Solar System Facts

The solar system is a collection of planets, satellites, and other bodies that are held in orbit by a single star, the Sun.  It includes comets and asteroids, as well as dwarf planets.  Knowledge of the solar system has increased dramatically in the last half century, due to leaps in technology and space exploration.

The Sun sits at the center of the solar system.  It is a small star, relatively speaking, but massive compared to the Earth and other planets: the Sun is over a million times larger than the Earth.  Inside the Sun, reactions are constantly taking place, which give off radiation and light to the solar system. 

Eight planets orbit the Sun at different distances.  The four closest to the Sun are small, rocky worlds, while the four that are much further away are gas giants with much lower densities.

Mercury, the smallest planet, is also the closest to the Sun.  It has high surface temperatures, no atmosphere, and long days, but an orbit of only about 88 Earth days.  Venus is the next planet in the solar system, and has the hottest surface temperature.  The atmosphere is mostly carbon dioxide, and the surface is filled with many active volcanoes.  Temperatures can reach over 800 degrees Fahrenheit!

Earth is the third planet in the solar system, and sits at a comfortable distance from the Sun of about 93 million miles.  This ensures that surface temperatures aren’t too hot or too cold to support life.  The moon is about one quarter the size of Earth, and is one of the brightest objects in the sky, except for the sun.

Mars, the red planet, has a much thinner atmosphere than Earth.  It has polar ice caps at the two poles, which contain the planet’s water.  Mars is a litter over half the size of Earth, and is much further away from the Sun, with an average distance of 155 million miles.  It has two moons, called Phoebe and Deimos.  Beyond Mars, there is an asteroid belt which contains many smaller objects orbiting the Sun.

The next planet, Jupiter, is a gas giant and the largest one orbiting our Sun.  Jupiter has a total of 63 moons in orbit, and also has a set of rings.  Jupiter has a mass about 318 times larger than that of the Earth’s, but since it is composed mainly of hydrogen and helium, it has a much lower density.  Saturn, the next gas giant, is known for its visible rings.  It is slightly smaller than Jupiter, but can still be seen with the naked eye, and has several moons as well.

Uranus and Neptune are even further from the sun, and they both have lower average temperatures.  Uranus is unusual because it rotates on its side, with the poles pointing towards the Sun.  Uranus has 27 satellites, and Neptune has 13.  The two planets are composed mainly of hydrogen, helium, and methane.

Beyond Neptune, many smaller objects, dwarf planets, and comets can be found that are still within the Sun’s gravitational pull.  Pluto is the most well-known of the dwarf planets.  The Kuiper Belt, which is the region where Pluto sits, contains many small icy objects orbiting the Sun.  Comets orbit the sun in highly elliptical patterns, and may not complete an orbit in hundreds of years.