GRAIL

Gravity Recovery and Interior Laboratory

Mission Profile

GRAIL (Gravity Recovery and Interior Laboratory) was a twin-spacecraft NASA Discovery mission, launched on 10 September 2011 aboard a Delta II 7920H-10 to map the Moon's gravitational field with unprecedented precision by measuring the varying distance between two identical spacecraft flying in tandem. Named Ebb and Flow, the probes measured tiny variations in the distance between them as they flew over regions of higher and lower density, revealing the subsurface structure of the lunar crust and mantle in extraordinary detail. GRAIL discovered that the Moon's crust is riddled with ancient fractures from massive meteorite impacts, significantly thinner on the near side than previously thought, and contains relics of ancient magmatic systems. Both spacecraft were deliberately crashed into a mountain near the lunar north pole in December 2012 at the end of their fuel supply.