Lunar Images Alter Understanding of Impact History
New images from the Lunar Reconnaissance Orbiter could change our view of the history of impacts on the Moon. In 1972 the Apollo 17 mission took samples from the region of the Serenitatis impact basin. Scientists believed that the impact that created the Serenitatis basin was responsible for the formation of the Apollo 17 impact melt samples, which were dated to 3.8 billion years ago. A geological feature known as the Sculptured Hills, which surround the Apollo 17 landing site, was also believed to have been created from ejecta from the Serenitatis impact.
The new images show that the Sculptured Hills lie on top of the rims of several craters known to be created after the Serenitatis basin. In addition, the Sculptured Hills have similar morphology to features created by ejecta from the impact that formed the nearby Imbrium crater. Thus, Spudis et al. argue that the Sculptured Hills, and possibly also the Apollo 17 samples, may have been formed from the Imbrium impact, not the Serenitatis. The Serenitatis basin could be older than scientists had thought, the authors suggest.
If the Apollo 17 samples are indeed formed from the Imbrium impact, not the Serenitatis, scientists will have to revise their understanding of the impact melting process of large body impacts because it was based in part on the assumption that those samples were formed from the Serenitatis impact. Alternatively, if the Apollo 17 samples are indeed from the Serenitatis basin-forming impact and the Serenitatis basin is 3.8 billion years old, then many of the impact basins and large craters on the Moon all must have been created within a short 30-million-year time window around 3.8 billion years ago — definitely a global impact “cataclysm” — the authors suggest. Either of these interpretations changes scientists’ view of the impact process and the history of the Moon.
Source: Journal of Geophysical Research-Planets, doi:10.1029/2011JE003903, 2011 http://dx.doi.org/10.1029/2011JE003903
Title: “The Sculptured Hills of the Taurus Highlands: Implications for the relative age of Serenitatis, basin chronologies and the cratering history of the Moon”
Authors: Paul D. Spudis: Lunar and Planetary Institute, Houston, Texas, USA; Don E. Wilhelms: U. S. Geological Survey (retired), San Francisco, California, USA; Mark S. Robinson: ASU School of Earth and Space Exploration, Tempe, Arizona, USA.
