No tricks in the title. This blog is simply about interesting information related to our planet’s original satellite. There’s not really an over-arching story, and not much questioning of power structures occurs. Still, at the very least it’s interesting trivia, and, if you’re like me, great facts to spout just for the sake of it when anything vaguely related to the moon comes up in a conversation.
Let’s start out with formation. For years, there were many competing theory about how the moon came into existence. There was capture theory, which stated that the moon was a large drifting asteroid that was captured by earth’s gravitational field. There was also fission theory, where the earth was supposedly rotating so fast in its early years of existence that a huge clump of material broke off and formed the moon. However, the currently accepted theory of lunar formation is the giant impact theory.
The giant impact theory suggests that the moon was not originally part of earth, but a large mass of rock that was formed in the relatively near vicinity to our planet. Roughly 4.5 billion years ago, this Mars-sized object that scientists call Theia collided with proto-earth. Upon impact, a huge cloud of debris was thrown up into earth’s orbit. Over time, this material coalesced to form a spherical orbiting body.
There are several pieces of evidence for the giant impact theory. First, the moon is made of very similar material to the earth, which is a strike against capture theory. Isotope ratios in lunar and terrestrial rock also suggest a similar origin. Second, astronomers have observed debris discs such as the one made by the Theia impact in other solar systems, and the behavior of these discs is what scientists would expect based on the giant impact theory. Furthermore, geologic evidence suggests that the moon once had a molten surface. Such a terrain is likely the product of a giant collision. Finally, the moon’s small iron core and low density relative to earth bolster the giant impact theory.
The collision between Theia and proto-earth was a significant event in our planet’s geologic history. In fact, scientists now believe that the formation of the moon was crucial to the formation of life on earth. Here is the reasoning behind this proposition.
In the aftermath of the collision, Earth had a vey rapid rotation of 12 hours, and the presence of the moon resulted in rapid tidal oscillations. The quick advancement and recession of the tides created high salinity low-tide environments that were the perfect laboratories for proto-nucleic acids. In these isolated pockets on proto-earth, conditions were favorable for the formation of life’s basic building blocks. Without the force of the moon to create these tidal pools, it is questionable whether life would have been able to begin at all.
Creating nice little tidal pools was not the only thing the moon did to help out life on this planet. Our friendly neighborhood satellite also stabilized the earth’s orbit and reduced fluctuations in the planet’s axial tilt, which diminishes the extremes of the seasons. Greater stability of environmental conditions is, of course, conducive to many forms of life.
A note about tides: I’ve been asked several times if it’s a myth that the moon influences the tides. Unlike that classic laughable myth about the moon being made of cheese, this one is absolutely a real effect. A large celestial body such as the moon really does have the effect of pulling our oceans ever so slightly closer to itself. The sun also has a lesser effect on our tides. When the earth, moon, and sun are lined up in a 180° angle so that the earth is between the other two bodies, tides are unusually high. Such tides are known as spring tides, not because they occur predominantly in spring, but because the water “springs” up. On the other hand, when the earth, moon, and sun form a 90° angle, tides are unusually weak, and such oceanic fluctuations are known by the magnificent term of “neap tides.” To me neap is such a funny little word. It sounds exactly like what it is describing. Something that is neap just doesn’t sound like it would pack a powerful punch.
Tidal friction does have an interesting side effect: it is slowly transferring gravitational potential energy from the earth to the moon. As a result, the moon is getting farther away from us each year. For every time our planet revolves around the sun, our satellite gets 3.8 cm farther away from us! In addition, the transfer of GPE is also slowing down earth’s orbit. A modern day is 1.7 milliseconds longer than one 100 years ago. Think of all that extra time each day we get that our great-grandparents didn’t have!
Astronomers know a fair amount about the lunar geology. There’s even a fancy word for it: selenology. Apparently it’s not so rare that spell check marks it as a misspelled word. As stated earlier, the moon is made of roughly the same material as the planet it orbits. Similar to Earth, silica is dominant in the crust. However, the moon has no atmosphere, and thus no weather or erosion. From a meteorological perspective, the moon is about as boring as you can get. However, there are still many fascinating aspects of its geology.
The moon used to have a global magma ocean, the result of the heat generated when it coalesced after its parents crashed into Earth. Scientists believe that this ocean was as much as 500 km deep! For comparison, the deepest part of Earth’s ocean, the Challenger Deep, is a “mere” 11 km in depth. Over time, the lunar magma ocean crystallized. At one time there was significant volcanic activity on the moon’s surface. Today this activity manifests itself in the form of maria, vast plains of basalt that was the product of ancient volcanoes.
Similar to its blue neighbor, the moon has a crust, mantle, and core. However, the moon’s crust is much thicker than earth’s, and its core is much cooler. Whilst our planet’s core is 6,000°C, the moon’s core temperature is 1,500°C. At that lower temperature you can just barely melt iron.
Although the moon has no more active volcanoes, it does have active fault lines. As our satellite cools, it shrinks. This shrinking is a slow process – in the past 300 million years, the moon’s diameter has contracted by only 50 meters. However, the phenomenon is still powerful enough to generate “moonquakes.” They’re like earthquakes, except, you know, on the moon. The most powerful moonquakes register 5 on the Richter scale.
One final note: 16 July 1969 was a long time ago. What have we been doing all these years? 50 years later, shouldn’t we have moon bases for now? After making up as much as 4% of the US’ entire government budget, the Apollo missions were shelved in 1972. Recent news, however, suggests that there may be some exciting moon exploration news coming up in the relatively new future. The US Gateway project is a proposal that will build a smaller space station to orbit the moon. Congress has already approved $450 million for preliminary studies of the project. As far as unmanned lunar exploration goes, this year China, Israel, and India all launched probes to the moon. NASA currently has so-called Artemis missions in the works, which will send a man and a woman to the moon by 2024. And of course, private companies such as SpaceX and Astrobiotic are also getting in on the moon exploration business.
When I started writing this blog, I figured that I had at most 300 words to say about the moon. This piece is a testament of my ability to ramble about nearly any topic. Now, however, it’s time to conclude all of this lunacy, and with any luck come up with an equally interesting topic for next week.
Green Humanist 