Planets Introduction

Mar. 3, 2024 - Written by Kevin Jie

A planet is a non-illuminating celestial body that orbits a parent star. A planet can vary in size, shape, and color; being arguably the most diverse celestial structure in the universe. Similarly to stars in the stellar life cycle, planets are often formed in relatively the same way but become their own object. This path is less of a cycle and more of a one-way. Before continuing, one common misconception must be cleared. Exoplanets and planets are identical. “Exoplanet,” is just a name given to any planet outside of the solar system.

Beginning with gaseous planets, the emergence of each is totally unique to the last. Most gaseous planets begin as gas rich particles that surround a young star. As the gas particles exist in this orbit around the star, sporadic movement within the star system will make gas particles collide and connect with one another, forming a base. Over time, the base will gain more and more mass, creating its own gravitational pull. From here, the soon to be gaseous planet will rapidly grow. 

Graphic design of a blue planet labeled 'Neptune' with the subtitle 'Planet - #05' on a white background, set against a dark blue background.
A simplified digital illustration of the planet Uranus, depicted as a light blue sphere, with text below reading 'URANUS PLANET - #06' on a white background.
Gas Giant Layers
A scientific poster featuring an image of Jupiter, the third planet from the sun, with brown and beige swirling cloud patterns. The poster includes text labeling it as 'Jupiter,' 'Planet-#03,' with a minimalist design and a brown background.
Illustration of Saturn with a beige color scheme, featuring a white square label with the text 'SATURN PLANET - #07' and a digital rendering of Saturn with its rings.

The gas planet will often grow into 3 layers starting from the seed. This consists of the core (either dense rock or ice), a gaseous mantle and a dense gaseous surface. For example, Jupiter has 3 layers: The core,  a metallic hydrogen mantle, and a molecular hydrogen surface. However, not all gaseous planets are specifically split up into a core, a metallic gas mantle, and molecular gas surface. Uranus and Neptune for instance, have mantles primarily composed of ammonia and methane ices. No two gas planets outside the same vicinity should have the exact same composition, as the growth of a gas planet is dependent on the conditions it was put under.

To the left is an illustration of the layers and size comparisons of the four gas planets of our solar system.

Proceeding, we arrive at terrestrial planets, the next general category that also happens to be the one most planets in the universe fall under. Terrestrial planets form nearly identically to gas planets. Both begin as a seed – this time, a chunk of rock – pulling in surrounding chunks where it will begin to rapidly grow into a planet. However, terrestrial planets, unlike gaseous planets, have a much higher chance of not having an atmosphere.  Factors such as location in the star system and the orbit of the planet can determine whether it has an atmosphere. This is mainly due to the fact that it is how well the planet is able to hold onto gasses that determines whether it can maintain an atmosphere. This is why many smaller terrestrial planets with a weaker gravitational pull have trouble holding onto one. It also explains why many planets that orbit too close to their sun can struggle to maintain an atmosphere under such extreme temperatures.

View of Earth from space showing city lights across continents at night, with stars in the background.
Close-up of a mineral or metallic substance with gold and silver flecks and colorful iridescent reflections.

On the other hand, atmospheric terrestrial planets have an entirely contrasting realm of possibility. With the capacity of capturing and retaining gasses, no matter how little, weather is now an option. The weather on the terrestrial planet is what shapes the land and makes life. Some of the earliest life forms here on Earth, microbial species, can also be found on worlds in which have or had an atmosphere, including gas planets. Though, terrestrial planets have a slightly different layering. The common layering of a terrestrial planet includes: the inner-core, the outer-core, the mantle, and the crust. It should be mentioned that the crust is the equivalent to the gaseous surface of a gas planet, but the crust of a terrestrial planet is significantly thinner. You may also notice that the core is split up into 2 parts. While they’re both fairly dense, the inner-core is solid and the outer-core is liquid.

Terrestrial Planet Layers

Graphic Created by Astron Analytics

Illustration of the planet Venus, labeled as 'PLANET #02'.
Illustration of the planet Mars with a label that reads "MARS PLANET - #04" against an orange background.

A question you may encounter is, “What’s the difference between the mantle and outer core?” Well, there isn’t any specific definition, but instead, the two layers are split based on comparative characteristics such as temperature, depth, and density; factors that vary from planet to planet. Furthermore, terrestrial planets don’t always have an inner and outer core, nor do some even have a mantle. Smaller terrestrial planets, or planets with less mass, usually only have 2 layers. These two being the core and the crust. Similarly to how a core can be split into two,  the crust can also be split into two: the inner-crust and the outer-crust. However, this only happens when the crust seems to span a large distance underground. It should be noted that the main difference between the two layers is composition rather than their state of matter (liquid or solid). With this being said, that’s the introduction to planets, describing the two main categories, how they form, and the common features found in the planets in both categories.

Astron Original Document -

Space: Introduction

Planets Introduction

Mar. 3, 2024 - Written by Kevin Jie

A planet is a non-illuminating celestial body that orbits a parent star. A planet can vary in size, shape, and color; being arguably the most diverse celestial structure in the universe. Similarly to stars in the stellar life cycle, planets are often formed in relatively the same way but become their own object. This path is less of a cycle and more of a one-way. Before continuing, one common misconception must be cleared. Exoplanets and planets are identical. “Exoplanet,” is just a name given to any planet outside of the solar system.

Beginning with gaseous planets, the emergence of each is totally unique to the last. Most gaseous planets begin as gas rich particles that surround a young star. As the gas particles exist in this orbit around the star, sporadic movement within the star system will make gas particles collide and connect with one another, forming a base. Over time, the base will gain more and more mass, creating its own gravitational pull. From here, the soon to be gaseous planet will rapidly grow. 

A poster featuring an image of Jupiter with its characteristic bands and storms, labeled 'JUPITER PLANET-#03'.
Digital illustration of Saturn with rings, labeled 'Saturn' and 'Planet - #07', on a beige background with a white square border.

The gas planet will often grow into 3 layers starting from the seed. This consists of the core (either dense rock or ice), a gaseous mantle and a dense gaseous surface. For example, Jupiter has 3 layers: The core,  a metallic hydrogen mantle, and a molecular hydrogen surface. However, not all gaseous planets are specifically split up into a core, a metallic gas mantle, and molecular gas surface. Uranus and Neptune for instance, have mantles primarily composed of ammonia and methane ices. No two gas planets outside the same vicinity should have the exact same composition, as the growth of a gas planet is dependent on the conditions it was put under.

To the bottom is an illustration of the layers and size comparisons of the four gas planets of our solar system.

Diagram of the layers of planets Neptune, Uranus, Saturn, and Jupiter, showing their cores, rocky, metallic, and gaseous layers with labels.
Illustration of planet Uranus with text labeling it as 'Uranus, Planet - #06' against a light teal background.
A digital graphic design of Neptune, the fifth planet, shown as a blue sphere inside a white square with a blue background. Text reads 'NEPTUNE PLANET - #05'.

Proceeding, we arrive at terrestrial planets, the next general category that also happens to be the one most planets in the universe fall under. Terrestrial planets form nearly identically to gas planets. Both begin as a seed – this time, a chunk of rock – pulling in surrounding chunks where it will begin to rapidly grow into a planet. However, terrestrial planets, unlike gaseous planets, have a much higher chance of not having an atmosphere.  Factors such as location in the star system and the orbit of the planet can determine whether it has an atmosphere. This is mainly due to the fact that it is how well the planet is able to hold onto gasses that determines whether it can maintain an atmosphere. This is why many smaller terrestrial planets with a weaker gravitational pull have trouble holding onto one. It also explains why many planets that orbit too close to their sun can struggle to maintain an atmosphere under such extreme temperatures.

Nighttime view of Earth from space, showing city lights across continents and the curvature of the planet.
Close-up of Earth’s surface showing gold-colored mineral deposits and shimmering minerals with a dark background.

On the other hand, atmospheric terrestrial planets have an entirely contrasting realm of possibility. With the capacity of capturing and retaining gasses, no matter how little, weather is now an option. The weather on the terrestrial planet is what shapes the land and makes life. Some of the earliest life forms here on Earth, microbial species, can also be found on worlds in which have or had an atmosphere, including gas planets. Though, terrestrial planets have a slightly different layering. The common layering of a terrestrial planet includes: the inner-core, the outer-core, the mantle, and the crust. It should be mentioned that the crust is the equivalent to the gaseous surface of a gas planet, but the crust of a terrestrial planet is significantly thinner. You may also notice that the core is split up into 2 parts. While they’re both fairly dense, the inner-core is solid and the outer-core is liquid.

Diagram comparing Earth's interior layers in more dense and less dense terrestrial planets. The more dense planet on the left shows crust, mantle, outer core, and inner core, with yellow and orange colors. The less dense planet on the right also shows crust, mantle, outer core, and inner core, with darker brown and red colors.

A question you may encounter is, “What’s the difference between the mantle and outer core?” Well, there isn’t any specific definition, but instead, the two layers are split based on comparative characteristics such as temperature, depth, and density; factors that vary from planet to planet. Furthermore, terrestrial planets don’t always have an inner and outer core, nor do some even have a mantle. Smaller terrestrial planets, or planets with less mass, usually only have 2 layers. These two being the core and the crust. Similarly to how a core can be split into two,  the crust can also be split into two: the inner-crust and the outer-crust. However, this only happens when the crust seems to span a large distance underground. It should be noted that the main difference between the two layers is composition rather than their state of matter (liquid or solid). With this being said, that’s the introduction to planets, describing the two main categories, how they form, and the common features found in the planets in both categories.

Graphic Created by Astron Analytics

A Mars-themed poster featuring an image of Mars against an orange background, with text that reads 'MARS PLANET - #04'.
Illustration of planet Venus with a brownish-orange surface, labeled 'Venus, Planet #02' on a white card against a light brown background.

Astron Original Document - Space Introduction