The fact that in the solar system between the orbits of Mars and Jupiter numerous small bodies move, the largest of which are only stone blocks in comparison with the planets, less than 200 years ago. Their discovery was a natural step towards the knowledge of the world around us. This path was not easy and straightforward.
Who, in the era of the discovery of the first asteroids, could have suggested that these small bodies of the solar system, bodies that were often talked about quite recently with a touch of neglect, would be the object of attention of specialists in various fields: natural sciences, cosmogony, astrophysics, celestial mechanics, physics, chemistry, geology , mineralogy, gas dynamics and aeromechanics? Then it was still very far away. It was still necessary to realize that one had only to bend down to pick up a piece of an asteroid from the earth – a meteorite. The science of meteorites – meteorics – originated at the beginning of the 19th century, when their parent bodies, asteroids, were discovered. But in the future it developed completely independently. Meteorites were studied by geologists, metallurgists and mineralogists, asteroids – by astronomers, mainly celestial mechanics.
It is difficult to give another example of such an absurd situation: two different sciences study the same objects, and practically no points of contact arise between them, there is no exchange of achievements. This does not contribute to the comprehension of the results obtained. But nothing can be done, and so it remains until new research methods – experimental and theoretical – raise the level of research so much that they create a real basis for the merger of both sciences into one.
This happened in the early 70s of the XX century, and we witnessed a new qualitative leap in knowledge of asteroids. This jump occurred not without the help of astronautics, although spacecraft have not yet descended on asteroids and even a satellite image of at least one of them has not yet been received. This is a matter for the future, which is apparently not far off. In the meantime, we are faced with new questions and are waiting for their decision.
Asteroids near the Earth
For almost 3/4 centuries, people did not suspect that not all asteroids move between the orbits of Mars and Jupiter. But in the early morning of June 14, 1873, James Watson discovered the Aerta asteroid at the Ann Arbor Observatory (USA). It was possible to follow this object for only three weeks, and then it was lost. However, the results of determining the orbit, although inaccurate, convincingly testified that Aerta was moving inside the orbit of Mars.
Asteroids that would approach the Earth’s orbit remained unknown until the end of the 19th century. Now their number exceeds 80.
The first asteroid near the Earth was discovered only on August 13, 1898. On that day, Gustav Witt discovered a faint object moving rapidly among stars at the Urania Observatory in Berlin. The high speed testified to its extraordinary proximity to the Earth, and the faint brilliance of a close object – to extremely small sizes. It was Eros, the first baby asteroid with a diameter of less than 25 km. In the year of its discovery, it passed at a distance of 22 million km from Earth. Its orbit was not similar to any still known.
Then the asteroids Albert, Alinda, Hannimed, Ivar, Amur, which passed by astronomical standards very close to the Earth, were discovered.
All asteroids discovered so far have direct motion: they move around the Sun in the same direction as large planets. In the vast majority of asteroids, the orbits are not very different from each other: they are slightly eccentric and have a small or moderate slope. Therefore, almost all asteroids move, remaining within the toroidal ring. The boundaries of the ring are somewhat arbitrary: the spatial density of the asteroids (the number of asteroids per unit volume) decreases with distance from the central part. In a few asteroids, due to the significant eccentricity and inclination of the orbit, the loop goes beyond this region or even lies entirely outside it. Therefore, asteroids are found far away outside the ring.
The volume of space occupied by the torus ring, where 98% of all asteroids moves, is huge – about 1.61026 km3. For comparison, we indicate that the volume of the Earth is only 1012 km3.
To be completely strict, it must be said that the path of an asteroid in space is not ellipses, but open quasi-elliptical coils stacked next to each other. Only occasionally – when approaching the planet – the turns noticeably deviate from each other. Planets are indignant, of course, not only the movement of asteroids, but also each other. However, the perturbations experienced by the planets themselves are small and do not change the structure of the solar system. They cannot cause planets to collide with each other. With asteroids, this is different. Asteroids deviate from their path either one way or the other. The farther, the greater these deviations become: after all, the planets are continuously “pulling” the asteroid, each towards itself, but stronger than all Jupiter. Observations of asteroids span even too small time intervals to detect significant changes in orbits.