explorer) instrument provides an unprecedented opportunity to study the clouds, dynamics and composition of the giant planet atmospheres at a spatial and spectral resolution never before possible. MUSE measures spectral 'cubes' in which each pixel of the 300 x 300 field of view is a complete spectrum covering the range spectral 480 to 930 nm. These 'cubes' allow us to map the spatial distribution of the clouds and colouring agents, estimate cloud top levels and determine spatial variations of ammonia abundance. While other ground-based and space-based instruments can provide partial coverage of these wavelengths (usually as images in discrete filters), only MUSE provides the unique combination of spatial and spectral coverage, which makes it a very powerful tool for studying clouds in giant planet atmospheres.
Analysis of existing MUSE observations has been used to model the distribution of cloud, chromophores and ammonia in Jupiter's atmosphere, but Jupiter's atmosphere continues to develop and the Juno mission is set to observe for several more years. Hence, continuing observations are vital and more are planned or remain waiting to be processed. At longer wavelengths, instruments such as VLT/VISIR provide thermal mapping that can be used to determine the vertical and spatial distribution of temperature and gaseous abundances. A set of MUSE observations was made within a few minutes of a set of VISIR observations on one night in 2018 and provides a golden opportunity to link cloud features to observed thermal anomalies. We envision that our VLT/MUSE programme could extend to further observations of Saturn also to compare and contrast these two worlds. In addition to these ground-based facilities, NASA's James Webb Space Telescope (JWST), scheduled for launch in 2021, is planned to make many observations of the gas giants over a wide wavelength range that will need to be understood and interpreted.
In this project, the student will analyse existing VLT/MUSE Jupiter observations and participate in proposing and reducing further measurements, gaining excellent experience in telescopic observational data analysis and gaining a deep insight into the atmospheric circulation and cloud formation on these worlds. The spectral cubes will be analysed with our sophisticated multiple-scattering radiative transfer model, NEMESIS. Given the t