Essay Questions from 11/8 Answer in paragraph form



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Essay Questions from 11/8
Answer in paragraph form


  1. The universe started with the Big Bang and has been expanding ever since.

Give a general description of our universe. Discuss distances, how matter is

distributed in space, and what tools we used to find this out.


Vocabulary to use: Light year, galaxy, star, nebula.
The universe contains everything that we can tell exists. All of the matter, and all of the energy. Mostly the universe consists of empty space. Really empty, with no atoms in it at all. But there are areas where matter is clumped together.

This empty space can stretch for hundreds of light years in all directions before you find a concentration of matter. A light year is almost 6 trillion miles long.

Nebulas are areas where a lot dust and gas collects, often after the explosion of a star. Nebulas are still mostly empty space, but with enough matter to form stars and planets. Stars are where most of the matter in the universe is found. For example, over 99% of the matter in our solar system is contained in the sun. All of the planets and asteroids are less than 1%. Stars are collected into galaxies, which contain 100s of billions of stars. These galaxies are where most of the matter in the universe is concentrated.



  1. Give a chronological explanation of how our solar system formed and why the terrestrial and gas giant planets ended up where they are.

Start with the explosion of the star before Sol, and the creation of the solar nebula.

Vocabulary to use: Gravity, planetessimal, protoplanet, collisions


About 5 billion years ago, a star exploded near where our solar system is now. It left behind all of the chemical elements that the star had been made of, the gasses, the dust and the atoms of metals. This material was the solar nebula, the nebula that our solar system formed from. Most of the matter in this nebula was near its center and the center started pulling other material towards it, through magnetic attractions and by gravity. This caused the whole nebula to start spinning and to flatten into a disk.

Eventually the center of the nebula became dense enough and hot enough for the sun to begin burning, through the fusion of Hydrogen into Helium. It pulled all of the matter near it into the sun so that today 99% of all the material in the solar system is in Sol, our star. As the solar nebula continued to spin, the matter left over started to pull together through gravity to form chunks of rock, metal and gasses. The bigger these chunks got, the stronger their gravity. They started to attract each other, adding their material together. We call the biggest chunks planetessimals – tiny planets. As the planetessimals continued orbiting the sun, they added together through collisions, cleaning up their orbits and getting larger. The largest of these objects are called protoplanets (proto meaning early or before). The protoplanets were the beginnings of the planets we have now. They were finished after their gravity pulled all of the material in their orbits to them.




  1. Write two paragraphs, one giving a description of a typical terrestrial planet, and another describing a typical gas giant planet. Include a description of the layering of the typical planet in each category.

The typical terrestrial planet has a iron and nickel core that makes up at least a quarter of its diameter. This core can be solid, liquid or both. Outside of the core is a thick layer of rock. This rock can be either solid or soft, like silly putty. Which a planet will have depends on both the size of the planet and where it is. Larger planets lose heat more slowly and keep this soft layer of rock (the mantle) longer. The surface of a terrestrial planet is solid. It may have many craters. The atmosphere of a terrestrial planet is thin, only 10’s of miles thick at the most, and made of the heavier gasses. This is because most of the lighter gasses like H and He, escaped to space when the planets were young and hot.



The typical gas giant planet is many times larger than the Earth. Gas giants have very small metal or rocky cores, since most of these materials stayed near the center of the solar nebula as the solar system formed. Then there is a thick layer of liquid or frozen gasses. This would be the planet’s surface. The atmosphere of gas giants is hundreds of miles thick and is over 90% hydrogen and helium. These planets are closer in composition to the sun than to the terrestrial planets, but they are not big enough to start fusion explosions and light up like the sun.


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