In 1969 Peale published a generalization of
Cassini's laws that explain the rotation of the Moon and other bodies subject to tides. In 1976 Peale published a procedure to determine the size and state of the core of
Mercury. In 1979 Peale and collaborators predicted that
Jupiter's satellite
Io might show widespread
volcanism as a result of the action of
tides. This prediction was confirmed by data from the
Voyager 1 mission which showed that Io is the most volcanically active body in the
Solar System. He died on May 14, 2015, in Santa Barbara, California. ==Honors==