How Does A Planet Differ From A Star?

How Does A Planet Differ From A Star?

The nebulae of gas and dust that form around newborn stars eventually coalesce into planets. Approximately a billion years ago, the conditions were ideal for the formation of Earth and the other planets in our Solar System.

The Sun is the center of our Solar System, which also includes seven other planets. There are two distinct planetary kinds. Mercury, Venus, Earth, and Mars are the four inner planets since they are the ones closest to the Sun. They are more compact and made primarily of minerals and metals. Jupiter, Saturn, Uranus, and Neptune are the four gas giants that make up the outer planets.

To begin with, what do planets even consist of? Whence did they initially emerge? Why would some be gaseous while others are rocky? How would you describe Earth? In this essay, I’ll make an effort to respond to these concerns.

Beginning Of The Solar System

The birth of our hero is a fascinating story, so let’s quickly recap it. A massive cloud existed in one of the spiral arms of the Milky Way five billion years ago. Astronomers identified this cloud, known as a nebula, as being composed of dust and gas, predominately hydrogen and helium with a trace amount of heavier atoms.

These more massive atoms were created long ago in the life of the Universe when other stars also eventually died. This nebula or cloud gradually shrank and collapsed in on itself. Once the atoms were no longer bound together, they began to bump into one another, creating friction and heat.

As the temperature increased, there was a corresponding increase in the frequency and intensity of atomic collisions. They heated up until the protons in the atoms’ nuclei began to fuse, a process known as nuclear fusion. In the process, they converted a negligible amount of mass into an enormous amount of energy, giving birth to a star. This is the origin story of our Sun.

stars planets dwarf planets

Origin Of The Solar System’s Planets

Rather than being swallowed up by the Sun, the remaining nebula material formed a flat disk of dust and gas around the star. An accretion disk is a name given to this disk. Sticking together is what prevents the disk material that has gathered during accretion from becoming a single mass.

Each planet was once just a speck of dust in the accretion disk. The smaller particles, such as atoms and molecules, started to clump together, or accrete. Some grains accumulated into balls, and later formed objects a mile in diameter, dubbed planetesimals, as a result of gentle impacts. Large enough for gravity rather than chance, these objects attracted similar ones.

Planetesimals may be shattered if they collided at high enough speeds. However, the objects merged and increased in size when the impacts were mild enough. These protoplanets orbited the Sun for 10–100 million years, with some following egg-shaped paths that increased the likelihood of collisions.

For a tremendous stretch of time, worlds merged and adapted to one another. In the end, eight planets remained in their original orbits, having survived the chaos. To qualify as a planet, an object must be in orbit around the Sun, have enough mass to be rounded by its own gravity, and have cleared its immediate area of smaller objects.

Environment On Earth

At the time of their formation, the rocky planets consisted mainly of molten rock. They gradually cooled over tens of millions of years. Due to their diminutive sizes, Mercury and Mars eventually hardened and became stiff to their very cores.

In all of the solar system, only Earth and maybe Venus has conditions that remain in a transitional phase. The planet has maintained a semi-liquid state. Both the crust and the mantle are made of rock that is stiff over relatively brief periods of time.

However, the mantle moves very slowly across geologic time scales. Magma is a heated liquid that surrounds Earth’s solid iron core, which spins at the center of the planet.

The term “Goldilocks Conditions” is used by certain scientists and major historians to characterize the current state of Earth. The children’s tale “Goldilocks and the Three Bears” in English is the source. Goldilocks, the protagonist of the story, accidentally enters the home of the three bears when they are out.

She samples the gruel, the chairs, and the beds, finding some to be too hot, too cold, too soft, too big, or too small, but one to be just right. As a planet, Earth is ideal for life since it is neither too hot nor too cold, too huge nor too small, and not too close to the Sun nor too far from it.

What’s A Planet?

As more and more objects were discovered in the Solar System that may be informally categorized under the “planet” umbrella without being actually relevant, the International Astronomical Union revised the definition of a planet in 2006 to make it more specific.

During this time, Pluto, which had been considered a planet for a very long, was controversially downgraded to the dwarf planet classification. The three criteria below must be met for an object to be considered a planet according to this revised definition.

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  • Any object that consistently orbits the Sun cannot be considered a planet.
  • The mass of a planet is sufficient to achieve hydrostatic equilibrium. So, it will be “shaped” by its own gravity into a nearly spherical form.
  • A planet’s orbit needs to be free of any other bodies. That means its satellites are the only significant objects in its orbit.

Last but not least, the presence of additional objects in Pluto’s “neighborhood,” notably in an area called the Kuiper belt, is what ultimately led to Pluto losing its planetary status.

What Sets A Planet Apart From A Star?

A massive, spherical celestial body that orbits the Sun or another star in the solar system. A planet is a celestial body that orbits the sun but does not move relative to the sun, revolving on its own axis and reflecting light from the sun.

Due to the lack of an internal lighting system, the only source of illumination on this planet is the solar system’s primary star, which rises in the sky at dawn and sets at dusk.

The names of the eight planets that make up our solar system are as follows: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

What’s A Star?

A little point of light in the night sky represents a huge sphere of burning gas somewhere in the universe. Independently reflecting light from its surroundings, a star is a body with a light that can be identified from a great distance. As a result of gravity and accretion, stars develop from nebulae, which are clouds of gas and dust, into hotter and denser protostars.

A star is an extremely bright celestial body that is undergoing nuclear fusion and is (nearly) completely spherical in shape due to the pull of its own gravity. Due to the fact that stars go through several phases over their lives, defining a star can be difficult. Main-sequence stars, which are stars during their primary fusion stages, fall under the aforementioned description.


Though some of these other labels may also have “star” in them, stars are classified differently depending on whether they are forming, in the process of dying, or have already died. Depending on their mass and composition, dead stars can either evolve into black dwarfs, neutron stars, or even black holes.

Light and infrared radiation are the most prominent forms of energy emitted by stars, while other forms of radiation such as ultraviolet, radio, and X-rays are also possible. A surface temperature of about 2100 to 40,000 degrees Celsius is possible. The stars cannot be accurately counted. The Milky Way galaxy contains an estimated 100 billion stars, according to astronomers.

Difference Between A Planet And A Star

There are times when trying to grasp the vastness of our cosmos feels like an impossible effort. Everything from planets to asteroids to stars to black holes to nebulae to pulsars may make your head spin.

There must be a system to readily identify and categorize all of these things. As such, let’s compare and contrast planets with stars to see what sets each apart. The definitions are all quite specific, so you won’t have to worry about confusing them again.

The five most notable distinctions between planets and stars are:

  • The solar system’s planets all travel in a circle around the sun. Planets do not circle stars.
  • Planets can be composed of a variety of materials, including rock, ice, gas, and water. The plasma forms stars.
  • In their own right, stars shine. No planet does.
  • When compared to the stars in their system, planets are always significantly cooler.
  • Stars are continually undergoing nuclear fusion within their cores. Such a thing never occurs on a planet.

1. Planets Orbit Stars But Stars Do Not.

Simply said, a planet is only a planet if it orbits a star, like Earth orbits the Sun. The mass of stars is higher than that of planets. When a planet is formed, its gravity “locks” it into its orbit around this massive object. Although it is feasible that the opposite may occur (a star orbiting a planet), this system has never been discovered due to the laws of physics.

According to one set of rules, stars stay still while planets go around them. Incorrect, seeing as how stars in other galaxies likewise orbit their own galaxy’s nucleus. It also doesn’t take multi-star systems into account.

These consist of two or more stars that circle each other or move in close proximity to one another. Do you recall the scene in “Star Wars” when Luke is on Tatooine and he looks up and sees that there are actually two suns setting? That’s a system with multiple stars.

2. Rock, Ice, Gas, And Water Form Planets. Plasma Form Stars.

After solid, liquid, and gas, plasma is the fourth fundamental state of matter. Because of its intangible nature and lack of a clear, universal description, plasma can be challenging to describe. Imagine a gas so heated that it begins to conduct electricity. Plasma manifests itself as a lightning bolt.

In the center of stars, nuclear processes generate such high temperatures that nearly all of the material becomes plasma. In contrast, planets can be constructed from a wide variety of materials. Mars, on the other hand, is largely composed of rock and ice, while Jupiter and Saturn are mostly composed of gas with only a small rocky core.

Even though plasma is a common feature of several planets, especially extremely hot worlds, it is not the primary ingredient in these worlds.

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3. Stars Produce Their Own Light, Unlike Planets.

The nuclear reaction occurring within stars makes them brilliant and able to radiate light. Much colder elements that do not create light make up planets. Similar to how we can see the Moon from Earth, this is the explanation for how we can observe other planets. Sunlight is being reflected off of them. The light of faraway planets’ host stars is reflected back to us as well.

In the interest of precision, there are a few cases where this guideline does not apply. Even though some planets emit faint amounts of light or radiation, this is typically not enough for it to be detected from a great distance. As an illustration, Jupiter emits heat that can be picked up by infrared sensors but is otherwise invisible to the naked eye.

stars vs planets difference

4. Stars In A Planetary System Will Be Warmer Than The Planet.

Depending on their composition, stars’ temperatures can range widely. The minimum temperature for red dwarf stars is 3,500 Kelvin. It is possible for blue supergiants to attain temperatures of up to 40,000 Kelvin.

The Sun’s surface temperature, at around 5,800 Kelvin, is on the lower end of the spectrum. The planets in a stellar system will always be cooler than their stars because they lack the vast amounts of thermonuclear processes occurring in their cores.

It is crucial to note that planets are only colder than the stars in their system. As long as the star it orbits is even hotter, it is possible (though highly unusual) for a planet to be hotter than other stars.

In 2017, astronomers discovered Kelt-9b, a hydrogen-atmosphere gas planet that orbits so close to a blue supergiant that the gas in its atmosphere reacts to the star’s temperature, heating the planet to temperatures of up to 4,000 Kelvin.

5. A Star Is Always Undergoing Nuclear Fusion, Unlike A Planet.

Hydrogen and helium make up the vast majority of a star’s composition. There are traces of a few additional gases, but they are the primary ones. Since you’d have to drill inside a planet to study its core, we don’t know much about them, but we do know that it can be solid, liquid, or a mixture of the two. Because of the lack of gases in their cores, chemical reactions similar to those in stars do not take place on planets.


Millions upon millions of twinkling points of light—stars and planets alike—light up the night sky. The difference between a star and a planet is not always clear, but what is the difference, exactly? A star is a celestial body that generates its own light through a nuclear fusion event at its center.

There are more than 10,000 stars visible in the night sky, but have you ever wondered if you were actually staring at one of these stars or one of the planets in our solar system? If you pay attention to the way the light sparkles, you can usually tell.

Since the visible stars are so far away, their light needs to travel through many layers of the Earth’s atmosphere before it reaches us, and this causes the star to twinkle while it does so. Even though planets don’t produce their own light, their proximity to Earth makes the light they emit much brighter than that of stars.

Ancient astronomers would monitor the motion of a certain light source over the course of several nights to determine whether or not they were looking at a planet or a star. Similarly to the sun and the moon, planets have a day and night cycle and travel the sky along a predetermined course.

Stars do move, but not in the same way that the planets of our solar system do. Because stars orbit the North Star in a circle, any light that appears to move in a straight line over the course of several nights is probably a planet.

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Maria D Ramsey

Hey Maria D Ramsey here, I am a journalist and author with a love for writing guides that help people improve their lives. I was born and raised in the United States, and my hobbies include cooking and reading novels.

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