Identifying the sources of colour and featural changes in Jupiter's atmosphere

Giant planet clouds are amongst the most beautiful and complex phenomena displayed by the planets of our solar system. 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.

In this project, the student will analyse existing VLT/MUSE observations the visible/near-IR spectra of Jupiter and Saturn and contrast these with existing near-IR VLT/SINFONI observations of Uranus and Neptune. He will also participate in proposing and reducing future observations, and will gain experience in telescopic observations and analysis. Both MUSE and SINFONI are Integral Field Unit spectrometers and the observed spectral 'cubes' will be analysed with a sophisticated multiple-scattering radiative transfer model, NEMESIS, previously developed to model observations of solar system planets. The student has access to real data to analyse from the start, with further data being acquired during their project, possibly in association with observations of Jupiter and Saturn by Juno and Cassini, respectively, in 2016-17. These data will be analysed to look for seasonal changes and also monitor occasional cloud upheaval events, such as the great storm on Saturn in 2010, the NEB outbreak on Jupiter in 2012 and the recent cloud outbreak on Uranus in 2014, which was so bright that it was visible to amateur astronomers. In addition, establishing a VLT/MUSE programme will provide invaluable context observations for the NASA/Juno mission, which arrives in Jupiter orbit in July 2016. This spacecraft will be placed in a polar orbit, with a low periapsis over Jupiter's north pole. The mission is primarily designed to determine Jupiter's internal structure by mapping its gravitational field, but remote sensing cameras will also observe narrow 'strips' of Jupiter as the spacecraft flies over the north pole. Interpreting these observations requires that we know how the observed 'strips' relate to the overall appearance and cloud structure of Jupiter. While simple ground-based imaging will be able to relate the strips to the wider context, only VLT/MUSE will be able to provide the spectral component, relating any composition/chromophore changes detected by Juno with the wide Jovian atmosphere. Thus, VLT/MUSE will be able to provide unique 'ground-support' to the Juno mission, and embed the student within the global community of giant planet astronomers.