The solar system
The solar system formed about 4.6 billion years ago, when gravity collapsed a cloud of gas and dust —already enriched with heavy elements from earlier generations of stars— into a rotating disk. The Sun formed at its center; in the surrounding disk, the planets and the rest of the bodies that orbit it today.
The Sun as a star
Every day we feel the heat and light of the Sun, a gigantic source of energy that has been emitting radiation for about 4.6 billion years without running out, even though it is surrounded by the vacuum of space: where does this continuous source of energy come from if there cannot be any chemical fire out there?
List the components of the Solar System and explain in one sentence what each type of body is.
List the components of the Solar System and explain in one sentence what each type of body is.
The planets: terrestrial and giant
When we measure the planets, a striking contrast appears: the Earth has a density of $5.5\ \text{g/cm}^3$, whereas Saturn has barely $0.7\ \text{g/cm}^3$ (less than water, which is $1.00\ \text{g/cm}^3$, so it would float): why are the four worlds closest to the Sun dense rocks and the four outer ones enormous gaseous spheres?
The diagram shows the Solar System on a qualitative scale (the orbits and sizes are not realistic). Name the planets labeled with numbers from 1 to 8, from closest to…
The diagram shows the Solar System on a qualitative scale (the orbits and sizes are not realistic). Name the planets labeled with numbers from 1 to 8, from closest to farthest from the Sun.
Explain the difference between a rocky planet and a gas planet, and classify the eight planets of the solar system into one of these two groups.
Explain the difference between a rocky planet and a gas planet, and classify the eight planets of the solar system into one of these two groups.
Dwarf planets and minor bodies
For decades it was thought that there were nine planets, but from the 1990s onwards telescopes discovered hundreds of icy worlds comparable to Pluto orbiting beyond Neptune: how did astronomers decide on the exact boundary between what is a planet and what is a minor body?
In 2006, Pluto came to be considered a dwarf planet. Explain which requirement of the definition of a planet it does not meet and name another dwarf planet in the solar…
In 2006, Pluto came to be considered a dwarf planet. Explain which requirement of the definition of a planet it does not meet and name another dwarf planet in the solar system.
What are the asteroid belt and the Kuiper belt? State where each one is located and what type of bodies it contains.
What are the asteroid belt and the Kuiper belt? State where each one is located and what type of bodies it contains.
Planetary motions and the habitable zone
Earth is currently the only planet with known life. Explain three characteristics of Earth that make it suitable for life, such as its distance from the Sun, the…
Earth is currently the only planet with known life. Explain three characteristics of Earth that make it suitable for life, such as its distance from the Sun, the presence of liquid water, or its atmosphere.
The real scales of the solar system
You are going to design a scale model of the Solar System in the hallway of your school, which is $50\ \text{m}$ long. You decide to represent the Sun with a basketball…
You are going to design a scale model of the Solar System in the hallway of your school, which is $50\ \text{m}$ long. You decide to represent the Sun with a basketball of $24\ \text{cm}$ in diameter (the actual diameter of the Sun is approximately $1\,390\,000\ \text{km}$).
- a) At that same scale, calculate what diameter the Earth should have (actual diameter: $12\,742\ \text{km}$) and compare it with a small everyday object (such as a pinhead or a grain of sand).
- b) Knowing that the average Earth-Sun distance is $1.5 \times 10^8\ \text{km}$ and Neptune's distance to the Sun is about $4.5 \times 10^9\ \text{km}$, calculate at what distance from the ball you would have to place both planets.
- c) Based on the results, justify whether the complete model fits in the hallway while simultaneously maintaining the scale of sizes and the scale of distances, and explain why Solar System diagrams in textbooks are often misleading.