Sodium Atoms in the Lunar Exotail: Observed Velocity and Spatial Distributions

TL;DR

This study provides the first detailed velocity and spatial maps of sodium atoms in the lunar exosphere's tail, revealing their distribution and dynamics influenced by lunar surface processes.

Contribution

It offers the first kinematically resolved maps of sodium emission in the lunar tail, linking spatial and velocity distributions to lunar surface sodium release mechanisms.

Findings

Sodium atoms form an elongated tail along the ecliptic.

Peak sodium emission drifts eastward by 3° per night.

Distributions are sensitive to lunar surface sodium velocities.

Abstract

The lunar sodium tail extends long distances due to radiation pressure on sodium atoms in the lunar exosphere. Our earlier observations measured the average radial velocity of sodium atoms moving down the lunar tail beyond Earth (i.e., near the anti-lunar point) to be $\sim 12.5$ km/s. Here we use the Wisconsin H-alpha Mapper to obtain the first kinematically resolved maps of the intensity and velocity distribution of this emission over a $15 \times 15 \deg$ region on the sky near the anti-lunar point. We present both spatially and spectrally resolved observations obtained over four nights bracketing new Moon in October 2007. The spatial distribution of the sodium atoms is elongated along the ecliptic with the location of the peak intensity drifting $3 \deg$ east along the ecliptic per night. Preliminary modeling results suggest the spatial and velocity distributions in the sodium exotail are sensitive to the near surface lunar sodium velocity distribution. Future observations of this sort along with detailed modeling offer new opportunities to describe the time history of lunar surface sputtering over several days.