George Wetherill, 80, a retired Carnegie Institution scientist and recipient of the nation’s highest scientific award for his seminal work on the formation of planets and the solar system, died July 19 of heart disease at his home in the District of Columbia.

Inspired by the research of Russian scientist Victor Safronov, who showed that swarms of small bodies called planetesimals could grow into large bodies such as the terrestrial planets (Mercury, Venus, Mars, Earth), Wetherill was one of the first scientists to develop theoretical models for how planetesimals aggregate and grow. His models enabled him to make predictions about the size and orbits of the inner planets as well as how collisions between bodies in the asteroid belt could result in asteroid impacts on Earth, including the one that led to the extinction of the dinosaurs.

Wetherill’s work also revealed the importance of Jupiter as protector of Earth and other planets. He showed that Jupiter’s enormous gravitational field provides a shield from orbiting asteroids and comets, deflecting most of them into the solar system. He estimated that 10,000 times as many objects as big as the asteroid that annihilated the dinosaurs would have hit Earth if Jupiter wasn’t standing guard.

George West Wetherill was born August 12, 1925, in Philadelphia and served in the Navy during World War II, teaching radar at the Naval Research Laboratory in Washington. He received four degrees in physics from the University of Chicago, including a master’s degree and a PhD (1953), and joined the Carnegie Institution’s Department of Terrestrial Magnetism as a member of the scientific staff that year.

He began working with an interdepartmental group of Carnegie scientists developing geochemical methods for dating rocks that involved natural radioactive decay. The group’s work forms the basis for all high-precision rock dating, going back to the early history of Earth. Later, his interests in age-dating techniques expanded to include extraterrestrial materials, including meteorites and rock samples from the moon.

From 1960 to 1975, he was professor of geophysics and geology and chairman of the department of planetary and space sciences at the University of California at Los Angeles, where he began his theoretical explorations into the origins of meteorites and the terrestrial planets. He returned to Carnegie in 1975 as director of the Terrestrial Magnetism Department, a position he held until his retirement in 1991.

He continued his research as director emeritus and was particularly interested in the discovery of planets orbiting other stars. He theorized that the organization of the solar system might not be unique. Complex threedimensional computer models he devised simulated how planets might have formed, showing that in almost every case a solar system like ours emerges.

Dr. Wetherill was elected to the American Academy of Arts and Sciences in 1971 and the National Academy of Sciences in 1974. In 1997, he received the National Medal of Science, the nation’s highest scientific award.