A Tenuous Lunar Ionosphere in the Geomagnetic Tail.

Area of Science:

• Space Physics
• Plasma Physics
• Lunar Science

Background:

• The Moon lacks a global magnetic field, leading to questions about its plasma environment.
• Understanding the Moon's interaction with Earth's magnetosphere is crucial for space exploration.

Purpose of the Study:

• To investigate the charged particle density in the lunar environment.
• To determine the characteristics and origin of the Moon's ionosphere.
• To assess the impact of the lunar ionosphere on the surrounding plasma.

Main Methods:

• Utilized electron plasma frequency oscillation measurements from the Acceleration, Reconnection, Turbulence, and Electrodynamics of Moon's Interaction with the Sun (ARTEMIS) mission.
• Analyzed data collected as the Moon traversed Earth's geomagnetic tail.

Main Results:

• Confirmed the existence of a tenuous lunar ionosphere with an average density of 0.1-0.3 cm^-3.
• The ionosphere is present at least 50% of the time in the geomagnetic tail, mainly on the dayside.
• Observed day-night asymmetry and dawn-dusk symmetry suggest photoionization of a neutral exosphere as the primary source.

Conclusions:

• The Moon possesses a persistent, albeit tenuous, ionosphere within Earth's geomagnetic tail.
• Photoionization is the dominant process creating the lunar-derived plasma.
• The lunar ionosphere significantly perturbs the local plasma environment in the geomagnetic tail.