The Evolution of a Spacecraft-Generated Lunar Exosphere.

Area of Science:

• Planetary Science
• Lunar Volatiles
• Spacecraft-Environment Interactions

Background:

• Spacecraft operations, particularly powered landings, act as volatile release experiments on airless bodies.
• Understanding the dispersal and persistence of these released volatiles is crucial for mission planning and interpreting scientific measurements.

Purpose of the Study:

• To investigate the transport and fate of water vapor released during a nominal lunar landing using numerical simulations.
• To assess the potential for contamination of lunar cold traps by spacecraft exhaust.
• To determine the sensitivity of exospheric evolution and deposition patterns to critical parameters like desorption activation energy.

Main Methods:

• Numerical simulations of water vapor transport during a lunar landing and for two subsequent lunar days.
• Modeling exospheric evolution and surface deposition patterns.

Main Results:

• Spacecraft exhaust water vapor is globally redistributed, with significant amounts reaching polar permanently shadowed regions (cold traps).
• Exospheric evolution and deposition are highly sensitive to desorption activation energy.
• Contamination of cold traps is likely to scale with exhaust mass and landing site proximity to the poles.

Conclusions:

• Spacecraft exhaust propagation is a widespread and long-lived impact on airless bodies, requiring consideration in mission planning.
• Measurements during future missions can constrain critical parameters like lunar surface "stickiness" (desorption activation energy).
• Understanding these impacts is vital for interpreting lunar measurements and studying the origin and distribution of lunar water.