Explorer typically refers to a spacecraft or satellite designed to explore outer space, including the planets and other celestial bodies within the solar system. These types of spacecraft are typically designed to carry out scientific missions, such as mapping the surface of a planet, studying the atmospheres of other worlds, searching for signs of past or present life, or collecting samples for analysis.
Some examples of Explorer missions include the Mariner and Viking missions to Mars the Galileo mission to Jupiter, and the Cassini mission to Saturn. Explorer spacecraft are typically launched by rockets and may be equipped with a variety of scientific instruments and other specialized equipment to carry out their missions.