Bruce Jakosky (1), Ariel Anbar (2), G. Jeffrey Taylor (3), and Paul Lucey (3)

(1) Laboratory for Atmospheric and Space Physics and Department of Geological Sciences, University of Colorado , Boulder , CO 80309-0392

(2) Dept. of Geological Sciences and Dept. of Chemistry & Biochemistry, Arizona State University, Tempe, AZ 85287

(3) Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawaii , 1680 East-West Rd. , Honolulu , HI 96822

19 July 2004

Executive Summary

The Moon preserves unique information about changes in the habitability of the Earth-Moon system. This record has been obscured on the Earth by billions of years of rain, wind, erosion, volcanic eruptions, mountain building, and plate tectonics. In contrast, much (most?) of the lunar surface still contains information that reflects events at the time of life's origin and subsequent evolution on Earth. Therefore, lunar research can address critical astrobiology science questions. In particular, the lunar record allows us to focus on two specific issues in the early solar systemóthe history of impacts and the history of exposure to radiation. The Moon, as Earth's closest neighbor, is probably the only body in the solar system where we can address these issues quantitatively.

Impacts probably played an important role in the earliest history of life on Earth. Large impacts would have temporarily altered the environment and creating hostile conditions in which life could not survive. Later impacts probably shaped life's evolution by forcing successive mass extinctions of large numbers of species. The terrestrial impact history is better recorded on the Moon than on the Earth. Central science goals are to determine the impact rate onto the Moon (and, by extension, the Earth) during the period when life was originating early in solar-system history, as well as in geologically recent times. We can use the beautifully preserved record on the Moon to help us to understand the habitability of the Earth at the time of life's origin and earliest evolution and determine the frequency of impact-driven mass extinctions and the subsequent course of evolution.

During Earth's earliest history, its surface also was bombarded by high-energy particles associated with solar activity (from a solar wind that was enhanced during early history and from solar flares) and galactic cosmic rays, and possibly from nearby supernovae and events associated with gamma-ray bursts. This bombardment must have had deleterious effects on life at the Earth's surface, and may have severely affected the formation and earliest evolution of life. These ancient events are recorded in the lunar regolith, formed throughout lunar history by the impact of micrometeorites and which were buried and preserved by subsequent lava flows. Sampling the effects of this radiation within these fossil regoliths, then, provides a window into the energetic-particle environment at the time that the regolith was buried, and sampling many different locations can provide detailed information over time. This will provide a better understanding of the environmental and evolutionary effects of changes in solar activity, of episodes of harsh radiation, and of energetic particle influx from outside the solar system.

Each of these problems can be addressed in a step-wise manner by a lunar science program that includes orbital imaging and remote sensing, in-situ analysis from landed spacecraft on the lunar surface, robotic sample-return missions, and human-exploration missions.

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