STOCKHOLM: A Canadian-American cosmologist and two Swiss scientists won this year's Nobel Prize in Physics on Tuesday for exploring the evolution of the universe and discovering a new kind of planet, with implications for that nagging question: Does life exist only on Earth?

Canadian-born James Peebles, 84, an emeritus professor at Princeton University, won for his theoretical discoveries in cosmology. Swiss star-gazers Michel Mayor, 77, and Didier Queloz, 53, both of the University of Geneva, were honored for finding an exoplanet — a planet outside our solar system — that orbits a sun-like star, the Nobel committee said.