Dr. Martin Elvis, Astrophysicist, Harvard-Smithsonian Center for Astrophysics
Effective planetary defense requires characterization: knowing whether a potentially hazardous object (PHO) is metallic, stony or carbonaceous, whether it is solid, fractured, or rubble, whether it is tumbling, and what size and shape it has, are all key inputs to threat mitigation decisions. At current rates it will take a century to characterize all approximately 20,000 near-Earth objects (NEOs) larger than about 100 m diameter (H < 22) with optical-near-IR spectra, light curves and accurate orbits (U < 3). Chelyabinsk-class (>= 15 m diameter) NEOs are even more challenging. NEO characterization is mission critical to threat reduction, and is a gating item. Without characterization, a well-planned defense is not possible.