Colourful bands of clouds and a swirling red storm make Jupiter one of the most visually interesting objects in the entire solar system.

The Planet

At 11 times wider than the Earth, Jupiter is by far and away the largest planet in the Solar System. Jupiter takes the place as the most massive of all planets, coming in at just under 318 times heavier than our planet. Unlike Saturn, this results in Jupiter having a gravitational pull that is approximately 2.5 times stronger than what we experience here on Earth.

Orbiting over 750 million kilometres from the Sun, Jupiter is the first of the outer planets. At this extreme distance, Jupiter takes almost 12 Earth years to orbit the Sun, meaning that from our perspective on Earth, Jupiter appears to move into a different zodiac constellation every year.

Jupiter is tied for 5th place for brightness in the sky, losing only to the Sun, the Moon and Venus, tying with Mars. This makes the giant planet instantly identifiable in the night sky, shining brighter than most other objects on any given night. Jupiter was observed by Galileo Galilei in 1610 through a telescope for the first time, where the astronomer observed 4 bright stars that moved across the sky, with the planet. After many observations, Galileo determined these stars to be moons orbiting Jupiter!

Jupiter as imaged by the Juno Orbiter - NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

The Atmosphere

Jupiter’s most distinguishing features are found within its atmosphere. The striped upper atmosphere of Jupiter changes from year to year in colour and size, however these bands are permanent enough to be named. The dark bands are referred to as belts, and the lighter ones known as zones. The boundaries of belts and zones produce regions of extreme turbulence, and many storms. Inside the zones, wind speeds of 360 km/h are common.

The most defining feature of Jupiter however, is its Great Red Spot. Known to exist from 1831, this storm has been raging for as long as humans have been observing the gas giant. The storm is currently wider than the Earth, however it has been shrinking, originally being over 2.5 times wider that it is currently when observed in 1831. Despite the shrinking, this storm is suggested to be a permanent feature of the planet’s dynamic atmosphere.

A comparison of the Galilean Moons and Jupiter's Great Red Spot - NASA/JPL/DLR

The Moons

Presently, Jupiter has a total of 80 moons, with 60 of them being little more than asteroids, measuring less than 10km in diameter. Jupiter is home to some of the largest moons in the Solar System, the Galilean Moons of Io, Europa, Ganymede and Callisto. These moons were first observed in 1610 by Galileo Galilei and were the first objects that were known to orbit a planet other than Earth. These moons are each unique and interesting, from Ganymede, the largest moon in the solar system, to the volcanically dynamic Io.

An artist's impression of Juno in Jupiter's orbit

The Missions

Since 1973, Jupiter has been visited by 9 spacecraft. Most missions to the giant planet are fly-by missions, consisting of a spacecraft hurtling past and hurriedly imaging and observing the planet. Fly-by spacecraft include Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses, Cassini and New Horizons. Each of these spacecraft received a boost of energy in the form of a gravitational assist, helping accelerate the craft towards their next destination.

Two orbiting missions, Galileo and Juno have successfully arrived in Jovian orbit. The first, Galileo, orbited the planet for 8 years, performing invaluable science before intentionally crashing into the atmosphere of the planet to burn up.

Juno is an active mission that has been in Jovian orbit since July 2016. Juno entered a polar orbit and returned some of the most visually stunning images of the planet ever taken. Following the success of its original mission, the probe has had 2 mission extensions and currently faces termination in September 2025.

How do I see Jupiter?

Jupiter is visible in the evening sky for the remainder of 2021 as an extremely bright star. The planet appears on the eastern horizon just after sunset, and will appear closer to the western horizon later in the year.

Riley Johnston

Riley is an experienced astronomy guide who has been working within the astronomy community for several years. He is incredibly passionate about the night sky and holds a Bachelor’s Degree in Science, Math and Education.

Riley Johnston


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