arXiv subjects

David B. Goldstein

Publications and source records attributed to David B. Goldstein.

5 recordsLinked to original sources

arXiv2026

Predicted Ejecta Dynamics and Observability of the 2026 Falcon 9 Upper Stage Lunar Impact

On Aug. 5 at 06:34 UTC, a Falcon 9 upper stage (~3,900 kg) will strike the lunar surface at 2.43 km/s, yielding a potentially visible debris plume. We present a study of the expected impact dynamics and resulting possibly observable debris field. The debris plume should reach roughly 15 to 20 km in altitude for the ejecta curtain and 75 to 100 km for the central ejecta spike, extend 183 km laterally from the impact point near the sunlit limb, and yield a peak dust column density above 10 km altitude of 6.08*10^7 m^-2. Simulated I/F exceeds dark-sky background brightness by several orders of magnitude for the first few minutes after impact, reaching I/F = 1.27*10^-3 at the earliest resolved time (t = 5 s). Above 10 km, peak I/F reaches 1.33*10^-5, still several orders of magnitude brighter than the dark sky.

astro-ph.EP↗

arXiv2026

Transport of water in a Transient, Impact-Generated Atmosphere on Mercury

Mercury's polar cold traps host water ice deposits that are likely populated with impact-delivered water via Mercury's exosphere. However, Mercury's near-sun location experiences an extremely high photodestruction rate that rapidly destroys water with a timescale of only ~3.5 hours. Here we use the PLANET DSMC code to investigate the fate of water from a single 1 km radius comet impact striking Mercury's North Pole (30 km/s at angle of 60{\deg}). We find that the evolving plume separates into four distinct phases: 1) an early plume phase in which ballistic escape and photodestruction reach their peaks, 2) a reentry phase in which water falling back toward the surface forms a self-shielded shock-topped atmosphere that migrates across the surface and ballistic loss ceases, 3) a quasi-steady phase in which a self-shielding dawn atmospheric enhancement (DAE) forms and drives, a tenuous migration of exospheric water to the cold traps with a longitudinal dependence, and finally 4) a late phase in which self-shielding ends and photodestruction dominates, effectively ending substantial water migration. In this work, we quantify the fates of the arriving water molecules, and describe some of the more important features of this highly unsteady, evolving three-dimensional atmosphere. We find that 23% of the initial water is photodestroyed, 65% of the water ballistically escapes the system (of which, 79% photodissociates prior to reaching the Hill radius), and 14% ends up in Mercury's cold traps, which is significantly more than the ~5% that migrates to the Moon's cold traps during an equivalent impact.

astro-ph.EP↗

arXiv2025

Interaction of a Vortex Pair with a Polymeric Fluid Layer

The interaction of vortical structures with boundaries has been extensively studied in Newtonian fluids, where conditions such as no slip walls, free surfaces, or contaminated surfaces dictate whether vortices rebound, dissipate, or generate secondary structures. In this work, we investigate a related but fundamentally different problem: the interaction of a vortex pair with a finite, non uniform layer of polymeric fluid. Numerical simulations employing the finitely extensible nonlinear elastic Peterlin model are used to examine the effects of polymer concentration, relaxation time, polymer layer thickness, and maximum polymer extension on the evolution of kinetic energy and enstrophy. The results show that, while the polymeric fluid dissipates vortical motion, vortex polymer layer interactions can also generate new coherent structures. In particular, the formation of secondary and tertiary vortices coincides with transient increases in kinetic energy, a behavior absent in the Newtonian case. Unlike classical vortex boundary interactions, where the primary vortex survives, we find that under certain conditions it completely dissipates upon interaction with the polymer layer. These findings emphasize that fluids with non-uniform polymer concentrations, act not only as dissipative agents but also as sources of vorticity, extending the traditional view of polymer induced drag reduction and providing new insight into vortex polymer interactions.

physics.flu-dyn↗

arXiv2023

Generation of Laminar Vortex Rings by an Impulsive Body Force

It is shown that laminar vortex rings can be generated by impulsive body forces having particular spatial and temporal characteristics. The method produces vortex rings in a fluid initially at rest, and once generated, the flow field automatically satisfies the boundary conditions and is divergence-free. Numerical simulations and analytical models show that the strength of these rings can be accurately predicted by considering diffusion alone, despite the nonlinear nature of the generation process. A particularly simple model, which approximates the source of vorticity within vertical slabs, is proposed. This model predicts the ring circulation almost as accurately as a model which uses the exact geometry of the source of vorticity. It is found that when the duration of the force is less than a time scale based on the force radius and fluid viscosity, the ring circulation can be predicted accurately using an inviscid model.

physics.flu-dyn↗

arXiv2020

Lunar Volatiles and Solar System Science

Understanding the origin and evolution of the lunar volatile system is not only compelling lunar science, but also fundamental Solar System science. This white paper (submitted to the US National Academies' Decadal Survey in Planetary Science and Astrobiology 2023-2032) summarizes recent advances in our understanding of lunar volatiles, identifies outstanding questions for the next decade, and discusses key steps required to address these questions.

astro-ph.IM↗