Did I get penalized by the duplicate content filter?

I recently saw my website disappear from google serps after being on the first page for about a year and a half. I started doing some investigating and found that a secondary domain name is listed in google serps instead.

My main website domain is pegasusgalaxy.com. I also registered pegasusgalaxy.net and set it to redirect to pegasusgalaxy.com using the options through my domain name registrar (godaddy). I haven't changed this setup since I first registered both domain names over two years ago.

Why did these domain names switch out in google serps. I don't understand what's going on. Any help would be appreciated.

 

Yes, I use coop, but that doesn't explain why my .net domain replaced my .com domain in the serps especially since my .net domain doesn't actually have any content. It just redirects to the .com.