The birth of the modern widely accepted theory of planetary formation—the solar nebular disk model (SNDM)—can be traced to the Soviet astronomer Victor Safronov. His 1969 book Evolution of the protoplanetary cloud and formation of the Earth and the planets, which was translated to English in 1972, had a long-lasting effect on the way scientists think about the formation of the planets. In this book almost all major problems of the planetary formation process were formulated and some of them solved. Safronov's ideas were further developed in the works of George Wetherill, who discovered runaway accretion. While originally applied only to the Solar System, the SNDM was subsequently thought by theorists to be at work throughout the Universe; as of 24 July 2024 astronomers have discovered 7,026 extrasolar planets in our galaxy.