The Kohl planet
The Kohl planet was a planet located in the Delta Quadrant. It was deserted when the USS Voyager approached it in 2372.
The planet used to be a major trading spot. About nineteen years prior, a major solar flare occurred which caused a glacial freeze on the planet's surface. Magnetic storms and extreme levels of radiation followed.
Evidence suggested an advanced culture with warp drive had existed on the planet, but there were no life signs and it appeared that the atmospheric disturbances would have prevented any escape attempts. The entire colony of 400,000 people was likely wiped out.
However, five Kohl had gone into a state of artificial hibernation in order to survive the effects of the ecological disaster on their world. (VOY: "The Thaw")