MESSENGER is a scientific investigation of the planet Mercury. Understanding Mercury, and the forces that have shaped it, is fundamental to understanding the terrestrial planets and their evolution.

MESSENGER is a MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission to orbit Mercury following three flybys of that planet. The orbital phase will use the flyby data as an initial guide to perform a focused scientific investigation of this enigmatic world.

MESSENGER will investigate key scientific questions regarding Mercury’s characteristics and environment during these two complementary mission phases. Data are provided by an optimized set of seven miniaturized space instruments and the spacecraft telecommunications system.

MESSENGER was launched successfully on 3 August 2004. On 2 August 2005, MESSENGER's flyby of the Earth-Moon system took place. Two flybys of Venus occurred on 24 October 2006 and 5 June 2007. The first flyby of Mercury will be on 14 January 2008, and MESSENGER will go into orbit about Mercury in March 2011.

MESSENGER is led by Dr. Sean C. Solomon, Director of the Department of Terrestrial Magnetism.