Pioneer 10 space probe To study other bodies in the Solar System, even the most powerful telescopes are limited in what images and other information they can provide. Manned space missions to other planets are dangerous and expensive. Most other worlds in our Solar System have environments that are too hostile or too distant for humans to explore (a trip to Neptune, for example, would take several years). In order to gather detailed information about other planets and moons, a number of space probes—unmanned, remote-controlled spacecraft—have been launched instead. Equipped with cameras and sensing equipment, they can transmit information back to Earth much more cheaply and safely.
US spacecraft Mariner 2 became the first space probe successfully to reach another planet when it flew by Venus in December 1962. From a distance of 34,800 kilometres (21,600 miles), its detectors captured data from Venus’s surface.
The Pioneer space probes were the first human-built objects to leave the Solar System.
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