bulk of the matter in the universe, they represent unique probes of galactic structure. Observations of microlensing events have particular promise for probing the mass function of brown dwarfs and understanding the composition of the galactic halo. With appropriate developments, microlensing could provide a shortcut to the detection of extrasolar terrestrial planets.

To ensure continued progress in this area, NASA and other agencies should foster coordination and collaboration among various search programs to enable ongoing discoveries and to follow up on possible candidate events. Because microlensing groups have different primary goals, the various agencies supporting primary and follow-up microlensing observations should work together to minimize potential disruptions caused by differences in their prime goals.

Measurement of higher-order microlensing events is required to determine the sources of lens effects in some cases. The reflex motion resulting from Earth's orbit around the Sun, for example, causes the trajectory of the background star relative to the lensing object to deviate from a straight line. This parallax effect induces asymmetries in the light curve of microlensing events which should be of order 1% if the lenses lie in the halo, but negligibly small if the lenses are in the Large Magellanic Cloud. Thus, a search for parallax asymmetries as an adjunct to the microlensing program will yield additional important information on the nature of the objects creating the lensing events.

The ultimate programmatic goal of NASA's Origins program—discovering another Earth—is a laudable one upon which no specific recommendation is laid. In addressing this goal, however, NASA should take the following actions:

• Continually assess the new information that studies of SMOs are providing on the formation, frequency, and characteristics of planetary systems, and invest judiciously in developing observational and theoretical techniques that will foster new discoveries. This investment should be in addition to the funding NASA is already providing for technological development of future large projects such as the Space Interferometry Mission and the Terrestrial Planet Finder. The funding must be flexible and peer-reviewed in recognition of the nature of the activities, which are distributed, principal-investigator-based projects to observe and model SMOs by using a variety of different approaches. The small-scale nature of these activities suggests that existing procedures (e.g., periodic peer review of proposals and resulting publications) will be adequate to identify and prioritize the approaches and techniques deserving of additional investment.

• Invest with care in select ground-based facilities, instrument, and computational programs that will significantly broaden the near-term opportunity for innovation in the identification and characterization of SMOs. Addressing the broader issue of the appropriate balance of support for ground-based programs among NASA, the National Science Foundation, and other appropriate agencies is beyond the scope of this report. This important topic is best addressed by the decadal survey committee in the context of the findings of the study on the federal funding of astronomical research currently being conducted by the NRC's Committee on Astronomy and Astrophysics.

• Consult with other agencies (e.g., the National Science Foundation) to avoid duplication and to open a broader set of opportunities for research and discovery through cooperative or collaborative funding.

In sum, SMO research is at the heart of trying to understand the matter content of the universe, the ubiquity and properties of planetary systems, and the relationship (in both genesis and physical properties) between stars and objects not massive enough to ever become stars. By studying SMOs we extend our understanding of the cosmos from the ubiquitous macroscale of stars through to the planets and, hence, ever closer to the human realm.

Front Matter (R1-R4)

Contents (R5-R6)

1. Charter and Organization of the Board (1-8)

2. Activities and Membership (9-33)

3. Summaries of Major Reports (34-101)

4. Short Reports (102-118)

5. Cumulative Bibliography (119-126)