any of a series of eight unmanned Soviet lunar and interplanetary probes. Zond 1 (launched April 1964) and Zond 2 (November 1964) were aimed at Venus and Mars respectively, but failed to send back data on the planets. Zond 3 (July 1965) transmitted closeup photographs of 3,000,000 square miles (7,800,000 square kilometres) of the lunar surface, including the hidden side, before going into solar orbit. Zond 5 (September 1968) became the first spacecraft to orbit the Moon and return to a soft landing on the Earth. Zond 6 through 8 (November 1968–October 1970) also made circumlunar flights; they carried biological specimens and transmitted photography of the Moon's surface.