Astronomy 66 - The Solar System - Terrestrial vs Jovian - Part 3
Overview
This lecture covers the concepts of planetary mass and density, explaining how they are measured and the differences between Jovian and terrestrial planets.
Mass of Planets
- Mass is the total amount of material contained within a planet.
- Mass cannot be determined just by looking at an object; you only see the outside.
- To measure mass, you must use a scale or other indirect methods.
- For planets, mass is determined by observing gravitational effects since we can't put planets on a scale.
- Planets with more mass have stronger gravity.
- Gravity can be measured by the speed at which moons orbit their parent planet.
- Jovian planets have higher gravity and therefore more mass compared to terrestrial planets.
- Bigger planets generally have more mass, but size alone doesn’t always determine mass.
Density of Planets
- Density refers to how tightly packed the material in an object is (mass per unit volume).
- Dense objects are compact; low-density objects are spread out.
- Density depends on both the amount of mass and the size (volume) of the object.
- More mass in the same volume equals higher density.
- Increasing the size while keeping the same mass decreases density.
- Formula: Density = Mass / Volume.
- Jovian planets, though more massive, are much larger, so their density is lower compared to terrestrial planets.
- Terrestrial planets are smaller but have high density due to closely packed material.
Composition of Planets
- Terrestrial planets are made mostly of rock and metal—primarily solid materials.
- Jovian planets have more gas and are less dense.
Key Terms & Definitions
- Mass — Total amount of material in an object or planet.
- Gravity — The force caused by mass; stronger mass means stronger gravity.
- Density — The amount of mass per unit volume (Density = Mass / Volume).
- Terrestrial Planets — Rocky, high-density planets like Earth.
- Jovian Planets — Gas giants, lower density but much more massive than terrestrial planets.
Action Items / Next Steps
- Review the differences between mass and density for terrestrial and jovian planets.
- Prepare examples of calculating density given mass and volume for discussion.