Facts About The Solar System

The solar system consists of the sun and every object that orbits around it, including the Earth, seven other planets, three dwarf planets, comets, asteroids and meteoroids, as well as the moon and the other satellites that orbit around the planets. The stars you see at night are not in the solar system. The sun is the solar system's only star and one of about 200 billion stars in the Milky Way galaxy, which is one of about 50 billion galaxies in the universe, according to "Discovering the Universe," an astronomy textbook.

Sun

The sun was formed 4.6 billion years ago after a "vast cloud of interstellar gas and dust" condensed and roughly 10 billion years after the universe was created, according to "Discovering the Universe." It contains about 99.85 percent of the solar system's mass, but is a "typical star," the textbook reports. Some stars are more than 1,000 times larger than the sun.

The sun has no solids or liquids. Its 100 percent gas surface has a temperature of 5,800 degrees Kelvin, the temperature scale that scientists commonly use, or roughly 10,000 degrees Fahrenheit. Temperatures in the sun's brightest areas can reach 4 million degrees Kelvin. The sun's energy is produced by hydrogen fusion and is measured by Albert Einstein's "E=mc squared" equation, with "E" representing energy, "m" representing mass and "c" representing the speed of light. The sun has three layers, and only one is visible.

Planets

The solar system's eight planets are, in order of distance from the sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. In 2006, the International Astronomical Union reclassified Pluto as a dwarf planet along with Eris and Ceres. Mercury is roughly 93 million miles away from the sun, the Earth about 241 million miles away and Pluto approximately 9.5 billion miles away, according to "Discovering the Universe."

The eight planets formed at about the same time as the rest of the solar system 4.6 billion years ago. They formed because of innumerable collisions of small particles. Most of the satellites rotating around the planets, including the Earth's moon, were created later. The Earth's moon is roughly 100 million years younger than the Earth.

The four planets closest to the sun are small compared to the next four planets. Jupiter's diameter is about 11 times larger than Earth's. Neptune, which is smaller than Jupiter and Uranus, is almost four times larger than Earth. Pluto, the ex-planet, is smaller than seven moons, including the Earth's moon.

Debris

For 800 million years after the creation of the solar system, "pieces of debris" frequently collided with the planets and scarred and shaped their surfaces, according to "Discovering the Universe." Today, the pieces of debris are called comets, asteroids and meteoroids. They orbit the sun and periodically collide with a planet.

Although asteroids and meteoroids both consist of rock and metal, they are distinguished by size. Asteroids are larger than a few hundred meters in diameter. Tens of thousands of asteroids orbit the sun. The much smaller meteoroids are called meteors after they enter the Earth's atmosphere and meteorites when they hit the Earth. Comets are icy rocks with "tails" made of gases and dust. The overwhelming majority of the millions of comets are beyond Pluto so they are rarely seen by people on Earth.