Radar waves beamed into the moon’s surface by China’s Yutu rover have revealed nine distinct subsurface layers directly beneath the rover’s landing site in the Sea of Rains. The multitude of rocky layers suggests that the moon has a more storied geological history than once thought, researchers report in the March 13 Science.
Yutu rolled onto the lunar surface in December 2013 (SN Online: 12/16/13). As the rover meandered near the rim of a nearby crater, two radar-emitting antennas probed the shallow lunar interior with radio waves. Whenever a burst of descending radio waves hit a boundary between two underground layers, a fraction of the waves reflected back to the rover. These reflected waves allowed the rover to peek roughly 400 meters into the moon’s innards and discern geological features formed as long as 3.3 billion years ago.
The researchers attribute the outermost layers to accumulated dust and the debris left over from a nearby impact crater. Deeper layers include the remains of five lava outpourings that flooded the region during the moon’s hot youth, the youngest dating back about 2.5 billion years.
The number and composition of these rocky deposits were distinct from those spotted at previous landing sites, the researchers note, suggesting that the moon’s geological past has been more eventful and varied than previously believed.
The discovery will probably be one of the final legacies of Yutu. The rover broke down in January 2014 while hibernating through its first harsh lunar night (SN Online: 1/28/14), having survived only a month of its expected three-month life span.