Io

Io was one of Jupiter's 79 moons, being the closest one and was one of the locations where the fight between Saitama and Monster Garou took place.

Monster Association Arc
After being sent flying from the recoil of their own Serious Punch collide, both Saitama and Garou land on Io. The fight between them continues on this Jupiter's moon. Soon, Io meets its end when Saitama uses one of his serious moves against Garou, Serious Table Flip, shattering it into smithereens.

Trivia

 * Now that Io has been destroyed, Jupiter only only has 78 moons in the One-Punch Man universe.