An Alien Concept is a two day limited time Event. On completion you will unlock the Weather Machine and gain access to The Snow Park. If you can complete the event within the limited time, you will also unlock the cool looking snow outfits.
Here is a rundown of what to do with explanations for anything that may be complicated.
Send a Sim to the Park and use one of the telescopes to search for UFOs 1min 30secs
Be Nice to an Alien 1min
Send your Sim back home from the Park. Go to your Sims home and you should find an Alien there. Tap the alien and select 'Be Nice'
Become Friends with an Alien 1min
Now you need to be friends. So just like you would with an other Sim, select the Alien and choose the Be Nice option again. After that you should be friends, if you are not, then do it more times until you are.
Go to the Park Instant
End is Nigh on a Soapbox - 12 hours
With you Sim in the Park, find the soapbox (crate) in the park, select it and choose the End is Nigh option - unfortunately this takes 12 hours!
Become best friends with the Alien - a bit of time
You'll find the Alien back at your house, so send your Sim back there from the Park. You just need to keep being nice to him until you become best friends. It won't take too long! Don't forget, some of the shorter time options give you proportionally more XP towards become best friends so if you have the time, go for some of the short time actions too. Try Be Funny for 11xp in 10 seconds a few times.
Browse Internet 4min 30secs
Send your Sim to a house with a computer or laptop and select the option to browse internet.
Be Nice to Osiris 1min
Simply tap your Alien friend again, and select the be nice option - only take a minute!
Spend 16,000 SImoleans on Electronics
There's no short cut to this one, you just have to open up the homestore, select furniture and then the electronics tab. Now purchase an item or some Items where the total cost is at least 16,000 simoleans. Obviously you don't have to purchase items for the house you are in, perhaps you have an empyt house somewhere that could do with a new TV ... or three...
Negotiate with a SIm-Eating Plant - 48 minutes (45min grow, 3 min negotiate)
For this you'll need a garden patch... Forgotten what one of those looks like? Well check the screenshot below.
Ok, with one of those selected, choose to grow a plant which has a green Warning triangle and an image of a plant with teeth. Grow one of those - any one... Lettuce is the quickest and takes 45 minutes.
Once the lettuce (or whatever has grown, select the plants, then if a sim eating plant appears in their place, select it and choose the negotiate option, that takes 3 minutes.
Read Fine Literature 12 hours
Head off to an bookcase (not a toddler or teen one!), select the option to read literature, this takes a whopping 12 hours.
Be Rude to Osiris 10 seconds
You've spent so long being nice to your Alien friend, now you have to be rude to him... How will he take it...I guess there is only one way to find out.
Woo-Hoo
For this tasks you'll need your married sims. Get them together and get them woo-hoo. If you don't have sims that are married, then you'll need to follow the steps to get them married. It is dealt with in this quest Love is in the Air, which you probably would have done already. Alternatively get two unattached sims to be romantic to each other until they are married. This will take a little while!
Deep Sleep 6 hours 30 mins
Send a Sim to bed and select the Deep Sleep option.
Be Funny to Osiris 10 secs
He should still be hanging around your house somewhere, find him, give him a tap and select the be nice option. If he is not around, just completely turn your device off again, then back on again.
Play Electronic on a Stereo 2 min 42 secs
Simply select a stereo - you should definitely have one of these because you've only just spend at least 16,000 Simoleans on electronics
An that's the end of the Quest! The weather machine is now unlocked and The Snow Park is available on the townmap. If you did it within the time limit, the snow outfits will also be available.