Jupiter

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass nearly 2.5 times that of all the other planets combined. Its diameter is 11 times that of Earth, making it a truly enormous world. Jupiter has been observed since prehistoric times and shines brightly in our night sky as the third-brightest natural object, after the Moon and Venus.

This giant planet plays an important role in our Solar System. It was the first of the Sun's planets to form, and its early movement influenced how the other planets developed. Jupiter's atmosphere is mostly hydrogen and helium, with traces of other elements and compounds like ammonia and water vapour. The planet is known for its stunning appearance, including colorful bands and the famous Great Red Spot, a massive storm larger than Earth.

Jupiter also has many moons—at least 115 moons orbit around it. Its four largest moons, called the Galilean moons—Io, Europa, Ganymede, and Callisto—are easily seen with binoculars. Jupiter is surrounded by faint planetary rings, and since 1973, it has been visited by several robotic probes to help scientists learn more about this fascinating planet.

Name and symbol

Jupiter was named after the chief god in both ancient Greek and Roman civilizations. The Greeks called him Zeus, and the Romans called him Jupiter. In 1976, the International Astronomical Union officially adopted the name Jupiter for the planet.

The symbol for Jupiter comes from a Greek letter zeta with a horizontal stroke. The word "Jovian" is used to describe things related to Jupiter, and the older word "jovial" means happy or merry, a mood people thought Jupiter brought in astrology.

Formation and migration

Main article: Grand tack hypothesis

See also: Formation and evolution of the Solar System

Jupiter is thought to be the oldest planet in our Solar System. It formed just one million years after the Sun and about 50 million years before Earth. Scientists believe Jupiter formed beyond the snow line, a place far from the Sun where it was cold enough for water and other gases to turn into solid pieces. These pieces helped Jupiter grow a solid core before it gathered a thick, gaseous atmosphere.

One popular idea, called the grand tack hypothesis, suggests that Jupiter started forming about 3.5 astronomical units (AU) from the Sun. As it grew, its gravity pulled it closer to the Sun, changing the paths of other young planets. Later, Jupiter and Saturn moved into a special balance, causing them to move farther from the Sun to where they are today. These movements happened over just a few million years and helped make space for Earth and the other inner planets to form.

Physical characteristics

Jupiter is a gas giant, which means it is made mostly of hydrogen and helium. It is the largest planet in our Solar System. Jupiter is about eleven times wider than Earth and has a volume 1,321 times that of Earth. However, it has a lower average density than Earth, which means it is less heavy for its size.

Jupiter’s atmosphere is mostly hydrogen and helium, similar to the composition of the Sun. It also contains small amounts of other gases like water, methane, and ammonia. Jupiter is very massive—about 318 times the mass of Earth, which is more than twice the combined mass of all the other planets in our Solar System. Because of this great mass, Jupiter has a strong influence on objects around it.

Jupiter spins very quickly, completing a full rotation in just under ten hours. This fast spin causes it to bulge slightly at the equator. Unlike Earth, Jupiter does not have a solid surface; it is made of gas that gets thicker and hotter the deeper you go. Scientists think Jupiter might have a small, dense core deep inside, but most of it is fluid. Jupiter also gives off more heat than it receives from the Sun, which makes it slowly shrink over time.

One of Jupiter’s most famous features is the Great Red Spot, a huge storm larger than Earth that has been swirling for centuries. Jupiter also has many smaller storms and bands of clouds that create its colorful appearance. The planet’s strong magnetic field creates a large area around it that protects its moons from harmful space radiation.

Orbital motion and observation

Jupiter is the only planet whose barycentre with the Sun lies outside the Sun. It orbits the Sun at an average distance of 778 million km, completing a full orbit every 11.86 years. Its orbit is nearly circular and tilted slightly compared to Earth's orbit.

Jupiter is usually the fourth-brightest object in the night sky after the Sun, the Moon, and Venus. Depending on its position, it can appear brighter or dimmer to us on Earth. Through a telescope, you can see Jupiter's four large Galilean moons and the cloud belts on its atmosphere. Larger telescopes can even show Jupiter's famous Great Red Spot.

Gravitational domain and influence

Planetary rings

Main article: Rings of Jupiter

Jupiter has a faint planetary ring made of dust. These rings have three parts: a halo, a main ring, and a gossamer ring. The main ring likely comes from material thrown off by the moons Adrastea and Metis. Thebe and Amalthea probably create the gossamer ring.

Moons

Main article: Moons of Jupiter

See also: Timeline of discovery of Solar System planets and their moons and Satellite system (astronomy)

Jupiter has 111 known natural satellites. The four largest are called the Galilean moons: Ganymede, Callisto, Io, and Europa. These big moons were discovered by Galileo.

Galilean moons

Main article: Galilean moons

The Galilean moons—Io, Europa, Ganymede, and Callisto—are some of the biggest moons in the Solar System. Their orbits follow a pattern where for every four orbits Io makes, Europa makes two and Ganymede makes one. This pattern causes their paths to stretch and squeeze, creating heat inside them. This heat makes Io very active with volcanoes, and it also affects Europa’s surface.

Classification

Jupiter’s moons are sorted into groups based on their paths around the planet. Most inner moons likely formed with Jupiter, while outer moons are thought to be captured asteroids.

Interaction with the Solar System

Jupiter’s strong gravity has shaped the Solar System. It affects the paths of planets and created gaps in the asteroid belt. Jupiter also controls many asteroids that stay near its path around the Sun, called Trojan asteroids. These are named after characters from the Iliad.

Impacts

Main article: Impact events on Jupiter

Jupiter often gets hit by comets and asteroids because of its strong gravity. In July 1994, Comet Shoemaker–Levy 9 crashed into Jupiter and was watched by telescopes around the world.

Observation and exploration history

Observations of Jupiter go back thousands of years. Ancient Babylonian astronomers studied Jupiter, and the Chinese called it the "sui star." They used its movement to help create a calendar based on twelve yearly cycles. Later, in the 4th century BC, these observations grew into what we now know as the Chinese zodiac.

In 1610, Galileo Galilei used a telescope to discover Jupiter’s four largest moons, now called the Galilean moons. This was the first time anyone had seen moons orbiting a planet other than Earth. Shortly after, another astronomer named Simon Marius also found these moons and gave them the names we still use today: Io, Europa, Ganymede, and Callisto. These discoveries helped support the idea that the Sun, not Earth, was at the center of our solar system.

In culture

See also: Jupiter in fiction and Planets in astrology § Jupiter

People have known about Jupiter since ancient times. It is bright enough to see without a telescope, even during the day when the Sun is low. Different cultures gave Jupiter names based on their gods and beliefs.

The Babylonians saw Jupiter as their god Marduk. The Greeks called it Zeus, their chief god, and the Romans called it Jupiter, their god of the sky and thunder. In India, it was named after Brihaspati, the teacher of the gods. In East Asia, it was known as the "wood star" and linked to the idea of the year star because it moves through the zodiac constellations.