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Asteroid, name introduced in 1802 by Herchel, planetary stars, solar system components, said today preferably small planets. An asteroid is a similar celestial body for the composition to a terrestrial planet but smaller, and generally devoid of a spherical shape; generally, it has a diameter of less than km, although there are large bodies because technically also very massive bodies recently discovered in the outer solar system asteroids are considered. It is thought that the asteroids are the protoplanetary disk residues that have not been incorporated into planets during the formation of the system. Most asteroids are located in the main belt, and some have satellites of asteroids. Often characterized by a high eccentricity orbits. very small asteroids, with the size of a boulder or even less, are known as “meteoroid”. Asteroids composed for the majority of ice are known instead as comets.
Some asteroids are remnants of old comets that have lost their ice in the course of repeated approaches to the Sun and are now composed mostly of rock.
The fateful day 1 January 1801 when the Italian astronomer Giuseppe Piazzi, Palermo Astronomical Observatory, discovered what was then called a “small planets”, not very bright, orbiting in the belt between Mars and Jupiter, and that later will be classified as an asteroid, scientists are trying to identify the origins of the individual “small planets” and of “corpuscles” families.
Taking as reference the formats asteroids in the solar system, those close to planets like Earth and Mars show the spectrum of the rocky minerals mixed with iron, while those closer to Jupiter tend to be dark and reddish, indicating a composition not very different from that the primordial nebula that about 4.5 billion years ago would have produced the planets to be condensed.
So, according to the most credible hypothesis, in a first phase the tiny solid particles are aggregated to form the bricks of the planets, but in the area beyond Mars, due to the effects of gravitational resonances with Jupiter‘s mass, the formations were prevented from bodies with a diameter greater than 1000 km.
The corpuscles who could not be incorporated into the planets in formation became asteroids, and among them, the largest reached a sufficient temperature to allow a chemical differentiation; the consequence was that in some of them formed the water, in other volcanic phenomena.
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