The universe is vast, perhaps infinite. In a remote place in this huge universe, there is a galactic cluster called Local Group. It is a small group of galaxies, no more than forty, where there are three main galaxies, one of which, the Milky Way, houses the Solar System in one of its arms.
The Solar System is our neighborhood. A neighborhood formed by more than one central star and eight planets. It is a wonderful and amazing corner of our universe, whose center is a small middle-aged star that formed about 5 billion years ago when the shock wave of a supernova collided and moved a nebula whose hydrogen and helium served as raw material for the formation of our central star and the gas giant planets, Jupiter, Saturn, Uranus and Neptune. In the area closest to the sun, the small rocky planets Mercury, Venus, Earth and Mars were formed, of which our home is the largest.
An asteroid belt that exists mainly between Mars and Jupiter, whose largest asteroid receives the name of Ceres; dwarf planets, such as Pluto and Eris; comets that spin around the sun in long orbits; meteors and meteorites, which penetrate the planets; the Kuiper belt, which is a ring of icy objects that orbit the Sun, complete the Solar System. It is likely that the small Pluto and its satellite Charon come from this belt, as well as many of the comets of the Solar System. Beyond the Kuiper belt, Oort Cloud orbits, housing the most distant comets of the system.
THE SUN. It may not be a huge star, like many in the universe, but it is our star, the cause of our existence. The whole system revolves around the Sun. As we saw above, the Sun originated about 5 billion years ago, it is in the middle of its life. Because it is a low mass star, when it is near its end, within 5 billion years, it will begin to grow and turn red as the hydrogen it contains depletes, becoming a red giant. It will be so large that it will occupy the orbits of Mercury, Venus and probably the Earth. However, for now, the sun is the source of heat and life for our planet. This star, which reaches a temperature of 6,000 Celsius or 10,800 Fahrenheit degrees on its surface called photosphere, has a volume one million three hundred thousand times that of Earth. The average distance between the Earth and the Sun is 150 million kilometers or 93 million miles, and is called Astronomical Unit, used as a reference to establish distances within the Solar System.
THE INNER, TERRESTRIAL OR ROCKY PLANETS. They are the four planets closest to the Sun: Mercury, Venus, Earth and Mars. They occupy the small region closest to the Sun. They are thought to have formed with the heaviest materials in the nebula that formed the Sun, and all four have a fairly similar structure: a metallic core with iron and nickel, mantle and rock crust, where silica predominates. All four have an atmosphere, although Mercury's is very weak. Only Earth and Mars have satellites. The largest is Earth and is the only one that houses life. If we compare them with our planet, without a doubt Mars is the most similar. His day lasts almost the same as ours, his axis is tilted like ours, and this allows seasonal changes during his year, which lasts twice as long as ours.
THE ASTEROID BELT. Beyond the group of terrestrial planets, there is a belt of rocky and metallic objects, in sizes ranging from small pebbles to 621 miles of diameter like Ceres, the largest of all. The region of asteroid belt occupies a space between the orbits of Mars and Jupiter, and even the satellites of Mars are two asteroids trapped by their gravitational force. It is believed that the asteroids could never be consolidated as a single planet because of the gravitational force of Jupiter. The asteroids collide constantly between them and it is even believed that many have been fired outside the Solar System.
THE GAS GIANTS. Jupiter, Saturn, Uranus and Neptune form the group of giant planets of the Solar System. Although they have a small rocky core, these planets are basically made up of gases, mainly hydrogen and helium. Atmosphere and planet are confused, with the gases becoming denser towards the nucleus. It is believed that the gaseous planets were formed of remaining materials from the nebula that caused the sun. The four have numerous satellites, especially Jupiter and Saturn. The latter has a spectacular ring system consisting of ice and dust particles. The gaseous giants are so far away that the Sun looks like any other star from them.
THE KUIPER BELT AND THE OORT CLOUD. They are the most remote regions of the Solar System, where dwarf planets and comets are found. The small Pluto, reclassified as a dwarf planet by the International Astronomical Union, is located in the Kuiper belt. Many other dwarf planets have been discovered there too. On the other hand, the cloud of Oort, seems to be a species of giant sphere of frozen objects, from where they seem to come comets that orbit the solar system. It is not clear yet its size and composition, nor the amount of potential comets it houses.
In our next virtual class we will visit the inner planets of Solar System to learn more about the closest neighbors to Earth.
