Almost all the meteorites that have fallen to the Earth during the entire existence of mankind were generated by five large "mega-asteroids" that fell apart in the distant past. Scientists who have published an article in the journal Nature Astronomy write about this.
“It seems that the differences in the composition of meteorites are due to the fact that their progenitors, which arose in the solar system about four billion years ago, consisted of extremely heterogeneous layers of rocks. I wouldn't be surprised if all the bodies from the main asteroid belt were created by the decay of a very small number of larger objects,”says Stanley Dermott of the University of Florida in Gainesville (USA).
Guests from the sky
In the past few decades, scientists around the world have been actively monitoring near-Earth asteroids and conducting a kind of space "census" among them, trying to understand how dangerous they are for humanity. There are so many asteroids in near-Earth space that astronomers had to create special scales to estimate how likely they are to fall to Earth.
Despite all this and the huge number of asteroids discovered in recent years with ground-based telescopes and the WISE infrared orbital observatory, many large asteroids and countless smaller objects the size of the Chelyabinsk meteorite, which fell to Earth in February 2013, remain undiscovered. humanity.
As NASA reported back in 2011 at the first presentation of the NEOWISE catalog, today we only know about five thousand asteroids about a hundred meters in size, while their total number is estimated at several tens of thousands. The number of smaller objects within the main asteroid belt can be even larger and reach a million.
Dermott and his colleagues have uncovered an unusual fact that unites almost all of these celestial bodies and may simplify their search and cataloging in the near future, studying the five largest "families" of asteroids.
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Astronomers use this word to refer to groups of asteroids that revolve in a similar orbit and have a similar composition and other properties, presumably indicating their common origin. As a rule, they are named by the name of either the largest or the first open "member" of the family.
The largest "groups" of asteroids, for example, the families of Flora, Vesta, Pulana, Evlalia and Nisa, include tens of thousands of small and large objects, whose diameter can reach several tens of kilometers.
The consequences of the space "billiards"
The authors of the article conducted a new "census" among these five families of asteroids, "blindly" analyzing the nature of orbital motion, brightness and all other physical properties of all asteroids living in the inner part of the main belt.
Similarly, as the astronomer notes, his team tried to "catch" those representatives of the five main families of asteroids, which for some reason were forced to somewhat change their orbit in the past.
In this search, scientists relied on a simple pattern known to astronomers for many decades - if an asteroid belongs to any family, then the angle of inclination of its orbit and its elongation depend strongly on its brightness.
These calculations unexpectedly showed that about half of the asteroids that were previously considered "ownerless" actually belong to one of these five families. In total, according to the planetary scientist, about 85% of the inhabitants of the closest part of the asteroid belt are included in one of these five groups, and the nature of the remaining 15% remains unknown.
If this is so, then why do the new members of these families have such a variegated mineral and chemical composition? As Dermott explains, metal meteorites are most likely fragments of the cores of these "mega-asteroids", and various rocky objects are fragments of the mantle, crust and other layers of their bowels.
The discovery of the common nature of most near-Earth asteroids, according to the astronomer, is extremely important in the context of protecting the Earth from possible asteroid "attacks". Now it will be easier for scientists to predict the chances of such an outcome of events and assess their consequences, knowing that they have a similar origin and composition.
In addition, studying them, Dermott concludes, will allow us to understand the conditions under which the "embryos" of the Earth and other planets, some of which were the progenitors of asteroids, were formed. This, in turn, will help scientists better and faster search for potential twins of our planet in other star systems.