In 1755 the philosopher Immanuel Kant published a remarkable booklet entitled. He not only expounded what would become the Kant-Laplace model for the cosmogony of the Solar System, but he theorized a perhaps infinite but mostly full of similar to , in the words of Kant but also predicted that the distance between the and the Earth had to increase with time.
From Kant to Darwin
Perfectly master of the concepts ofNewtonian, in the absence of the Newtonian mathematics developed simultaneously by and d’Alembert, Kant understands that the conservation law of and the existence of friction of the oceans deformed by the of the Moon, due to the rotation of the Earth, lead to dissipate the kinetic energy of rotation on itself of our blue Planet. The slowdown of the Earth’s rotation causing the decrease of its angular momentum, must lead to an increase in that of the Moon around the Earth to ensure the conservation of the total angular momentum Earth + Moon and therefore an increase in the distance between the two celestial bodies – su all these basic notions of mechanics can be consulted on two Nobel laureates And .
During Kant’s life, but in the next half century, d’Alembert, Lagrange and Laplace developed intensivelyand it is on this basis also that the English astronomer and mathematician George Howard (1845-1912) solidly embodied, around 1880, Kant’s ideas on the slowing of the earth’s rotation and the gradual recession of the Moon. For the record, and as the name suggests, Georges is indeed one of the sons of (1809-1882) the famous naturalist and English whose work on living organisms have revolutionized biology.
These works of Darwin accompany his cosmogonic theory of the Moon, a very interesting theory but whose exposition would take us too far. You can get a taste of itof the great British astronomer, mathematician and geophysicist Harold Jeffreys who would also contribute to the theory of his compatriot George Darwin to whom the treatise is dedicated.
The ideas of Kant and Darwin will finally be definitively verified in the course of the twentiethAnd century and a turning point in this sense will come thanks to the American and Soviet lunar program, which will deposit return reflectors on the Moonlaser at 180 ° and that they will then make a round trip from theirs on earth. Since 1969, therefore, we have a laser between the Moon and the Earth that has allowed us to prove it they were far apart from each other with an estimated speed of 3.83 cm / year.
Even the geological archives have not been left out because we have someof corals that have similar growth rings depending on the of the day on Earth and also that of the year. It is thus shown that in the period of , (more precisely about 380 million years ago) a year had 400 days but its duration was almost the same as today. It was therefore necessary to deduce that the length of the day was only about 22 hours and therefore that the rotation of the Earth had actually slowed down, which as we have seen implies that the Moon was in the past closer to the Earth.
Fifty years after Neil Armstrong’s first step, the instruments deployed on the Moon by the Apollo 11 mission are still used by French scientists. Thanks to reflective panels placed on the lunar ground, they measure the distance that separates our planet from its satellite. The key is valuable lessons on the rotation of the Moon or the composition of its core. © CNRS
A Moon born 1.4 billion years ago?
However, by inserting in thefrom the Darwinian theory of the motions of the Moon and the Earth, the value measured by the laser beam, it turns out that the Moon and the Earth must have been in contact about 1.4 billion years ago. This result is in good qualitative agreement with the theory that the Moon arises from a collision between the Earth and a planet the size of Mars, but quantitatively it is not good at all because we know that the Moon is more than 4 billion years old and that it would have been born from the Earth-Theia collision about 4.4 billion years ago.
We have therefore been facing for about 50 years a paradox that has been called the Gerstenkorn event, that is a contact between the Earth and the Moon 1.4 billion years ago, a contact that certainly does not occur at that moment.
A research group from the Paris-PSL Observatory within the Institute of Celestial Mechanics and Computation of Ephemeris (IMCCE) has investigated this problem and has just announced that it has solved the puzzle in an article published in Letters A&A but of which a free access version can be found on.
Previous attempts to resolve the contradiction by improving tide theory, particularly the ocean models of Webb (1982) which had represented fundamental advances in showing the appearance ofmechanical (similar to those that make a swing swing when the excitation is good) between ocean waves and the forcing of tidal forces, which led to a sharp increase in the dissipation of Earth’s rotational energy, had not yet taken into account either the tidal current or the age of the Moon.
Continents interacting with tidal waves
The comparison with experience, in fact, is not linear and, until now, there was a risk of circular reasoning. In fact, as regards the history of the movements of the Earth-Moon system, there are also cyclostratigraphic archives in thein relation to the deposits linked to the rhythms of the tide, linked to the variation of the tide deposition between neap and spring tides, as well as the famous . However, to interpret this data, it is also necessary to have a of these movements in relation to celestial mechanics up to a certain point.
So that the empirical models of the Earth-Moon history that are widely used today bythey are problematic. Finally, as explained in an IMCCE press release, empirical models do not allow for the deduction of physical information about the Earth-Moon system.
The tides are mainly the result of the attraction of the moon and the sun and the rotation of the earth on itself. Satellite measurements allow you to obtain animations that visualize changes in the height of the seas, represented by levels of gray. These level changes are the sum of many components, called tidal waves. The animations highlight the properties of the tidal wave M2, the effect of the attraction of the moon (period, amplitude, wavelength, vibration nodes and speed of propagation) and of the tide wave K1, effect the inclination of the lunar orbit with respect to the equator (phase opposition and critical latitude). © Credits Scientific authors: Le Provost Christian and Lyartd Florent (Legos, UMR CNRS, Toulouse) Director: Ternay Jean-François (CNRS AV) Production: Legos, CNRS AV Distributor: CNRS Images
To overcome these difficulties, theand IMCCE geophysicists have perfected their modeling taking into account millions and billions of years of . The movements of the continental blocs not only change the times of of the Earth over time, which affects the rotation of the Earth and the movements of its axis of rotation, but also changing the shape of the oceans, leading to more complex tidal waves and energy dissipations than initially considered.
Eventually, the researchers not only eliminated the contradiction represented by the Gerstenkorn event, but also achieved remarkable consistency between the new modeling’s predictions and the history of the evolution of the Earth-Moon distance.
The IMCCE press release exposing this finding concludes with the following comments:
” This study is interdisciplinary and will have a very broad impact in several fields (geophysics,, astronomy). Provides the former of the evolution of the Earth-Moon system that perfectly with the current dissipation of the tides and the age of the Moon, solving a fifty-year paradox. Furthermore, this model fits very well with the available geological data. It will most likely therefore become the standard reference for geoscientific studies. This study clearly demonstrates that the cyclostratigraphic approach is very relevant for finding the past rotational state of the Earth. It also consolidates the entire cyclostratigraphic field. This model differs from those previously published by allowing resonances of greater amplitudes. This is essential for regulating the rate of current dissipation. These results will then also consolidate the theory of ocean tides, showing the important effect of these ocean resonances. Furthermore, they can be generalized to the ocean tides of exoplanets “.