The Moon as a Giant Tape Recorder for Solar System and Solar Events

A unique lunar property The moon has a unique property compared to the terrestrial and gas giant planets of our solar system. This property consists of the ability to record and preserve evidence of both external and internal events and processes over a time span that includes most of solar system history. Every exposed surface of the moon accumulates implanted solar wind atoms, is modified by both solar flare events and cosmic rays, is exposed to solar UV which may make changes in crystal structures and composition, and is impacted by micrometeorites which create craters, melts soil, produces agglutinates, sprays melted rock, and produces vapor from highly heated silicates and oxides. The “signal” from all of these events and processes is recorded in the uppermost regolith layer, in individual soil grains, and by exposed rock surfaces. This signal consists of chemical changes, changes in morphology and texture of soil grains, implantation of atoms from the sun, radiation damage for cosmic rays and solar flare events, and other modifications driven directly by the complex interaction between solid lunar rocks and soil and the environment of the solar system. Even rare events such as nearby supernovae may have left a series of distinctive changes in lunar material. This recorded signal, if found and properly decoded, is a record of these types of events over the history of the moon. If not covered up, this recorded signal is overwritten and destroyed by later events; the record of earlier events disappears. However, processes exist which can preserve some of this record. For example, the moon has had some endogenic surface modification over the past 4 gy. While lava flows, pyroclastic deposits, and volcanic vents are common in the mare areas, much of the moon has been modified only by external impacts during the period time since the end of the great basinforming impact events. Surfaces covered by volcanic flows and ejecta become a reasonably permanent record of events in the early solar system. In addition, except for the smallest micrometeorites, all lunar impact events create ejecta and debris which cover exposed rock and soil. This coverage is continuous near the crater, becomes discontinuous out a few crater diameters, and may also include rays which may extend extremely long distances. As a consequence, most exposed rock and regolith surfaces are eventually covered to some degree by these impact ejecta.