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J. Virtanen, K. Muinonen (Univ. Helsinki), E. Bowell (Lowell Observatory)
We are assessing the collision probabilities for Earth-approaching asteroids in the case of small numbers of observations and/or short observational arcs. Our methods are based on the statistical initial-orbital-ranging technique, which results in a rigorous a posteriori probablility density for the orbital elements. We provide initial upper bounds for the collision probability in the primary close approach together with the actual rigorous collision probabilities both in the primary and subsequent close approaches. Thus, we provide an independent comparison of collision probabilities published, e.g., at the NeoDys WWW-site. We also aim to offer an independent WWW collision probability service at the University of Helsinki in the near future. We are applying the methods to, e.g., the lost asteroid 1998 OX4 for which we find non-vanishing probabilities for a collision with the Earth for a number of years after 2012. We will be looking into the possibility of speeding up both the approximate and rigorous collision probability computation as well as the orbital-ranging technique---also in view of the forthcoming WWW service to be up-to-date.