Solar system

Our solar system consists of the sun and everything that travels around it. The sun is at the center of the solar system and is surrounded by eight full-size planets, including Earth, as well as a variety of other celestial bodies. Planets and other space bodies orbit, or revolve, around the sun, which exerts gravitational pull to keep the solar system together.

The solar system itself is a part of a larger system in space called the Milky Way Galaxy. A galaxy is a large group of stars and other space objects. In modern times, astronomers have discovered that the Milky Way is one of many galaxies in space, raising the question as to whether intelligent life exists somewhere in the vastness of space.

Overview

Scientists believe that an event known as the Big Bang occurred in space billions of years ago. This theory proposed that the universe was once contained in a single area, but the energy inside it became so hot that it exploded. The explosion expanded the universe immensely, sending particles such as molecules, atoms, and electrons out into space. Eventually, the universe cooled and the particles began to cluster into clouds of dust and gas. Stars formed within these clusters when gas and dust clumped together.

Our solar system was created when a cloud of gas and dust collapsed in on itself and began to swirl together. Scientists theorize that this collapse, called a nebula, may have been caused by the explosion of a nearby star. As the gas and dust spun more and more rapidly, a small mass formed in the middle of it. This mass collected the gas and dust around it and grew in size until it formed into a star. Eventually, the star in the center grew so hot that it ignited, forming the sun. The materials that did not get absorbed by the sun also collided together, forming smaller masses. These masses eventually transformed into planets, asteroids, moons, comets, and other space objects.

The Planets

Planets are large space objects with distinct characteristics. The word planet derives from the Greek word for wanderer, which is how the ancient astronomers described these “wandering lights” in the sky. Our solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The first four of these planets are considered the inner planets, or terrestrial planets. They are made primarily of rock. Only rocky materials could survive the heat from the sun originally, which is why the planets closest to the sun formed as they did. The other four planets, the outer planets, are made primarily of gas, due to gaseous and icy materials settling farther out in space.

A region known as the asteroid belt also formed between the terrestrial planet Mars and the gaseous planet Jupiter. This region contains smaller bodies that never matured into planets, such as asteroids, comets, dwarf planets, dust, and gas. Most astronomers consider the asteroid belt an important demarcation line in space, as the inner planets are on one side and the outer planets appear beyond it.

In early times, the people of Earth did not realize there were other planets besides ours. Eventually, ancient scholars noticed that certain lights in the sky moved among the stars. They called these objects planets and named them after the Roman gods. Only six planets were known by the late 1700s—Earth, Jupiter, Mars, Mercury, Venus, and Saturn. After the invention of the telescope, astronomers identified three more planets—Uranus, Neptune, and Pluto. However, Pluto lost its planetary status in 2006, when astronomers discovered another space object like it in size, Eris, and realized they needed a clearer way to classify planets. The International Astronomical Union issued a ruling on what makes a planet a planet: it orbits the sun, it is round with mass, and it is sufficiently strong to keep its orbit clear of other objects. Pluto failed to meet this criteria and was downgraded to a new category, dwarf planet, which caused considerable confusion among the public.

In 2018, a meteorite found in the Sudanese desert ten years before was analyzed by scientists at the Swiss Federal Institute of Technology, who found that the diamonds embedded in the meteorite contained traces of chromite, phospate, and iron-nickel-sulfide, minerals that form only under extreme pressure. That amount of pressure can be exerted only by a planet the size of Mercury or Mars. The researchers thus concluded that the meteorite was a piece of a former planet in our solar system that was destroyed. Astronomers theorize that there were multiple "protoplanets" of this sort that collided and shattered, with the debris eventually forming the current planets of the solar system.

Other Space Objects

Planets and dwarf planets are not the only objects in the solar system. The solar system includes moving objects made of rock or frozen gas and dust, such as asteroids and comets. It also includes objects that orbit other planets—moons. A moon travels around a planet the same way the planets travel around the sun. Moons can be either small or large—in fact, some moons in the solar system are larger than the planet Mercury. Titan, one of Saturn's moons, is so large that it has both lakes and rivers. Jupiter's largest moon, Europa, has an ocean of water. Though Earth has only one moon in its orbit, Luna, some planets have many. Jupiter, for example, has 95 known moons. In total, astronomers believed there were over 290 moons and other, smaller satellites orbiting the various planets in our solar system by 2024.

Discoveries

Throughout history, scientists have made many discoveries about the solar system. For example, ancient people believed that Earth was the center of the solar system. They thought all other space objects, including the sun, orbited Earth. It was not until the sixteenth century, when mathematician and astronomer Nicolaus Copernicus devised the heliocentric model of the universe, that the sun was moved to its rightful place at the center.

Scientists and astronomers have learned even more about the universe since then. For example, the famous astronomer Galileo was the first to observe the rings around Saturn in 1610. For over three hundred years, astronomers believed that Saturn was the only planet with rings. However, it was later discovered that Jupiter, Uranus, and Neptune also have ring systems.

In recent times, scientists have focused on discovering Earth-like planets in other solar systems. The goal is to determine whether life on other planets— intelligent or not—is possible. The search for evidence of extraterrestrial life also applies to our own solar system, where scientists continue to hunt for signs of microbial life on planets like Mars and moons like Europa. In the 2020s, some astronomers hypothesized that another planet might exist beyond Neptune.

Bibliography

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