Jupiter has been studied from ground-based observatories for centuries, and more recently with the Hubble Space Telescope, but our detailed knowledge of the planet comes primarily from unmanned space probes that sent photographs and scientific data back to Earth. Between 1972 and 1977 the planet was visited by the pioneer 10 and 11, Voyager 1 and 2, and Ulysses spacecraft. The spacecraft Galileo orbited Jupiter for eight, from 1995 to 2003, and sent an instrumental probe into the atmosphere. It penetrated to a depth of 140 km before being crushed by the atmospheric pressure.