We still don't have the event, so, another clue: ET phone home.
And the original posting count, (which was not quite exact), was a very good clue indeed.
I thought that identfying the designer of the Lincoln penny as being "out of this world" (10/25 post) would have been enough to specify the event , but if you want explicit: the penny is attached to the Curiosity Mars rover as a calibration target, so I suppose the event would have been the first landing of US currency on Mars