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Monte Carlo Atmosphere Model. Dana Crider, CUA Rosemary Killen, U. Md. Mecury’s Exosphere. Surface bounded exosphere The atmosphere is collisionless The surface is the exobase - PowerPoint PPT Presentation
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Monte Carlo Atmosphere Model
Dana Crider, CUA
Rosemary Killen, U. Md.
Mecury’s Exosphere
• Surface bounded exosphere– The atmosphere is collisionless– The surface is the exobase
• Since individual particles do not interact, Monte Carlo modeling is an excellent tool. Different scenarios can be run separately, and co-added in whatever proportion is physically appropriate.
Mecury’s Exosphere
SOURCES• Comets
• Micrometeorites
• Solar Wind
• Regolith
• Hermean Interior
RELEASE MECHANISMS• Ion sputtering
– Mid-to-high latitude
• Impact vaporization– Isotropic unless there is an
assumed surface distribution of the element released
• Thermal vaporization– Highly dependent on the
assumed time-dependent distribution of materials in the regolith
BALLISTIC HOPS
• Once released from the surface, particles follow a trajectory under the influence of gravity and radiation pressure
• Mercury’s eccentricity leads to high radial velocity at some true anomaly angles, causing annual differences in the effectiveness of radiation pressure.
SURFACE PROCESSES• What happens when the
particle encounters the surface? – Rebound (elastic or
inelastic)– Thermalize and reemit– Partial thermalization– Stick (either permanently
or until dawn)
SINKS• Photoionization
– Products can either return to surface or escape. Returned products can be followed in simulations
• Gravitational escape– Aided by radiation pressure
• Sticking to surface– Long-duration cold traps exist
at high latitude
Monte Carlo ModelINPUT
NUMERICAL NEEDS• Random seed• Number of particles• Box size• Time steps
PHYSICAL VARIABLES• Release mechanism
– Spatial distribution
– Initial velocity
• Sticking module– Rerelease velocity
– Spatial distribution
• True anomaly angle– Radiation pressure
– Photoionization
Monte Carlo ModelOUTPUT
• Statistics for a set of physical inputs– Dominant loss mechanism– Average hop parameters (distance, height,
number of hops)– Particle lifetime
Monte Carlo ModelOUTPUT
• 3-D atmospheric distribution given source– Position and velocity of particles in the atmosphere– Model abundance can be scaled to real abundance
by multiplying by the source rate– Multiple sources can be co-added in proportion to
get cumulative atmosphere– Flexible to allow any cut through simulated
atmosphere for comparison with viewing geometry for comparison with observations
Monte Carlo ModelOUTPUT
• Spatial distribution of loss processes, which can feed additional source processes– Magnetospheric recycling– Nightside sticking, dawn desorption
Photon stimulated desorption source
Conclusions
• Our Monte Carlo exosphere model paired with upcoming observations will provide insight into hermean surface, atmosphere, and magnetosphere interactions: – Understand surface-atmosphere interactions
especially in terms of sticking and re-release– Compare atmospheric distribution for different
release mechanisms