Thu. Feb 29th, 2024
Jupiter and Saturn

Want to brush up on your planetary science?

Let’s learn more about Jupiter and Saturn:

Table of Contents


Jupiter is by far the largest planet in our solar system. At just over 140,000 kilometers in diameter, all the other planets combined could be placed within Jupiter’s enormous mass. And, if you hollowed out Jupiter (like a pumpkin), you could fit over 1,000 Earths inside!


Jupiter is the model for a class of planets known as “gas giant” worlds. These planets share four basic things in common. They are all:

    • much bigger than the earth
    • they have many satellites (moons): Jupiter has 67 moons at last count
    • composed mainly of gas
    • Located in the outer part of our solar system.

Jupiter, despite its tremendous size and volume, has the fastest rotation speed. While on Earth a day lasts 24 hours, on Jupiter a day lasts just under 10 hours. This rapid speed of rotation, combined with its gaseous composition, causes Jupiter’s atmosphere to form astonishing patterns: belts, eddies, eddies, and at least one giant red spot that has been seen for more than 300 years.

The “Red Spot” (bottom left in the image above) is an intense area of ​​high pressure (like a hurricane in reverse) known as an “anticyclonic disturbance.” Only the Red Spot could fit two or three Earths inside it.

While Jupiter has many satellites, there are four that are especially easy to see and were discovered by Galileo more than 400 years ago; hence they are known as Galilean moons.

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These moons are tidally locked to Jupiter and orbit around it in just under 10 hours. As such, the moons (which are very easy to see with binoculars) take on different patterns that change noticeably throughout the night.


In this image, Jupiter is seen with Io (on the left) and Ganymede (on the right). Also note that the Great Red Spot has rotated to the bottom right in the image below compared to the bottom left in the image above.


Saturn is one of the original wandering stars known since ancient times. Of all the ancient planets, Saturn was the slowest moving (it takes 30 years to orbit the Sun once) and was associated with majesty and grandeur.

When Galileo turned his “optical tube” toward the stars, he observed the rings and drew them in his journal. The views of him through his first telescope (in 1610) were quite poor. However, observations of it made just over 400 years ago (in 1616) were good enough to show that Saturn was different from all other planets.

I didn’t understand what I was seeing, but we have since learned that this planet is surrounded by an immense and spectacular ring system.

Galileo's sketch
Like Jupiter, Saturn is a gas giant planet of immense size (about 120,000 kilometers in diameter). Its rotation speed is just over 10 hours, which compared to Earth’s 24-hour day is quite fast.

Like Jupiter, Saturn’s rotation speed and chemical composition have created cloud belts, although they are fainter and show less contrast than those of Jupiter.

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As big as Saturn is, it’s actually not very dense. If you placed the planet in a giant bathtub, it would probably float! However, due to the ring system, Saturn was nicknamed the crown jewel of the planets.


Saturn’s rings are made of ice and dust particles ranging from the size of a thumbnail to a small building.

Most likely, they are remnants of the initial formation and collisions of the planets and early material in the solar system.

Saturn has more than 62 moons and many of these moons are believed to help “guide” the ring material into a constant orbit.

Saturn’s largest moon, Titan, is larger than Mercury and has its own atmosphere. Titan goes through its own liquid cycle. Like Earth, it rains on Titan!

Rain accumulates in rivers, ponds and lakes which then evaporate forming clouds. However, unlike Earth, Titan’s liquid cycle is made up of methane instead of water.