Jean-Pierre Lebreton

Jean-Pierre Lebreton could barely contain his exultation as a faint radio signal originating from an international probe on the surface of Titan, one of Saturn's moons, was picked up in Germany on Jan. 14 at 11:20 a.m. "Right on time," the 55-year-old French physicist and leader of the Cassini-Huygens mission remembers thinking. "It was a very emotional moment. It was hard not to cry."

Lebreton and his team of scientists at the European Space Agency (ESA) had spent much of the past 20 years preparing for that moment. Finally, their mission to land a probe on Titan was accomplished. The Cassini-Huygens probe, which took off from Cape Canaveral on Oct. 15, 1997, and spent all those years making its way to its destination, is a joint effort by ESA and the U.S.'s NASA. Lebreton has worked on it almost exclusively since he joined ESA after earning his doctorate in math and physics at the Université d'Orléans in France. "I came to ESA in 1978 as a post-doc for two years, and I'm still here," says Lebreton, who reads works by the late astronomer Carl Sagan for fun.