MESSENGER spacecraft at Mercury, computer artwork. MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) is a robotic NASA spacecraft orbiting the planet Mercury, the first spacecraft ever to do so. It was launched aboard a Delta II rocket in August 2004 with the aim of studying Mercury's chemical composition, geology, and magnetic field. It is equipped with an array of scientific instruments and has solar panels (black) for power generation. The 3.6-metre-long boom carries a magnetometer (lower right) that will be used to map Mercury's magnetic field and search for magnetised rocks in the planet's crust. A sunshade (top left) protects the spacecraft from the intense heat of the Sun.