Planets (and Exoplanets)
We all live on Earth – our beautiful, blue-green planet. While Earth is the only one in our solar system with life, it’s definitely not the only planet! But no human has been on any one except Earth. Attempts at a Mars landing are still in the works. So without having landed humans on another planet, what do we know about the planets in our universe?
What Exactly Is a Planet?
Have you ever heard about the Pluto debacle? Well, once upon a time, our solar system had 9 planets, and Pluto was the very last one. Now, however, Pluto is no longer considered to be one by scientists. To understand why this happened, we need to go to the official definition!
- Have enough mass to have a nearly round shape. This is because smaller celestial objects don’t have enough self-gravity. Because of this, they can’t pull themselves into a sphere!
- Have cleared their orbits of other objects and floating debris. This means that they have to be big and have strong gravitational fields. If its gravity is strong enough, it will either pull other floating objects in, or push them out of its orbit!
Dwarfs, Satellites, and Exoplanets
Be careful not to mistake planets with satellites or dwarf planets! Satellite is a broader term. Satellite refers to any celestial object that orbits another celestial object. So the Moon is a satellite of Earth, and Earth is a satellite of the Sun! Satellites can also be natural or man-made!
A dwarf planet is almost exactly like a normal one, except for the last criteria. A dwarf planet, like Pluto, isn’t big enough to have a strong gravitational field. As a result, they can’t clear their orbits of other objects!
How Do Planets Form?
The Different Types of Planets
Ice giants, like Neptune and Uranus, used to be classified under gas giants. Scientists found out recently that these two planets were different! Neptune and Uranus contain heavier substances than gas giants! Ice giants, then, are composed of heavier elements like oxygen, sulfur, carbon, and nitrogen.
Other Great Resources
NASA Spaceplace on Exoplanets: https://spaceplace.nasa.gov/all-about-exoplanets/en/
What are Gas and Ice Giants: https://www.scienceabc.com/nature/universe/what-are-gas-giants-and-ice-giants-and-why-are-they-called-so.html
Terrestrial Planets: https://www.space.com/17028-terrestrial-planets.html
How do Planets Form: https://lco.global/spacebook/planets-and-how-they-formed/
Facts about the Planets for Kids: http://www.planetsforkids.org
Planets of the Solar System: https://www.youtube.com/watch?v=RJ2bQWH6GCM
Exploring our Solar System: https://www.youtube.com/watch?v=Qd6nLM2QlWw
NatGeo Solar System 101: https://www.youtube.com/watch?v=libKVRa01L8