My middle school students will be working on reports on the moons of the outer solar system this week. When I was in middle school, the gas giants had what we thought were a lot of moons, but that number has greatly increased as telescopes have improved and probes have been sent to the outer solar system.
| Planet | Number of moons (1975) | Number of moons (2007) |
| Jupiter | 12 | 63 |
| Saturn | 11 | 48-60 |
| Uranus | 5 | 27 |
| Neptune | 2 | 13 |
As more moons are discovered, their diameters are becoming smaller. The following table shows the average diameter of moons discovered in orbit around Jupiter for various time periods:
| Time period | Average diameter of moons discovered (km) |
| 1600s | 4208 |
| 1800s | 262 |
| 1900-1970 | 55 |
| 1970s | 37 |
| 2000s | 3 |
Some questions:
- How many moons will we say Jupiter has when we can observe rocks only 100 meters in diamter?
- Will there be another astronomical crisis when Jupiter has 1000 moons? Will astronomers have to debate the question, “What is a moon?” just like they had to go through the “What is a planet?” issue?
Grace and Peace
GeoChristian 