It is known that the Moon is gradually moving away from the Earth. It’s because of the tides. Tidal mountains in the Earth’s oceans slow the Earth’s rotation slightly. This rotational energy has to stay somewhere, causing the Moon to end up in a much wider orbit.
It moves very slowly: the average distance between the Earth and the Moon increases by 38 mm per year. But if the moon had been at a closer distance for a long time, you’d expect the effect to be stronger. And if you then carefully calculate, you will come to the conclusion that the Moon sat on the lap of the Earth one and a half billion years ago.
In fact, it is almost certain that the Moon formed from the debris of the collision of the Earth with another celestial body, but this happened much longer ago: about 4.4 billion years. Here’s the riddle: If you assume the current “drift velocity”, the Moon will never be old.
In an article submitted for publication in a trade journal Astronomy and astrophysics Jack Lascar and his colleagues have come up with a solution to the puzzle. The distribution between land and water on Earth is constantly changing due to continental drift. According to the calculations of the French team at the observatory, there is a big difference in the movement of the tides, whether there were several continents, as now, or one giant continent, for example, 200 million years ago. It also makes a difference whether the “center of gravity” of the continents is close to the equator, or at the North or South Pole.
In addition, our planet had no continents at all during the first billion years; The Earth was then a “water world”. Using a computational model that takes all of these effects into account, Laskar and colleagues show that the effect of tides on the Moon’s deflection has varied greatly over the geologic past. For example, it is still possible to reconcile the current rate of removal with the advanced age of the moon.
Matthias Green of Bangor University in Wales, who has previously made similar calculations over the past quarter billion years, calls it “an interesting study that seems to clarify the question of the distance between the Earth and the Moon.” However, it is a fairly simple model, he says. “It’s nice that they hatch at the right age from the moon, but that doesn’t necessarily mean every detail is correct.”
The current “drift velocity” of the Moon has no practical consequences for humanity. Only in a few hundred million years will it be noticeable on Earth: the apparent diameter of the Moon will then be smaller than the diameter of the Sun, so that a total solar eclipse cannot occur again.
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