9.2 - Our Solar System

Scientists describe our solar system as the Sun and all the planets andother celestial objects, such as moons, comets, and asteroids, that are heldby the Sun’s gravity and orbit around it.

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The Formation of our Solar System

The most accepted theory on how our solar system was formed is calledthe nebular theory. A nebular is a cloud of dust and gases in space,which is essentially an area of star formation.

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Summary of the Nebular Theory:

After the Sun was formed, the solar wind blew against the nebulafrom which it is formed, pushing the gas and dust away from the Sun.

The leftover dust continued to spin, creating a thin disk around thenew star.

Small bodies began to form in the disk, forming into planets, moons,asteroids, and comets.

Watch: “The Nebular Theory”Unit 4 - Exploring Our Universe 3 / 8

The Planets

A planet is an astronomical body that orbits one or more stars and iscapable of forming into a spherical shape under its own gravitation force.

In our solar system, there are eight planets. There are two broadcategories to classify these planets: the rocky inner planets and the gasgiants.

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The Planets

A planet is an astronomical body that orbits one or more stars and iscapable of forming into a spherical shape under its own gravitation force.

In our solar system, there are eight planets. There are two broadcategories to classify these planets: the rocky inner planets and the gasgiants.

Watch: “The Planets”

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The Rocky Inner Planets

The four rocky inner planets are called: Mercury, Venus, Earth, andMars.

These planets formed similar to how a small snowball, when rolling it onsticky snow, can grow in size. When particles of dust and gas slammedinto each other during our solar system’s formation, some began to sticktogether, resulting in these planets.

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The Four Gas Giants

The four gas giants are called: Jupiter, Saturn, Uranus, and Neptune.

The solar wind blows gases away from the Sun; however, not all the gasesescape the solar system. Beyond the asteroid belt is the “snow line”. Onthe Sun side of this line, the Sun’s radiation keeps water in its gaseousphase. Past this line, water can cool to form droplets and then freeze.

The gas giants may have grown as they did because ice acted as a kind ofglue to cause gas particles to stick together.

Watch: “Why does Saturn have rings?”Unit 4 - Exploring Our Universe 6 / 8

Measuring Distances in Space

One unit used to measure distances in space is the astronomical unit(AU). One AU equals the average distance between the Sun and theEarth, about 150 million km.

Common Distances from the Sun (AU):

Mercury: 0.4 AU

Mars: 1.5 AU

Jupiter: 5.3 AU

Neptune 30.0 AU

View: “Our Solar System (to scale)”Watch: “Visualizing the Size of the Planets”

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Other Objects in the Solar System

The Asteroid Belt - Circling the Sun at about 3 AU is a huge bandof billions of rocks called asteroids.

Dwarf Planets - similar to planets (have a spherical shape), but havean unusual orbit that contains many other objects. (ex: Pluto)

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Other Objects in the Solar System

Comets - a celestial object made of ice and dust which travels in anelliptical orbit around the Sun.

Meteors and Meteorites - A meteor (a “shooting star”) is ameteoroid that collides with the gas molecules in Earth’s atmosphereand heats up to very high temperatures. If a meteor does not burn upand strikes Earth, it is called a meteorite.

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