Solar System
Grains Accretion of Dust Nebula
In countless galaxies, cosmic islands shine stars. The space among them is filled with an interstellar gas, unused star-forming matter, nebulae, remains of supernova explosions, huge clouds of dust and many other objects. About 4.6 billion years ago in a galaxy - now we call it Milky Way, to which belongs our solar system, a cloud of dust began shrinking by its own gravity – accretion. It was big, about one light-year in diameter. It become thicker, started to rotate, reached critical temperature and density, a thermonuclear reaction was ignited, and there was a new, young star, our Sun. Part of the unused star dust containing almost all particles the young Sun drew to itself, from it formed a rotating protoplanetary disk and lighter remains blew by force of strong radiation away from its surroundings beyond the edge of the disk. Today, this rare material is hidden on the periphery of today’s solar system in Kuiper belt and Oort cloud, from which it sometimes reaches the Sun in the form of comets. In the rotating disk particles gathered together into larger units and grew up to planetesimal forms – the actual predecessors of planets.
New Worlds
By collisions of planetesimals and other compact remains from previous accretion (gravitational cumulating of the matter), grew near our Sun eight planets with their companions - moons, dwarf planets and minor planets. Lighter particles were used for formation of large planets – Jupiter, Saturn, Uranus and Neptune. And those formed with heavier particles - Mercury, Venus, Earth and Mars - /terrestrial planets/ remained closer to the Sun. All those new planets were heavily bombarded by the remaining cosmic trash, which was at the end driven into a gravitational trap between Mars and Jupiter, to the asteroid belt. Sometimes a rock escapes from there, and on its way to the Sun, which attracts it, can endanger the Earth. After the large cosmic bombardment, the surface of the planets was almost in a liquid state, the oldest rocks were created by its solidification. The surfaces of the planets and moons, which retained due to a stronger gravity a gaseous envelope - atmosphere, were made even. The others, without a gaseous envelope, are still covered with craters. Our entire solar system is uniquely beautiful, and when the planets move near the Zodiac and we can observe them, it takes our breath away.
Illustrations: Akad. mal. Jitka Bílá
