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# Earth

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Distance Location of in (circled) from the Sun: 149 million kilometers Characteristics 6,022 to 4.543 billion years old 1 M⊕ (5.9722±0.0006×10^24)
«The Blue Marble», the most famous photograph of the Earth.

Earth is the third planet from the Sun. It is the largest terrestrial planet and also the fifth largest planet. It also has the highest density out of all the Solar System planets.

Earth is special due to its life-sustaining conditions. It has water (in three (solid, liquid, gas) of the four (solid, liquid, gas, plasma) states of matter) for living things to drink, an atmosphere so we can breathe and not have serious cancer. It actually has three moons: The Moon (aka Luna), 2016 HO3,[1] and Cruithne.[2] 2016 HO3 and Cruithne are «Quasi-satellites», which were found to technically orbit both the Sun and the Earth.

## Structure

The structure of the Earth is divided into ${\displaystyle 5}$ layers: The lithosphere, which contains the crust and a small portion of the next layer, the asthenosphere, the rest of the mantle, the outer core, which generates the Earth's magnetic field that protects us from deadly solar rays, and the inner core.

Layer Name Depth (km) Temperature (oC)
Lithosphere (crust + upper asthenosphere) ${\displaystyle >8}$ (ocean)

${\displaystyle >40}$ (crust)

${\displaystyle 35}$ to ${\displaystyle -14}$
Asthenosphere ${\displaystyle 200}$ ${\displaystyle 1,300}$
Mantle ${\displaystyle 2,886}$ ${\displaystyle 500-4,000}$
Outer Core ${\displaystyle 2,250}$ ${\displaystyle 4,230}$
Inner Core ${\displaystyle 1,220}$ ${\displaystyle 5,430}$

## Atmosphere

The Earth has an atmosphere that extends to ${\displaystyle 100}$ kilometers above the Earth's surface. Air referrers to any part of the atmosphere. ${\displaystyle 78\%}$ of the atmosphere is made out of Nitrogen, while ${\displaystyle 21\%}$ is made out of breathable oxygen. The remaining ${\displaystyle 1\%}$ is made out of other gases like hydrogen, helium, and argon. The layers of the atmosphere are:

• Troposphere ${\displaystyle (6-20}$ km)
• Stratosphere ${\displaystyle (50}$ km)
• Mesosphere ${\displaystyle (85}$ km)
• Thermosphere ${\displaystyle (690}$ km)
• Exosphere ${\displaystyle (10,000}$ km)

Even though the thermosphere goes up to an altitude of ${\displaystyle 690}$ kilometers, the defined boundary between the atmosphere and space, called the Kármán line, is placed at an altitude of ${\displaystyle 100}$ kilometers.[3]

## Magnetic Field

The Earth has a magnetic field to protect us from harmful solar rays. All magnets have a north pole and a south pole. The Earth's magnetic poles are slightly off-target, since the magnetic north pole is 2,000 km away from the geographical north pole and the south pole is located off the coast of Antarctica. Since opposite sides attract and like charges repel each other, the forces made by a pole would point toward the opposite pole! The inner core of the Earth is what generates the magnetic field, in other words, the inner core is a giant magnet.

## References

1. https://arxiv.org/abs/1608.01518
2. http://burtleburtle.net/bob/physics/cruithne.html
3. The 100 km Boundary for Astronautics by Dr. S. Sanz Fernández de Córdoba. Published by Fédération Aéronautique Internationale on 2004-06-24.