Astronomy 65 - The Solar System - Terrestrial vs Jovian - Part 2

Astronomy 65 - The Solar System - Terrestrial vs Jovian - Part 2

Overview

This lecture introduces the two main types of planets in our solar system—terrestrial and Jovian—and details their similarities and major differences.

Types of Planets in the Solar System

• The four outer planets (Jupiter, Saturn, Uranus, Neptune) are called Jovian planets (Jupiter-like).
• The inner planets (Mercury, Venus, Earth, Mars) are called terrestrial planets (Earth-like).
• Earth serves as the model for terrestrial planets; Jupiter for Jovian planets.

Common Features of All Planets

• All planets orbit the Sun.
• Every planet is round in shape (no square or oddly-shaped planets in reality).
• All planetary orbits are ellipses (elliptical in shape).
• Planets orbit the Sun in the same direction.
• All planets orbit roughly in the same plane, making the solar system essentially flat.
• These shared characteristics are due to the way the solar system formed.

Major Differences Between Terrestrial and Jovian Planets

Orbits

• Terrestrial planets have small orbits (close to the Sun).
• Jovian planets have large orbits (far from the Sun).

Size

• Terrestrial planets are small in size.
• Jovian planets are large in size.
• Jupiter is the largest planet; Mercury is the smallest.

Rings

• Terrestrial planets have no rings.
• Jovian planets all have rings (not just Saturn, but also Jupiter, Uranus, and Neptune).

Planethood Criteria

• To be considered a planet, a body must orbit the Sun directly.
• Some moons are larger than Mercury but are not planets because they orbit planets, not the Sun.

Key Terms & Definitions

• Jovian planet — A giant, Jupiter-like planet (Jupiter, Saturn, Uranus, Neptune).
• Terrestrial planet — A small, rocky, Earth-like planet (Mercury, Venus, Earth, Mars).
• Ellipse — An oval shape that describes the orbits of all planets.
• Orbit — The path a planet takes around the Sun.

Action Items / Next Steps

• Make space in your notes for a running list of differences between terrestrial and Jovian planets.
• Prepare for discussion on why Pluto is not considered a planet (next class).
• Look ahead to an explanation on planetary rings and the solar system's formation.