Titan is the second largest moon in the solar system. The jovian moon Ganymede is larger.?
Question:
Answer:
Good question! Both worlds are fairly similar in size, but the difference lies in two things.
1) Surface activity. Ganymede has been dead (no volvcanoes etc) for a very, very long time (lots of craters -> been dead for a long time). Titan looks like it may be active still today, and if not it certainly was active much more recently (geologically speaking). Since the gasses the populate the atmosphere are a result of melting surface features, you need some activity to get the gas.
2) Titan is farther away from the sun, and hence colder. A world needs to hold onto the gas in the atmosphere. Put a nitrogen molecule on Ganymede and it will quickly leave the planet (like helium on Earth). Why? Well the gas gets hot, moves fast and can escape the gravity of the world. In Titan's case the gas does not get as hot, and hence moves slower, thus remaining trapped on the world.
Titan is more volcanic than Ganymede, spewing stuff into the air, whereas Ganymede is mostly ice
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