From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Planet Monmasu (モンマース 惑星, Monmāsu Wakusei; FUNimation "Planet Monmaasu") is a planet in the Northern Galaxy.
Dragon Ball GT
Planet Monmasu was a planet where everything was ten times the normal size. One of the Black Star Dragon Balls landed on Planet Monmasu.
Planet Monmasu is the second level in Dragon Ball GT: Transformation. Enemies encountered here are Giant Bees, Giant Spiders, a Giant Turtle, and a Giant with a Black Star Dragon Ball stuck in one tooth.