Moon shrinkage (Hazards & Disasters)
Moon shrinkage is a recently confirmed phenomenon based upon photographs from NASA’s Lunar Reconnaissance Orbiter spacecraft. The diminution of size in the Earth’s moon is thought to be the result of cooling and contraction over recent geologic time. [1] Chief evidence for these recent conclusions are the appearance of relatively new cliff formations, and the recent interpretation that these uplifted cliffs are likely the result of contraction of the moon’s size, with resulting crustal change.
Even though the magitude of the shrinkage is judged to be relatively small at an estimated radius decrease of about 100 meters, the conclusions are significant in their revelation of a new chapter in the moon's natural history, and more broadly of insights on geological processes common to many celestial bodies.
History of the moon’s formation
The origin of the Earth's moon has been dated to a time of approximately 4.5 billion years before present. While there are several hypotheses of the actual genesis, the prevailing thought is that the moon resulted from a giant impact of a large planet-sized body with the proto-Earth. [2] This collision would have spewed considerable matter into the region coincident with the present lunar orbit, which material may have accreted to form our moon.The impact theory is the only explanation consistent with the angular momentumof the Earth-moon system, and also consistent with the almost identical isotopic ratios of oxygen and tungsten on the Earth and moon.
Discovery of widespread lunar scarps
In early U.S. Apollo missions lobate scarps on the moon were discovered through interpretation of images from the high-resolution panoramic camera installed on Apollo 15, 16, and 17. Since those missions orbited over topographic features near the lunar equator, and thus mapped only about one fifth of the lunar surface, the scarps first observed were suspected to be equatorial anomalies. The sequence of events that confirmed the moon's shrinkage included a discovery of more widespread detected scarps in the Lunar Reconnaissance Orbiter (LRO) images later than the Apollo 17 era, seven of which are at high lunar latitudes (exceeding 60 degrees). This discovery confirms that the scarps are a widespread lunar phenomenon, making a shrinking moon the most likely explanation for their broad distribution.
Faulting phenomena throughout our Solar System
The lunar scarps are interpreted as manifestations of thrust faults, where a section of the lunar crust cracks and juts out. This upthrust is a consequence of cooling contraction of the moon, forcing the mantle and lunar crust were forced to respond with thrust faulting. A number of the resulting lunar scarps manifest a semi-circular geometry or lobe-shaped appearance, giving rise to the term lobate scarp. Other celestial bodies within our Solar System exhibit lobate scarps including occurrences on the planet Mercury. In the case of the Earth's surface, upthrust phenomena are widespread, generally associated with tectonic plate movement; many of these Earth plates undergo repeated and strong collisions,often creating mountains of great stature such as the Sierra Nevada Range; furthermore, examples abound of other extraterrestrial faulting such as the solar system's largest gorge on the planet of Mars. In this case the gorge is thought to have developed from divergent faulting in an environment of abundant vulcanism over long time periods. [3]
Research implications
It is difficult for some to appreciate the value of space exploration. Discovery of the moon shrinkage through high resolution imagery from the NASA space program has amplified man's understanding of geologic processes common to the Earth itself as well as other celestial bodies. Moreover, the relationships revealed add insight to the Earth formation, particularly in enhancing our understanding of the giant impact collision that may have occurred to the Earth approximately 4.5 billion years before present. [4] Thus the exploration of space is not just about gaining knowledge of worlds beyond our own, but also to advance the understanding of fundamental scientific processes common to other celestial bodies. [5]
References
- Nancy Neal-Jones, Bill Steigerwald and Isabel T.Lara. 19 August, 2010. NASA's LRO Reveals 'Incredible Shrinking Moon' . U.S. National Aeronautics and Space Administration.
- Keveh Pahlevan and David J.Stevenson. 2007. Equilibration in the aftermath of the lunar-forming giant impact. Earth and Planetary Science Letters 262
- B.van Wyk de Vries and O.Merle. 1996. The effect of volcanic constructs on rift fault patterns. Geological Soc. America. vol.24, pp 643-646
- University of Chicago, Dept. of Geology and Paleontology. 1946. The journal of geology: Volumes 54-55, University of Chicago Press, Journals Division
- Nasser Kehtarnavaz and Mark Noel Gamadia. 2006. Real-time image and video processing: from research to reality. 97 pages
