In a major find, NASA's Lunar Reconnaissance Orbiter (LRO) has provided researchers strong evidence that the Moon's volcanic activity slowed gradually instead of stopping abruptly a billion years ago.Scores of distinctive rock deposits observed by the orbiter are estimated to be less than 100 million years old.This time period corresponds to Earth's Cretaceous period - the heyday of dinosaurs.Some areas may be less than 50 million years old."This finding is the kind of science that is literally going to make geologists rewrite the textbooks about the moon," said John Keller, LRO project scientist at NASA's Goddard Space Flight Centre in Greenbelt, Maryland.The deposits are scattered across the moon's dark volcanic plains and are characterised by a mixture of smooth, rounded, shallow mounds next to patches of rough, blocky terrain.Because of this combination of textures, the researchers refer to these unusual areas as irregular mare patches (IMPs).
The features are too small to be seen from Earth, averaging less than a third of a mile across in their largest dimension.One of the largest, a well-studied area called Ina, was imaged from lunar orbit by Apollo 15 astronauts."The large number of these features and their wide distribution strongly suggest that late-stage volcanic activity was not an anomaly but an important part of the moon's geologic history," Keller explained.Based on a technique that links such crater measurements to the ages of Apollo samples, three of the IMPS are thought to be less than 100 million years old, and perhaps less than 50 million years old in the case of Ina."The existence and age of IMPs tell us that the lunar mantle had to remain hot enough to provide magma for the small-volume eruptions that created these unusual young features," said lead study author Sarah Braden from the Arizona State University in the US."These young volcanic features are prime targets for future exploration both robotic and human," added Mark Robinson, LRO principal investigator at the Arizona State University.The study appeared in the journal Nature Geoscience.