The solar system is made up of the sun and everything that orbits around it, including planets, moons, asteroids, comets and meteors.It extends from the sun, which the ancient Romans called Sol, and passes through the four inner planets, through the asteroid belt to the four gas giants, to the Kuiper belt in the form of a disk, and beyond to the sun region in the form of a tear.
Scientists estimate that the edge of the solar system is about 9 billion miles (15 billion kilometers) from the sun. Behind the heliosphere lies the giant globular Oort cloud, which is believed to surround the solar system.
Discovering the solar system.
For thousands of years, astronomers have been tracking points of light that seemed to move between the stars.The ancient Greeks called them planets, meaning “hikers” Mercury, Venus, Mars, Jupiter and Saturn were known in ancient times, and the invention of the telescope added the asteroid belt, Uranus, Neptune, Pluto, and many of the moons of these worlds.
The dawn of the Space Age saw dozens of probes launched to explore our system, an adventure that continues to this day. Only one spacecraft so far, Voyager 1, has crossed the threshold into interstellar space.
Astronomers are now searching for another planet in our solar system, a true ninth planet, after revealing evidence of its existence on January 20, 2016. The so-called “ninth planet,” as scientists call it, is about 10 times the mass of Earth and 5,000 times the mass of Pluto.
_ The formation of the solar system.
Many scientists believe that our solar system may have formed from a giant rotating cloud of gas and dust known as the solar nebula.When the nebula collapsed due to its gravity, it rotated faster and was flattened into a disk. Most of the material was pulled toward the center to form the sun.
Other particles collided inside the disk and stick to each other to form asteroid-sized bodies called planets, and some of them combine to become asteroids, comets, moons and planets.
The solar winds from the Sun were so powerful that they washed away most of the lighter elements, such as hydrogen and helium, from the inner planets, leaving behind mostly small, rocky worlds.
The solar wind was much weaker in the outer regions, resulting in gas giants consisting mostly of hydrogen and helium.
_ The sun.
The sun is by far the largest object in our solar system, containing 99.8% of the mass of the solar system. It casts most of the heat and light that makes life possible on Earth and possibly anywhere else.
_ The moon.
The moon is defined as a celestial body that creates an orbit around a planet, including the eight major planets, dwarf planets and minor planets.The moon can also be referred to as a natural moon, although it is distinguished from other astronomical bodies orbiting another object.
Other than the four Galileo moons, Titan Saturn and Triton Neptune are two other moons that can be compared in size to Earth’s moon.
In fact, these seven satellites are the largest natural satellites in the solar system, with a diameter of more than 3000 km. Only the inner planets Mercury and Venus have no moons.
The solar system contains 150 moons that have been discovered so far.
The planets revolve around the sun in elliptical paths called ellipses, and the sun is slightly further from the center of each ellipse. NASA has a fleet of spacecraft that monitor the sun to learn more about its composition, and to make better predictions about solar activity and its impact on Earth.
Inner solar system.
The four inner planets – Mercury, Venus, Earth, and Mars – are made up mostly of iron and rocks.
They are known as terrestrial or Earth-like planets due to their similar size and composition.
Earth has one natural moon – the moon – and Mars has two moons – Demos and Phobos.
The asteroid belt lies between Mars and Jupiter.Asteroids are small planets, and scientists estimate that there are more than 750,000 of them with diameters greater than three-fifths of a mile (1 km) and millions of smaller asteroids.
Here is the dwarf planet Ceres, which has a diameter of about 590 miles (950 km). A number of asteroids have orbits that bring them closer to the solar system, which sometimes leads to collisions with Earth or other inner planets.
_The outer solar system.
The outer planets – Jupiter, Saturn, Uranus and Neptune – are giant worlds with thick outer layers of gas.
Among these planets, they have dozens of moons in a variety of compositions, ranging from rock to icy and even volcanic (as in the case of Jupiter).
Nearly all of the planets’ mass is made up of hydrogen and helium, giving them structures like those of the sun. Beneath these outer layers, they don’t have solid surfaces – the pressure from their thick atmosphere melts within, although they may contain rocky cores.
Rings of dust, rocks and ice surround all of these giants, with Saturn the most famous of them.
Comets are often known as dirty snowballs, and they mainly consist of ice and rock. When a comet’s orbit approaches the sun, some of the ice in its central core turns into gas that is released from the sunlit side of the comet, which the solar wind carries outward to form a long tail.
Short-term comets that complete their orbits in less than 200 years are thought to originate from the Kuiper belt in the form of a disk, while long-range comets that take more than 200 years to return are thought to come from the globular Oort cloud.
Meteorites are pieces of rocks and minerals produced by asteroids and a group of other planets, which survived during their presence in the atmosphere and fell to the ground, most of the meteorites on Earth range in size from the size of a pebble to the size of a fist, but some of them exceed the size of some buildings.
Charles Choi (14-11-2017), “Solar System Facts: A Guide to Things Orbiting Our Sun”، space
“Meteors & Meteorites”, solarsystem.nasa.gov
JOHN CARL VILLANUEVA (19-3-2010), “What Is A Moon?”، www.universetoday.com