Threat from Within: Excitation of Venus's Co-orbital Asteroids to Earth-crossing Orbits

All five currently known asteroids in the 1:1 mean-motion resonance (co-orbital) with Venus cross Earth's orbit. We explore a scenario in which these near-Earth asteroids originate in a reservoir of asteroids co-orbiting with Venus on low-eccentricity orbits. Such an asteroid reservoir was proposed as the only viable source of Venus's co-orbital dust ring. So far, efforts to discover low-eccentricity Venus co-orbital (LEVCO) asteroids have been unsuccessful; however, their existence has not been ruled out. We show that LEVCO asteroids, stable for millions to billions of years, eventually evolve into Earth-crossing configurations, where they may pose a threat to Earth. We find that the orbits of these asteroids cross Earth's orbit for 22.5 million yr, on average, an order of magnitude longer than the corresponding Earth-crossing time of most asteroids escaping from the main belt. Using the results of the latest survey of LEVCO asteroids, we conclude that, given their absolute magnitudes, H, most of the observed Venus co-orbitals likely do not originate from the hypothetical population of LEVCO asteroids. However, we infer that there are up to similar to 500 asteroids originating from the LEVCO region with H < 26.3 (10-40 m in diameter) that currently cross the orbit of Earth. Up to similar to 20 of those have H < 24.1 (30-100 m in diameter), easily detectable by various near-Earth asteroid surveys. We estimate the current mass of the LEVCO reservoir as M approximate to 10(13)-10(16) kg, 3-6 orders of magnitude lower than the current mass of the main belt, depending on their size-frequency distribution.