 In 1997, Soter took a position at the American Museum of Natural History's Hayden Planetarium, and eventually progressed to the position of research associate.He also made significant contributions to research related to the ancient Greek city Helike.In 2007, after the IAU voted on a definition of planet, Soter published an article in "Scientific American" in which he outlined a mathematical formulation, the "planetary discriminant," to describe how the IAU's requirement that a planet must have "cleared its neighborhood" of other objects might be applied in practice.