So – you’re still interested in astronomy?6 min read

Hello again. If you remember, last time we took a look at 10 things you wanted to know about Mercury. This time, I thought it would be a great idea to consider 10 facts you might find interesting about one of the biggest influences in our Solar System – Jupiter.

1. So, just how big an influence does Jupiter Have?

At 741 million kilometers away, (484 million miles) Jupiter is the fifth planet out from the sun, and the first of what are known as the Jovian planets. (The others being Saturn, Uranus and Neptune).




As you can see from the picture, she is termed a gas giant, with a mass one thousandth that of the sun, and more than two and a half of all the other planets combined.
You may remember from earlier blogs, it is believed the presence of this leviathan in our solar system was one of the contributing factors to the formation of the Main Asteroid Belt, as the influence of her mass and gravity prevented the accretion of what might have been another planetary disc.
Interesting Fact: As mentioned, Jupiter has a mass 2.5 times that of all the others bodies in the solar system combined. (So massive, that her barycentre – the point between two objects where they balance each other – actually lies above the Sun’s surface.)  Despite her bulk, Jupiter would need to be about 75 times as massive to fuse hydrogen and become a star, and yet, the smallest red dwarf sun is only 30% larger than her radius.


2. How big is Jupiter?

Jupiter has a diameter of 142,984 km (88,846 miles). Although termed a gas giant, some scientists now believed that our largest planet has an extremely dense core, overlaid by a very deep layer of liquid metallic hydrogen. Above this, the extensive atmosphere divides into two main bands. A thicker lower deck, some 5000 km (3,107 miles) in altitude, and a much thinner upper deck. Then we come to the cloud band of ammonia crystals, and ammonium hydrosulfide, which has been measured at only 50 km (31 miles) thick. Because of the abundance of lightning storms, it is also thought this thin layer contains water.


3. Jupiter is famous for its red spot. What is that?

The Great Red Spot is a persistent anticyclonic storm that has existed since at least the 17th century. Located at 22 degrees south of the equator, it varies in size between 2 – 3 times that of Earth. Let’s get a sense of perspective. Take a look at the picture below.




The white oval below the Great Red Spot is another storm, and THAT is about the same size of Earth. Cool eh?


4. What is Jupiter actually made of?

The upper atmosphere consists of 75% hydrogen and 25% helium by mass. However, that changes the further you descend. The interior contains only 71% hydrogen and 24% helium by mass. (The other 5% being made up of methane, water vapor, ammonia and silicate based compounds). Because Jupiter isn’t a solid body, her atmosphere rotates at different speeds. (Thus the bands) The fastest zone is the equator. The slowest, (by 5 minutes) are the polar areas. The areas in between gradually blend between the two.


5. Any other cool facts?

Of course. When viewed from Earth, Jupiter has an apparent magnitude 0f -2.94, making her the 3rd brightest object in the night sky after the Moon and Venus, and easily bright enough to cast shadows.

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Note: At certain times of the year, Mars can appear brighter at certain points in its orbit.


6. How many moons does Jupiter have?

Aha! So far, 67 – Yes, Sixty-Seven – confirmed moons have been discovered orbiting Jupiter. The most massive of them, the four Galilean moons, (Io, Europa, Ganymede & Callisto), were discovered in 1610 by Galileo Galilei, and were the first objects found to orbit a body that was neither the Earth nor the Sun.


7. How long does it take Jupiter to orbit the Sun?

Jupiter orbits our Sun once every 11.86 Earth years. However, because of an orbital eccentricity, her distance from the solar center can vary by up to 75 million kilometers (46 million miles) – Remember last month? That’s larger than the distance of Mercury from the Sun!


8. Being so big, Jupiter must have an impressive electromagnetic field then?

Jupiter’s broad magnetic field is 14 times more powerful than the Earth’s, making it the strongest in the Solar System apart from sunspots. The field is believed to be generated by eddy currents – swirling movements of conducting materials – within the liquid metallic core. But that’s not the whole story. Look at the comparison picture below.


The volcanoes on Io, emit large amounts of Sulfur dioxide, which forms a gas torus along the moon’s orbit. This gas is ionized in the magnetosphere, producing sulfur and oxygen ions. They, together with the hydrogen ions originating from the atmosphere of Jupiter itself, form a plasma sheet along Jupiter’s equatorial plane. This sheet co-rotates with the planet, causing a deformation of the dipole magnetic field into a magnetodisk.

About 75 Jupiter radii from the planet, the interaction of the magnetosphere with the solar wind generates a bow shock. Now, the magnetosphere is surrounded by something called a magnetopause, (that’s the boundary between the magnetosphere and plasma). This is located on the inner edge of the magnetosheath.

The solar wind acts on these regions, elongating the magnetosphere on the lee side, extending it until it almost reaches Saturn. The four largest moons of Jupiter all orbit within the magnetosphere, which protects them from the solar wind.

9. Are there any other surprises?

There certainly are!

Not everyone realizes Jupiter has a ring system. Just take a look at the picture below.



The system is comprised of three main segments. 1- The inner torus of particles, which is known as the halo. 2- A brighter main ring. 3- The gossamer outer rings. Unlike Saturn, these segments are made from dust, not ice, and it is thought that a number of the smaller, inner moons, also contribute material to their substance..


10. Is there anything about Jupiter that might surprise us?

There certainly is.

Jupiter has the fastest rotation of all the planets in the solar system, completing a full rotation on its axis in slightly less than 10 hours. It’s so fast, that when you look at Jupiter close up, you notice a very distinct bulge at the equator, where her diameter is 9,275 km (5,763 miles) longer than if you measured the diameter through the poles.

So, there you go. I hoped you enjoyed this brief look at Jupiter. Next time, we’ll look at 10 interesting things about the final planet out in our Solar System. Neptune.

See you then!




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Andrew Weston

Andrew P. Weston is Royal Marine and Police veteran from the UK who now lives on the beautiful Greek island of Kos with his wife, Annette, and their growing family of rescue cats. An astronomy and law graduate, he is the creator of the international number one bestseller, The IX, and also has the privilege of being a member of the Science Fiction and Fantasy Writers of America and the British Fantasy Society. When not writing, Andrew devotes some of his spare time to assisting NASA with one of their remote research projects, and writes educational articles for and Amazing Stories. He also enjoys Greek dancing and language lessons, being told what to do by his wife, and drinking Earl Grey Tea. If you would like to find out more, visit his blog or website at:

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