Dr. Paul Chodas (Calculating Orbits for Asteroids and Comets; Predicting Comet and Asteroid Impacts) is a Research Scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, where he has worked for over 15 years on the orbital dynamics of comets and asteroids. His work has contributed to the understanding of cometary non-gravitational forces, the use of radar data in asteroidal and cometary orbit determination, and the techniques for computing impact probabilities for comets and asteroids. Dr. Chodas was leader of the team that determined the trajectories of the fragments of Comet Shoemaker-Levy 9 and predicted the precise times and locations of their impact on Jupiter. These predictions were widely used by the scientific community and were key to the success of many observing programs. He is currently a member of the Radio Science Team for the Near-Earth Asteroid Rendezvous (NEAR) mission, which is en route to the asteroid Eros, arriving in 1999.

On Friday, Dr. Chodas will give a technical talk titled "Calculating Orbits for Asteroids and Comets". He will discuss astrometric observations, and how to make them as useful as possible for determining orbits. He will review preliminary orbit determination methods, used when only a few observations are available, and then discuss the high-precision orbit estimation methods needed to make long-term orbit predictions.

On Saturday, he will give a more general talk titled "Predicting Comet and Asteroid Impacts." In this presentation, he will talk about Near Earth Objects, discuss the frequency with which they impact the earth, and give a status report on search efforts. He will then relate the false alarm story of the possible collision of asteroid 1997 XF11 with the earth in 2028. Dr. Chodas will finish by discussing the warning time we might have if an asteroid or comet really was on a collision course with our planet.