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  • Writer's pictureolivershearman

Phenomenal planet profile - outer system gassy planets

This is a bit of a unique blog post set as I have included some of my ebook contexts to share all the incredible knowledge that I have dredged up on the planets.

This is the second of two parts in these blog posts. This post focuses on Jupiter, Saturn, Uranus and Neptune, while the other blog post focuses on the inner rocky planets. Hopefully this might lead to some fantastic planet based lessons for you and your students in the future!


Jupiter is the largest planet in the Solar system. It has a huge size and is about 2.5 times the mass of all the other planets combined! As with the other gas giants, the planet is made up of mainly gas and liquid and has no solid surface that we can detect or consider as a true surface. The planet is made up of mainly Hydrogen and Helium with traces of other compounds and elements throughout. In spite of its massive size, Jupiter is the fastest rotating planet in the Solar system; this adds to atmospheric disturbance which is already turbulent due to the cold of the higher clouds near space the heat of the core from gravitational compression. Since the core could be around the 35,000 C mark and the higher clouds can be closer to - 160 C, this causes cataclysmic rebalancing in terms of atmospheric storms and raging weather.

One of the most famous features of Jupiter is the great red spot, a vast and powerful storm that has been going on for hundreds of years and is a couple of times larger than the diameter of the Earth. Like a hurricane on Earth, the middle is calmer but around the edges the wind can rip along at up to 680 km/h. Yet unlike a hurricane, it has no true eye since there isn’t a liquid surface close enough to pull up from and it probably works a bit differently internally as well.

One of Jupiter’s features that is like Saturn but less well known is that Jupiter has rings!

Jupiter has narrow dark rings made up of dust and tiny pieces of rock. NASA’s Voyager 1 discovered these rings in 1979 and while small; they do add another element of unique beauty to Jupiter.

Jupiter’s magnetic field is many times stronger than Earths, with estimates ranging up to 20,000 times, it is vastly larger and more powerful than Earth’s magnetic field.

It is often considered that we actually have a lot to thank Jupiter for as well, since without this planet in our Solar system it would be far more likely that we would be hit with an asteroid or comet far more frequently than is currently the case. Though, it may have also been in the past that Jupiter and Saturn helped push smaller formation bodies towards the inner solar system and actually made more bombardment happen, however a lot of the crust and atmosphere we have reflects complex interactions with asteroids and comets and primal material from the early solar system. So is Jupiter truly a protector for Earth and a ‘shepherd of asteroids and comets’, in recent years, it seems the jury is still out.

Associated as Zeus in Greek mythology, the king of the gods and god of the sky and thunder. The romans also named Jupiter the king of the gods and really looking at its’ place in the solar system, you have to give them credit for getting it right.

Planet profile: Jupiter:

· Approximate size: Diameter: 142,984 km or 1,43 x 10^5

· Approximate mass: 1.898 x 10^27 kg

· Distance from the Sun: 7.79 x 10^8 km

· Orbital period: 4331 days or about 11.86 years

· Spin period: 9.9 hours

· Approximate gravity: 59.5 m/s^2 or about 6.07 g’s

· Axis tilt: 3.1 degrees relative to its orbit.

· Number of moons: 79 moons – current at time of writing - the main moons of Jupiter are: Ganyemede, Callisto, Io and Europa.

· Average temperature: -110 C

The Moons of Jupiter:

While there are many moons of Jupiter, the main four moons of Jupiter are those that Galileo discovered in early January 1610. These moons are the ones that we call the Galilean moons.

Ganymede is the largest moon in the Solar system; it is bigger than Mercury and Pluto and only slightly smaller than Mars. If it were orbiting the Sun it would almost certainly be a planet unto itself. It seems to mostly have an icy surface and crust and appears to have a partly liquid (molten) core that generates a magnetic field. In recent years it seems possible that it may have salty water deep beneath its surface.

The second biggest moon is Callisto and it is mainly made up of ice and rock. It orbits the furthest out of the four big moons discovered by Galileo, what we call the Galilean moons – Ganymede, Callisto, Europa and Io).

The third biggest moon is Io and it is only a little bit bigger than the Earth’s moon, but is vastly more volcanically active! Io orbits so tightly with Jupiter that it only takes about a day and a half to go around the planet. It has unusual colouring, which is colourful in yellow, orange, red and black colouration. A lot of the volcanic activity gives up Sulfur onto the surface, which is what give Io this odd colouration. Since Io interacts gravitationally with Ganymede and Europa, this flexing and pulling with Jupiter’s gravity as well is what provides the energy for such strong volcanic activity.

Europa is the smallest Galilean moon, but we believe has liquid water and is one of the key places of focus in the search for extra-terrestrial life. There is a huge amount of excitement about the possibility of water under a thick ice surface on Europa. The amount of water could exceed all the water on all the oceans on Earth and is a staggering possibility. Similar to Io, Europa could be interacting gravitationally helping to heat the moon’s core. Scientists think that Europa has everything needed to spark life, but we still aren’t sure yet and hopefully in the future we will send a probe in the future.

The four moons are all tidally locked to Jupiter, which means that for every time they orbit the planet they also rotate once.

Perhaps in the future we might be able to explore Jupiter’s moons particularly the four mentioned above and if so, what would it look like? One artists conception of this exploration could look like the below:


Saturn is often described as one of the most beautiful jewels of the Solar system owing to its large and stunningly visible rings. The rings are mostly made of ice and a little bit of dust, they are incredibly wide stretching a long way around the planet, but very thin with only about 20 metres thickness - barely anything in planetary terms. Saturn is the least dense planet in the Solar system with an average density of 0.687 gram/cubic centimetre. For comparison, Earth is about 5.52 grams/cubic centimetre; water for comparison is about 1 g/cc, which means theoretically that if you could find a bucket of water big enough Saturn would float.

One of the unique things about Saturn is that it is the flattest planet we have in the Solar system. Since Saturn has such low density and fast rotation, it is flatter top to bottom than it is across the middle. Saturn has the fastest winds in the Solar system with incredible wind speeds of up to 1,800 km per hour thundering around the planet. Saturn’s magnetic field strength is slightly weaker than Earth’s. While Saturn is a gas giant, it is suspected that the planet has a dense rocky core. Saturn’s atmosphere is made of about 95% Hydrogen, 4% Helium and trace elements throughout.

The Greeks knew Saturn as Cronus and was correspondingly known to the Romans as the god Saturnus that is who the planet is named after. In mythology, he is meant to be the father of Jupiter, the king of the gods and was often associated with harvest.

Planet profile: Saturn:

· Approximate size: it’s diameter is: 120,536km or 1.21 x 10^5 km

· Approximate mass: 5.68 x 10^26 kg

· Distance from the Sun: 1.43 x 10^9 km

· Orbital period: 10,747 days or 29.42 years

· Spin period: 10.7 hours

· Approximate gravity: 9.0 m/s^2 or 0.92 g’s

· Axis tilt: 26.7 degrees relative to orbit

· Number of moons: 62 moons (the main moons of Saturn are: Enceladus, Dione, Titan, Hyperion, Iapetus, Mimas, Tethys and Rhea).

· Average temperature: -140 C

The Moons of Saturn:

Discovered by the Dutch Astronomer Christiaan Huygens in 1655, Titan is the largest moon of Saturn and is the second largest moon in the Solar system behind Ganymede. It has a dense atmosphere made of mainly Nitrogen and methane and the planet itself is composed mainly of water, ice and rock. The atmosphere of Titan means that it sometimes has methane rain falling on its surface and has actual lakes of methane and other hydrocarbons awash on its surface. Titan’s atmosphere is actually so dense that it is about 1.5 times thicker than our own atmosphere.

Enceladus is the other exciting moon of Saturn and is a small ocean moon covered in ice. One of the reasons this moon is quite so exciting is its jets of water vapour that fly out in vast plumes adding to Saturn’s ring, meaning Enceladus is literally shooting some of its liquid insides out into the void of space. It has been hypothesized that the eruptions are caused by cracks in the icy surface which have high pressure, firing ice and water skyward when the pressure becomes too much. Since Enceladus’s surface is shifting and buckling, it seems to have too much heat for its size and while we can’t yet explain how it does this, it does seem hint at the potential for life.


Uranus is the seventh planet in our Solar system, discovered in 1781 by William Herschel and named after the ancient Greek god Ouranos. Uranus has the most unusual rotation in that it has retrograde rotation like Venus, however, it also has an unusual tilt so that the north and south poles are almost where the equator is on Earth. Think of it like looking down onto a spinning top. It has often been theorized that the unusual tilt is caused by a massive collision that occurred in the past, which caused the drastic changes to the orbital axis. Uranus does have rings, but these are rather narrow, similar in nature to Jupiter’s rings. Uranus is also thought to be the coldest planet in the Solar system with a minimum surface temperature of around -220 C making it the coldest of the eight planets.

Uranus has a relatively uniform appearance and looks rather dull in appearance. This is because the upper-most layer of its atmosphere is methane clouds that absorbs red wavelengths and thus only reflects blue-green colours. Uranus is mainly composed of Hydrogen and Helium with trace amounts of methane and acetylene. One puzzling aspect of Uranus is that it does not emit more energy than it receives from the Sun, unlike the other gas giants. Two possible theories are that the previous collision which caused its axial tilt, may have also taken much of the heat energy from gravitational compression, the other is that there may be a mechanism keeping the heat from reaching the surface of Uranus.

Planet profile: Uranus:

· Approximate size: Diameter: 5.11 x 10^4 km

· Approximate mass: 8.68 x 10^25 kg

· Distance from the Sun: 2.87 x 10^9 km

· Orbital period: 30,589 days or 83.75 years

· Spin period: 17.2 hours

· Approximate gravity: 8.7m/s^2 or 0.89 g’s

· Axis tilt: 97.8 degrees relative to orbit

· Number of moons: 27 known moons

· Average temperature: -195 C

The Moons of Uranus:

The five main moons of Uranus are Miranda, Ariel, Umbriel, Titania and Oberon. All the major moons show features of previous tectonic activity, though what this means is not yet clear. Miranda is only about as wide as the state of New York and a small icy world with incredible cliffs and canyons spread across the world. These moons are not deeply studied and while interesting, are essentially small, cold, dead worlds so far removed from us that they are currently all but inaccessible. There is only 1 spacecraft, the Voyager 2 that has ever visited the Uranus planetary system.


Neptune is currently the furthest planet in the Solar System and has a striking blue colouration. Neptune was discovered in 1846 by John Couch Adams or Jean Joseph Le Verrier depending on whose side you take. Neptune is mostly made of Hydrogen and Helium and similar to Uranus in composition. The Greeks originally knew Neptune as Poseidon, but the romans knew Neptune with the same name as the god of the seas.

Planet profile: Neptune:

· Approximate size: Diameter: 4.95 x 10^4 km

· Approximate mass: 1.02 x 10^26 kg

· Distance from the Sun: 4.5 x 10^9 km

· Orbital period: 59,800 days or 163.7 years

· Spin period: 16.1 hours

· Approximate gravity: 11 m/s^2 or 1.12 g’s

· Axis tilt: 28.3 degrees relative it’s orbit

· Number of moons: 14 moons (main moon: Triton)

· Average temperature: -200 C

The Moons of Neptune:

Triton is particularly interesting as it is the only large moon that orbits in a retrograde orbit around its planet (ie: opposite to its spin). This means that Triton was probably a captured object. Triton is also one of the coldest moons in the solar system, when Voyager 2 flew past; it measured temperatures of -235 C on its surface. Since it is so distance, cold and quiet, there is not much more to say about this far away frozen moon.

The Solar System:

An approximate size comparison regarding the planets of the Solar system.

The Solar system has some amazing aspects that we have not considered, such as the further out dwarf planets or the asteroid belt between Mars and Jupiter. I should mention that there are a large number of comets that occasionally make their way into the inner solar system, planet X the illusive tenth planet has yet to be discovered and the further out the Oort cloud at the edge of the Solar system. You might have noticed planet 10 no longer makes sense since Pluto is no longer a planet, which is why we not call the possible new planet, planet X.

However, planet X and the Oort cloud are more of a local consideration in the universal scheme of things. So while looking at the planets helps us understand the rest of the universe; we as a scientific community are not ready to investigate asteroids and comets in other stellar systems.

It is worth mentioning that the Solar system has some incredible resonances to consider which are caused by gravitational dissipation. A prime example of this, is Pluto and Neptune who have a 2 : 3 resonance structure, which means that for every 3 orbits Neptune completes, Pluto completes 2. Another spectacular example is in the main moons of Jupiter, the moons Io, Europa and Ganymede are in a 1 : 2 : 4 resonance with each other. This means that for every 4 orbits of Io, Europa will complete 2 orbits and Ganymede will complete 1 orbit. Some people even make sound tracks to go with animations of these orbits to help understand the concept.

If you would like to learn more about the universe, then please do consider purchasing my good value ebook part 1, 2 and 3 - link here.

Thanks for reading.

Cheers and stay curious

Oliver - The Teaching Astrophysicist

(Note: This blog post was NOT generated by AI and is conceived, typed and uploaded by a real person.)

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