Characteristics Of Outer Planets: Some Important Facts!

Arpitha Rajendra
Jan 24, 2024 By Arpitha Rajendra
Originally Published on Dec 06, 2021
Learn about these interesting characteristics of outer planets.
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Age: 3-18
Read time: 7.8 Min

Neptune and Uranus are referred to as 'ice giants' because of the presence of high amounts of volatiles on them.

Due to the great distance from the Sun, the gas and ice giants take longer to orbit. The greater the distance from the Sun, the more time these planets take to complete one trip around our Sun.

Giant planets and their moons are located in the outer region of our Solar System. These planets include Jupiter, Saturn, Uranus and Neptune, and the dwarf planet Pluto. There are many short-period comets and centaurs that also orbit in this area. Solid objects in our outer Solar System have a high proportion of volatiles, like methane, ammonia, and water, due to their large distance from the Sun compared to the ones in the inner Solar System. The giant outer planets are called Jovian planets, and they make up around 99% of the total mass that orbits the Sun. Saturn and Jupiter together are around 400 times the mass of our planet and contain large amounts of gases, which are Hydrogen and Helium in liquid form. Therefore, the term 'gas giants' was assigned to them. Neptune and Uranus are less massive than the giants and are made of ice. These two planets measure up to less than 20 times the mass of Earth each. Gas giants have numerous moons.

If you enjoy reading these facts about the characteristics of outer planets, then make sure to read some more interesting facts about the four outer planets and when the planets align here at Kidadl.

Differences Between Inner And Outer Planets

The distance between the inner and outer planets is huge.

Our Solar System is divided into inner and outer planets. These two parts are divided by an asteroid belt. Inner planets in the inner Solar System consist of the planets closest to the Sun. These inner planets (within the asteroid belt) include Earth, Mars, Venus, and Mercury. These are terrestrial planets due to their solid surfaces. Outer planets or Jovian planets in the outer Solar System (beyond the asteroid belt) consist of Jupiter, Saturn, Uranus, and Neptune. Inner planets have a solid surface and are made of heavier elements like Nickel and Iron with few to no moons. Inner planets also have a short orbit around the Sun.

Earth's atmosphere is made of Nitrogen and Oxygen with no planetary rings and one moon. Currently, our Earth is the only planet that supports life. Although, Mars is under study as there were signs of water on the planet's surface in the past. This planet's atmosphere is made of Argon, Nitrogen, and carbon dioxide. Mars has two tiny moons called Deimos and Phobos. The inner planet, Mercury, is surrounded by a tenuous atmosphere made of Sodium, Potassium, Oxygen, Hydrogen, and Helium surrounding the planet. It has no moons. Venus was previously considered a twin to our planet Earth. However, later discoveries showed that the surface of Venus has a lead-melting temperature.

Outer planets are much bigger than inner planets. Jovian planets or gas giants are mostly made of gas (Hydrogen and Helium), while the inner terrestrial planets are rocky planets with a rocky core. The gas giant, the planet Jupiter, is the largest planet with numerous moons and faint rings. It is also the brightest in the night sky after our Moon and Venus. The largest planet has a stormy atmosphere, and the Great Red Spot is one of its major storms. The Great Red Spot rotates counterclockwise and has a period of 14 Jovian days or six Earth days. This gas giant may have a relatively small rocky core at the center. Four of Jupiter's moons were visible through telescopes for hundreds of years. Currently, there are 8o known Jupiter moons.

Some similarities between inner and outer planets are that they both follow an elliptical orbit, are spherical, are on the same orbital plane, and have the same materials.

How Were The Outer Planets Formed?

The four outer planets have a strong magnetosphere due to a strong magnetic field and rapid rotation.

Astronomers believe that gas giants formed as icy and rocky planets, like the inner planets. Although, the core sizes allowed gas giants (especially Saturn and Jupiter) to get Hydrogen and Helium out of the gas cloud from which the Sun previously condensed when it was formed. Neptune and Uranus have bigger orbits and are smaller in size compared to Saturn and Jupiter, making it harder for the planets to collect Hydrogen and Helium. The atmospheres of Uranus and Neptune are more polluted with heavy elements like methane and ammonia due to their small size. Many out of thousands of exoplanets are massive gas giants or hot Jupiters, which are very close to their parent stars.

Saturn is easily identified by the planet's rings. There are seven known large rings with well-defined gaps and divisions between them. Astronomers are still investigating how these rings got there. Saturn has many moons. The magnetosphere and atmospheric composition of Saturn are similar to the planet Jupiter. Saturn almost has 60% of the planet Jupiter's volume; however, it is two-thirds of the size of Jupiter. This planet is also the only planet less dense than liquid water. Saturn's rings are made of rock and ice particles. There are 83 known moons of Saturn, mostly made of ice. Saturn takes 29 Earth years per orbit around the Sun, and one day is equal to 10.7 hours on Earth.

The metallic Hydrogen layers of Saturn and Jupiter conduct electricity.

The Moons Of The Outer Planets

The outer planets have no solid surfaces.

Astronomers believe that giant planets may have moved in orbits before reaching their current positions; however, the extent of their movement is unknown. There are many moons around these four planets. Many moons formed when their parent planets were formed, which is indicated by the rotation of planets in the same direction as a planet closest to the equator. One of many moons of Neptune, called Triton, orbits the planet in the opposite direction to Neptune's rotation. This indicates that Triton was perhaps captured by the once large atmosphere of Neptune as the planet passed by in the Solar System. Several tiny moons rotate far away from their parent planet's equator, indicating that they were also trapped by great gravitational pull.

William Herschel first discovered Uranus in 1781, and it is the lightest planet of all outer planets. Uranus orbits our Sun on its side and has over 90 degrees of axial tilt to the ecliptic. Uranus has a core that is much colder compared to other giants in our Solar Systems, radiating less heat into space. Uranus is made up of ammonia, methane, water, Hydrogen, and Helium around a rocky core. It also has faint rings. There are 27 known moons of Uranus, including Umbriel, Titania, Ariel, Miranda, and Oberon. The Voyager 2 of the voyager missions was the last spacecraft to visit Uranus. Uranus takes 84 Earth years to complete one orbit around the Sun, and one day there is 17 hours on Earth.

Notable Characteristics Of Outer Planets

The four outer planets have liquid interiors with gas in their outermost parts.

A magnetic field is generated around a planet due to the interaction between its rotation and materials present in the outer core of a planet, like metal and molten rock. Some planets have no magnetic field, while others have magnetic fields that vary in strength. Jupiter has the largest magnetic field in our Solar System. This is due to the fast rotation of Jupiter, lasting around 9.8 hours on Earth. However, the magnetic field is produced by the liquid metallic hydrogen outer core of Jupiter and not the inner core. Due to the strong metallic field, the magnetosphere around Jupiter is bigger than our Sun.

Metallic hydrogen covering the rocky core in Saturn produces its magnetic field. The core gets heated due to the rapid rotation of Saturn that is the same as 10 hours on Earth, and the gravity pulls Helium towards the center. This is the only planet in our Solar System that has its magnetic field lined up with its axis of rotation. The magnetic field of Uranus is much more complicated than those of other planets. The magnetic field has a 59-degree tilt from its axis, which does not run through the planet's center. Unlike Earth, Uranus has four poles. The great tilt of Uranus creates a magnetic field that has diverse strengths. Astronomers think that the salty ocean beneath the surface Uranus generates the magnetic field and not the core.

Neptune is more massive and dense than Uranus, but it is slightly smaller than the planet Uranus. Neptune does not radiate as much internal heat as Saturn or Jupiter; however, it radiates more than Uranus. There are 14 known moons rotating around Neptune. It also has six rings. Triton is the largest moon of Neptune, which is geologically active with liquid nitrogen geysers. Neptune contains ammonia, methane, water, Hydrogen, and Helium with an Earth-sized core. NASA's Voyager 2 was the only spacecraft to visit this planet in 1989.

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked learning about the characteristics of outer planets, then why not take a look at some fun facts about the second planet from the Sun or which planet Ganymede orbits around?

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Written by Arpitha Rajendra

Bachelor of Engineering specializing in Aeronautical/Aerospace Technology, Master of Business Administration specializing in Management

Arpitha Rajendra picture

Arpitha RajendraBachelor of Engineering specializing in Aeronautical/Aerospace Technology, Master of Business Administration specializing in Management

With a background in Aeronautical Engineering and practical experience in various technical areas, Arpitha is a valuable member of the Kidadl content writing team. She did her Bachelor's degree in Engineering, specializing in Aeronautical Engineering, at Nitte Meenakshi Institute of Technology in 2020. Arpitha has honed her skills through her work with leading companies in Bangalore, where she contributed to several noteworthy projects, including the development of high-performance aircraft using morphing technology and the analysis of crack propagation using Abaqus XFEM.

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