The largest planet in the solar system is Jupiter. It is named after the ruler of the ancient Roman gods. Jupiter is more massive than all the other planets put together. With its many moons, the planet seems like a miniature solar system.
Jupiter is the fifth planet from the sun. It travels around the sun at an average distance of about 484 million miles (780 million kilometers).
With a diameter of about 89,000 miles (143,000 kilometers) Jupiter is so huge that it could contain more than 1,000 Earths. Its great mass gives the planet a strong pull. Its gravity is much greater than the Earth's.
Jupiter has many properties in common with its neighbors Saturn, Uranus, & Neptune. These four planets are called the gas giants because they consist almost entirely of gases.
Although photographs of Jupiter seem to show a solid surface, what can actually be seen are layers of clouds. When viewed through a telescope, the clouds appear as colored spots, dark belts, & bright zones. The clouds extend for thous&s of miles. At the base of the clouds the pressure is so strong that the gases are squeezed into a liquid metal form. This thick, hot liquid surrounds a rocky core.
Jupiter's atmosphere is similar to the sun's. It is mostly hydrogen with some helium. The planet also contains very small amounts of methane, ammonia, & water.
Temperatures vary greatly on Jupiter. At the tops of the clouds it is as cold as −240° F (−153° C) while the core may reach temperatures of 45,000° F (25,000° C).
Jupiter has complex weather patterns & violent storms. Its most distinctive feature is a huge storm called the Great Red Spot. The storm is oval-shaped & more than twice as wide as the Earth. Strong winds in the Great Red Spot swirl around in a spiral, as in a hurricane. The Great Red Spot has been observed from Earth for more than 300 years.
Like all planets, Jupiter has two types of motion, known as orbit & spin. Jupiter completes one orbit around the sun about every 12 Earth years. In other words, one year on Jupiter is equal to roughly 12 Earth years. Jupiter spins very rapidly on its axis. It takes less than 10 hours to complete one rotation. Thus, one day on Jupiter lasts less than 10 hours. (For more information on orbit & spin, see planets.)
Like Saturn, Jupiter has a narrow system of rings. The rings are made up of tiny rocks & dust particles. They are much smaller & dimmer than Saturn's rings, however, & because of this they were not discovered until 1979.
At least 40 satellites, or moons, orbit Jupiter. Many of them are very small, though Jupiter has four large moons. In fact, these large moons might be considered planets themselves if they orbited the sun & not Jupiter.
The four large moons are very different from each other. Fiery Io has many active volcanoes. Europa has a shell of recently formed water ice & a smooth surface. Callisto, on the other h&, has many craters. Its surface is ancient. Ganymede, the solar system's largest moon, is bigger than the planet Mercury. Scientists believe that Europa, Callisto, & Ganymede may have water beneath their surfaces. This is important because water is extremely rare in the solar system other than on Earth.
Because Jupiter can be seen from Earth without a telescope, the planet has been known since ancient times. The Italian astronomer Galileo used a telescope to discover Jupiter's four major moons in 1610. They were the first objects in the solar system to be discovered through a telescope.
The United States National Aeronautics & Space Administration (NASA) launched four unmanned spacecraft toward Jupiter in the 1970s. These Pioneer & Voyager missions flew past Jupiter & sent back the first close-up photographs of the planet. In addition, the missions studied Jupiter's atmosphere, storms, moons, & magnetic field.
The unmanned Galileo spacecraft was launched in 1989. When it reached Jupiter in 1995, it released a probe. The probe became the first man-made object to make contact with a gas giant. It sailed through the upper atmosphere & measured the chemical composition, temperature, & pressure. As expected, the probe was destroyed within about an hour by the extreme heat & pressure. Before it was destroyed, the probe gave scientists much information about Jupiter & its four largest moons.
The Galileo spacecraft also recorded the spectacular destruction of a comet known as Shoemaker-Levy. The comet smashed into Jupiter in July 1994 causing tremendous explosions on the planet.
