Messenger spacecraft at Mercury, computer artwork. The Messenger spacecraft is due to be launched during a 13-day window from 2 August 2004. It will enter orbit around Mercury in March 2011, after first performing three fly-bys of the planet to map its surface and study its composition. The spacecraft 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 magnetized rocks in the planet's crust. A sunshade (white) protects the spacecraft from the intense heat of the Sun.