Jasmine Grover Content Strategy Manager
Content Strategy Manager
Planets are the astronomical bodies that orbit a star in space. The word 'planet' literally translates into "wanderer". These planets do appear to wander across the sky. The stars also wander or move in the sky from East to West but they appear to be fixed relative to each other. However, planets move relative to the stars that appear fixed, in a forward or a backward motion. This is why they are known as wanderers. In this article, we will learn more about various types of planets of our solar system.
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| Table of Content |
Key Takeaways: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Solar System, Moon, Planet
What is a planet?
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A planet refers to an astronomical body that is in a revolving motion around the star or a stellar remnant. It is massive enough to be rounded by the gravity of the star but not massive enough to cause thermonuclear fusion. It clears its neighboring regions of planetesimals. In simple words, we can say that a planet is a celestial body that moves around the sun in fixed orbits. They reflect the light of the sun as they do not have any light of their own. As they are much closer to us, unlike the stars, planets don't appear to twinkle in the sky. Our earth is also a planet. It is the only planet in our universe that is known to sustain life.
Planets
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Planets in solar system
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There are eight planets in our solar system which are:
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
From the Earth, we can only observe the first five planets with the naked eye which are
Mercury, Venus, Mars, Jupiter, Saturn. Uranus and Neptune were discovered only after the telescopes were invented.
- The first four planets are known as rocky planets and are made up of rock. Their inner cores are formed of metals.
- The next four planets are known as gas giants and are formed of gases like hydrogen, helium, and methane. They are gigantic in size when compared to rocky planets.
Planets in our solar system
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Along with their motion around the sun, the planets also rotate on their own axis in the same way as the Earth does. Earth takes 24 hours to rotate around its own axis. The time a planet takes to revolve around the sun is known as its period of revolution.
- Jupiter rotates every 10 hours.
- Venus takes about 243 days to rotate on its axis.
- Earth takes 365.26 days or 1 year to complete its revolution around the sun.
The further away a planet is from the sun, the more time it takes to revolve around the sun.
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Mercury
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Mercury is the closest planet to the sun in our solar system. Along with that, it is also the smallest one. [Read a Further Explanation on: Which is The Nearest Plant to the Sun?]
- In terms of size, Mercury is just a little bit larger than the moon of the Earth.
- Traveling around the sun with a speed of 29 miles per second, Mercury is the fastest planet.
- Since it is closer to the sun, it just has to travel a short distance to go around the sun. One year on Mercury is equal to just 88 Earth days.
- It is a terrestrial and rocky planet that has a solid surface full of craters just like the surface of our moon.
- There are no moons orbiting Mercury.
- It has a thin exosphere or atmosphere which is mainly composed of Oxygen, Sodium, Hydrogen, Helium, and Potassium.
- Mercury does not have any rings.
- Mercury has extreme temperatures due to solar radiation.
- Despite being the closest to the sun, Mercury is not the hottest planet in our solar system.
Mercury
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Venus
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Venus is our closest planetary neighbor. It is one of the four rocky planets of our solar system.
- It is similar in density and size to Earth.
- Venus has a toxic and thick atmosphere that is made up of carbon dioxide.
- It has thick yellow clouds of sulphuric acid that are responsible for trapping heat and thereby causing a greenhouse kind of effect.
- Venus is the hottest planet in our solar system.
- At its surface, it has a crushing air pressure.
- It rotates backward in its axis as compared to most planets of the solar system.
Venus
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Earth
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Earth is the only known planet that sustains life. It is the fifth-largest planet in our solar system.
- It is also the only planet having liquid water on its surface.
- Of the four closest planets to the sun, Earth is the largest one.
- A day on Earth is equal to 24 hours while a year is made of 365 days.
- Earth has one natural satellite, known as the moon.
- The atmosphere of the Earth is composed of 78% of nitrogen, 21% oxygen, and 1% other gases which makes an ideal combination to live and breathe.
Earth
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Mars
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Mars is a cold, dusty, desert world that has dynamic seasons.
- It has a very thin atmosphere that is mostly formed of argon, nitrogen, carbon dioxide with a little water vapor and oxygen.
- A day on Mars comprises a little over 24 hours. To complete its revolution, Mars takes 687 Earth days.
- The solid surface of Mars has experienced changes due to impact winds, volcanoes, chemical reactions, and crustal movement.
- Phobos and Deimos are the two moons of Mars.
- It is known as the Red Planet due to the presence of iron minerals in the Martian soil that causes that soil or the atmosphere to look red.
Mars
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Jupiter
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Jupiter is the fifth planet of the solar system having windy clouds of water and ammonia.
- Jupiter is the largest known planet in our solar system now. Its mass is twice the mass of all the rest of the planets combined.
- The popular Great Red Spot is a giant storm on Jupiter that has raged for hundreds of years and that is bigger than even the Earth.
- The rotation period of Jupiter is 10 hours while a Jovian year comprises about 12 Earth years.
- It is a gas giant whose atmosphere is mostly made up of Hydrogen and Helium.
- Jupiter is known to have even more than 75 moons.
Jupiter
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Saturn
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Saturn is the second-largest planet in the solar system that is located sixth in place from the sun.
- It is a unique planet as it is adorned by thousands of spectacular ringlets.
- It is a massive ball that is mostly made up of Hydrogen and Helium just like Jupiter.
- Saturn takes 29 Earth years to orbit around the sun while it takes 10.7 hours to rotate on its own axis.
- Saturn has over 82 moons, out of which 53 are known and 29 of them are awaiting confirmation.
- It does not have a proper solid surface like Earth.
Saturn
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Uranus
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The seventh planet of the solar system is known as Uranus which has the third-largest diameter of all the planets.
- It is about four times the size of the Earth.
- A Uranian day is made up of 17 hours while a Uranian year comprises 84 Earth years.
- Most of the mass of Uranus is a hot and dense fluid made up of icy materials such as methane, ammonia, and water that is located above a tiny rock core.
- Uranus has 27 moons which are known after the characters of the works of Alexander Pope and William Shakespeare.
- Just like Venus, Uranus also rotates from East to West. However, Uranus is known to rotate on its side.
Uranus
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Neptune
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Neptune is the most distant planet from the sun. It is cold, dark, and is whipped by supersonic winds.
- It takes 16 hours for Neptune to rotate on its axis while it takes Neptune 165 Earth years to complete its revolution around the sun.
- Neptune is known to have 14 moons, all of which are named after nymphs and gods of Greek mythology.
- It has five main rings in addition to four ring arcs. They are faint in appearance.
- The atmosphere of Neptune is composed of atomic helium, molecular hydrogen, and methane.
- The rings of Neptune are mainly clumps of debris and dust that are mainly formed as a result of the gravity force of the nearby moon.
Neptune
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Satellites
Satellites are the objects in the solar system that orbit the planets. The natural satellite of our Earth is the moon. Venus and Mercury are the only two planets that don't have any satellites.
Why is Pluto no longer a planet?
Pluto was earlier considered a planet as it resembled a planet in multiple ways. However, the International Astronomical Union devised a new definition of a planet. As per the latest definition, a planet can be defined as an object that
- revolves around the sun.
- Has an almost spherical shape.
- Has enough gravity so that the space close to its orbit is free of other objects such as asteroids, comets, rocks, etc.
Pluto does not satisfy the last criteria of being labeled a planet because a comet-like object is present in its orbit. Therefore, Pluto is known as a dwarf planet.
Pluto: A Dwarf Planet
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Things to Remember
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- A planet refers to an astronomical body that is in a revolving motion around the star or a stellar remnant.
- Mercury is the closest planet to the sun in our solar system
- Venus is the hottest planet in our solar system.
- Earth is the only known planet that sustains life.
- Mars is a cold, dusty, desert world that has dynamic seasons.
- Jupiter is the largest known planet in our solar system now. Its mass is twice the mass of all the rest of the planets combined.
- Saturn has over 82 moons, out of which 53 are known and 29 of them are awaiting confirmation.
- The seventh planet of the solar system is known as Uranus which has the third-largest diameter of all the planets
- The atmosphere of Neptune is composed of atomic helium, molecular hydrogen, and methane
- Satellites are the objects in the solar system that orbit the planets.
Sample Questions
Ques. How do planets differ from stars? (3 marks)
Ans. The basic differences between stars and planets are as tabulated below:
| Stars | Planets |
|---|---|
| Stars are incredibly hot celestial bodies having very high temperatures. | Planets are celestial bodies that have relatively low temperatures. |
| Stars don't rely on external sources of light as they produce light of their own. | As planets are incapable of producing their own light they are dependent on another celestial body such as a star for the production of light. |
| Stars appear to be twinkling in the night sky. | Planets do not display this twinkling effect. |
| Stars change their position however a difference in their position can be noticed only after a significant period of time. | Planets constantly change their position as they move around the sun and around their own axis too. |
| Stars are made of light elements like Hydrogen, Helium, etc. | On the other hand, planets are made up of a combination of solids, liquids, and gases. |
Ques. Which planet rotates clockwise? (3 marks)
Ans. Venus is the only planet in our solar system along with Uranus that is known to rotate around the sun in a clockwise direction. When observed from the north pole, all the planets are seen in a rotation motion on their elliptical orbits in an anticlockwise direction.
All orbits of the planets aren't circular. Instead, they are elliptical in shape. Though Venus moves in elliptical orbit when observed; we can notice that it is almost circular in shape. Venus has a minute eccentricity of a little bit more than 0.01. The inclination at which Venus moves is 177 degrees while the inclination of Earth, a planet moving in an anticlockwise direction, is near 23 degrees.
It is believed that Venus was hit by an asteroid at high speed. This heavy asteroid is believed to have caused the shift in the direction of rotation of Venus. While another set of astronomers believed that Venus initially rotated in the anticlockwise direction, after which it slowed down and became static. It then resumed its motion in a clockwise direction.
Just like Venus, Uranus also rotates from East to West. However, Uranus is known to rotate on its side.
Ques. Which planet is known as the red planet? (5 marks)
Ans. Mars is known as the 'Red Planet' as it appears as an orangish red star in the sky. The color of Mars led to it being named after the god of war. The red appearance of the planet is due to the rusty iron appearance of its soil. Some of the prominent features of Mars are:
- Mars is a neighbor of the earth as it is located 4th from the sun, about 142 million miles.
- Phobos and Deimos are the two moons of Mars.
- Almost all the surface of Mars is covered with red dust.
- A Martian day is made up of 24.6 hours while 687 Earth days make up a Martian year.
- Gravity on Mars is about one-third the gravity on Earth.
Ques. Which planet is closest to the sun? (5 marks)
Ans. Mercury is the closest planet to the sun in our solar system. It takes just 88 days to move around the sun.
- It is the smallest planet in the solar system.
- It experiences dramatic changes in the temperatures of day and night as it is closest to the sun.
- Due to extreme temperatures and solar radiation, it is not an ideal fit for life.
- It is a terrestrial planet that has a rocky surface full of craters.
- Mercury does not have any moons.
Ques. Which planet has the most moons? (5 marks)
Ans. Currently, Saturn has the most moons in our solar system. It has a total of 82 moons, out of which 53 are confirmed and 29 moons are yet awaiting confirmation for their discovery and hence official naming.
- The moons of Saturn range in size from Titan which is larger than Mercury to small moons.
- The shape of the moons of Saturn also contributes by collecting material from the magnetosphere and the rings of Saturn.
- Saturn is the second-largest planet in our solar system.
- It is a gas giant that is mostly formed of Helium and Hydrogen.
- Out of all the planets, Saturn is known to have the most spectacular system of rings, with 7 rings and multiple divisions and gaps between them.
Ques. Which planet is the farthest from the sun? (5 marks)
Ans. Neptune is the farthest planet from the sun with a distance of about 4.5 billion kilometers or 2.8 billion miles.
- A Neptunian day is made up of 16 hours while a Neptunian year is made of 165 Earth years.
- The atmosphere of Neptune is mostly made up of methane, atomic helium, and molecular hydrogen.
- The 14 known moons of Neptune are named after nymphs and sea gods of Greek mythology.
- There are 6 rings of Neptune. However, they can't be seen as they are very faint.
- It is a cold, dark, and windy planet.
- It is known as the blue planet.
Ques. Why do planets not twinkle? (3 marks)
Ans. The planets do not twinkle like the stars in the sky due to the following reasons:
- They are closer to our Earth as compared to the stars. As the planets are nearby, they appear to be much bigger than the stars and the light coming from them sees just a minor atmospheric refraction shift.
- Planets do not produce any light on their own. Instead, they rely on stars and reflect the low-intensity light that reaches them.
- As the planets are closer, the shift isn't enough and the twinkling effect gets canceled out.
Ques. Why do planets orbit in the same direction? (3 marks)
Ans. As the interstellar cloud collapsed into planets and other celestial bodies, each of them carried a part of the initial angular momentum of the system. Gravity condensed the clouds of dust and gas, increasing the conservation of angular momentum. It flattened the cloud out into a plain disk. Therefore, all the planets that were formed within this disk ended up orbiting the sun in their orbits in the same direction with the same spin direction and in almost a similar orbital plane.
Venus and Uranus are exceptions to this as they were probably hit by other bodies in space which altered their spin and changed their direction.
Ques. What is a dwarf planet? How are they different from planets? (5 marks)
Ans. As per the latest definition, a planet can be defined as an object that
- revolves around the sun.
- Has an almost spherical shape.
- Has enough gravity so that the space close to its orbit is free of other objects such as asteroids, comets, rocks, etc
The only difference between a regular planet and a dwarf planet is regarding the area surrounded by both celestial bodies. A dwarf planet does not clear the area around them while a regular planet does so.
In regards to this definition, some objects in our solar system that have been identified as dwarf planets till now are Pluto, Makemake, Haumea, Eris, and Ceres.
- Pluto: Pluto is a dwarf planet that is located in the Kuiper Belt region that exists beyond the orbit of the planet Neptune. It is smaller in size than the moon of the Earth. It has blue skies and red snow. Pluto has a thin atmosphere of carbon monoxide, methane, and nitrogen.
- Ceres: Ceres is the largest known object to exist between the orbits of Mars and Jupiter. It is the only dwarf planet that is situated in the innermost solar system. It completes a rotation on its axis every 9 hours. Earlier, it was regarded as an asteroid until it was recognized as a dwarf planet in 2006.
- Makemake: This dwarf planet is also located in the Kuiper belt region. It takes about 305 years to complete one trip around the sun. It has one provisional moon.
- Haumea: Haumea is also found in the Kuiper Belt in the solar system. It is about the same size as Pluto. It completes its revolution in 285 Earth years. It has two known moons named Namaka and Hi'iaka.
- Eris: Eris is the largest dwarf planet that is identified in our solar system. It takes 557 Earth years to complete its orbit around the sun. It does not have any identified rings. It has a rocky surface just like Pluto. Its moon is known as Dysnomia.
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