Jupiter

Jupiter

Could Jupiter have been a star instead of a planet? Jupiter is the fifth planet from the Sun and the biggest planet in our solar system. More than 1,300 planets the size of Earth could fit inside Jupiter. If you could lump together all eight of the other planets in the solar system, the resulting planet would still be smaller than Jupiter! In some ways, Jupiter is more like a star than a planet.

A FAILED STAR?

Like the Sun and other stars, Jupiter is a huge ball of hydrogen gas and helium gas. It gives off more heat than it receives from the Sun. Many moons and several thin rings go around Jupiter. Jupiter’s moons and rings are like a little solar system.

Our solar system formed from a big cloud of gas and dust. The Sun formed at the center. The Sun sucked in gas and got bigger and bigger and hotter and hotter. Finally, it was big enough and hot enough to become a star and shine. Jupiter formed the same way. But Jupiter never got big and hot enough to become a star like our Sun. There was not enough gas in the solar system to make two stars. Jupiter is more like a star that failed.

WHAT’S IT LIKE ON JUPITER?

You could never land a spacecraft on Jupiter. Jupiter does not have a hard surface. Astronomers (scientists who study space) call Jupiter a gas giant because it’s made almost entirely of gas. From space, Jupiter looks striped. The stripes are actually bands of colored clouds that circle the planet.

The clouds near the top of the atmosphere are bathed in deadly radiation. Jupiter's highest clouds are also very cold. The clouds get hotter deeper down. Strong winds blow in opposite directions in each band of clouds. In one band, the winds blow toward the east. In the next band, they blow toward the west.

Big storms rage in the clouds around Jupiter. The biggest storm is called the Great Red Spot. Three planets the size of Earth could fit across the Great Red Spot. This storm may have lasted for hundreds of years.

Deeper into the planet, the gas gets thicker and heavier. It gets so heavy that some of it gets squeezed into a layer of liquid hydrogen. Astronomers think that there might be some rock and metal in the center, or core, of Jupiter.

JUPITER’S MOONS AND RINGS

Jupiter has more moons than any other planet in our solar system. About 400 years ago, Italian astronomer Galileo Galilei turned a telescope to the sky and discovered moons going around Jupiter. The four biggest moons are the ones that Galileo discovered. Astronomers call them the Galilean satellites. Their names are Io, Ganymede, Europa, and Callisto.

Io is covered with volcanoes. Many of the volcanoes on Io are active, which means they are erupting or might erupt again someday. Io has more volcanoes than any other planet or moon.

Ganymede is the biggest moon in our solar system. It is even bigger than the planets Mercury and Pluto!

Europa and Callisto are covered with ice. Astronomers think that enormous oceans of water may lie under the ice.

The rings around Jupiter are thin, dark, and hard to see. They are made of rock and tiny bits of dust.

HOW DO WE KNOW ABOUT JUPITER?

The ancient Romans named the planet after Jupiter, their chief god, because it shines so brightly in the night sky.

In the early 1600s, Galileo became the first person to study Jupiter with a telescope. He helped prove that Jupiter and all the planets go around the Sun. Before then, astronomers thought that the Sun, other stars, and all the planets went around Earth. Today, astronomers use much more powerful telescopes to look at Jupiter and other objects in space.

Several spacecraft have visited Jupiter. The first, in 1972, was Pioneer 10. Cameras on the spacecraft took pictures of Jupiter. Instruments on the spacecraft made measurements of the planet.

In 1994, astronomers watched a comet crash into Jupiter. Jupiter’s gravity tore the comet apart as the comet got close. Pieces of the comet smashed into Jupiter’s atmosphere. The impacts caused huge explosions. Powerful winds on Jupiter then blew the remains of the comet away.