- A layer of water sublimes on top of tectonic plates, making it easier to melt the rock, which helps volcanoes.
- Primary Atmosphere: made up of mostly hydrogen and helium.
- Secondary Atmosphere: gasses added to atmosphere (outgassing or evaporation) and removed from atmosphere through atmospheric sinks (condensation, chemical reactions with surface materials, and thermal escape).
- Graph shows speed of molecules moving (due to their temperature) and escape velocity (proxy for gravity).
- Gasses are either heated up a lot and fly off, or the escape velocity is so low that even cold particles can fly off,.
- How to read the graph: a planet can hold on to gasses below it on the graph.
To hold on to gasses better:
- Colder planet (so gas particles move less)
- More gravity (to hold on to gas particles)
- World atmosphere depends on distance from sun, and gravity.
- Venus probably had a similar atmosphere to Earth, but greenhouse effect made it very hot and water boiled off.
Measuring spectrum though subtraction
- You can take a spectrum of a planet as it passes in front of a star, subtract the star, and get the planet’s spectrum.