Description Among near-Earth objects (NEOs), there is a group that can approach Earth with close distance and has the probability of impacting Earth and cause damage, which is also known as the potentially hazardous object (PHO). For instance, very recently the asteroids 2019 OK approached Earth only at the closest distance of 71354 km.  For these PHOs, as their orbits cannot be determined very accurately from the ground, there exists uncertainty of their position and velocity, which makes the prediction of their closest encouter with Earth uncertain, in terms of the closest distance and the time epoch. Therefore, the impact might happen with some probability. This project aims to evaluate this impact probability given the uncertainty of the PHO's position in space and to provide references for planetary defense strategies. Programming (MATLAB or Python, etc) is required.   Key Objectives

1. be familiar with the classification and group or distribution of the PHOs, understand the origination of the uncertainties/errors of their position and velocity
2. evaluate this impact probability by propagating the trajectory of the small body with its initial uncertainties
3. recommends for planetary defense strategies