Question 1

The dark side of the theory

Accepted Answer

The Giant Impact Hypothesis is put forward for the first time in 1946 by Canadian geologist Reginald Daly. According to this hypothesis  4.5 billion years BP, a gigantic cloud of   gas and dust  collapsed due to gravity, which led to the formation of our Sun. The remainder of the cloud carried on rotating, forming thus the protoplanetary disk, and then the planets, moons, and asteroids. Daly's hypothesis was taken up in the 1970s as scientists relied on data provided by the Apollo lunar missions to devise a collision scenario with a celestial body of the size  of planet Mars, which will be subsequently named Theia. In 2001,  new computerised models reinforced the credibility of this  hypothesis.Then, in 2012, more sophisticated  simulations contributed to the refinement of the scenario : impact angle, velocity, amount of material ejected… Whilst this latest version offers insights on a number of  issues,, it nonetheless overlooks a major mystery : the remarkable  similitudes in the Earth and the Moon's respective geochemistry. Meanwhile, scientists relentlessly keep on digging deep – literally et intellectually.

Question 2

Funfact | Greek mythology

Accepted Answer

According to Greek mythology, Theia is the daughter of the sky god Uranus and earth godess Gaia. She is also mother to the Moon.

Question 3

Celestial - and family -  mechanics

Accepted Answer

Several family-related scenarios were put forward to explain  the relation between the Earth and the Moon.The Moon as a sister of the Earth : the most ancient hypothesis, it posited both astral bodies had formed simultaneously, at the same place, from the same matter cloud. Their différences in density and the Moon not orbiting the Earth  exactly in the same plane as the equator were the weak points of this theory.The Moon as a daughter of the Earth : the British  mathematician and astronomist  George Howard Darwin, son to Charles Darwin, proposed that the Moon  detached from the Earth as the result of rapid rotation forming  an equatorial ridge which would have been ejected. The« Pacific Hole » would stand as evidence of this. It can explain  the  difference in density between the two astral bodies; however the differences in orbital planes is the major flaw of this theory. Moreover,  plate tectonics provide since 1967 a very different explanation for the formation of the  Pacific ocean with no connection to a hypothetical lunar detachment.The Moon as a spouse  to the Earth : formulated at the beginning of the 20th century, this idea suggests that  the Moon had formed elsewhere in the solar system before being captured by the Earth. This hypothesis might explain their differences in density while posing a problem in terms of celestial mechanics : for such a capture to succeed, the two astral bodies should have been very close to each other basically. Furthermore, the great chemical similarities between lunar rocks and the Earth's mantle has made it effectively irrelevant.

Question 4

Funfact | Another cup of stabilty ?

Accepted Answer

Thanks to its gravitaional pull, the Moon stabilises the axis of rotation of the Earth, without which the axial tilt of our planet would be varying considerably, bringing chaos on  climate and the seasons – which would have complicated  the evolution of life.

Question 5

Funfact | The longest day

Accepted Answer

The Moon  moves away from the Earth by about 3,8 cm per year. This recession has a surprising consequence : it gradually slows down the rotation of the Earth, which in turn makes the days longer. Nowadays, a day lasts 24 hours. 200 million years ago, it lasted about 23 hours and  4 billion years ago, roughly 5 to 6 hours.

Lunar riddle and cosmic collision

It was poked in the eye by a rocket and is home to a mysterious black monolith, it was also visited by Tintin, whereas H.G. Wells' main characters encountered the local residents, i.e. the Selenites. So, how was the Moon formed?

And there you have it: the Earth is no longer alone. Like many other planets, it now has a satellite: the Moon.

Informations complémentaires

The dark side of the theory

Funfact | Greek mythology

Celestial - and family - mechanics

Funfact | Another cup of stabilty ?

Funfact | The longest day

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