Asteroid Orbit Determination using Gaia FPR: Statistical Analysis

The Gaia mission has provided astrometric observations of unprecedented accuracy for more than7 156000 asteroids. The reported astrometric uncertainties are of the order of milliarcseconds, about8 two orders of magnitude smaller than that of traditional ground-based observations. The accuracy of9 Gaia data requires a high fidelity orbit determination process, especially in the observation modeling.10 We present a statistical analysis of Gaia Focused Product Release to test the accuracy of the reported11 positions and associated uncertainties. We find that center-of-light offsets due to phase variations need12 to be modeled to properly fit the observational data. Prediction tests show that the uncertainty in the13 fitted orbits can be optimistic unless the observational uncertainty is inflated to account for errors in14 finding the center-of-mass of the body. Moreover, errors in the masses of small-body perturbers can15 cause differences in the orbital solution that exceed formal uncertainties of the best constrained orbits.16 As an example, we provide an update of the impact hazard analysis of 1950 DA, one of the asteroidsobserved by Gaia, and find that the impact probability in the year 2880 increases to 2.7 × 10−417 .