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On this day in space! Sept. 10, 2011: NASA launches GRAIL probes to the moon to map lumpy lunar gravity
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On Sept. 10, 2011, NASA launched twin spacecraft to the moon as part of the Gravity Recovery and Interior Laboratory (GRAIL) mission. The probes were designed to map the moon's gravitational field in unprecedented detail. The goal was to reveal the "lumpy" gravity caused by the moon's uneven mass distribution.
The GRAIL mission consisted of two identical spacecraft flying in tandem in lunar orbit. By precisely measuring the distance between them, scientists could detect tiny variations in gravity. These variations reflected the moon's internal structure, including hidden features such as buried craters and volcanic structures.
The launch occurred from Cape Canaveral Air Force Station in Florida. The spacecraft took about three months to reach the moon. Once in orbit, the pair began a science phase that lasted roughly 90 days.
The mission produced the highest-resolution gravity map of any celestial body at the time. It revealed that the moon's gravity is far from uniform, with dense regions known as mass concentrations. These findings helped scientists understand how the moon's crust and mantle evolved over billions of years.
The data also provided clues about the moon's interior, including the size of its core. This information is critical for understanding the early history of the Earth-moon system. It also has practical implications for future lunar landings, as spacecraft must account for gravity anomalies.
NASA officials and scientists hailed the mission as a major success. The twin probes completed their mission in December 2012. They were deliberately crashed into the lunar surface, ending their journey.
The GRAIL legacy continues today. Its gravity maps remain a reference for planetary scientists and mission planners. As NASA prepares to return astronauts to the moon under the Artemis program, GRAIL data will help ensure safe and precise landings.
