How often are Alien abductions?

They're pretty rare. I forgot exactly which patch it was, but they nerfed them pretty hard. I have had GTW since launch and since the nerf I haven't had a spontaneous abduction yet. You can encounter them more with the Scientist Career and the satellite produced through it.

They happen in any world, I think. But you need the Get To Work pack and you pretty much have to trigger them someway these days. Have a sim in the scientist career use the Observatory, the satellite dish or the Out Of This World computer, use the Contact Aliens interaction on the Observatory. I’ve had it trigger by interacting with aliens in world (some I made just for that purpose, and some I met at Alien Night at the bar). A scientist can also build the rocket ship and go to Sixam, which will definitely increase your chances.

I don’t know if building the rocket and going on the alien adventure at City Living’s GeekCon is a trigger as well, but it’s kind of fun for storytelling and can’t hurt.

I get them quite often, but I have some Sims in the scientist career and play with aliens too, all in one rotational save.

I don't know when they were nerfed but before I used MCCC to prevent them happening I used to have abduction events quite often (since at least late 2019, when I first got Get To Work).

https://youtu.be/-e95uNyonmA

I can confirm they do happen in Newcrest - I've had quite a few happen there, as all my sims live there first. I even once had my two alien founders abducted from there within seconds of each other - and both came back pregnant (setting on MCCC allowing female alien preg)!

ETA: If you want to meet aliens, Alien Night is the easiest way. Tuesday nights at the bars, I do believe.

The latest alien abduction to occur to my sim was just the other day when my female sim was abducted. I didn't worry, but when she came back she was pregnant with alien baby! NOOOO! Thank heavens for MCCC, I snuffed that little crumb cruncher real quick. Since when does a female sim get pregnant by aliens?

"bshag4lv;c-17991050" wrote:
The latest alien abduction to occur to my sim was just the other day when my female sim was abducted. I didn't worry, but when she came back she was pregnant with alien baby! NOOOO! Thank heavens for MCCC, I snuffed that little crumb cruncher real quick. Since when does a female sim get pregnant by aliens?

You may have both males and females selected under Occult for alien pregnancies. Might want to check.

To me they seem to come in waves. I tried out Eco Lifestyle when it was available as a trial version a couple of weeks ago and during that my sim got abducted 3 times - and she wasn’t even in the scientist career, but it later turned out that at least three sims among her friend/acquaintances were aliens in disguise.

When I picked up my Cottage Living test save again afterwards, my sim in that save (who’s not in the scientist career either) got abducted 2 times pretty shortly after my return from the alien-filled Eco test. It almost felt as if the influx of aliens had spilled over to the Cottage save. So far my sim has identified three disguised aliens among her list of friends/acquaintances.

It doesn't happen often. If you can you should use mcc to make it happen more. space rocks also help.
I think the cursed lot trait also helps,but it is bugged at the moment and causes fires.
so use at your own risk.