When the Moon Cracked
Has the moon once split? In the Islamic faith, Muslims believe that Prophet Muhammad once split the moon into two halves when questioned about his ability to perform a miracle. While no research has ever backed up the claim that the moon was once split, what we do know is that the surface of the moon is full of cracks.
Like most things in outer space, the moon is ancient and formed roughly 4.3 billion years ago [1]. Since its formation, asteroids have bombarded the moon’s surface leading to engravements and crater [2]. It is strongly believed that many of the cracks visible on the lunar surface are due to these asteroid impacts. Interestingly, these cracks are not always shallow and can extend to the depth of about 12 miles (the average distance a person travels after walking for 3 hours).
Not much is known about the crack formations of the lunar surface, but research has thoroughly documented craters Craters, often referred to in the literature as the ‘megaregolith’, are formations on the upper surface of the moon that sustained the greatest impact from asteroid damage [3]. In simplest terms, they are the damaged areas of the moon that do not cause any known danger (at least so far) in comparison to cracks that may expand.
Distribution of Impact Craters on the Lunar Surface
Figure adapted with permission from Wiggins et al under the Creative Commons License 4.0 [3]
To better focus our understanding of the cracks of the lunar surface, scientists at Brown University used computer simulations to mock the conditions of how high-speed objects can break pieces of the moon’s crust into fragments about a meter wide resulting in deep cracks [3]. Impacts from objects about half a mile wide would lead to these 12 miles deep cracks that extend laterally up to 186 miles (that’s almost a 3-hour drive). These simulations suggested that the early beginnings of the moon had been exposed to fractures.
Researchers were curious to apply their simulations to mimic asteroid impacts that could have damaged Earth and compare that to impacts on the lunar surface. Their findings indicated that Earth would not be impacted to a great degree by space rock bombardments as opposed to the impact craters and cracks documented on the moon. Why so? It has to do with gravity!
To understand the relationship of gravity on fragmentation and later cracks of the lunar surface, researchers at Brown University utilized simulations of a 1-km impactor [3]. This value was chosen to be representative of the surface transition to an area containing at least one-meter sized lunar fragments positioned around the point of impact. They found that with an increase in the speed of gravitational waves (186,000 miles per second), there will be a decrease in fragmentation by impact. The finding translates to a lower likelihood of crack formation on the moon [3]. It can be suggested that areas of low gravity mean high impact and fragmentation. It is unknown why but can be attributed to the fact that the moon lacks an atmosphere which means low states of gravity. Comparing that to our dear home planet, the existence of our atmosphere makes gravitational pull a reality (certainly does not make Earth immune from asteroid impact as history has proven that they do visit) but we are less likely to experience asteroid bombardment.
Although not many investigative studies have solid conclusions on the impact of lunar crack formation, there is some evidence that cracks on the moon are expanding [3]. Research in this area is critical as we do not know if these lunar cracks do indeed expand and if so, how these expansions affect the overall integrity of the moon and eventually its relationship with Earth?
References
- Stevenson, D. J., & Halliday, A. N. (2014). The origin of the Moon. Preface. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 372(2024), 20140289. https://doi.org/10.1098/rsta.2014.0289
- Crawford, I. A., & Joy, K. H. (2014). Lunar exploration: opening a window into the history and evolution of the inner Solar System. Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, 372(2024), 20130315. https://doi.org/10.1098/rsta.2013.0315
- Wiggins, S. E., Johnson, B. C., Bowling, T. J., Melosh, H. J., & Silber, E. A. (2019). Impact fragmentation and the development of the deep lunar megaregolith. Journal of Geophysical Research: Planets, 124, 941– 957. https://doi.org/10.1029/2018JE005757
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