Uncertainty parameter

The uncertainty parameter (U) is an integer between 0 and 9 that quantifies the uncertainty in a perturbed orbital solution for a minor planet in a concise fashion, the Minor Planet Center (MPC) has introduced the U parameter.^[1] 0 indicates a very small uncertainty and 9 an extremely large uncertainty.^[1] In practice, U is rarely larger than 6.^[1] The U value should not be used as a predictor for the uncertainty in the future motion of near-Earth asteroids.^[1]

The uncertainty parameter is listed as "Uncertainty Parameter U" by the MPC and as "condition code" by the JPL Small-Body Database Browser.^[2]

This uncertainty is related to several parameters used in the orbit determination process including the number of observations (measurements), the time spanned by those observations (observation arc), the quality of the observations (e.g. radar vs. optical), and the geometry of the observations. Of these parameters, the time spanned by the observations generally has the greatest effect on the orbital uncertainty.^[3]

Objects such as 1995 SN55 with a condition code (Uncertainty Parameter U) of E are considered lost. 1994 WR12 has an Uncertainty Parameter of 8, and the next good chance to observe the asteroid may not be until November 2044 when the uncertainty will allow it to pass somewhere between 0.03–0.19 AU from Earth.^[4]

References