An artist's depiction of the twin spacecraft that comprise NASA's Gravity Recovery And Interior Laboratory (GRAIL) mission. During the GRAIL mission's science phase, spacecraft (Ebb and Flow) transmit radio signals precisely defining the distance between them as they orbit the moon in formation. As the two fly over areas of greater and lesser gravity caused by both visible features, such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft will change slightly. Mission scientists use this information to create a high-resolution map of the moon's gravitational field. The data will allow scientists to understand what goes on below the lunar surface. This information will increase knowledge of how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds we see today.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate in Washington. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Maria Zuber. GRAIL is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.

For more information about GRAIL, please visit http://grail.nasa.gov.