Large asteroid impacts on Earth would leave footprints on the Moon

During the last billion years, the Moon and the Earth may have been hit simultaneously by clusters of small celestial bodies accompanying at least one large impact, such as the one that caused the Chicxulub astroblema. This is suggested by a recent study of lunar soil samples brought back to Earth by the Chinese Chang’e 5 mission.

Plate tectonics and erosion have erased many pages of the history of our Blue Planet. Some of these pages are related to the history of the Solar System, for example in relation to the bombardment of small celestial bodies, whether they are comets or asteroids. However, some giant astroblems are known on Earth, for example the Manicouagan in Quebec, which is one of the oldest known impact craters and also the largest “visible” impact crater on Earth. With a diameter of about a hundred kilometers, geologists give it an age of about 213 to 215 million years. Let us immediately remember that it occurred about ten million years before the Triassic-Jurassic extinction and therefore cannot be responsible for it.

Larger but not very significant and also not visible from space, we know well the Chicxulub astroblem in Yucatan, an astroblem that we know played an important role in the great biological crisis of the Cretaceous-Tertiary, about 66 million years ago. crisis dramatically marked by the disappearance of non-avian dinosaurs.

Our satellite, the Moon, does not have the same memory problems, being devoid of plate tectonics, a water cycle, and a windy atmosphere. Therefore, we might expect to find ancient traces of the history of the Earth-Moon pairing, as well as the Solar System and even the Galaxy in various forms in the lunar regolith.

In general terms, the theory of the formation of the Solar System tells us that the impacts of small celestial bodies on Earth are not only decreasing in frequency but also in the size of the impacting bodies. Thus, if the Earth was undoubtedly hit by a small planet the size of Mars more than 4.4 billion years ago, the famous Theia at the origin of the Moon, such an event may not occur for a few billion years, although we must be careful to protect ourselves from impacts that can release energies much higher than that of the Hiroshima bomb (the Earth is hit regularly every year by impacts that release comparable energy).

A chaotic asteroid bombardment?

However, the discovery of chaos in celestial mechanics and the appearance of the phenomenon of planetary migration in the history of the Solar System described by simulations such as those of the Nice Model suggest that there are times when the bombardment can become a bit more intense. One can also think of the occurrence of collisions between large asteroids in the Main Belt between Mars and Jupiter, giving rise to the sending of various small bodies resulting from the fragmentation of these large asteroids and which will then darken towards the inner Solar System, and will behave much more. like a sudden rain for planets like the Earth and the Moon.

In fact, a team of researchers led by Alexander Nemchin of Space Science and Technology Center (SSTC) of Curtin University in the State of Western Australia, has just provided interesting elements in support of this scenario in an article published in open access at Progress of science.

The researchers studied some of the lunar rock samples brought back from the Moon thanks to the Chinese mission Chang’e 5 in 2020. They came from the northwestern part of the Ocean of Storms, in a mostly flat area, located about 90 kilometers northeast . from the Mons Rümker region.

These samples contained a kind of volcanic glass beads, that is, drops of rock melted by the energy released by the impact of a small celestial body of considerable size and which were also projected far away by the energy of the impact before cooling. On Earth, these would be microscopic examples of what are called tektites, from the German term Tektitforged by the Austrian geologist Franz Eduard Suess from the Greek τηκτός / tēktós which means “molten”.

Cosmochemical methods can be used to date these pearls and several “waves” of production have been demonstrated over the last two billion years, waves that indicate peaks in the meteorite bombardment of the Moon in a context of exponential decay.

Surprisingly, some of these peaks appear to correlate with the ages of large astroblems on Earth, such as Chicxulub.

In fact, this is what Alexander Nemchin explains in a press release from Curtin University: We combine a wide range of microscopic analytical techniques, numerical modeling, and geological studies to determine how and when these microscopic glass beads on the Moon formed. We have found that some of the age groups of the lunar glass beads precisely match the ages of some of the largest impact craters on Earth, including the Chicxulub impact crater, responsible for the extinction of the dinosaurs. The study also found that large impact events on Earth, such as the Chicxulub crater 66 million years ago, could have been accompanied by a series of smaller impacts. If correct, this suggests that age-frequency distributions of impacts on the Moon could provide valuable information about impacts on Earth or the inner Solar System. »

For reasons still unknown, there would therefore be periods in which the regular orbits of the small bodies of the Solar System would be destabilized, which would lead them to move towards orbits in which they could collide with the Earth or the Moon. Similar increases are certainly possible in the future, but when?

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