How can this habitable planet have a moon with a naturally occurring atmosphere?

Assuming the planet is earth-like, with more surface water and atmospheric oxygen, and within the habitable zone of a sun-like star, how can a moon orbiting this planet retain a thick atmosphere?

The moon is NOT habitable, and has little or no atmospheric oxygen. The atmosphere is thick enough to form a visible haze around the moon, like Titan.

Unlike Titan, however, the moon and planet would be close enough to the host star to be heated in a similar manner to Luna, and with an atmosphere, the surface temp would likely be even hotter. The problem is, I do not know how to prevent a subsequent runaway greenhouse effect and prolong the life of the atmosphere without chilling the moon (and consequently, the planet).

So how can a moon retain a thick atmosphere without compromising the habitability of the host planet?

posted over 5 years ago

Tardigreat‭

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