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4 mins read 20 Sep 2021

Curtin University Models Nearly Invisible Ancient Lunar Impacts

New research from Curtin University is shining a light on ancient lunar impacts and why this part of the Moon’s geological history renders impacts nearly invisible. 

The Moon gets its distinctive cratered appearance from many impacts throughout its formation, but some of its earliest impacts may have not left such visible evidence. Credit: Kev Chapman/Flickr.

Researchers from Curtin University have created a model of early impacts on the Moon, bringing scientists another step closer to understanding the Moon’s formation. This new research, published in Nature Communications, explores why the Moon looks the way it does today, and why we may not be able to see the Moon’s oldest impact sites. 

“In this research, we set out to explain the discrepancy between theory and observations of the lunar crating record,”  said lead researcher Associate Professor Katarina Miljkovic, from Curtin’s School of Earth and Planetary Science and the Space Science and Technology Centre. 

“Translating this finding will help future research understand the impact that the early Earth could have experienced and how it would have affected our planet’s evolution.”

This paper is not the only recent study of the Moon to come out of Curtin University. Earlier this year, a research paper was released outlining a new analysis of samples brought back from the Moon by the Apollo 17 crew. This also comes at an exciting time for Curtin University with the recent launch of Western Australia’s first spacecraft, which was designed, coded, and built by the university. 

Modelling Ancient Lunar Impacts

A model of a lunar impact showing the difference between impacts early in the Moon’s formation with a thick melt layer (lunar magma ocean), and later in its formation with no melt layer. Credit: Miljkovic et al. 2021.

The researchers, led by Associate Professor Miljkovic, modelled different impacts on the surface of the Moon at varying points in its formation. They compared how impact basins formed with varying thicknesses of the Moon’s crust, simulating the early Moon as it cooled and transformed into the Moon we know today. Their results suggest that the Moon may have been subject to higher rates of impact in its early life than previously thought.  

The Moon’s formation began roughly 4.5 billion years ago. One of the most prominent theories of the Moon’s formation is that a giant impact occurred with the then-forming Earth, and the debris from that impact then formed the Moon. When the Moon first formed, however, it was not with a solid crust but with a global magma ocean.

“These large impact craters, often referred to as impact basins, formed during the lunar magma ocean solidification more than four billion years ago, should have produced different looking craters, in comparison to those formed later in geologic history,” Associate Professor Katarina Miljkovic said. 

A period of intense impacts by asteroids has permanently scarred the surface. However, earlier impacts from early in the Moon’s formation may have left hardly any trace in its geological record. Credit: NASA.

There have been estimates that there were potentially hundreds of crater-forming impacts soon after the Moon first began to form. However, based on the craters visible today, these early impacts are largely unaccounted for in the crater record. Associate Professor Katarina Miljkovic stated that this may be because the evidence of these early impacts may look significantly different from later craters. 

“A very young Moon had formed with a global magma ocean that cooled over millions of years, to form the Moon we see today. So when asteroids and other bodies hit a softer surface, it wouldn’t have left such severe imprints, meaning there would be little geologic or geophysical evidence that impact had occurred.” 

“The timeframe for the solidification of the lunar magma ocean varies significantly between different studies, but it could have been prolonged enough to experience some of the large impact bombardment history typical for the earliest periods of the solar system evolution.”

“As the moon ages and the surface cools, it becomes harder, and the bombardment imprints are a lot more noticeable by remote sensing,” she said.

So when you next look up at the Moon, remember that whilst craters can tell us a history of the Moon’s formation, they may not reveal the full story.  

 Read the full paper from Nature Communications