Comparison of predictions of asteroids' close encounters with the Earth

Prediction of future close encounters of asteroids with the Earth belongs to sensitive information as it has a direct relation to the possible collision with the Earth. Observations of asteroids collected by the IAU Minor Planet Center (MPC) generally constitute the same source of astrometric and radar measurements for orbital computations and subsequent close approaches. We report here on a cross-identification of such events between different lists of predictions provided by the well-known world professional services: IAU MPC (Forthcoming Close Approaches To The Earth and the Running Tallies), the JPL Center for NEO Studies (CNEOS), the ESA SSA-NEO Coordination Centre (NEOCC) through its Space Situational Awareness Programme, and DynAstVO, the newly opened service of IMCCE at Paris Observatory PADC centre. We have selected two one-year windows, separated by 4 months, for generating the lists of predictions. Each event that has declared calculated geocentric distance of close approach less or equal 0.05 AU in one of the lists was cross-identified with the events in other sources. The comparisons were made with respect to the orbital propagations provided by the JPL HORIZONS on-line solar system data and ephemeris computation service. It appears that the actual predictions made by all these services can be significantly different, not only in epochs and distances of close encounters, but also in the entry list of asteroids. We have found that in both comparison window cases, all the services produce predictions that agree in less than 50% cases with respect to the general set formed as a union of all tables. The highest overlapping belongs to DynAstVO and NEOCC while the lowest to IAU/MPC. These differences in the prediction lists may be explained by peculiarities of the algorithms used, frequency of the orbital updates, different weighting schemes applied in the orbital determinations. We emphasise the necessity of additional astrometric/radar measurements of potentially hazardous asteroids, especially those which constitute the differences in such predictions