Star Trek: 10 Strangest Space Anomalies You May Have Forgotten

In the Deep Space Nine episode One Little Ship, the Defiant was ordered to investigate a rare subspace compression anomaly that was recently discovered by the Federation. This anomaly had the unique ability to shrink anything that entered it, an effect that Starfleet Command hoped would teach them the secret to creating transwarp corridors (although the series never followed up on this idea).

After the Defiant sent Dax, O'Brien, and Bashir into the anomaly in a runabout to test the shrinking effect, the Defiant was attacked and boarded by the Jem'Hadar. The crew aboard the shrunken runabout, undetected by the Dominion, had to save their crew by flying the shrunken runabout into the Defiant's interior through the aft plasma vent.

After the invading Jem'Hadar were defeated, the runabout and it's crew were able to return to their original size by retracing the path they flew into it, apparently meaning that the anomaly can also grow things, depending on how you enter it.

We learned in the episode that the effect literally changed the size of their individual atoms (as O'Brien was told he could not breathe the Defiant's air, due to the air molecules being too large), but, oddly, this is the only time this effect was used.