Marvellous Moon

Since ancient times, the moon has enthralled and fascinated mankind. The second brightest object in the sky after the sun and located at an average distance of about 380 thousand km from Earth, the Moon is Earth’s only natural satellite.

The moon has many myths and legends attached to it; in fact almost every civilisation had some very interesting thesis about the moon and its origin. For instance it was believed in ancient India that the moon was a storehouse of elixir, the drink of immortality and that it waned because the gods were emptying it and waxed because it was being filled up again.

The Maoris have an even more interesting theory. According to the myth, one night Rona, daughter of Tangaroa (the sea-god) while walking back home with a bucket of water, hurt her foot on a rock and cursed the moon for not having provided enough light. The moon overheard the remark and grabbed Rona along with her water-basket. And each time she upset her bucket, it rained.

The Chinese believed that there were twelve moons, since there were twelve months. At the start of each month, their mother would wash them in a lake in the westernmost part of the world and then send a child on a journey to reach the other end of the world. It was believed that the moon was made of water and a hare or a toad lived in there.

Many more theories have abounded, including many with supposed scientific backgrounds, including one that said that the moon & the stars were vents that allowed the hot gases surrounding the earth to escape. But in the modern era, three major theories held forth for a long time.

The first one was that the Earth and the moon were formed at the same time from the Sun. But the theory failed to take into account the fact that the basic composition of the Earth and the moon are different. For instance Earth has an iron core, while the moon completely lacks iron.

The second theory, proposed in 1878 by George Howard Darwin (son of Charles Darwin, the famous evolutionist), was that during the initial stages of its evolution, the Earth revolved so fast that a chunk split off because of the sun’s gravity and became the moon. The theory became more interesting when geologist Osmond Fisher further proposed that the Pacific Ocean’s basin was created when the chunk ripped off the Earth’s surface. The theory was called the ‘fission’ theory and remained popular till almost the mid 20th century. Although it explained the lack of a large core and the fact that both have similar oxygen-isotopes, analysis has shown that the Earth would have had to rotate at mind-boggling speeds in order to get the moon into orbit. Also the Pacific Ocean basin was formed only about 70 million years ago and so the theory does not have much substance.

A third theory stated that the moon formed elsewhere and was captured by the Earth while it passed by. Although this might explain the difference in the compositions, it does not explain the similar isotopes of two bodies formed in different parts of the universe. Also unexplained is the fact that the moon has almost no core. Besides according to most model analysis, it is unlikely that a speeding object would settle so smoothly into earth’s orbit, it would more a hit-or-miss proposition. And even if it somehow did, the moon would have been elongated.

But the theory that has gained most credence after rock samples were made available by the Apollo project is the impact theory, according to which a giant object (perhaps as large as Mars) collided with Earth and the moon was formed from the matter that was blown-out of both Earth and the object due to the impact. According to estimates this occurred about 4.5 million years ago, when the Earth was being formed.
The reason why the Earth has an iron core and the moon does not is because the iron had already entered the interiors of the Earth by the time the impact occurred and so the matter that was ejected was a rocky layer from the surface of the two. This also explains the similarity in the oxygen isotopes.

But some researchers and scientists feel that this theory too is not conclusive enough and more studies need to be done. They claim that the only reason for the wide acceptance of the theory is because of the lack of a better alternative theory.

One thing that has been confirmed by the tests is that the both the Earth & the moon were formed nearly at the same time, almost 4.5 billion years ago. A fascinating aspect is that rock samples taken from the surface of the moon at different locations differ greatly from each other; this is because the moon lacks an atmosphere and its surface was thus bombarded, especially in its early days, by a very large number of meteorites. These diverse objects resulted in varied rock compositions in different parts of the moon.

Also rocks that are more than 4 billion years old still exist as they are because the soil there does not weather like it does on Earth. Thus we can study the solar system, as it was 4 billion years ago, by studying the rock samples obtained from the moon.

Truly the moon never ceases to amaze.