Jupiter is the giant of the solar system. It is an incredible world, more than three hundred times the mass of the Earth and eleven times as big. Jupiter is the largest planet in the solar system by far. Most of Jupiter is made of hydrogen and helium gas. If you could somehow take all that gas away then you’d probably find a small core of solid material only about ten times the mass of the Earth. Other compounds like methane gas, water, and ammonia exist in Jupiter’s atmosphere and help color it so that we can see the great streaks and storms that race around the planet. Since most of Jupiter is made up of these huge amounts of gas, we call it a gas giant planet. We have found lots of gas giant planets around other stars. They are so big that they are easier to find than the smaller planets like the Earth. But the only gas giants in our solar system are Jupiter and Saturn, which both are the heavyweights of the solar system.

Illustration of the inside of Jupiter. Below the gas that we see then the pressure is so high that the hydrogen gas becomes like a liquid metal! Most of the inside of Jupiter is this amazing substance, probably with a core of very dense matter at the center.

In many ways Jupiter is more like a star than a planet, except it would need to be about 70 times more massive to turn into a real star. Because of its incredible size at the center of Jupiter the temperature is thought to be about 64,000F! This is mainly because Jupiter’s own weight or gravity is compressing things – and as you compress things they get hot. Since the middle of a planet is under constant pressure, it’s also very hard for things to cool down, which is why the temperature keeps going up. The pressure in Jupiter’s core is about 40 million times the pressure that we feel standing on the surface of the Earth!

Weather on Jupiter

Although Jupiter is so large it only takes about 10 hours for it to rotate. Huge storms of swirling gas are created in its atmosphere. The most famous is Jupiter’s Great Red Spot. We know that his storm is at least 200 years old, because we have books by ancient astronomers mentioning this amazing feature that they also noticed on the planet. It is a good thing they remembered to write this down for us to find! The Great Red Spot is big enough that you could fit the planet Earth inside its “eye,” or center.

Image of Jupiter’s Great Red Spot.

Like the Earth Jupiter has a magnetic field that makes a great invisible bubble surrounding the planet, except Jupiter’s magnetic field is at least 14 times more powerful than Earth’s. This is probably because of all the metallic hydrogen spinning around deep inside Jupiter. Although the great magnetic bubble helps protect Jupiter from powerful particles that stream through our solar system it also focuses all of that energy into places around it. This can make it impossible for humans, or even robotic spacecraft, to survive without protective shielding from that radiation.

Jupiter’s moons and rings

Jupiter is a huge planet and it has an astonishing total of about 63 moons that we have found so far! Some of these moons are very small, but the biggest ones are as big as the planet Mercury. The most famous of Jupiter’s moons are Io, Europa, Ganymede, and Callisto. They were first recognized by Galileo Galilei, the first astronomer to use a telescope to observe the planets, four hundred years ago! Since Galileo first discovered these moons, they are now known as the Galilean moons, or Galilean satellites, of Jupiter.

These moons are remarkable worlds in their own right. The moon Io is being stretched and squashed by Jupiter’s gravity so much that it is hot and molten inside and has active volcanoes shooting great jets of material out into space, even as you’re reading this! None of the moons has much of an atmosphere but at this distance from the Sun temperatures are a chilly -200 F. So Europa, Ganymede, and Callisto have huge amounts of frozen water on their surfaces. Beneath the icy crust of Europa there may be a vast ocean of liquid water, as much as twice the volume of all of Earth’s oceans combined! Ganymede is actually bigger than the planet Mercury, and it too shows signs that there might be liquid water deep below its frozen surface.

Places like these are extremely interesting in the search for living things, since there are similar places in the deep oceans and polar regions on Earth that seem to be able to support life.

Illustration of the four largest moons of Jupiter, known as the Galilean moons. From left to right: Callisto, Ganymede, Europa, and Io.

Jupiter also has a very faint set of rings, small particles of dusty rock encircling the planet. This dust probably comes from some of the smaller moons orbiting Jupiter.

Think About It

Because Jupiter is so big, it also has a huge amount of gravity. Thanks to this, it attracts asteroids and other space rocks that come charging through the solar system. While Jupiter may also miss and actually send some rocks crashing into the inner solar system, where we live, it also acts like a big brother to the Earth, protecting it from lots of rocks that might otherwise smash into the Earth. Some scientists even believe that life may not have been able to exist on the Earth like it does today without a giant Jupiter absorbing and protecting us from all those dangerous rocks flying around our solar system

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