# What is the current accepted theory as to why Titan has retained its atmosphere?

Titan (moon of Saturn) is unique in that it possesses a very thick atmosphere. However, Titan is certainly is not the largest of the moons - Ganymede being larger.

What is the current accepted theory as to why Titan has retained its thick atmosphere?

It's not really known why only Titan has a thick atmosphere while moons like Ganymede don't.

One thought is that temperatures may have been too high (well above ~40K) in the Jovian subnebula of our solar system due to the greater gravitational potential energy release, mass, and proximity to the Sun, greatly reducing the $NH_{3}$-hydrate inventory accreted by both Callisto and Ganymede. The resulting $N_{2}$ atmospheres might have been too thin to survive the atmospheric erosion effects that Titan has withstood.

http://adsabs.harvard.edu/abs/2012ttt..work...25N (this paper critiques the previous idea of a $CH_{4}$ supported atmosphere)