NEO population, velocity bias, and impact risk from an ATLAS analysis

We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, "solarsystem-to-pixels"fake-asteroid simulation to debias detections of real NEOs by the ATLAS survey. Down to absolute magnitudes H = 25 and 27.6 (diameters of ~34 and 10 m, respectively, for 15% albedo), we find total populations of (3.72 ± 0.49) × 105 and (1.59 ± 0.45) × 107 NEOs, respectively. Most of the plausible sources of error tend toward underestimation, so the true populations are likely larger. We find the distribution of H magnitudes steepens for NEOs fainter than H ~ 22.5, making small asteroids more common than extrapolation from brighter H mags would predict. Our simulation indicates a strong bias against detecting small but dangerous asteroids that encounter Earth with high relative velocities - i.e., asteroids in highly inclined and/or eccentric orbits. Worldwide NEO discovery statistics indicate this bias affects global NEO detection capability to the point that an observational census of small asteroids in such orbits is probably not currently feasible. Prompt and aggressive followup of NEO candidates, combined with closer collaborations between segments of the global NEO community, can increase detection rates for these dangerous objects.