but they fail to provide phase information, nor do they allow polarimetric studies such as those needed to identify liquid water. In preparation for the study of extrasolar planets, there could be particular value in making synoptic observations of Earth. For example, the vantage from the Moon (or a similar orbit) could allow the monitoring of specific properties of Earth as it would appear as a single point object, going through phases. Such data might identify readily measurable properties that are diagnostic of our habitable world, such as looking for possible evidence of oceans from the polarization of Sun glint and of vegetation from any cyclical spatial variation of the strong chlorophyll absorption edge in the visible to near-infrared spectrum.

We know that small amounts of material are redistributed from one body to another by impacts (e.g., meteorites), and the Moon retains a record that extends over 4 billion years (perhaps earlier if there was no terminal cataclysm). On the Moon, however, impacts pulverize or melt most impactor material while repeatedly mixing the regolith and megaregolith. Very small amounts survive as mineral grains or rock fragments. Nevertheless, some materials, such as zircons, are particularly refractory and may be preserved in lunar regolith. Nonlunar zircons would be geochemically distinctive and, if found, they would provide information about timing, composition, and conditions on their parent body, possibly including the habitability of early Earth. Existing lunar samples might be used to evaluate whether such materials exist in a detectable amount and, if promising, methods could be developed for prospecting likely environments on the Moon and processing large amounts of lunar material to search for unusual components foreign to the Moon that could be returned to Earth for advanced forms of analysis.

The Moon may also constitute a testbed for astrobiological studies. The isolation of the Moon from Earth can be biologically quite complete, which could make the Moon an appropriate place to study biota in a fully sterile and sterilizing environment. This could include developing a lunar facility for assessing the potential biological impact of martian materials to Earth’s environment. The exceedingly low organic levels in lunar regolith also may allow the Moon to be a useful testbed for very sensitive life-detection technologies.


Remote Sensing of Earth From or Near the Moon

Earth observations from the Moon offer the another opportunity to acquire unique data to look at Earth in a bulk thermodynamic sense, particularly as an open system exchanging radiative energy with the Sun and space, in a way never done before—“Earth as a whole planet” (as illustrated in Figure 6.2). This is a fundamental scientific goal with very appealing prospects for climate and Earth sciences in general. Climate research requires stable,

FIGURE 6.2 Simulated images of various phases of Earth as seen from the Moon over a period of days in both summer (top) and winter (bottom). SOURCE: Graphics created by Starry Night® and are used with permission from Imaginova Corporation. Starry Night is a registered trademark of Imaginova Corporation.

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