I don't know of a way without the use of mods. But if you are not averse to using mods, this is the one I use, though I think you have to register to download.
"bluegenjutsu_NoAlienAbductionsAndNoAlienHouseholds"
http://simsasylum.com/tfm/index.php...res-seasons-ep/
Or
You can try to see if this mods works.
https://modthesims.info/d/493379/mo...abductions.html
No Alien Abductions
Base Chance - 0%
Telescope Bonus Chance - 0%
Space Rock Bonus Chance - 0%
Maximum Space Rock Bonus Chance - 0%
Total Maximum Chance - 0%
Or if you have NRass Retuner.
Sims3.Gameplay.ActorSystems (
https://simsarahsarah.tumblr.com/retuner)
AlienUtils > kAbductionBaseChance > 0 (Default:0.01)
AlienUtils > kAbductionMaxSpaceRockBonus > 0 (Default:0.6)
AlienUtils > kAbductionSpaceRockBonus > 0 (Default:0.15)
AlienUtils > kAbductionTelescopeBonus > 0 (Default:0.14)
AlienUtils > kAlienHouseholdNumMembers > 0 (Default:5)
AlienUtils > kAlienHouseholdSpaceRocksForBonus > 5000 (Default:5)
AlienUtils > kAlienHouseholdVisitChanceActive > 0 (Default:0.02)
AlienUtils > kAlienHouseholdVisitChanceActiveHighLTRMod > 0 (Default:0.08)
AlienUtils > kAlienHouseholdVisitChanceActiveSpaceRockMod > 0 (Default:0.15)
AlienUtils > kAlienHouseholdVisitChanceOffspring > 0 (Default:0.1)
AlienUtils > kAlienHouseholdVisitChanceRandom > 0 (Default:0.2)
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