Auroral X-ray emissions from the gas giant planets: remote sensing and in situ magnetospheric diagnostics

Abstract

The thesis begins by introducing the reader to the fundamental concepts used throughout the field of space physics today (Chapter 1) and then applies them to the the jovian magnetosphere, the largest coherent object (or fully unified structure if visible to the naked eye) within our Solar System (Chapter 2). This chapter focuses on the structure and internal dynamics of the jovian magnetosphere observed throughout the literature, with particular emphasis of the complex X-ray auroral emissions at the poles. This chapter concludes by analysing previous literature and the ongoing effort to search for the complicated magnetospheric driver, or drivers, responsible for these complex emissions at the gas giant planets - the largest open question in our field, which this thesis aims to answer. The studies that are contained within this thesis focus on constraining the magnetospheric driver, or drivers, responsible for the X-ray auroral emissions at the gas giants, in particular at Jupiter. The research throughout focuses on observations performed by the Chandra X-ray telescope (CXO), using the onboard high resolution camera (HRC), combined with by other remote sensing data, such as ultraviolet observations form the Hubble Space Telescope (HST), and in situ spacecraft data from Juno , when available to provide vital magnetospheric context (Chapter 3). The first work chapter (Chapter 4) is a case studying analysing a Chandra observation during a compression event while Juno was near its apojove position, the furthest point from Jupiter in its orbit. The mapping analysis of the X-ray auroral emissions was carried on using a newly developed and freely available Python pipeline (Weigt, 2021), utilising the high spatial resolution of Chandra. This mapping algorithm is used throughout this thesis. Chapter 5 then applies these analytical methods, techniques and definitions to the full ∼ 20-year Chandra dataset of the northern auroral emissions to determine the more extreme and typical behaviour of the northern X-ray emissions. This case study eludes to the possibility of numerous magnetospheric drivers likely located in the noon and dusk flank of the jovian magnetosphere, based on the Grodent Anomaly Magnetic field model (Grodent et al., 2008), with a statistically significant region at noon. Comparisons of the timing and mapping analysis with previous literature highlight that the X-ray emissions may be associated with ultra-low frequency wave activity in the form of Shear Alfven waves. ´ Chapter 6 expands on the the idea of multiple drivers through the creation of physics-informed auroral families during the Juno-era, allowing us to associate morphological features with magnetospheric drivers located throughout the jovian system. The X-ray auroral morphologies identified in this case study may also be a useful monitor of magnetospheric conditions at Jupiter. The penultimate chapter (Chapter 7) changes focus to the exploration of kronian X-rays, analysing Chandra observations aimed to monitor Saturn’s magnetospheric response during a rare planetary alignment with Jupiter. Due to the orbits of the planets, this event occurs once in every ∼ 19-20 years, analysing this unique parameter space for the first time. This case study predicts the flux and power of the emissions and compares with solar flux data from Geostationary Operational Environmental Satellites (GOES) to find any correlations between solar activity and the counts detected from Saturn’s disk emissions. The thesis concludes with an exploration into future work, further utilising the Chandra data as much as possible and comparing with other datasets to provide more coherent catalogues of the temporal and spatial behaviour of the auroral emissions that can be used for future studies.

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ORCID for Diego Altamirano: orcid.org/0000-0002-3422-0074

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