Nice update there. I have this idea to show that the alien already got old, maybe just add beard etc. and those following him would be his kids and grandkids (the current un-bearded version), further implicating that they still can’t decide even after many generations has passed. But of course, it’s your decision. 
About setting the thumbnail, though it has been noted in the FAQ, I myself find it a bit confusing at first before realizing it’s as ‘easy’ as it need to be : just add " |thumbnail " after the image size in the code line after you upload am image for the thumbnail, just don’t forget the vertical slash ( | ) before ‘thumbnail’.
As an example, below is the code you get after uploading an image :
I set the image display size in the post to half hence the ‘50%’ but it’s optional and won’t affect the thumbnail, and here’s where you should insert the code for setting the thumbnail (highlighted) :
Hope this solves it.