Mystery shrouding moon continues

While the presence and proximity of the moon in the sky mesmerises us, it has been baffling astronomers for centuries. Though we take its appearance for granted, the moon is still a mystery to us and we are still intrigued by its origins.

It was Galileo who first noted the moon had similar surface features like that of the earth. Many theories have been hypothesised regarding the birth of the moon.

Earlier, astronomers were of the opinion that the moon may have been formed elsewhere in the universe or around another heavenly body and may have got pulled into the earth’s gravitational field.

Another theory said that the moon was co-formed along with earth in the solar system. One more theory suggested multiple fragments of a young earth fusing together to form the moon. But many aspects remained unclear from these suppositions.

George Darwin in the 19th century predicted that the moon may have been formed by a huge fission occurring in the earth, billions of years ago when the solar system was being formed. The hot mass and high spinning of earth spewing molten matter must have ejected a huge chunk. But many modern scientists discounted this theory as it could not satisfactorily explain various other aspects.

But the longest standing, widely accepted theory, till recently, was the Giant Impact Hypothesis of the 1970s. By this, it was suggested that a proto-planet ‘impactor’ — a huge mass of the size of Mars — must have collided with earth a few billion years ago. This impact led to a huge cloud of space debris which eventually cooled and fused to form the moon.

This impactor called Theia — after the Greek moon goddess Selene’s mother — was theorised to be nearly half the size of the present earth. This theory was tweaked and modified over the years by scientists experimenting on moon samples. And when the Apollo mission brought back samples of moon rocks, they contained the same oxygen isotope ratios as that of earth, suggesting that the moon and earth were geochemically related.

Though this explains the geochemical similarities with earth, its small iron core and angular momentum, what it fails to explain is the absence of impactor material in the moon and earth.

Recently, a group of Israeli scientists came out with a new theory by simulating nearly 800 cycles of impact to explain the origin of moon. Though standing on the shoulders of the impact theory, they have revived the concept of an earlier proposition which says the moon could be formed by multiple impacts.

The difference, as projected by them, is that instead of one big impact, several smaller impacts on a nascent earth led to the formation of several small moons called ‘moonlets’. Amalgamation of around 20 such moonlets, naturally colliding and coalescing in orbit, resulted in the formation of the present moon.

Technological progress
Well aided by technological advancements, they conducted the impact experiments in simulators and arrived at their conclusion: clearly explaining the geochemical similarity, details of the core, angular momentum and other factors. This theory further opens a window for more experiments and evidences that follow in justification of their conclusions.

Despite all this analysis, it is interesting to know that the moon is slowly moving away from us — at a rate of around 3.5 cm per year, which again is not a constant figure. This is principally due to the tidal forces of the earth’s magnetic field which are broadening the orbit (the path of the moon around earth).

This, in turn, will affect the life on earth, albeit billions of years hence. The opposite tidal force exerted by the moon on earth causes a slowing down of the earth’s spinning.

For example, in the earlier stages, moon was a mere 25,000 km away from earth, which resulted in a higher spinning of earth and each day had only five hours; however, as moon was pushed farther away, to today’s 4,00,000 km , creating a braking effect on earth’s spinning, earth slowed down to the present 24 hour day — after about 4.5 billion years.

It is found that moon has a molten core and quakes are common under the surface; it is bone dry and without atmosphere, a soundless surface; impacts of meteors will lead to further changes.

The mystery shrouding the moon continues, and may be in future, earth will lose its lone satellite or will witness the formation of others. Whatever may be the outcome, all these will affect the life on earth.

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