Star Trek: The Animated Series, season 1, episode 3
One of Our Planets Is Missing
Summary
The Enterprise encounters a giant cloud creature that feeds on the energy of the planets that lie in its path. They determine that it is heading for Mantilles, home to a Federation colony governed by former Starfleet officer Bob Wesley (featured in the TOS episode "The Ultimate Computer)".
Summary from Wikipedia, CC BY-SA 4.0.
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