Most antonyms related to "atmosphere" are going to revolve around specific atmospheres:
The atmosphere is inhabitable. — The atmosphere is uninhabitable.
The atmosphere/aura in here is electric! — The atmosphere/aura in here is dead.
The opposite of having an atmosphere is simply not having one. This could also be described as "vacuum":
That moon has no atmosphere. — That moon has an atmosphere.
That moon is surrounded by an atmosphere. — That moon is surrounded by a vacuum.
There is one other concept that could work as an antonym of atmosphere and this relates to the idea of the atmosphere as a location:
The creature lives in the atmosphere of that moon.
The creature lives on the surface of that moon.
The creature lives in space near that moon.
In this sense, both "surface" and "space" could be considered antonyms but it would technically be more accurate to say that "atmosphere" has no antonym.
In short, "vacuum" could be used as an antonym given the appropriate context and usage but it only truly relates to the air/environment surrounding a celestial body. I can see a rather weak argument for "surface" or "space" but it is stretching the definition of "antonym" quite a bit. There is no appropriate antonym for aura unless you choose to define one as such for the sake of a story:
Alice was surrounded by a tangible atmosphere/aura but Bob only had vacuum.