Dead Moon(1992)

Alpha 27, the one planet in the galaxy that is fit for human habitation. For many years, the space observation system here was used for a wide range of research. One day, horrifying news arrived- a giant comet was hurtling toward the solar system, on its present course, it was going to colide with the moon. and then….Nothing! For some strange reason the humans and the moon seemed completely unaffected. The humans were unaware that a new nightmare had already begun. The giant comet had changed shape- it was not a comet at all, it was an alien mothership!