Overview
This lecture covers the rings of Uranus and Neptune, why they are hard to see, how sunlight affects their composition, and the mystery of Neptune’s disappearing rings.
Rings of Uranus and Neptune
- Both Uranus and Neptune have rings, though they are very hard to see in visible light.
- Unlike Jupiter's rocky rings, Uranus and Neptune's rings are made of ice due to their cold environments.
- Their ice is primarily methane ice, not water ice, due to the extreme cold far from the Sun.
Sunlight’s Effect on Rings
- Sunlight continuously breaks down ice in planetary rings.
- For water ice (like Saturn's rings), sunlight breaks it into hydrogen and oxygen gases that escape to space, shrinking the ice.
- For methane ice (CH₄), sunlight breaks it into carbon and hydrogen; carbon remains as a solid layer on the ice.
- The carbon layer turns the ice black, making the rings difficult to see because they no longer reflect sunlight well.
- This carbonizing process is called "carbonization," and the rings become carbonized methane ice.
Visibility Differences: Rings vs. Clouds
- Clouds on these planets circulate and avoid long-term sunlight exposure, so they stay bright and visible.
- Ring particles stay exposed to sunlight, so carbon builds up and darkens them.
Disappearing Rings of Neptune
- Neptune’s rings have been observed disappearing rapidly over the last 40 years.
- If the rate continues, Neptune’s rings could vanish in about 100 years.
- The cause for the disappearance is unknown; it's not observed on other planets.
- Neptune’s year is 165 Earth years, so its seasons last about 40 Earth years each.
- We have only observed one Neptune season, so changes in the rings could be seasonal.
Fun Fact about Neptune
- Humans have never observed Neptune complete a full orbit since its discovery.
Key Terms & Definitions
- Methane Ice — Frozen methane (CH₄) found on outer planets due to extreme cold.
- Carbonization — Process where sunlight breaks down methane ice, leaving black carbon behind.
- Neptune Year — The time Neptune takes to orbit the Sun, equal to 165 Earth years.
Action Items / Next Steps
- Review differences between water ice and methane ice in planetary rings.
- Remember the process of carbonization and its effects on ring visibility.
- No homework or readings assigned for this topic.