The first of NASA’s two spacecraft to study the Moon in unprecedented detail has entered lunar orbit.
On 31 December 2011, NASA's Gravity Recovery And Interior Laboratory (GRAIL)-A spacecraft was successfully placed into orbit around the Moon. GRAIl-A’s lunar orbit is highly elongated, measuring 90 km by 8,363 km, and lasts approximately 11.5 hours to complete.
The next stage of the GRAIL mission occurs on 1 January 2012, when GRAIL-A's twin, the GRAIL-B spacecraft, performs its own maneuver, to achieve lunar orbit.
The GRAIL spacecrafts will begin collecting data in March 2012. They will transmit radio signals precisely measuring the distance between them, as they orbit the Moon in formation. As they fly over areas of greater and lesser gravity caused by both visible features, such as mountains and craters, and masses hidden below the lunar surface, the distance between the two spacecrafts will vary slightly.
Scientists will translate this information into a precise map of the lunar gravitational field. The data will also allow scientists to study the internal structure of the Moon. This information will lead to a better understanding of the evolution of Earth and its neighboring rocky planets.
References
NASA
www.nasa.gov/
Wikipedia
Further Reading
http://www.nasa.gov/grail