Can other player land on a gate already occupied by another player and then close that gate

Only players with explored markers may close gates. Players without explored markers will be drawn through the gate during the Arkham Encounters Phase.

If both inestigators emerged from the same gate after finishing their Other World exploration, both get an explored marker, and the investigator who goes first may try to close the gate. If he doesn't want to/fails to close the gate, the other investigator at the gate location may try to close it. But both investigators must've explored the Other World to be able to do this.

Thanks, logical, should have thought of it