- During the formation of the Sun, the conditions were not, of course, the same at different distances from the Sun and changed over time. The substance remained cold only far from the Sun. Near it, it was strongly warmed up and the dust was exposed to full or partial evaporation. Only later, when the gas cooled down, did it condense again, but most of the volatile substances contained in the interstellar dust was lost and no longer entered the new dust.
The evolution of the protoplanetary disk led to the formation of planetesimals in it, from which the planets then grew. The composition of the planetesimals formed at different heliocentric distances, due to the different composition of dust that went on their construction, was different. It so happened that asteroids are planetesimals formed on the border of hot and cold zones of the protoplanetary disk, which have survived to this day. - Asteroids were formed in the protoplanetary cloud as loose aggregates. Small gravity could not compress the planetesimals thickened from dust. Due to the radioactive heat, they were heated up. This heating, as J. Wood"s calculations have shown, was very effective: because the loose body is well kept warm. Heating began at the asteroid growth stage. Their substance in the central parts of the body warmed up and baked, and maybe even melted, but the dust on the asteroid surface was still pouring out, adding to the loose, heat-insulating layer. Aluminum-26 is now considered to be the main source of heating. Collisions of asteroids with each other at the beginning also led to the compaction of their substance. Asteroids became compact bodies. But further disturbances from the growing planets led to an increase in the speeds with which the collisions occurred. As a result, more or less compact bodies were already broken.
- The collisions were repeated many times, shaking, shaking, stirring, welding the wreckage, and crushing again. Only the largest asteroids can retain their spherical shape, acquired during the formation period if they manage to avoid collision with few bodies of comparable size. Collisions with smaller bodies will not be able to significantly change it. Small asteroids should and do have an irregular shape, formed as a result of many collisions and not subject to further leveling under the influence of gravity. Craters that appear on the surface of even the largest asteroids in a collision with small bodies, "do not swim" over time.
- They remain in place until they are wiped out in the next small-body asteroid impact or immediately destroyed by a large body impact. Therefore, the mountains on the asteroids can be much higher, and the depressions are much deeper than on Earth and other planets: the average deviation from the level of smooth surface on large astroids is 10 km and more, as evidenced by radar observations of asteroids. why modern asteroids are probably badly "packaged" lumps. Small asteroid fragments, of course, come into Earth"s orbit from the asteroid ring. This is due to the mechanism of successive resonant orbital swaying under the influence of planetary disturbances, which is not yet quite clear in detail. But the swaying occurs only in some areas of the ring.
Asteroids from different places of the ring come in differently effective, and the debris in the vicinity of Earth"s orbit may not be representative of those objects that are moving beyond the orbit of Mars. And only the slowest and strongest of them survive in the Earth"s atmosphere, which leads to further selection.
- Therefore, our collections undoubtedly lack many varieties of asteroid substance, and it is possible that the notion of an asteroid substance as a dense and compact substance is nothing but an outdated, meteor-influenced delusion. Conclusion No matter how great the success of asteroid studies today is, the future is likely to belong to spacecraft research. They can solve many of the difficulties faced by researchers, but there is no doubt that they will face new challenges.
Currently, a lot of attention is paid to the problem of possible collision of asteroids of different sizes with the Earth, the need to build a global system of tracking and warning of dangerous asteroids, methods of collision resistance. Indeed, the impact of the asteroid on the Earth is quite large enough in size and weight may well lead to the disappearance of human civilization and nature in its current state. But fortunately, the probability of such a collision is very small.