Jupiter
Jupiter is the largest planet in our solar system. It is so massive that all the other planets combined could fit inside it more than twice over. Jupiter is a gas giant, made mostly of hydrogen and helium. It has no solid surface to land on, just deeper and deeper layers of gas and liquid. Its most famous feature is the Great Red Spot: a hurricane bigger than Earth that has been raging for hundreds of years.
- Position 5th planet first of the gas giants
- Distance from Sun 778 million km 5.2 AU
- Diameter 139,820 km 11 times wider than Earth
- Day length 9h 56m fastest spin of any planet
- Year length 12 Earth years one trip around the Sun
- Moons 95+ including Io, Europa, Ganymede, Callisto
Where Jupiter sits
Jupiter is the fifth planet from the Sun, sitting beyond the asteroid belt. It orbits at about 778 million km from the Sun, more than five times Earth's distance. Even though it's so far away, Jupiter is so big and bright that you can often see it with the naked eye from your back garden. It looks like a very bright star.
Jupiter vs Earth
The solar system's biggest planet compared to home
Jupiter is 11 times wider than Earth. You could fit 1,321 Earths inside Jupiter.
Jupiter has more mass than all the other planets, moons and asteroids combined, more than twice over.
If you could stand on Jupiter (you can't, it has no surface), you'd weigh two and a half times more than on Earth.
Jupiter spins faster than any other planet, with a day of less than 10 hours. Its rapid spin makes it bulge noticeably at the equator.
Jupiter takes 12 Earth years to make one trip around the Sun. A child born when Jupiter was in one place would be a teenager before Jupiter returned to that spot.
Jupiter has at least 95 known moons, more than any other planet (although new ones are being discovered every year).
A planet made of gas
Jupiter has no solid surface. If you tried to land a spacecraft on Jupiter, it would just keep sinking. The atmosphere gets gradually thicker and hotter as you go down, turning from gas into liquid, and then into a strange hot soup of metallic hydrogen near the core. Somewhere deep down there might be a small rocky or icy core, but no one has ever seen it.
Jupiter is roughly 90% hydrogen and 10% helium, with traces of ammonia, methane and water. These are the same ingredients as the Sun, just in different amounts. Some astronomers describe Jupiter as a "failed star". If it had been approx. 80 times more massive, it could have started nuclear fusion in its core and become a small star itself.
The Great Red Spot
Jupiter's most famous feature is the Great Red Spot, a giant storm that has been raging for at least 350 years. It was first spotted by astronomers in the 1660s and has been there ever since. The storm is wider than Earth and rotates anticlockwise, with winds of up to 680 km/h.
For a long time the Great Red Spot was even bigger, perhaps three times Earth's width. Today it's slowly shrinking, and scientists aren't sure why or how long it will last.
The Galilean moons
Jupiter has at least 95 moons, but four of them are big enough to see with a small telescope from your back garden. They're called the Galilean moons because they were discovered by the astronomer Galileo Galilei in 1610. They were the first objects ever discovered orbiting a planet other than Earth. Their discovery proved that not everything in the universe goes around our planet.
Io: the volcanic moon
Io is the most volcanically active body in the entire solar system. It has hundreds of active volcanoes that constantly spew sulphur and lava across the surface, giving Io its strange yellow, orange and brown colour. The volcanoes are caused by Jupiter's immense gravity stretching and squashing the moon as it orbits.
Europa: an ocean under ice
Europa is covered in a smooth shell of ice, but beneath that shell is a deep ocean of liquid water. Europa probably has more water than all of Earth's oceans combined. That makes it one of the most exciting places to look for extraterrestrial life. NASA's Europa Clipper spacecraft is on its way there now.
Ganymede: bigger than a planet
Ganymede is the biggest moon in the solar system. At 5,268 km across, it's even bigger than the planet Mercury. If it orbited the Sun instead of Jupiter, we'd probably call it a planet.
Callisto: the cratered one
Callisto is the most cratered object in the solar system. Its surface hasn't changed much for billions of years, so you can still see the marks from every major asteroid impact going right back to the early days of the solar system.
Jupiter's rings
Jupiter has rings, just like Saturn, but they're so faint and thin that they weren't discovered until 1979 when the Voyager 1 spacecraft flew past. Jupiter's rings are made of tiny dust particles, probably blasted off Jupiter's small inner moons by micrometeorite impacts. You can't see them from Earth, even with a powerful telescope.
The solar system's vacuum cleaner
Jupiter's massive gravity acts a bit like a giant vacuum cleaner, attracting many of the asteroids and comets that wander into the inner solar system. This may have helped life on Earth: without Jupiter, our planet would probably get hit by big objects much more often, which would make it harder for complex life to develop.
The comet that crashed into Jupiter
In 1994, a comet called Shoemaker-Levy 9 broke into 21 pieces and slammed into Jupiter over the course of a week. The impacts left scars in Jupiter's atmosphere that were visible for months. The biggest piece exploded with the energy of 600 times the world's entire nuclear arsenal. It was the first time humans ever witnessed the collision of two solar-system objects, and it gave scientists serious concern about what would happen if a similar comet ever hit Earth.
Missions to Jupiter
Several spacecraft have visited Jupiter, including the Voyager probes (1979) which gave us our first close-up photos, the Galileo orbiter (1995-2003), and the Juno spacecraft which has been orbiting Jupiter since 2016. Juno has revealed cyclones bigger than countries swirling around Jupiter's poles and helped scientists understand what's deep beneath the clouds.
Two new missions are now on their way: JUICE (a European mission to study Jupiter's icy moons) and Europa Clipper (a NASA mission to study Europa's ocean for signs of life).