Hey so this literally works every single time on my game when I want an abduction.
1. Do the buydebug cheat and put some average plants on your lot like apple tree, watermelon, and etc. oh and don't worry if their wilted (i usually put them in the front yard and bunched up together)
2. In the morning have your sim use the telescope for at least 2hrs
3. Have your sim collect two space rocks (size does not matter as long as they are space rocks)
4. Have you sim go home and analyze the space rocks and keep them in your inventory
5. When it hits 11pm go ahead and start stargazing
Now the aliens may not come until like 2:30 am but they still come now once your male sim has been abducted make sure you save your game about 20mins before that alien abduction moodlet disappears because if it disappear and doesn't show the unexpected weight gain you can just go back to main menu without saving and usually the second time is the charm. I can literally do this back to back and get an alien abduction oh and you do not need to put out new plants after each abduction.
*Warning* If you have a witch in your household or maybe friend that can perform sunlight charm stay away from them because one day my witch had did it on her own and then my male sims "unexpected weight gain" moodlet was gone. Hope you have fun and let me know if these steps work really good for you. :)