Saturday, September 25, 2010

Ball shrinkage

You should really have that checked out.  
No, not you.  What's wrong with you?  Get your mind out of the gutter.

I'm talking about the moon.  You know, that big glowing ball in the sky, the one with all the craters, making its surface look somewhat like a face.  Yeah, that thing.

Well according to NASA:
Newly discovered cliffs in the lunar crust indicate the moon shrank globally in the geologically recent past and might still be shrinking today
The moon formed in a chaotic environment of intense bombardment by asteroids and meteors. These collisions, along with the decay of radioactive elements, made the moon hot. The moon cooled off as it aged, and scientists have long thought the moon shrank over time as it cooled, especially in its early history.
 The moon is covered in fault structures known as "lobate scarps."  It is estimated that the lobate scarps formed less than a billion years ago, which is only about a quarter of the lifespan of the moon.
Based on the size of the scarps, we estimate the distance between the moon's center and its surface shrank by about 300 feet," said Watters, lead author of a paper on this research appearing in Science August 20.

The scarps are relatively small; the largest is about 300 feet high and extends for several miles or so, but typical lengths are shorter and heights are more in the tens of yards (meters) range. The team believes they are among the freshest features on the moon, in part because they cut across small craters. Since the moon is constantly bombarded by meteors, features like small craters (those less than about 1,200 feet across) are likely to be young because they are quickly destroyed by other impacts and don’t last long.
Lobate scarps are found on other worlds in our solar system, including Mercury, where they are much larger. "Lobate scarps on Mercury can be over a mile high and run for hundreds of miles," said Watters. Massive scarps like these lead scientists to believe that Mercury was completely molten as it formed. If so, Mercury would be expected to shrink more as it cooled, and thus form larger scarps, than a world that may have been only partially molten with a relatively small core. Our moon has more than a third of the volume of Mercury, but since the moon's scarps are typically much smaller, the team believes the moon shrank less.

 Thrust faults are formed when the lunar crust is pushed together, breaking the near-surface materials. The result is a steep slope on the surface called a scarp as shown in this diagram. Credit: Arizona State University

I wonder how the much the moon could shrink and what effects that would have on the Earth's tides and life on Earth.  It is interesting to think about.  

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