Yarkovsky effect
From 1978 to present, he has served as a Geophysicist in the Laboratory for Terrestrial Physics, National Aeronautics and Space Administration (NASA), Goddard Space Flight Center in Greenbelt, Maryland. He studies secular effects in the solar system such as tidal friction, the Yarkovsky effect, and the Yarkovsky–O'Keefe–Radzievskii–Paddack effect (YORP) effect. One of his many contributions while at NASA was conducting research to understand the dynamics of orbital decay of artificial Earth satellites. Current interests include asteroids and asteroid pairs.