To those wondering why "planetfall" for Sid Meyer's Alpha Centauri: it was a recurrent term in the game, the "start of history".

And the starting prompt was:

$NAME3, a new era of struggle and opportunity awaits you. The UN Starship Unity has arrived in the Alpha Centauri system after a forty year voyage. All contact with Earth has been lost. After Captain Garland's assassination by an unknown assailant, the crew mutinied and split into factions. In the ensuing conflict, some seized control of the Unity's colony pods. You now shape the destiny of your $<M1:$FACTIONADJ0> faction, which has just made PLANETFALL!