The term 'Martian Explorer' refers to a robotic vehicle sent to explore the surface of Mars. The most well-known example of this is the Mars Exploration ROVER, commonly referred to as 'ROVER', which was a robotic vehicle designed to explore the Martian surface and search for evidence of past or present life. The ROVER was launched in 2003 and has since been used to explore the planet's surface, providing valuable data and insights into the geology and climate of Mars.