A Study of Six Near-Earth Asteroids

Summary We consider here 6 Earth-orbit-crossing asteroids (ECAs) as possible targets for a future Discovery-class space mission. Five of these bodies have a common feature that their orbits have orbit periods that almost exactly match the one-year orbit period, with various inclinations and eccentricities. As a consequence of perturbations and finite volumes of position and velocity uncertainty that arise for near-encounter events, the long-term motion of multiple encounter asteroids relative to Earth are quasi-periodic. We also examine one non-resonant asteroid (2004 MN4), because it is projected to have three near-impact encounters in 2029, 2034 and 2036. The 2029 encounter miss distance is presently estimated to be ~ 5.6 +/-1 Earth radii; the subsequent miss distances and associated uncertainty cannot be reliably estimated at present. 2004 MN4 has an estimated diameter of ~400m. An impact by a body of this size may produce significant loss of life and is therefore of obvious significance. We review the orbit evolution and structural properties of these primitive asteroids. It is anticipated that understanding the composition and morphology of these primitive bodies would provide substantial insight into the history of the solar system. The diameter of the ECAs discussed varies from less than 100m to several km. Their near proximity and scientific importance makes them attractive targets for near term missions. Early missions should be aimed at understanding their physical properties and orbits, as well as developing insights that may someday be needed to deflect or destroy these bodies. For the particular case of 2004 MN4, we evaluate all opportunities for near-term missions before the 2029 encounter. Two low energy opportunities are found ~2012 and ~2020. Such missions would provide an opportunity to track the object precisely during the 2029 encounter to accurately predict the subsequent encounters, and finally, to measure seismic response to the Earth's tidal forces during the encounter; we believe this would help us to understand its structural properties. These launch opportunities are very important