Y can a outer planet’s moon the size of the planet Mercury hav a thick atmosphere when Mercury itself has none

Question

A Because of the concentration of gases in the vicinity of a Jovian planet, the moon formed in an unusually dense environment.

B The moon is outgassing its atmosphere, so that the atmosphere is continually regenerated.

C The moons in the outer Solar System are subject to frequent impacts from the icy bodies – the atmosphere can arise from the gaseous materials emitted by these impacts.

D The temperature in the outer Solar System is low enough that the gases in the moon’s atmosphere do not reach escape velocity.

E If the moon formed more recently than Mercury, it may still have its atmosphere but will eventually lose it.

Answer 1

D.

Answer 2

D is part of it, but it also has to do with the magnetic field of the body... Mercury doesn't have a strong enough magnetic field to support an atmosphere. Also, (this is just an educated guess and may not be accurate) I believe, that if an atmosphere could form on mercury, it is close enough to the sun that it would be destroyed.

Answer 3

D
But also the close proximity to the Sun boiled off any atmosphere that Mercury may have possessed.

Answer 4

I'm also going with D.

Answer 5

D