Outer Planets: UPSC Note on Outer Planets

Introduction

Outer planets, also known as Jovian planets, are gas giants, usually composed of hydrogen and helium. Though the composition of these planets is quite similar to their parent star, i.e., Sun, their core is liquid with gaseous outer layers. Jupiter, Saturn, Uranus, and Neptune are the four outer planets from left to right. Due to their distinct characteristics like numerous moons, magnetosphere, planetary rings, and significant atmospheric activity, these outer planets of the solar system are distinct from the inner planets, although they lack a solid surface.

Difference between inner planets and outer planets:

The outer and inner planets differ from each other in the following ways:

Feature	Inner Planets	Outer Planets
Position	Inner planets lie between the Sun and the asteroid belt.	These are located beyond the asteroid belt.
Planets	The four inner space planets include: Mercury Venus Earth Mars	The outer space planets include: Jupiter Saturn Uranus Neptune
Composition	Inner planets are formed of dense and heavy materials like metals and rocks. Refractory minerals, like silicates, form the mantles and crusts of these planets. Metals, like iron and nickel, form the cores of these planets.	Outer planets are formed of less dense and light materials like gases and even ice and rock. Jupiter and Saturn are primarily formed of hydrogen and helium, while Uranus and Neptune are primarily formed of hydrogen, helium, ice, and rock. The core of these planets is either solid or liquid in nature, while the outer layers are gaseous in nature.
Similarly to Sun	They are less similar in nature to the Sun.	They are more similar in nature to the Sun.
Other names	Inner planets are also called terrestrial planets.	The outer planets of the solar system are also called gas giant planets or Jovian planets.
Size	They are comparatively smaller.	They are larger in size than the inner planets.
Nature	They are rocky in nature.	They are gaseous in nature.
No. of moons	Inner planets have either no or very few moons.	Outer planets have multiple moons.
Rings	These planets do not have any ring system around them.	All of these planets have rings around them; the rings of Saturn are even observable from Earth.
Atmosphere	Inner planets have a substantial atmosphere to form the weather.	Outer planets have a magnetosphere as well as significant atmospheric activity.

Characteristics of outer space planets

Jupiter

Jupiter is the largest planet in our solar system and the third-brightest natural object in the night sky, after the moon and Venus. It is also the fourth-brightest object in the sky, after the Sun, Moon, and Venus
It has no solid surface and comprises swirling patterns of liquids and gases
Jupiter spins at a rapid speed of 10 Earth years. Its rapid rotation gives Jupiter the shape of an Oblate spheroid with a slightly bulged centre
Jupiter has 67 known satellites and 4 large moons, also known as Galilean satellites, namely lo, Europa, Callisto, and Ganymede, with Ganymede being the largest
The outer atmosphere of Jupiter is separated into several bands, which causes storms and turbulence

Saturn

Saturn is one of the outer solar system planets, which has a very prominent ring system. There are 7 known rings of Saturn with well-defined gaps and divisions between them
The rings of Saturn are composed of ice and primordial dust
Titan is the largest of Saturn’s 62 prominent moons, as well as the second-largest moon in the solar system
It has a substantial, nitrogen-rich atmosphere – the only planet in the solar system to have this atmosphere
It rotates quickly, at a rate of 10.7 Earth hours and takes about 29 Earth years to complete one revolution around the Sun
Its mass is 95 times that of Earth, while its volume is 755 times that of Earth

Uranus

Uranus is one of the outer planets that tips and spins on its sides
The axis of rotation lies around the plane of its orbits. In other words, the poles of Uranus lie where the equators of other planets lie
Uranus is a large planet and situated extremely far away, i.e. 2.8 billion km away from the Sun
It has 14 times the mass of Earth and has less density than Earth
Uranus has a unique retrograde rotation, i.e. opposite to the Sun’s rotation
Uranus has a high fraction of icy materials like ammonia (NH3), methane (CH4), and water
It has 27 moons along with magnetic and electric fields

Neptune

Neptune and Uranus are twin outer planets of the solar system
Neptune is a gas giant with an atmosphere consisting of helium, hydrogen, and methane gases. Its mantle is made up of methane ices, ammonia, and water, while the core is made up of ice and rock
Neptune has 14 satellites, with Triton and Nereid being the most prominent among them
At 2100 km/h, Neptune boasts of the strongest sustained winds among all the planets of the solar system
There is also an Earth-sized blemish on Neptune called “The Great Dark Spot”
Neptune was the first planet in the solar system to be located with the help of mathematical calculations

Basic information of the outer planets

Planet	Surface temp. in °C	Period. of Revolution	Distance from the sun (AU)	Size rank	Density (gm/cm3)	Specific gravity (m/s2)		Moons	Period of Rotation
Jupiter	-150	11.9 yrs.	5.2	1	1.3	24.9	2.53	79	9.9 hrs.
Saturn	-180	29 yrs.	9.6	2	0.7	10.4	1.06	62	10.7 hrs.
Uranus	-214	84 yrs.	19.2	3	1.3	8.8	0.9	27	17 hrs.
Neptune	-220	164 yrs.	30.0	4	1.6	11.1	1.13	13	16 hrs.

Conclusion

Outer planets, or Jovian planets, are primarily composed of gases with a significant share of hydrogen and helium. Jupiter and Saturn (gas giants), Uranus and Neptune (ice giants) are the four outer planets. The common characteristics of the outer planets include low density, lighter materials, presence of numerous moons, rings in the atmosphere, gaseous nature, and large size.