What are space probes?

Space probes are unmanned spacecraft, which are sent into space to investigate celestial phenomena. Unlike a satellite, a space probe leaves the orbit of the Earth and flies to a remote destination, like Mars or Venus. Thus, for instance, the Soviet Union sent space probes, named Venera, to Venus in the 70's and the 80s in order to study the unique features of the hot planet. Some of them reached the surface of Venus and sent back radio signals to the Earth for about an hour. Then they failed because the surrounding pressure and temperature were too high for them to withstand. Other probes, however, have remained functional for longer periods of time. Thus, the probes Voyager 1 and Voyager 2 sent into space in 1977 are still sending back images of the depths of space. Both have now travelled beyond the solar system.