What do we know about the giants of the solar system?

You ggas giants are very large planets, made mostly of gases such as hydrogen and helium. They even have a rocky core, but it is very small in relation to the size of the atmosphere.

No Solar system there are four of these exotic worlds. Are they Jupiter, Saturn, Uranus e Neptune. The expression “gas giant” has an interesting origin. Evidence shows it was first used in 1952 in a science fiction play by James Blish.

The last four planets in the solar system are our gas giants (Source: Pixabay/WikiImages)The last four planets in the solar system are our gas giants (Source: Pixabay/WikiImages)Source: Pixabay

At that time, before the period of space exploration, everything we knew came from telescopic observations. It wasn’t until 20 years later, in 1972, that the Pioneer 10 made the first flyby over Jupiter and we were able to confirm the identity of our neighbors.

Despite being grouped in the same category, our gas giants differ greatly from each other, being Jupiter e Saturn much bigger than Uranus e Neptune. In addition, the composition of the atmospheres of each one also has its particularities. See below for details on each of them.


Jupiter it is the largest planet in our solar system, with a diameter 22 times that of Earth. It is visible in the night sky with the naked eye, so it was already known to ancient peoples.

Most of its mass is believed to be made up of liquid metallic hydrogen. This theoretical substance is only possible to exist under extremely high conditions of temperature and pressure and creates a very powerful magnetic field.

The planet’s magnetism generates a curious phenomenon. He is responsible for the aurora, both northern and southern, a show of lights at the north and south poles, just like here on Earth. But there they shine brighter than anywhere else in the solar system.

Jupiter is the largest planet in the solar system (Source: Unplash/Planet Volumes)Jupiter is the largest planet in the solar system (Source: Unplash/Planet Volumes)Fonte:  Unplash

The rotation movement of this giant lasts only 10 Earth hours. The translation is slower, it takes 12 years for it to complete one revolution around the Sun.

And Jupiter also has rings. They were discovered by the Voyager spacecraft in 1979, but they are much less flashy than those on Saturn. They are made up of more dust and less ice, so they reflect less sunlight.

Because it is gaseous and cold, conditions on the planet are very inhospitable. But Jupiter may harbor life elsewhere: on one of its moons. Today there are 79 of them confirmed, and the best known were discovered by Galileo Galilei, one of the most prestigious astronomers who ever lived.

Four were discovered by him: Io, Europa, Ganymede and Callisto. And precisely in the second of them, the researchers believe that there is an immense ocean under the rocky surface. The hypothesis has caused a furor in the astronomical environment, because it would allow the satellite to harbor life.

NASA’s Juno spacecraft arrived on the planet in 2016 and is looking for answers to our questions there. It adds to other efforts being made to better understand it, such as the use of the Hubble telescope.


With about nine times the radius of the Earth, Saturn is famous for its beautiful rings. In the solar system, it comes right after Jupiter and the atmosphere of the two is very similar, as both contain mainly helium and hydrogen.

As well as its partner, Saturn it has been known since antiquity and can be seen with the naked eye. It is the second largest planet in the solar system. It is also the one with the most moons. There are already 82 confirmed, and just like on Jupiter’s Europa, some are capable of containing life.

In addition, in the rings there are numerous “little moons”, smaller satellites, with diameters between 40 and 500 meters.

Saturn is famous for its rings (Source: Unplash/Planet Volumes)Saturn is famous for its rings (Source: Unplash/Planet Volumes)Fonte:  Unplash

The rings extend between 6,000 and 120,000 kilometers away from the planet, with an average of 20 meters thick. They are composed mostly of ice and dust, with particular up to 10 meters in diameter.

There are two main hypotheses about the origin of the rings. The first says that they are the remains of an ancient moon destroyed by Saturn. The second assumes that they are remnants of the nebular material from which the planet originated.

There are still many things we don’t know about this gas giant. For example, the full length of a day (its rotation time).

Image of Saturn taken by the Hubble Telescope (Source: NASA/ESA/A. Simon)Image of Saturn taken by the Hubble Telescope (Source: NASA/ESA/A. Simon)Source: NASA/ESA

Astronomers have tried to measure this period as a basis for the emission of radio waves, in the same way as for Jupiter, but the results are still inconclusive. It is estimated to last a little over 10 Earth hours. The translation is well known, it takes 29.5 years.

On Saturn, the Cassini spacecraft has completed more than a dozen years of observation. But research is still advancing and much needs to be done to unravel the mysteries of this giant.


Uranus it was the first planet discovered through a telescope. Since he is not visible to the naked eye, this was the only way to see him. The Voyager 2 spacecraft was the only one that ever visited it. In their images, the giant is seen with a practically uniform light blue surface, without clouds or deformations.

This is the only one in the solar system which is rotating in the “horizontal”, sideways. In addition, to complete the strangeness, the translation movement is in a different direction from the others, with the exception of Venus. This indicates that a massive collision in the past knocked the planet off axis.

Uranus It takes a lifetime to go around the Sun. Literally: it takes 84 years to complete the translation movement. It takes almost 7 years for it to pass through each of the zodiac constellations as seen from here, and its rotation takes 17 hours.

Uranus' surface is the most homogeneous in the solar system (Source: Unplash/Planet Volumes)Uranus’ surface is the most homogeneous in the solar system (Source: Unplash/Planet Volumes)Fonte:  Unplash

As it spins on its side, magnetic north and south are very different from the poles. This causes some curious seasonal effects. Imagine, for example, a world where the south pole points directly to the Sun while in the north reigns the darkness of night.

Like other gas giants, Uranus has rings. They were first seen in 1977 and today there are more than a dozen of them confirmed.

Although not the outermost planet in the solar system, it is the coldest. All the heat that Uranus has comes from the Sun. Unlike here on Earth, it doesn’t have a core capable of generating extra energy to heat it up.

Uranus and its counterpart, Neptune, are often called ice giants because they have a slightly different composition than the two planets that precede them. In addition to hydrogen and helium, its atmosphere also contains significant amounts of water, methane and ammonia, as well as traces of other hydrocarbons.

The planet also has several moons. There are 27 in total, all named after characters in the work of Shakespeare and Alexander Pope, renowned English writers. The biggest are Miranda, Ariel, Umbriel, Titania and Oberon.


Neptune it also has a radius about four times that of Earth. Like Uranus, its atmosphere is mainly composed of hydrogen and helium with significant amounts of hydrocarbons such as methane and possibly nitrogen.

It was discovered in 1846 and was also only visited by Voyager 2 in 1989. In the images taken by the probe, it has a stronger blue color than Uranus, caused by some compound or phenomenon still unknown.

There are a total of 14 confirmed moons orbiting it. The largest and main one is Triton, with so much mass that it takes on a spherical shape. Scientists believe that the moon was once a dwarf planet in the past.

Neptune is the furthest planet from the sun (Source: Unplash/Planet Volumes)Neptune is the furthest planet from the sun (Source: Unplash/Planet Volumes)Fonte:  Unplash

It’s just that it rotates in the opposite direction to the planet’s equator. This is strong evidence that this moon was captured by this world as it passed close to it, and has been there ever since.

Neptune also has a system of rings, but they are fragmented and formed by several arcs. The researchers cannot explain the reason for this phenomenon, since by the laws of rotational motion, the arcs should spread out in a uniform ring with time.

Its translation takes 164.8 Earth years. This means that it was only in 2011 that the planet completed its first orbit around the Sun since it was discovered by us. Its rotation is estimated at 16 hours.

Triton, largest moon, may have been a dwarf planet kidnapped by Neptune (Source: Wikimedias Commons/Pablo Carlos Budassi)Triton, largest moon, may have been a dwarf planet kidnapped by Neptune (Source: Wikimedias Commons/Pablo Carlos Budassi)Source: Wikimedia Commons

Neptune has more total mass than its Uranus counterpart. Still, it’s slightly smaller. That’s because the huge amount of matter generates much more gravity, which in turn squeezes everything contained in the planet more tightly, making it more compact and denser.


Astronomers believe that these giants were once like rocky planets, only bigger. This size, however, was the differential, since with the mass comes a strong gravitational field capable of kidnapping everything that passes close by.

That’s how they started to incorporate hydrogen and helium from the gas cloud that existed here a long time ago, when the Sun was still condensing. Uranus and Neptune, which have larger orbits, were harmed in this process. This would also explain the more complex atmosphere of the latter two.

It is also believed that most of their moons formed along with them. This is implied because most of them rotate in the same direction as their rotational motion. But there are exceptions, such as Neptune’s moon Triton.

James Webb Telescope promises to answer questions we still don't have answers to (Source: Wikimedia Commons/NASA)James Webb Telescope promises to answer questions we still don’t have answers to (Source: Wikimedia Commons/NASA)Source: NASA

Gas giants have impressed humanity since ancient times. No wonder they were named after the most powerful Roman gods of all. And it’s no different these days.

With research underway, we are on the verge of experiencing new phenomena that are totally unlike anything we have ever witnessed in the past. Mainly with lesser known planets so far, like Uranus and Neptune.

The James Webb telescope, launched in 2021, promises to be a lens for these scientific advances. He has a unique ability to shed new light on these distant worlds. Astronomers promise: this is just the beginning of the journey.

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