“Meridian” is episode eight of season three of Star Trek: Deep Space Nine.
The Defiant is doing a survey in the Gamma Quadrant – despite the Dominion threat, Sisko has convinced Starfleet that they need to keep exploring – when a planet, Meridian, suddenly appears out of nowhere in front of them.
There are a few inhabitants on the planet, and they say that their planet swaps between this dimension and another, one in which they exist as beings of pure conciousness. The time spent in normal reality has been decreasing, and this will eventually spell the planet’s destruction. Jadzia gets rather involved with one of the inhabitants, enough that they want to spend more time together, but the planet will disappear again quite quickly, and not return for another 60 years.
Back on DS9, a business associate of Quark’s (played by Jeffrey Combs, who later has a recurring role on Enterprise as Commander Shren, a one off appearance in Voyager and has more than a few different roles in this series, usually under a lot of prosthetics) becomes rather infatuated with Major Kira. Enough so that he wants Quark to make a special holoprogram featuring the major. Kira is not impressed when she finds out.