Far fewer meteorites hit the moon than scientists thought

(ORDO NEWS) — An analysis of the porosity of the lunar crust made it possible to more accurately assess the history of the meteorite bombardment of our satellite.

The study was conducted by scientists from the Massachusetts Institute of Technology (USA). Based on data from the GRAIL space mission , they created a map of the density of the lunar crust.

And with the help of computer simulations, they recreated how the density changed throughout the history of the moon. According to the new model, five times fewer meteorites fell on the satellite than according to some previous estimates.

By the abundance of craters on the Moon, one might think that the entire history of meteorite falls is “recorded” on the surface.

In fact, in the turbulent first hundreds of millions of years after the formation of the bodies of the solar system, there were so many collisions that the craters overlapped each other. The heavy bombardment lasted from 4.4 to 3.8 billion years ago.

“We know that so many meteorites hit the Moon that what we see on the surface no longer reflects the entire history of the falls, because at some point new collisions began to erase the old ones,” explains Jason Soderblom , one from the authors.

“What we found is that this preserves the crustal porosity created by such collisions, and this allows us to estimate the total number of meteorite impacts much more accurately.”

Scientists believed that all collisions inevitably increase the porosity of the crust. Computer simulations have shown that this is not the case. Almost all of the “porosity” of the Moon was formed during the first powerful collisions. And further small meteorites compressed the once formed faults and cracks.

In the model, the team took into account the age, size, and location of 77 of the largest craters on the Moon’s surface, as well as their present-day porosity, compiled from surface gravity data from the GRAIL mission.

For the standard of the initial density of the Moon, the authors chose the youngest crater, which was not so much subjected to further collisions. The scientists then calculated how many collisions it takes to reach the density of the remaining, older craters.

The results are interesting. It turns out that at the beginning of the period of late heavy bombardment, the porosity of the Moon was about 20% (for comparison, for pumice – 60-80%). By the end of the period, it dropped to the current 10% due to the impacts of small meteorites.

As the model showed, for such a decrease in porosity, it took about twice as many small meteorites as craters on the surface of the modern Moon. “According to previous estimates, there could be many more, even ten times more than craters on the surface, and we predict fewer impacts,” Soderblom added.

Such an assessment is important not only for the Moon, but also for all the bodies of our system. The amount of additional matter and various compounds that arrived at the Earth’s satellite and other bodies after their formation depends on the number of fallen meteorites.

This, in turn, affects the history of the formation and evolution of planets in the solar system.

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