Mathematics – Probability
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.u41c0832o&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #U41C-0832
Mathematics
Probability
5420 Impact Phenomena, Cratering (6022, 8136), 5422 Ices, 6022 Impact Phenomena (5420, 8136), 6250 Moon (1221)
Scientific paper
The presence of water ice trapped within permanently shaded regions on the Moon was first posited in the early stages of lunar exploration and remains a possibility decades later. The Lunar Prospector Spectroscopy Experiment observed high abundances of hydrogen generally distributed near both lunar poles relative to the hydrogen abundance measured at the equator. Many emplacement mechanisms for this observed hydrogen are hypothesized, including: fluid inclusions from impacting stony meteorites, retention of solar hydrogen released in solar flares, adsorption of water, and recent impact of a comet. We investigate the feasibility of water ice delivery to the moon via comet impacts. Here we present a novel set of calculations for the fate of cometary water impacting the moon. Using the RAGE hydrocode (Holmes et al. 1999) and the Pactech/SAIC equation of state for water, we model impacts of solid water ice spheres into basalt targets. We use 100 m, 1 km, and 10 km diameter impactors and impact velocities ranging from 15 to 45 km/s to test water retention rates on the Moon. Water retention rates are measured by summing the mass of projectile material with velocities higher than lunar escape velocity moving through the outflow boundaries for the duration of our simulations. The escaped impactor mass is then subtracted from the total mass of the impactor to produce the mass of water retained. We conduct an independent test of this method by following the trajectories and velocities of Lagrangian tracer particles placed within the ice projectile at time t= 0 s. Initial simulations suggest that as much as 40% of ice projectile debris remains gravitationally bound to the moon after 30 km/s impacts. These simulations also illustrate scale independence; the volumetric percent of impactor escaped is the same for 100 m and 1 km diameter impactors at 30 km/s. Finally, we discuss other considerations for the likelihood of cometary impacts producing polar hydrogen abundances, including the probability of cometary impact and water mass flux, the effect of obliquity of the impact on vaporization of the impactor, and the migration of water vapor to the cold traps in the lunar polar regions. LA-UR 06-6232
Asphaug Erik
Coker Robert
Gittings Michael
Ong Lawrence
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