Abstract
Abstract We estimate the total population of near-Earth objects (NEOs) in the solar system using an extensive, “solar-system-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.
Highlights
The question of the total population, down to some minimum size, of solar system objects in various categories is an old one that has been addressed in many different ways for classes ranging from Oort Cloud objects to the hypothetical Vulcanoids inside the orbit of Mercury
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 Asteroid Terrestrial-impact Last Alert System (ATLAS) survey
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
Summary
The question of the total population, down to some minimum size, of solar system objects in various categories is an old one that has been addressed in many different ways for classes ranging from Oort Cloud objects to the hypothetical (but probably nonexistent) Vulcanoids inside the orbit of Mercury. The 2.4 × 104 known main belt asteroids larger than 5 km (assuming a 15% albedo) certainly constitute the vast majority of such objects in existence; and the 902 known NEOs larger than 1 km are believed to make up 97% of the true population above this size limit (Stokes et al 2017) In both populations, surveys have detected many thousands of much smaller objects. This magnitude limit is brighter than most surveys, ATLAS covers a greater solid angle on the sky per night than any other planetary defense survey, and unlike others, does not avoid the Galactic plane This rapid scanning of the whole accessible sky serves ATLAS’ mission to function as a “last alert”—that is, to detect small but dangerous asteroids incoming for impact.
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