The Moon’s geologic history is far more complex than previously thought, according to preliminary results of tests by the Chinese Yutu, or “Jade Rabbit”, lunar rover using ground-penetrating radar. Scientists believe it experienced explosive pyroclastic volcanic lava flows.
“The pyroclastic events were an unexpected surprise,” says the study’s lead author Professor Long Xiao of the China University of Geosciences.
“Images of the landing site show a featureless terrain, however the radar data found many layers of structure below the surface with many episodes of volcanism including lava flows and explosive eruptions,” says Xiao.
The lava flows took place over immense timeframes. The deepest took place 3.3 billion years ago, while those nearer the surface are 2.5 billion years old.
China’s Chang’e-3 lander touched down in the northern Mare Imbrium basin on the lunar nearside on 14 December, 2013 – the first landing on the moon since 1976.
The lander carries three cameras and a small ultraviolet telescope, while Yutu carries geoscience instruments including a visible-infrared imaging spectrometer, an X-ray spectrometer, and ground-penetrating radar. Images from both show the lander near the rim of a 450-metre-wide crater, estimated to be between 27 and 80 million years old.
The landing site is a relatively flat surface covered in a layer of thin lunar soil known as regolith. This is strewn with basalt boulders up to four metres in size, and numerous small craters ranging from a few centimetres to tens of metres in diameter.
Just a few hours after landing, the Jade Rabbit rover travelled 114 metres in a zig zag pattern using two ground penetrating radar antennas to record constant measurements of the sub-surface geology down to depths of 400 metres.
The radar detected nine separate sub-surface layers including regolith, ejecta from the nearby crater, and numerous layers of lava with different compositions.
One layer, called layer G, consisted of very fine material rather than lava.
“This is similar to pyroclastic explosive rock [found on Earth] which has important scientific implications because explosive eruptions mean volatiles,” says Xiao.
Bill Condie is a science journalist based in Adelaide, Australia.