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Integration of the orbit of asteroid (29075) 1950 DA, which is based on radar and optical measurements spanning 51 years, reveals a 20-minute interval in March 2880 when there could be a nonnegligible probability of the 1-kilometer object colliding with Earth. Trajectory knowledge remains accurate until then because of extensive astrometric data, an inclined orbit geometry that reduces in-plane perturbations, and an orbit uncertainty space modulated by gravitational resonance. The approach distance uncertainty in 2880 is determined primarily by uncertainty in the accelerations arising from thermal re-radiation of solar energy absorbed by the asteroid. Those accelerations depend on the spin axis, composition, and surface properties of the asteroid, so that refining the collision probability may require direct inspection by a spacecraft.
Useful predictions of asteroid encounters with planets, in which the statistical uncertainty in the time of closest approach is +/-10 days or less, are generally limited to an interval within a few decades of the time spanned by positional measurements (astrometry), unless optical astrometry spans several years or high-precision delay-Doppler radar measurements are available. This is because long-term solar system dynamics can be a highly nonlinear prediction problem, and measurement error propagation increases the positional uncertainties of an asteroid with time. Here we consider the trajectory of asteroid 1950 DA over a much longer time period and estimate the probability of an Earth encounter.
The possibility of a close approach to Earth was initially recognized in the course of a recent radar experiment that used dynamical force propagation methods that have been used successfully for previous, comparatively short-term predictions of asteroid orbits. Then, because of the quality and extent of the orbit measurements, we examined several factors that are normally neglected in asteroid trajectory prediction and hazard studies so as to more accurately characterize trajectory knowledge and confirm the initial impact probability calculation. These factors include computational noise, galactic tides, perturbations due to the gravitational encounters of the asteroid with thousands of other asteroids, an oblate Sun whose mass is decreasing, the role of planetary mass uncertainties, acceleration due to solar wind and radiation pressure acting on the asteroid, and the acceleration of the asteroid due to thermal emission of absorbed solar energy.
Asteroid (29075) 1950 DA was discovered on 23...