-Title of Thesis: “Influence of Magnetic Field Line Draping on Charged Particle Irradiation of Europa’s Surface Ice”

-Defense Date: January 12th, 2024.

-Defense Time: 3:00pm

-Defense Location: Ford ES&T, L1205

-Committee: Sven Simon (Advisor), James Wray, Annalisa Bracco, Tamara Bogdanovic, Lucas Liuzzo

-Abstract: 

Europa, the smallest of the Galilean moons of Jupiter, orbits within its parent planet's inner magnetosphere. When the Galileo spacecraft visited Europa in the late 1990s, its magnetometer measured signatures consistent with a secondary magnetic field centered at the moon. It was found that such an induced field could only be generated by a highly-conducting, liquid water layer locked beneath the moon's icy crust. The presence of this subsurface ocean has since made Europa one of the most promising locations to search for extraterrestrial life. Analysis of the ocean is, however, thwarted by the 10s to 100s of kilometer thick ice shell under which it in encased, and any investigation is (for now) limited to the moon’s surface. Unfortunately, the surface is exposed to a harsh radiation environment. At its location within Jupiter's magnetosphere, Europa is located within a region of dense, energetic magnetospheric plasma which hammers down on the surface. This charged particle bombardment makes the upper surface uninhabitable to any organic signatures, drives surface chemistry, generates the moon's dilute exosphere by ejecting neutral material from the surface, and is potentially harmful to spacecraft. Characterizing the intensity and spatial distribution of this charged particle irradiation is therefore critical not only to understanding the evolution of Europa's surface and exosphere, but is also of utmost importance to spacecraft safety. The impact locations of charged magnetospheric particles onto Europa's surface is determined by the dynamics of these particles both in Jupiter's global magnetosphere and in the moon's local electromagnetic fields. The dense plasma within Jupiter's equatorial plasma sheet continually washes over Europa's orbital trailing hemisphere. This flowing plasma interacts with the induced field from Europa's subsurface ocean, as well as electric currents within the moon's ionosphere, drastically warping the background Jovian field. Such perturbations may deflect particles and shield the moon's surface, or focus irradiation onto regions which previous studies have determined to be relatively ``safe". In order to develop a comprehensive picture of magnetospheric particle irradiation at Europa and its effect on the surface, we combine a three-dimensional hybrid model of the moon's perturbed electromagnetic environment with a relativistic particle tracer in order to map how the field perturbations affect the irradiation patterns. We calculate ion and electron irradiation patterns, energy deposition, and sputtering rates, and compare our results with observations from both the Galileo spacecraft and Hubble Space Telescope. We find that the electromagnetic field perturbations strongly affect the irradiation patterns of magnetospheric ions, but not of electrons, and that exogenic particle irradiation is essential to explain several observed features of Europa’s surface and exosphere.