A critical-list minor planet (critical list numbered object or critical object) is a numbered minor planet for which existing measurements of the orbit and position are especially in need of improvement.
[2] The list typically contains asteroids that have been observed at a small number of apparitions, especially on opposition, or that have not been adequately observed for more than 10 years, while other observatories create their own, customized lists.
[5] Lowell Observatory publishes their own critical list, distinctly different from the MPC, instead focusing on objects with high ephemeris uncertainty.
Specifically, objects with computed ephemeris uncertainty greater than 2 arcseconds over the next 10 years, and objects whose orbits degrade significantly when temporally isolated observations are ignored, are included in the list.
[3] As of December 2024[update], the MPC includes 650 objects in their observable critical list.