Timothy Cassidy

Learn More
We describe a direct simulation Monte Carlo (DSMC) model of Enceladus’ neutral cloud and compare its results to observations of OH and O orbiting Saturn. The OH and O are observed far from Enceladus (at 3.95 RS), as far out as 25 RS for O. Previous DSMC models attributed this breadth primarily to ion/neutral scattering (including charge exchange) and(More)
The full set of high-resolution observations from the Galileo Ultraviolet Spectrometer (UVS) is analyzed to look for spectral trends across the surface of Europa. We provide the first disk-resolved map of the 280 nm SO2 absorption feature and investigate its relationship with sulfur and electron flux distributions as well as with surface features and(More)
We study the orbits, tidal heating and mass loss from satellites around close-in gas giant exoplanets. The focus is on large satellites which are potentially observable by their transit signature. We argue that even Earth-size satellites around hot Jupiters may be immune to destruction by orbital decay; detection of such a massive satellite would strongly(More)
BACKGROUND Eosinophilic esophagitis (EoE) is a clinicopathologic disorder first described in 1978 which has gained significant recognition over the past 10 years. Numerous prevalence studies have been performed around the globe, both in pediatric and adult populations documenting a prevalence between 0.002% and 6.5%. The aim of this study is to assess the(More)
Concurrent programming poses a unique set of problems for quality assurance. These difficulties include the complexities of deadlock, livelock and divergence, which can be extremely difficult to detect and debug. A variety of tools have been developed to assist designers and developers of concurrent applications. Some of these tools, such as VeriSoft, are(More)
An intense flux of ions and electrons from the jovian magnetosphere both alters and erodes Europa’s surface, producing a tenuous atmosphere. This chapter discusses the physical processes that create and remove the atmosphere, such as ion erosion (sputtering), radiation-induced chemical alteration of the surface (radiolysis), and atmospheric loss processes(More)
Results from a three-dimensional ballistic model of Europa’s O2 atmosphere are presented. Hubble Space Telescope (HST) ultraviolet observations show spatially non-uniform O2 airglow from Europa. One explanation for this is that the O2 atmosphere is spatially non-uniform. We show that non-uniform ejection of O2 alone cannot reproduce the required morphology,(More)
[1] The Cassini imaging science subsystem observed Europa in eclipse during Cassini’s Jupiter flyby. The disk-resolved observations revealed a spatially nonuniform emission in the wavelength range of 200–1050 nm (clear filters). By building on observations and simulations of Europa’s Na atmosphere and torus we find that electron-excited Na in Europa’s(More)
[1] Analysis and interpretation of observations from the MESSENGER spacecraft in orbit about Mercury require knowledge of solar wind “forcing” parameters. We have utilized the Wang-Sheeley-Arge (WSA)-ENLIL solar wind modeling tool in order to calculate the values of interplanetary magnetic field (IMF) strength (B), solar wind velocity (V) and density (n),(More)
Space weathering is the collection of physical processes acting to erode and chemically modify planetary surfaces directly exposed to space environments of planetary magnetospheres, the heliosphere, and the local interstellar environment of the solar system. Space weathering affects the physical and optical properties of the surfaces of planetary bodies, so(More)