Why do scientists think Titan has an atmosphere while the large ...

[LaDunn]

Why do scientists think Titan has an atmosphere while the large moons of Jupiter (Ganymede, Callisto, Europa and Io) do not?
 
  A) The jovian satellites lost their atmospheres because of Jupiter's thermal radiation.
  B) The jovian satellites never formed atmospheres because the solar nebula was too hot there.
  C) The jovian satellites had their atmospheres stripped by Jupiter's gravitational pull.
  D) The jovian satellites experienced too many collisions in their lifetimes to maintain atmospheres.
  E) Titan got its atmosphere by accreting gases from Saturn. The jovian satellites were competing with one another to do this, so it was unsuccessful for any of them.

Question 2

Why is the post-Main Sequence structure of a high mass star sometimes described by an onion-layer model? Explain.
 
  What will be an ideal response?

[bimper21]

Answer to Question 1

B

Answer to Question 2

Late in the evolution of massive stars, fusion reactions create cores within cores within cores, etc. Hydrogen fusion occurs in a layer around a layer of helium fusion which occurs around of layer of carbon fusion... around oxygen fusion... around neon fusion... etc. The deeper you go, the heavier elements you find made, and the higher the temperature needed to sustain that particular fusion reaction.