Overview
This lecture discussed the number of moons around each planet, clarified common misconceptions, and explained why the count for outer planets is uncertain.
Moons of the Terrestrial Planets
- Mercury has zero moons.
- Venus has zero moons.
- Earth has one moon.
- Mars has two moons.
- Terrestrial planets (Mercury, Venus, Earth, Mars) have few or no moons.
Moons of the Jovian Planets
- Jupiter has at least 68 confirmed moons; the exact number is unknown and keeps increasing.
- Saturn has at least 50 confirmed moons.
- Uranus has at least 20 confirmed moons.
- Neptune has at least 10-20 confirmed moons.
- Jovian planets (Jupiter, Saturn, Uranus, Neptune) have many moons—often dozens or more.
Why the Moon Counts Are Uncertain
- Distant planets are harder to observe, making their moons harder to detect.
- Many moons around Jovian planets are much smaller than Earth's moon.
- The farther a planet is, the less certain we are of its exact moon count; more may be discovered.
Common Student Mistakes
- Students often mistakenly think Venus has one moon; only Earth does.
- Venus has no moons—a fact often confused on tests.
Key Terms & Definitions
- Terrestrial planets — Mercury, Venus, Earth, and Mars; rocky and have few or no moons.
- Jovian planets — Jupiter, Saturn, Uranus, Neptune; gas giants with many moons.
Action Items / Next Steps
- Review the number of moons for each planet.
- Remember: Only Earth among the terrestrial planets has one moon.
- Prepare for questions about planet moons on upcoming tests.