Spent yet another day off Simming, evenly split between 2 and 3. Saw this happen in 3 for the 1st time... 
Seems to happen randomly-no more "triggering" it by looking through a telescope
Sims2
says
ts2 challenges podcast going on now btw
Actually, the telescope (from some sources) increases the odds, but it is no longer necessary.
Also, having Space Rocks increase chance of abduction.