I show that the WFIRST microlensing survey will enable detection and precision orbit determination of Kuiper Belt Objects (KBOs) down to Hvega = 28.2 over an effective area of ∼ 17 deg2. Typical fractional period errors will be ∼ 1.5% × 100.4(H−28.2) with similar errors in other parameters for roughly 5000 KBOs. Binary companions to detected KBOs can be detected to even fainter limits, Hvega = 29, corresponding to R ∼ 30.5 and effective diameters D ∼ 7 km. For KBOs H ∼ 23, binary companions can be found with separations down to 10 mas. This will provide an unprecedented probe of orbital resonance and KBO mass measurements. More than a thousand stellar occultations by KBOs can be combined to determine the mean size as a function of KBO magnitude down to H ∼ 25. Current ground-based microlensing surveys can make a significant start on finding and characterizing KBOs using existing and soon-to-be-acquired data.

Abstract
1. INTRODUCTION
2. KBOS IN MICROLENSING DATA
3. ASTROMETRY FROM A MICROLENSING SURVEY
4. WORLD COORDINATE SYSTEM
5. PRECISION OF ORBIT DETERMINATION
6. FINDING KBOS IN THE DATA
    6.1. Finding KBOs in Unexpected Orbits
7. BINARY COMPANIONS AND MASS MEASUREMENTS
    7.1. Detection of Unresolved Companions
8. KBO SIZE ESTIMATES FROM OCCULTATIONS
    8.1. OccultationMeasurements
    8.2. Occultation Noise
9. EFFECTS OF GEOSYNCHRONOUS ORBIT
10. EDGE EFFECTS
11. KBO LOST AND FOUND
12. EXPECTATIONS BASED ON PREVIOUS KBO SURVEYS
    12.1. Expected KBO Detections
    12.2. Expected Occultations
    12.3. Expected Binary KBO Detections
13. APPLICATION TO GROUND-BASED MICROLENSING SURVEYS
14. CONCLUSIONS
REFERENCES

• ANDREW GOULD(Department of Astronomy, Ohio State University) CORRESPONDING AUTHOR